Cloudsley Thompson 1958 Spiders Scorpions Centipedes and Mites

SPIDERS, SCORPIONS, CENTIPEDES AND MITES

FRONTISPIECE:

H e a d of Solifugid

(Photo:

Richard

L.

Cassell)

Spiders,

Scorpions,

Centipedes and Mites THE ECOLOGY AND NATURAL HISTORY OF WOODLICE, 'MYRIAPODS' AND ARACHNIDS

By J. L. CLOUDSLEY-THOMPSON M.A., PH.D. (CANTAB.), F.R.E.S., F.L.S. Lecturer University

in

Zoology,

of London

King's

PERGAMON N E W YORK PARIS

•

•

PRESS

LONDON

LOS ANGELES

1958

College

PERGAMON 122 10638

East

South

55th Wilton

Place,

PERGAMON 4

&

5

Fitzroy

PERGAMON 24

Rue

PRESS

Street,

des

New Los

PRESS Ecoles,

22, 47,

Angeles

PRESS Square,

INC. York

N.Y. California

LTD.

London

W.l

S.A.R.L. Paris

e

V

Copyright

L.

Cloudsley-Thompson

Library of Congress Card Number 5 7 - 1 4 4 9 9

PRINTED IN

GREAT BRITAIN BY R O B e R T MACLEHOSE A N D CO LTD. THE U N I V E R S I T Y PRESS, GLASGOW

CONTENTS PAGE PREFACE

VII

INTRODUCTION

IX

Chapter

I.

Chapter Chapter

II. M I L L I P E D E S III.

Chapter

WOODLICE

1 15

CENTIPEDES

40

IV. OTHER ' M Y R I A P O D S '

61

Chapter

V. S C O R P I O N S

70

Chapter

VI. SOLIFUGAE

87

Chapter

VII.

Chapter

VIII.

Chapter

99

W H I P - S C O R P I O N S A N D OTHERS

IX. HARVEST-SPIDERS

Chapter Chapter

FALSE-SCORPIONS

132

X. SPIDERS XI.

114

148

MITES A N D T I C K S

182

EPILOGUE

204

GENERAL B I B L I O G R A P H Y

207

CLASSIFICATORY INDEX

209

GLOSSARY A N D I N D E X OF S C I E N T I F I C TERMS

220

INDEX OF GENERAL T O P I C S

227

V

PREFACE 'If anybody shall reprove me and shall make it apparent u n t o me that I do err, I will most gladly retract. F o r it is the t r u t h that I seeke after, by which I am sure that never m a n was h u r t and as sure that he is h u r t that continueth in any error or ignorance whatsoever.' MARCUS AURELIUS

T h i s b o o k was conceived largely a t t h e sink, w h e r e m o s t m o d e r n h u s b a n d s have to s p e n d so m u c h of their leisure.

My deepest

t h a n k s a r e t h e r e f o r e d u e t o m y d e a r wife w h o s h o u l d e r e d far m o r e t h a n h e r s h a r e of t h e d o m e s t i c d r u d g e r y in o r d e r t h a t I m i g h t slip a w a y t o j o t d o w n m y i d e a s . I w o u l d also like t o e x p r e s s m y g r a t i t u d e to my friends and colleagues at h o m e and abroad w h o have so generously sent me reprints of their publications.

In many

c a s e s I h a v e n o t b e e n a b l e t o q u o t e t h e s e i n t h e b i b l i o g r a p h i e s for reasons of space, b u t my debt to the work of others in attempting t o c o v e r a v e r y w i d e field i n a s i n g l e v o l u m e m u s t b e a b u n d a n t l y clear to t h e reader. J. L . C - T . April

vii

1957

ACKNOWLEDGMENTS I should like to make grateful acknowledgment to the following for t h e use of several of the photographs and illustrations within this book: t h e Editors of Discovery, Naturalist, The Field and Science News; G. Fryer, R. F . Lawrence, E. A. Robins, J. H. P. Sankey, D u c k w o r t h & Co., Shell P h o t o graphic Unit, Zoological Society of L o n d o n , and to F r a n k W. L a n e for photographs by Richard L. Cassell, Walker van Riper and H u g h S p e n c e r .

Vlll

INTRODUCTION ' T h e evaporating power of the air m a y be the p r i m a r y factor u p o n which the organisation of the entire terrestrial fauna depends.' R. HESSE, W. C. ALLEE and K. P. SCHMIDT

The A r t h r o p o d a i s t h e d o m i n a n t p h y l u m o f t h e I n v e r t e b r a t e s . I n the oceans, m i n u t e crustaceans comprise the major c o m p o n e n t of t h e z o o p l a n k t o n u p o n w h i c h t h e food chains o f t h e whales a n d l a r g e r fishes a r e b a s e d : o n l a n d t h e m e d i c a l , e c o n o m i c a n d b i o logical i m p o r t a n c e o f i n s e c t s a n d m i t e s e s p e c i a l l y , c a n s c a r c e l y b e over-stressed. T h e s e m a y b e v e r y c o g e n t reasons for t h e i r investigation, b u t they are not t h e m o s t i m p o r t a n t . T h e little creatures are interesting in their o w n right, a n d research into t h e details of t h e i r lives p r o v i d e s m e n t a l e x e r c i s e t h a t i s a s o u r c e o f u n e n d i n g pleasure and interest. Questions are sometimes asked as to t h e use of academic res e a r c h . T h e a n s w e r m a y b e t h a t i t lies i n m a n ' s n a t u r e t o e x p l o r e t h e s e c r e t s o f t h e u n i v e r s e , for c o m p a r a t i v e l y f e w i n t e l l e c t u a l a n d aesthetic pursuits are motivated by purely practical considerations. Scott d i d n o t go to t h e S o u t h P o l e in search of coal, n o r d i d B e e t h o v e n w r i t e his string q u a r t e t s for e c o n o m i c reasons. T h e best e x c u s e for c l i m b i n g M o u n t E v e r e s t m a y h a v e b e e n t o g e t t o t h e t o p , o r s i m p l y b e c a u s e i t w a s t h e r e . P e r h a p s t h e last w o r d o n t h e s u b j e c t w a s w r i t t e n b y J . S . B a c h . ' T h e a i m a n d final r e a s o n o f all music is the glory of G o d and the recreation of the m i n d . ' A n d so f o r all t h e a r t s a n d s c i e n c e s ! M a n y excellent books have recently been written a b o u t insects a n d o f all t h e t e r r e s t r i a l A r t h r o p o d a t h e y a r e t h e m o s t c a t h o l i c . O v e r 600,000 species are k n o w n to science a n d the total n u m b e r in existence probably exceeds a million. T h e r e are m o r e species of b e e t l e s i n t h e w o r l d t h a n o f all o t h e r a n i m a l s p u t t o g e t h e r . O n e o f t h e s e , Niptus hololeucus c a n live o n c a y e n n e p e p p e r a n d t h r i v e o n sal a m m o n i a c . T h i s s p e c i e s h a s b e e n k n o w n t o live i n t h e c o r k s o f ix

x

INTRODUCTION

e n t o m o l o g i s t s ' c y a n i d e k i l l i n g - b o t t l e s a n d n o less t h a n 1,547 s p e c i m e n s w e r e t a k e n f r o m a j a r o f c a s e i n t h a t h a d b e e n s t o p p e r e d for t w e l v e y e a r s . T h e f l y Psilopa petrolei i n h a b i t s p u d d l e s o f c r u d e p e t r o l e u m ; a n d b o t h flies a n d b e e t l e s a b o u n d i n c e r t a i n h o t s p r i n g s in the western United States where the temperature approaches 50° C . T h e largest insects i n c l u d e t h e African G o l i a t h beetle, Goliathus regius w h i c h m e a s u r e s f o u r i n c h e s i n l e n g t h a n d t w o i n b r e a d t h , a n d t h e V e n e z u e l a n Dynastes hercules, r e a c h i n g a l e n g t h o f 6 | i n c h e s , w h i l e t h e m a g n i f i c e n t b u t t e r f l y Ornithoptera victoriae of t h e S o l o m o n I s l a n d s h a s a w i n g - s p a n e x c e e d i n g o n e foot. In c o n t r a s t s o m e o f t h e p a r a s i t i c H y m e n o p t e r a a r e c o n s i d e r a b l y less than one h u n d r e d t h of an inch in length, despite the complexity of their structure. T h e diversity and versatility of the insects is n o w h e r e equalled in the animal kingdom, b u t in this volume I hope to show that the o t h e r t e r r e s t r i a l A r t h r o p o d a , a l t h o u g h s o m e w h a t n e g l e c t e d , will well r e p a y f u r t h e r a c q u a i n t a n c e . F o r m a n y years, t h e majority of zoologists w h o have worked on t h e A r t h r o p o d a h a v e t e n d e d t o c o n c e n t r a t e t h e i r efforts e i t h e r o n the m a r i n e Crustacea or on the insects. A p a r t from systematists, c o m p a r a t i v e l y few h a v e p a i d m o r e t h a n s u p e r f i c i a l a t t e n t i o n t o t h e remaining m e m b e r s of the p h y l u m and although increasing n u m b e r s a r e n o w d o i n g s o , t h e r e i s a m p l e s c o p e for n e w r e c r u i t s a s t h e r e a d e r will s o o n realise. It is n o w generally recognised that the Collembola are not insects a n d the same m a y be t r u e of other A p t e r y g o t a . Nevertheless, these animals have always come within the scope of the entomologist a n d receive attention in m a n y w e l l - k n o w n entomological textbooks. I have not, therefore, included t h e m in this book even though the Pauropoda and Symphyla have been noticed. Indeed, i t i s n o w b e l i e v e d t h a t t h e l a t t e r a r e closely r e l a t e d t o t h e I n s e c t a . C o n s e q u e n t l y t h e selection of g r o u p s discussed in t h e following chapters m a y appear somewhat arbitrary from a systematic point o f v i e w : b u t i t will, I h o p e , b e f o u n d t o h a v e p r a c t i c a l j u s t i f i c a t i o n . L i f e o n l a n d e n t a i l s a n u m b e r o f p r o b l e m s for a n i m a l s . L a r g e r forms require structural support, respiratory organs m u s t become m o d i f i e d for air b r e a t h i n g a n d t h e r e i s n o l o n g e r t h e s u r r o u n d i n g w a t e r i n t o w h i c h t o x i c e x c r e t o r y p r o d u c t s c a n freely diffuse, w h i l e

INTRODUCTION

XI

m e c h a n i s m s for t h e c o n s e r v a t i o n of w a t e r a n d t h e m a i n t e n a n c e of a constant internal m e d i u m m u s t be evolved. T h a t these p r o b l e m s a r e b y n o m e a n s easily o v e r c o m e i s s h o w n b y t h e fact t h a t s e v e r a l invertebrate phyla are almost entirely marine while others as yet possess few terrestrial species. I n d e e d , t h e A r t h r o p o d a have b e e n u n u s u a l l y successful in exploiting t h e terrestrial habitat a n d by adaptive radiation have succeeded in establishing themselves in n e a r l y all t h e h a b i t a b l e c o r n e r s o f t h e e a r t h . E a c h a s p e c t o f t h e i r a d a p t a t i o n t o life o n l a n d affects a n d i s affected b y o t h e r a s p e c t s . F o r e x a m p l e , i t m i g h t a p p e a r a fairly s i m p l e m a t t e r f o r a n o r g a n i s m to eliminate water-loss by the evolution of an integument completely impervious to water-vapour; b u t such an i n t e g u m e n t w o u l d also b e i m p e r v i o u s t o o x y g e n a n d c a r b o n d i o x i d e . A r e s p i r a t o r y m e c h a n i s m has therefore had to be evolved which p e r m i t s gaseous exchange w i t h o u t excessive water-loss. If t h e i n t e g u m e n t is rigid and provides support, then growth becomes impossible except by m o u l t i n g a n d t h i s l i m i t s size. T h e p h y s i o l o g y o f n u t r i t i o n a n d e x cretion t o o are closely c o n c e r n e d w i t h w a t e r c o n s e r v a t i o n a n d superimposed u p o n this basic physiological r e q u i r e m e n t are the inn u m e r a b l e c o n c o m i t a n t s of b e h a v i o u r a n d ecology. T h e r e are two obvious ways in which small animals can escape desiccation on dry land. O n e is to avoid dry places a n d to remain m o s t , i f n o t all o f t h e t i m e , i n a h u m i d e n v i r o n m e n t ; t h e o t h e r , t o evolve an i m p e r v i o u s i n t e g u m e n t . B o t h m e t h o d s have b e e n exp l o i t e d b y t h e A r t h r o p o d a a n d e a c h h a s its d r a w b a c k s a n d a d vantages. Indeed, on the basis of this character the terrestrial m e m b e r s o f t h e p h y l u m can b e divided r o u g h l y into t w o m a i n ecological g r o u p s : t h e first i n c l u d e s w o o d l i c e , c e n t i p e d e s , m i l l i p e d e s a n d t h e i r allies w h i c h lose w a t e r r a p i d l y i n d r y air; t h e s e c o n d , t h e A r a c h n i d s and insects w h i c h are covered with a layer of wax t h a t renders them comparatively independent of moist surroundings. In t h e following c h a p t e r s t h e significance of this generalisation will b e c o m e a p p a r e n t . F o r m s l a c k i n g a n e p i c u t i c u l a r w a x - l a y e r are almost entirely nocturnal in habit, and can w a n d e r abroad only after n i g h t f a l l w h e n t h e t e m p e r a t u r e d r o p s a n d t h e r e l a t i v e h u m i d i t y of t h e air rises. In contrast, m o s t insects, spiders a n d m o s t o t h e r Arachnida are potentially diurnal except perhaps in deserts and other regions with rigorous climates where, anyway, the majority

Xll

INTRODUCTION

of t h e i n h a b i t a n t s avoid t h e excessive m i d - d a y heat a n d d r o u g h t by their nocturnal behaviour. (Conversely, arctic animals are nearly always diurnal in habit.) T h e m o r e primitive g r o u p s such as scorpions, w h i p - s c o r p i o n s , spiders of t h e families Liphistiidae, T h e r a phosidae, Dictynidae, Dysderidae and so on, have probably become secondarily adapted to nocturnal habits as a result of c o m p e t i t i o n w i t h m o r e efficient s p e c i e s . A t t h e s a m e t i m e , h o w e v e r , m a n y of t h e m are large a n d s o m e w h a t v u l n e r a b l e a n d m a y n e e d to escape the attentions of potential predators in this way.

F I G . 1. Rate of water-loss in dry air at different temperatures, and corresponding saturation deficiencies, from a woodlouse (Porcellio), millipede (Oxidus), spider (Lycosa) and insect (Pieris larva). In the woodlouse and millipede the rate of water-loss is proportional to the saturation deficiency of the atmosphere, b u t in the spider and insect it is negligible below about 30° C, the critical t e m p e r a t u r e at which their epicuticular wax-layers b e come porous. Rate of water-loss is expressed in milligrams per square centimetre of surface area per h o u r . (After CloudsleyT h o m p s o n , 1955.) O n t h e o t h e r h a n d , l i q u i d w a t e r c a n also b e v e r y d a n g e r o u s t o small animals that m a y b e c o m e water-logged, or trapped by surface t e n s i o n . T h e i r e n v i r o n m e n t m u s t b e n e i t h e r t o o w e t n o r t o o dry. T h i s is especially t r u e of species lacking a waterproofing w a x l a y e r . B e c a u s e t h e y a r e s u s c e p t i b l e t o d e s i c c a t i o n , t h e y a r e also susceptible to water uptake by osmosis: consequently they tend to

INTRODUCTION

Xlll

i n h a b i t t h i c k l e a f - l i t t e r , o r b u r r o w d e e p i n t o t h e soil w h e r e t h e y a r e less l i a b l e e i t h e r t o b e c o m e w a t e r - l o g g e d o r d e s i c c a t e d . Rigid, mechanistic behaviour patterns in response to environmental stimuli have been evolved by m e a n s of which the animals find and maintain themselves in suitable habitats. Physiological and m o r p h o l o g i c a l a d a p t a t i o n s a l o n e w o u l d o b v i o u s l y b e insufficient t o s u p p o r t t h e life o f a n y f r e e - l i v i n g a n i m a l . O r i e n t a t i o n a n d b e h a v i o u r m e c h a n i s m s m u s t also b e e v o l v e d t o r e t a i n o r g a n i s m s i n environments to which they are suited, to enable t h e m to find food, m a t e , a n d i n d e e d t o carry o u t t h e i n n u m e r a b l e functions essential for their c o n t i n u e d existence.

F I G . 2. Woodlice. Trichoniscus pusillus (length 4 m m ) , Porcellio scaber (length 14 m m ) and Armadillidium vulgare (length 15 m m ) . (After W e b b and Sillem, 1906.) T h e ecology of animals is therefore governed not only by the f a c t o r s o f t h e i r e n v i r o n m e n t s , p h y s i c a l a n d b i o l o g i c a l , b u t also b y their o w n physiological r e q u i r e m e n t s and behaviour. T h e interrelationships b e t w e e n living o r g a n i s m s a n d their e n v i r o n m e n t s include b o t h inter-specific a n d intra-specific factors. T h e s e rel a t i o n s h i p s a r e specific for e v e r y o r g a n i s m a n d c o n t i n u o u s t h r o u g h o u t its life: t h e y a r e r e c i p r o c a l i n t h a t t h e o r g a n i s m i s n o t m e r e l y i n f l u e n c e d b y , b u t a t t h e s a m e t i m e p o s i t i v e l y affects its e n v i r o n m e n t , a n d a r e i n d i s s o l u b l e b e c a u s e t h e o r g a n i s m c a n n o t exist i n d e p e n d e n t l y o f its e n v i r o n m e n t . C o n s e q u e n t l y e c o l o g y i s a v a s t a n d c o m p l e x subject a b o u t w h i c h c o m p a r a t i v e l y little is yet k n o w n . O n e a d v a n t a g e o f t h i s lies i n t h e fact t h a t i t i s still p o s s i b l e , a s

XIV

INTRODUCTION

C h a r l e s E l t o n p o i n t e d o u t i n 1 9 2 7 , for a l m o s t a n y o n e d o i n g e c o logical w o r k o n t h e r i g h t l i n e s , t o s t r i k e u p o n s o m e n e w a n d e x c i t i n g fact o r i d e a . E c o l o g y h a s b e e n d e s c r i b e d a s scientific n a t u r a l h i s t o r y a n d a c curate identification m u s t be m a d e of any animals studied. O n e of the objects of this book is to indicate some of the i n n u m e r a b l e problems awaiting elucidation and to provide a guide to sources for t h e identification of t h e British species in particular, as well as t o o t h e r r e l e v a n t l i t e r a t u r e . I t i s h o p e d t h a t i t will i n t e r e s t n a t u r a l h i s t o r y w o r k e r s i n t h i s c o u n t r y a n d a b r o a d : i t m a y also b e o f u s e t o u p p e r school biology teachers. At the same time, however, I believe that m a n y university students may find in it information, although s i m p l y p o r t r a y e d , t h a t will b e o f v a l u e t o t h e m b o t h i n t h e j o y s o f the field a n d t h e gloom of t h e examination hall. 1

1

Inevitably this is somewhat arbitrary and no d o u b t , reflects a bias towards the works with which I am m o r e familiar. Both m o d e r n and old publications have been quoted, especially where the latter have useful illustrations.

CHAPTER

I

WOODLICE Classification and distribution Woodlice are included in the sub-order Oniscoidea of the crustacean order Isopoda. T h e y form a reasonably homogeneous g r o u p a n d are of particular interest because there are several c o m m o n s p e c i e s s h o w i n g d i f f e r e n t d e g r e e s o f a d a p t a t i o n t o life o n land. T h e majority are b e t w e e n one and two centimetres in length, a n d t h e s m a l l size of c e r t a i n g e n e r a s u c h as Platyarthrus, Trichoniscus a n d Sphaerobathytropa is a l m o s t c e r t a i n l y a s e c o n d a r y f e a t u r e correlated w i t h various regressive characters s u c h as a simplification in t h e s t r u c t u r e of t h e eyes a n d a p p e n d i c e s , r e d u c t i o n in t h e n u m b e r o f b o d y s e g m e n t s a n d loss o f p i g m e n t a t i o n . A n a n a l o g o u s p h e n o m e n o n is found in the Acari.

F I G . 3. Fifth thoracic segment of a female Oniscus asellus cut across to show the brood p o u c h with eggs. (After W e b b and Sillem, 1906.) T h e O n i s c o i d e a are s o m e w h a t oval i n f o r m a n d their b o d i e s are arched, t h e c u r v e varying i n different genera a n d species. T h e head bears t w o large antennae a n d a smaller pair of antennules anterior to t h e m . T h e thorax consists of seven segments which are o f t e n c o n s i d e r a b l y b r o a d e r t h a n t h e six s u c c e e d i n g o n e s t h a t f o r m A

1

S.S.C.M.

2

WOODLICE

the a b d o m e n . E a c h of t h e thoracic s e g m e n t s carries a pair of w a l k i n g legs a n d i n t h e f e m a l e , a t t h e t i m e w h e n t h e e g g s a r e laid, a p a i r o f p l a t e s a r i s e s o n s e g m e n t s t w o t o five. T h e s e p l a t e s t o gether form a b r o o d p o u c h in w h i c h t h e eggs are carried until they h a t c h a n d i n w h i c h t h e y o u n g r e m a i n for s o m e t i m e a f t e r w a r d s . T h e a p p e n d a g e s o f t h e a b d o m e n a r e also p l a t e - l i k e , w i t h t h e e x c e p t i o n o f t h e last p a i r o r u r o p o d s . T h e e n d o p o d i t e s o r p l e o p o d s a r e h o m o l o g o u s w i t h t h e gills o f a q u a t i c I s o p o d s a n d h a v e a respiratory function, while t h e o u t e r exopodites act as a protective c o v e r . I n t h e m a l e t h e first t w o p a i r s o f a b d o m i n a l a p p e n d a g e s a r e specially

modified,

their

endopodites

being

long

and

pointed,

while the u r o p o d s are often considerably larger t h a n in t h e female a n d t h e i r s h a p e i s s o m e t i m e s o f v a l u e i n classification.

F I G . 4. Pleopods of first thoracic segment of Porcellio scaber showing pseudotracheae. Male on the left, female on the right. (Diagrammatic.") In a c o m p r e h e n s i v e s u r v e y of t h e Oniscoidea, V a n d e l (1943) recognises s o m e 18 families, of w h i c h five are i n c l u d e d in the British fauna. T h e s e are t h e Ligiidae, Trichoniscidae, Oniscidae, Porcellionidae a n d Armadillidiidae. T h e geological history of the C r u s t a c e a i s a l o n g o n e a n d fossils o c c u r i n t h e O l d R e d S a n d s t o n e of the Devonian period a n d in the Carboniferous Coal Measures. Fossil woodlice, however, have not b e e n found below the U p p e r Eocene which might suggest that colonisation of the land has been achieved s o m e w h a t late in t h e history of t h e g r o u p . W h e n t h e y do

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appear, however, they are generically indistinct from living forms, a n d Vandel believes that the ancestors of woodlice b e c a m e terrestrial d u r i n g t h e second half of t h e Palaeozoic era. He bases this c o n c l u s i o n o n t h e fact t h a t all t h e m a i n t y p e s o f o r g a n i s a t i o n within the Oniscoidea have a world-wide distribution and consequently m u s t have a very ancient origin. T h e m o s t p r i m i t i v e a n d a t t h e s a m e t i m e t h e least well a d a p t e d of t h e woodlice to terrestrial conditions are littoral species b e l o n g ing to t h e family Ligiidae. T h e r e are two British species in this f a m i l y , Ligia oceanica, t h e l a r g e s t of t h e B r i t i s h w o o d l i c e — u p to 30 mm in length and rather m o r e than twice as long as b r o a d — a n d t h e s m a l l e r Ligidium hypnorum w h i c h i s s o m e t i m e s f o u n d far i n land, nearly always in t h e n e i g h b o u r h o o d of water. Ligia oceanica h a s a w i d e d i s t r i b u t i o n a r o u n d t h e s h o r e s of G r e a t Britain a n d indeed of practically t h e whole n o r t h coast of E u r o p e . I t also o c c u r s i n F r a n c e , S p a i n , M o r o c c o a n d A m e r i c a . A l t h o u g h n e v e r f o u n d far f r o m t h e sea, i t i s t r u l y t e r r e s t r i a l a n d c a n w i t h s t a n d p r o l o n g e d s u b m e r s i o n i n sea w a t e r o n l y i f t h i s i s w e l l aerated. T h e n o r m a l habitat is in deep n a r r o w crevices in the rocks j u s t a b o v e h i g h - t i d e level, u n d e r stones o n s a n d y b e a c h e s o r on t h e sides of quays: h e n c e t h e n a m e 'quay-louse' or 'quayl o w d e r ' . I n S t . K i l d a Ligia h a s b e e n f o u n d i n t h e c r e v i c e s o f b o u l d e r s o v e r 4 5 0 ft. a b o v e sea level, b u t o n t h a t e x p o s e d islet spray is often b l o w n to this h e i g h t (Nicholls, 1931). I have f o u n d s p e c i m e n s over a mile inland on t h e Isle of M a n . T h e family T r i c h o n i s c i d a e also o c c u r s i n v e r y m o i s t places, b u t t h e Porcellionidae a n d Armadillidiidae are found in progressively d r i e r l o c a l i t i e s . N o w t h i s s e q u e n c e i s also o n e o f i n c r e a s i n g m o r p h o logical s p e c i a l i s a t i o n w i t h i n t h e g r o u p , t h e s i g n i f i c a n c e o f w h i c h will be c o n s i d e r e d below. H a t c h e t t ( 1 9 4 7 ) h a s f o u n d t h a t i n M i c h i g a n Armadillidium nasatum d o e s n o t o c c u r o u t s i d e b u i l d i n g s , w h i l e A. vulgare is chiefly f o u n d a r o u n d h u m a n h a b i t a t i o n s ; Cylisticus convexus p r e f e r s r o c k y r e g i o n s a n d Ligidium longicaudatum o c c u r s o n l y i n v e r y w e t s i t u a t i o n s . Metoponorthus pruinosus is s o m e w h a t u r b a n in its d i s t r i b u t i o n . Porcellio scaber lives o n b e a c h e s , r i v e r b a n k s a n d o t h e r m o i s t s i t u a t i o n s . P. spinicornis r e q u i r e s a h a b i t a t w h e r e p l e n t y of l i m e i s a v a i l a b l e a n d P . rathkei i s g e n e r a l l y d i s t r i b u t e d b u t m o r e

4

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a b u n d a n t i n d e c i d u o u s w o o d l a n d s t h a n e l s e w h e r e , w h i l e P . demivirgo d e f i n i t e l y p r e f e r s m o i s t w o o d l a n d s i t u a t i o n s . W i t h regard to t h e British species, Heeley (1941) notes t h a t Trichoniscus pusillus i s a b u n d a n t i n v e r y m o i s t w o o d l a n d s , t h o u g h t h e a n i m a l s a r e f r e q u e n t l y o v e r l o o k e d o w i n g t o t h e i r s m a l l size a n d d a r k c o l o u r i n g . T h e y c a n easily b e m i s t a k e n f o r y o u n g Philoscia. T h e y f a v o u r t h e t h i c k s o d d e n l a y e r s o f d e c a y i n g l e a v e s w h i c h lie beneath the trees throughout the winter and during the s u m m e r t h e y live a m o n g s t t h e r e s u l t i n g leaf m o u l d b e n e a t h l o w b u s h e s well s h a d e d from t h e s u n , or w i t h i n r o t t i n g twigs. Philoscia muscorum is fairly c o m m o n in m o i s t s h a d y s i t u a t i o n s in m o o r s and woodlands, particularly a m o n g s t t h e roots of grasses beneath bushes and brambles and at the base of tree trunks, where t h e soil r e c e i v e s t h e d r i p p i n g s f r o m t h e t r e e s a n d i s s h a d e d f r o m t h e s u n . T h i s s p e c i e s i s s o m e w h a t local a n d r e s t r i c t e d i n i t s d i s t r i b u t i o n a n d i s p r e s e n t m a i n l y i n w o o d l a n d . Oniscus asellus o n t h e o t h e r h a n d i s t h e c o m m o n e s t o f all w o o d l i c e a n d i s f o u n d a l m o s t everywhere that d a m p conditions prevail, particularly beneath half b u r i e d s t o n e s a n d b a r k . I t s e e m s t o p r e f e r r a t h e r m o r e m o i s t s i t u a t i o n s t h a n Porcellio scaber a n d m a y o f t e n b e f o u n d w i t h t h e latter in the same tree, b u t usually nearer the g r o u n d where the w o o d is old a n d rotting. Porcellio scaber i s also v e r y c o m m o n , p a r t i c u l a r l y b e n e a t h t h e d r y loose bark of vertical t r u n k s of living trees. It s o m e t i m e s inhabits d a m p houses a n d has b e e n found in heaps of clinker and t h e n e s t s of w o o d a n t s , Formica rufa. F i n a l l y , Armadillidium vulgare is p a r t i c u l a r l y c o m m o n on c h a l k lands, on h e a t h s a n d slopes covered w i t h low scrub such as are f o u n d i n r a i l w a y c u t t i n g s a n d o n r o a d s i d e s . T h e s p e c i e s also o c curs in the neighbourhood of houses and builders' yards where t h e r e is loose c e m e n t or lime, b u t is n e v e r very n u m e r o u s in w o o d land. It can even survive u n d e r dry stones w a r m e d by the sun. N o w Heeley claims that it is possible to predict which species of w o o d l o u s e w i l l b e p r e s e n t i n a g i v e n h a b i t a t b y its w a t e r - c o n t e n t . I n h i s e x p e r i m e n t s , h o w e v e r , h e p r o v i d e d a m o i s t s u r f a c e for t h e a n i m a l s in t h e f o r m of a carrot as food. It has since b e e n s h o w n that woodlice of the same species, if desiccated a n d subsequently k e p t i n u n s a t u r a t e d air, b u t w i t h a c c e s s t o m o i s t p l a s t e r o f P a r i s

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5

surfaces, regain their weight by absorption of water t h r o u g h the m o u t h . T h e s e experiments explain h o w woodlice which are k n o w n t o l o s e w a t e r i n all b u t s a t u r a t e d air, c a n n e v e r t h e l e s s s u r v i v e i n d e f i n i t e l y i n u n s a t u r a t e d air p r o v i d e d t h a t a m o i s t s u r f a c e i s available ( E d n e y , 1954).

General behaviour In different p a r t s of t h e c o u n t r y t h e r e are m a n y c u r i o u s s u p e r stitions a b o u t woodlice. F o r example, in some places their presence indoors is regarded as u n l u c k y and any food on w h i c h they m a y happen to wander is considered poisoned. On the other hand, in c e r t a i n o t h e r d i s t r i c t s u n t i l v e r y r e c e n t l y a f e w live w o o d l i c e t h r u s t d o w n t h e t h r o a t o f a c o w w e r e b e l i e v e d t o h a v e beneficial effects a n d ' t o p r o m o t e t h e r e s t o r a t i o n o f t h e c u d ' . N o d o u b t t h i s is w h y in Shropshire and neighbouring counties woodlice or slaters are s o m e t i m e s referred to as ' c u d - w o r m s ' . At o n e t i m e too, w o o d l i c e w e r e p r e s c r i b e d t o b e s w a l l o w e d alive a s a r e m e d y for s c r o f u l o u s s y m p t o m s a n d for d i s e a s e s o f t h e l i v e r a n d d i g e s t i v e o r g a n s . I t i s s u r p r i s i n g t o o h o w m a n y local n a m e s h a v e b e e n g i v e n t o w o o d l i c e : C o l l i n g e ( 1 9 3 5 ) l i s t e d n o less t h a n 6 5 r a n g ing f r o m 'Bubble b u g s ' (Stafford), ' C h e e s e - p i g s ' (Berkshire) a n d 'Coffin-cutters' (Ireland) to ' M o n k e y peas' (Kent), 'Pennypigs' (Wales), 'Sink-lice' ( L a n c a s h i r e a n d Stafford) a n d ' T i g g y h o g s ' ( N o r t h a m p t o n s h i r e ) . I n A m e r i c a t h e y are k n o w n a s ' S o w bugs'. H u m i d i t y is an e n v i r o n m e n t a l factor of p r i m e i m p o r t a n c e , b o t h t o w o o d l i c e a n d t o m y r i a p o d s , a s t h e y all lack a w a t e r p r o o f i n t e g u m e n t . W o o d l i c e are very sensitive to h u m i d i t y gradients and aggregate in areas of high h u m i d i t y . T h e m e c h a n i s m by w h i c h this o c c u r s i s t w o - f o l d : firstly, t h e a n i m a l s s h o w a d e c r e a s e i n a c t i v i t y a n d s p e e d i n m o i s t air a n d s e c o n d l y t h e y c h a n g e direction m o r e frequently in d a m p places so that once they have arrived in a moist situation they tend to remain there. T h i s reaction to the r e l a t i v e h u m i d i t y o f t h e air i s also c o m b i n e d w i t h a v o i d a n c e o f light a n d a reaction t h a t causes t h e m to m a k e contact w i t h as m u c h of their surroundings as possible. T h e result of this is that not only do the animals enter n a r r o w crevices, b u t they b u n c h together and consequently protect each other from evaporation.

6

WOODLICE

H o w e v e r , a reversal of t h e response to light occurs w h e n w o o d lice b e c o m e s o m e w h a t d e s i c c a t e d , s o t h a t i f t h e i r d a y t i m e h a b i t a t should dry up they are n o t restrained t h e r e until they die, b u t b e c o m e attracted to light a n d are t h e n able to w a n d e r in t h e open u n t i l t h e y find s o m e o t h e r d a m p d a r k h i d i n g p l a c e w h e r e t h e y again b e c o m e p h o t o - n e g a t i v e ( C l o u d s l e y - T h o m p s o n , 1952). T h e c l e a r e s t a d a p t a t i o n t o t e r r e s t r i a l life i s t o b e f o u n d i n t h e pleopods. T h e s e are variously modified a n d in t h e m o r e advanced forms bear tufts of invaginated tubules forming 'lung-trees' or ' p s e u d o t r a c h e a e ' . E a c h t r e e o p e n s to t h e exterior by a slit-like aperture near the edge of the pleopod, and the m i n u t e ramifying tracheae are thin-walled t u b e s s u r r o u n d e d by blood w h i c h carries oxygen to t h e tissues of t h e b o d y . W h e n t h e air is dry, t h e p l e o p o d s a r e p r o b a b l y k e p t m o i s t b y w a t e r t h a t diffuses f r o m t h e b o d y fluids of t h e animal. L i k e m o s t o t h e r w o o d l i c e , Ligia oceanica i s n o c t u r n a l i n h a b i t a n d e m e r g e s d u r i n g t h e n i g h t at low tide to feed on seaweeds such a s Fucus a n d o t h e r a l g a e . T h e s p e c i e s i s s t r o n g l y p h o t o - n e g a t i v e and tends to remain u n d e r cover on moonlight nights. E d n e y ( 1 9 5 4 ) h a s r e c e n t l y p o i n t e d o u t t h a t Ligia c a n live o n l a n d a s a result of wide osmotic tolerance rather t h a n by developing osm o t i c i n d e p e n d e n c e . S i n c e o t h e r s p e c i e s o f w o o d l o u s e c a n lose m u c h w a t e r b y e v a p o r a t i o n w i t h o u t d y i n g , i t s e e m s likely t h a t such osmotic i n d e p e n d e n c e is characteristic of t h e g r o u p as a w h o l e . T h e c o l o u r o f Ligia r a n g e s f r o m a d a r k g r e y i s h - g r e e n t o a light, dirty b r o w n , while y o u n g s p e c i m e n s have t w o lightcoloured patches on the m i d d l e of the dorsal side. T h e British Ligia oceanica, as w e l l as t h e A m e r i c a n L. baudiniana a n d L. exotica, h a v e b e e n f o u n d t o s h o w w e l l m a r k e d c o l o u r r e s p o n s e s d u e t o t h e e x p a n s i o n a n d c o n t r a c t i o n o f c o l o u r p i g m e n t cells o r chromatophores, so that they b e c o m e light w h e n placed on a white background and t u r n dark on a black background. In addition there is a diurnal r h y t h m of colour change and they tend to be dark by day and pale by night. T h e family Trichoniscidae includes a n u m b e r of small, elongat e d w o o d l i c e t h a t a r e fairly w i d e l y d i s t r i b u t e d i n d a m p p l a c e s u n d e r m o s s , b a r k , fallen l e a v e s , l o g s a n d s o o n . T h e O n i s c i d a e a r e less d e p e n d e n t o n m o i s t u r e , b u t t h e c o m m o n Philoscia muscorum

WOODLICE

7

w h i c h c a n b e d i s t i n g u i s h e d f r o m Oniscus asellus b y its n a r r o w b o dy a n d pretty m a r b l e d appearance is again usually found in moist situations u n d e r rubbish heaps, d a m p moss and the carpet of dead leaves in w o o d s . A c u r i o u s little, w h i t e , b l i n d w o o d l o u s e is Platyarthrus hoffmannseggi. I t i s easily r e c o g n i s e d b y its b r o a d f l a t t e n e d b o d y u p t o 3-6 m m i n l e n g t h w i t h d e n t i c u l a t e e d g e s t o its s e g m e n t s a n d s h o r t , stout antennae. T h i s species occurs t h r o u g h o u t the British Isles a n d t h e r e s t o f E u r o p e , a n d its r a n g e e x t e n d s i n t o N o r t h A f r i c a . I t is usually found in the nests of ants and the burrows of woodb o r i n g b e e t l e s . T h e s p e c i e s w a s d e s c r i b e d i n 1833 b y B r a n d t f r o m s p e c i m e n s t a k e n i n P r u s s i a a n d w a s first n o t i c e d i n B r i t a i n l i v i n g w i t h several species of ants at L u l w o r t h Cove, in 1859. A l t h o u g h it h a s n o e y e s , Platyarthrus a p p e a r s t o b e v e r y a v e r s e t o l i g h t a n d quickly hides if disturbed. A N e w Z e a l a n d s p e c i e s of Trichoniscus, T. commensalis, h a s i n dependently evolved the same habit of associating w i t h ants. It is r a t h e r l a r g e r t h a n Platyarthrus a n d i s n o t q u i t e w h i t e , b u t g e n e r a l l y m a r k e d with bands or patches of pale b r o w n on a white ground. M o r e o v e r , i t i s n o t b l i n d b u t p o s s e s s e s fairly p e r f e c t e y e s p r o v i d e d with the normal amount of pigmentation. O n e of t h e largest a n d m o s t c o m m o n of woodlice is the garden s l a t e r Oniscus asellus w h i c h r e a c h e s a l e n g t h o f 1 5 m m a n d a b o u t half t h a t w i d t h . A g a i n t h e p l e o p o d s are w i t h o u t p s e u d o t r a c h e a e , b u t Oniscus s p p . s e e m t o w a n d e r i n d r i e r p l a c e s t h a n a n y o f t h e species m e n t i o n e d previously. A n u m b e r of species occur in the f a m i l y P o r c e l l i o n i d a e , of w h i c h Porcellio scaber is t h e m o s t u s u a l a n d h a s b e e n r e c o r d e d f r o m all o v e r t h e B r i t i s h I s l e s . I t r e a c h e s a size e v e n l a r g e r t h a n t h a t of Oniscus asellus a n d is v e r y v a r i a b l e in colour, b u t it is usually a dark slaty grey w i t h irregular lighter markings. It can be recognised by t h e transverse rows of small tubercles t h a t cover t h e back of t h e head a n d b o d y . T h i s family is b e t t e r a d a p t e d t o live i n d r i e r c o n d i t i o n s t h a n a n y o f t h e p r e c e d i n g and the pleopods bear well-developed pseudotracheae although a certain a m o u n t of respiration also takes place t h r o u g h t h e integument of the body. T o t h e same family belongs t h e r e m a r k a b l e desert woodlouse Hemilepistus reaumuri w h i c h i s n o t u n c o m m o n i n N o r t h A f r i c a a n d

8

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t h e M i d d l e E a s t . T h e a n i m a l s live t o g e t h e r i n v e r t i c a l h o l e s 5 - 6 cm in diameter and m a n y centimetres in depth. A digging rea c t i o n is r e l e a s e d by a t e m p e r a t u r e of 35° C if t h e soil is d r y , a n d 4 5 ° C if it is m o i s t . T h e h e a d is p l a c e d a g a i n s t a s m a l l s t o n e or s o m e o t h e r r i g i d b o d y : t h e a n t e r i o r legs t h e n lift t h e s a n d b a c k w a r d s while t h e posterior ones t h r o w it away. S o m e t i m e s several animals c o m b i n e to dig a single hole and frequently t w o woodlice can be seen digging head to head. T h e pill-woodlice or A r m a d i l l i d i i d a e are so called b e c a u s e of t h e i r h a b i t o f r o l l i n g i n t o a b a l l like a little a r m a d i l l o . T h e a b i l i t y to do this is by no m e a n s restricted to this family however, b u t has evolved i n d e p e n d e n t l y in several diverse g r o u p s . In f o r m s that can curl up completely t h e head has b e c o m e flattened in an anterop o s t e r i o r d i r e c t i o n s o t h a t its h e i g h t i s m u c h g r e a t e r t h a n its l e n g t h a n d t h e front p a r t i s covered b y t h e last a b d o m i n a l a p p e n dages or u r o p o d s w h e n t h e animal rolls u p . ( I n other woodlice t h e u r o p o d s p r o j e c t like a c o u p l e o f s m a l l t a i l s f r o m t h e h i n d e r e n d o f t h e b o d y ) . T h e m o s t c o m m o n B r i t i s h s p e c i e s i s Armadillidium vulgare, s o m e t i m e s c a l l e d t h e 'Pill b u g ' , w h i c h r e a c h e s a l e n g t h o f 18 mm a n d is a little m o r e t h a n twice as long as b r o a d . T h e colour varies from completely black to pale yellow, b u t t h e m o r e usual shades are light grey. A s a l r e a d y m e n t i o n e d , w o o d l i c e h a v e little a b i l i t y t o p r e v e n t loss o f w a t e r b y e v a p o r a t i o n a n d e x c r e t i o n , a n d a l t h o u g h t h e y c a n r e g a i n lost w a t e r b o t h b y a c t i v e l y d r i n k i n g a n d a b s o r b i n g m o i s ture t h r o u g h their pleopods, they can only survive on land as a result of b e h a v i o u r m e c h a n i s m s t h a t k e e p t h e m in cool, m o i s t places. D u r i n g t h e day t h e y n o r m a l l y collect at t h e m o i s t e n d of a h u m i d i t y g r a d i e n t a n d avoid t h e light: it is at n i g h t t h a t dispersal to n e w environments mostly takes place. C h a n g e s in behaviour b e t w e e n d a y a n d n i g h t h a v e r e c e n t l y b e e n d e m o n s t r a t e d i n Oniscus asellus t h a t c a n p e r h a p s b e c o r r e l a t e d w i t h t h e e c o l o g y o f t h e s p e c i e s a s f o l l o w s : a fall i n t h e i n t e n s i t y o f t h e h u m i d i t y r e s p o n s e after d a r k e n a b l e s t h e a n i m a l s for a t i m e t o w a l k i n d r i e r p l a c e s than their day-time retreats, b u t increased photo-negative beh a v i o u r after e x p o s u r e t o d a r k e n s u r e s t h a t t h e y r e t u r n t o c o v e r a t daybreak, a n d t h u s no d o u b t avoid t h e early bird (Cloudsley-

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T h o m p s o n , 1952). T h e d e g r e e o f n o c t u r n a l activity i n different species is correlated w i t h the ability to w i t h s t a n d water-loss by t r a n s p i r a t i o n ( C l o u d s l e y - T h o m p s o n , 1956). I s o p o d s s h o w a r e g r e s s i o n i n t h e size o f t h e i r s e n s e o r g a n s which m a y be correlated with reduction in the rapidity of movem e n t o n b e c o m i n g terrestrial, for t h e a q u a t i c f o r m s are rapid s w i m m e r s . Ligia s p p . h o w e v e r , w h i c h c a n r u n p a r t i c u l a r l y r a p i d l y , have retained t h e big eyes of t h e i r m a r i n e ancestors. In a recent review of the adaptations of woodlice to the terrestrial habitat, E d n e y (1954) c o n c l u d e s t h a t different species can withstand terrestrial conditions of drought to varying degrees, but p r o b a b l y all s p e c i e s s p e n d m o s t o f t h e t i m e i n a n a t m o s p h e r e s a t u r a t e d w i t h w a t e r v a p o u r a n d m e r e l y differ i n t h e l e n g t h o f time that they are capable of surviving away from d a m p n e s s . T h u s e v e n Armadillidium a n d Hemilepistus s p p . c a n v e n t u r e i n t o d r y p l a c e s w i t h i m m u n i t y o n l y for c o m p a r a t i v e l y s h o r t p e r i o d s . E d n e y a l s o s u g g e s t s t h a t t h e r e a s o n w h y s o little p r o g r e s s h a s b e e n m a d e t o w a r d full e x p l o i t a t i o n o f t h e l a n d b y w o o d l i c e m a y lie i n t h e fact t h a t t h e c o n q u e s t o f t h e l a n d b y t h e I s o p o d a t o o k p l a c e v i a t h e l i t t o r a l z o n e , for Ligia a n d Halophiloscia a r e u n d o u b t e d l y primitive morphologically. N o w animals crossing this zone may well be subjected to extremely h i g h t e m p e r a t u r e s , a n d t h e ability t o lose h e a t b y e v a p o r a t i o n o f w a t e r m a y h a v e c o n s i d e r a b l e s u r vival v a l u e i n all s p e c i e s .

Food and feeding habits W o o d l i c e are o m n i v o r o u s a n d no d o u b t useful as scavengers. S o m e species are of economic i m p o r t a n c e because t h e y do not confine t h e i r a t t e n t i o n t o d e a d a n d decaying m a t t e r b u t s o m e t i m e s attack seedlings, ripe fruit s u c h as p l u m s , p e a c h e s or m e l o n s , a n d m u s h r o o m s — i n d e e d t h e y w i l l e a t a n y t h i n g t h a t i s soft a n d juicy t h o u g h they do m o r e mischief by disfiguring t h a n by cons u m i n g a n y l a r g e q u a n t i t i e s . T h e y a r e s o m e t i m e s difficult t o d i s lodge f r o m h o t h o u s e s as t h e y find shelter in every little crevice. N i c h o l l s ( 1 9 3 1 ) h a s s h o w n t h a t a l t h o u g h Ligia oceanica f e e d s p r i n c i p a l l y o n Fucus vesiculosus a n d o t h e r a l g a e , n o t h i n g e d i b l e c o m e s a m i s s , p a r t i c u l a r l y i f i t b e i n t h e n a t u r e o f a n i m a l offal, a n d cannibalism frequently takes place in captivity. T h e gut contents

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10

of one individual were found to include moss capsules and part of a s y n c y t i u m of Vaucheria. T h e s m a l l , m y r m e c o p h i l o u s Platyarthrus hoffmannseggi f e e d s o n fungi a n d their spores, t h e excreta of ants a n d other vegetable m a t t e r . S o m e s p e c i e s , e s p e c i a l l y Oniscus asellus, a r e d e c i d e d l y m o r e o m n i v o r o u s t h a n o t h e r s s u c h a s Porcellio scaber w h i c h c o n f i n e s its d i e t l a r g e l y t o t h e b a r k o f t r e e s a n d Trichoniscus pusillus w h i c h lives a l m o s t e n t i r e l y o n d e c a y i n g l e a v e s . A c c o r d i n g t o B r i s t o w e ( 1 9 4 1 ) * , w o o d l i c e will e a t s p i d e r s ' e g g s i n c a p t i v i t y , a n d a s t h e y a r e o f t e n t o b e f o u n d i n u n t e n a n t e d cells b e s i d e e m p t y e g g - s a c s it can be s u p p o s e d that t h e y d e v o u r A r t h r o p o d eggs w h e n e v e r an o p p o r t u n i t y o c c u r s . Armadillidium vulgare r e q u i r e s c h a l k in its d i e t , a n d t h i s m a y b e c o r r e l a t e d w i t h its e x c e p t i o n a l l y t h i c k l y c a l cified i n t e g u m e n t . 1

Enemies Woodlice are eaten by birds, reptiles, amphibia, and m a n y other insectivorous animals including spiders, harvest-spiders, mites and c e n t i p e d e s . T h e n u m b e r o f s p e c i e s o f s p i d e r w h i c h will d e s t r o y a w o o d l o u s e is, h o w e v e r , s o m e w h a t l i m i t e d . Armadillidium vulgare r o l l s i n t o a b a l l d i r e c t l y i t i s a t t a c k e d , a n d its h a r d , t h i c k i n t e g u m e n t s a v e s i t f r o m i n j u r y , e v e n f r o m l a r g e s p e c i e s s u c h a s Tegenaria atrica a n d Araneus diadematus. A c c o r d i n g to B r i s t o w e ( 1 9 4 1 ) * Porcellio, Oniscus a n d Philoscia s p p . s e c u r e s o m e p r o t e c t i o n f r o m the chitin with w h i c h their dorsal surface is covered so long as they r e m a i n dorsal surface u p p e r m o s t . In addition t h e y are distasteful to m o s t spiders, w h i c h reject t h e m except in t i m e s of food shortage w h e n their normal aversion is overcome by hunger. Distastefulness i s m o s t m a r k e d i n Porcellio s p p . a n d least i n Philoscia s p p . ( e x c e p t for Platyarthrus hoffmannseggi w h o s e m y r m e c o p h i l o u s h a b i t r e n d e r s i t l e a s t likely t o a t t a c k b y s p i d e r s ) . O n t h e o t h e r h a n d t h e c a v e a n d c e l l a r s p i d e r Meta menardi o f t e n o w e s i t s s u r v i v a l in s u b t e r r a n e a n s i t u a t i o n s t o t h e p r e s e n c e o f w o o d l i c e , a n d Dysdera crocota a n d D . erythrina h a v e j a w s s p e c i a l l y a d a p t e d t o g r i p a n d p e n e t r a t e t h e crustacean cuticle. At one time it was believed that certain tegumental glands 1

F o r references m a r k e d with an asterisk see bibliography of general works at the end of the volume.

WOODLICE

11

known as 'Weber's glands' played an important part in respiration. F o r nearly half a c e n t u r y t h e c o n c e p t t h a t these glands s e c r e t e d a fluid w h i c h m o i s t e n e d t h e gills c r e p t i n t o a l m o s t e v e r y text-book dealing with the subject of respiration in woodlice. Great, therefore, was the surprise of G o r v e t t (1950), w h o has m a d e a s p e c i a l s t u d y o f t h e g l a n d s o f w o o d l i c e , t o find t h a t ' W e b e r ' s g l a n d s ' d o n o t i n fact e x i s t e i t h e r i n t h e a n i m a l s o r i n t h e p u b l i c a tions of their supposed discoverer. Gorvett traced the m y t h to an 'inaugural dissertation' on respiration in woodlice published in 1909, i n w h i c h g l a n d s d e s c r i b e d b y W e b e r w e r e confused w i t h c e r t a i n s t r u c t u r e s i n t h e a b d o m e n t h a t h a d b e e n d e s c r i b e d , also incorrectly, by N e m e c in 1895-6. Apparently the accounts of W e b e r and N e m e c had never been compared, or it would at once have b e e n realised t h a t t h e two a u t h o r s w e r e dealing w i t h entirely different a n d totally u n r e l a t e d s t r u c t u r e s . A t l e a s t five k i n d s o f t e g u m e n t a l g l a n d s d o , h o w e v e r , o c c u r i n w o o d l i c e , o f w h i c h t h e r o s e t t e a n d l o b e d g l a n d s h a v e s o far b e e n investigated by G o r v e t t . S o m e of t h e latter discharge an acid secretion smelling of b u t y r i c acid, b u t others possess an odourless, n e u t r a l s o l u t i o n . T h e g l a n d s v a r y i n n u m b e r a n d size i n d i f f e r e n t species, b u t their variation a p p e a r s to be i n d e p e n d e n t of habitat or e v o l u t i o n a r y p o s i t i o n : i n fact t h e i r f u n c t i o n i s p r o b a b l y t o a c t a s a deterrent to enemies, principally hunting-spiders, since they do not s e e m to p r e v e n t excess evaporation as has s o m e t i m e s b e e n suggested. T h e y are t h u s analogous to t h e repugnatorial glands of millipedes, h a r v e s t - s p i d e r s a n d m a n y insects ( G o r v e t t , 1956). Woodlice do not seem to be attacked to any great extent by parasitoidal insects. T h o m p s o n (1934) m a d e a detailed s t u d y of t h e i r T a c h i n i d p a r a s i t e s d u r i n g w h i c h h e d i s s e c t e d 1,737 s p e c i m e n s of Porcellio scaber a n d Oniscus asellus c o l l e c t e d f r o m v a r i o u s localities i n E n g l a n d a n d F r a n c e b u t o n l y 9 . 1 % w e r e p a r a s i t i s e d , a n d t h e a v e r a g e p a r a s i t i s m o f O . asellus w a s o n l y 3 . 1 % . H e c o n cluded, therefore, that D i p t e r o u s parasites are not factors of major i m p o r t a n c e in t h e control of woodlice: certain species are scarcely p a r a s i t i s e d a t all a n d i n t h e c a s e o f o t h e r s , s t a r v a t i o n a n d c a n n i b a l ism c o m e into play as d e n s i t y - d e p e n d e n t factors controlling the 1

1

See discussion of density-dependent and d e n s i t y - i n d e p e n d e n t factors

on p . 1 4 1 .

12

WOODLICE

size o f p o p u l a t i o n s b e f o r e p a r a s i t e s c a n i n c r e a s e sufficiently t o b e c o m e of ecological i m p o r t a n c e .

Reproduction and life cycle Like other Crustacea, woodlice carry their eggs in a thoracic brood p o u c h or m a r s u p i u m and a whole family of newly hatched young may be found huddled up on the underside of the mother. T h e n u m b e r o f e g g s v a r i e s f r o m s e v e n p e r b r o o d i n Trichoniscus t o 1 0 0 - 2 0 0 o r m o r e i n Armadillidium. T h e n e w l y h a t c h e d larvae have a distinct h e a d a n d eyes, segm e n t e d b o d y and short, s t u m p y limbs. T h e y are incapable of m o v e m e n t f o r t h e first t h r e e d a y s a s t h e i r a p p e n d a g e s a r e t i g h t l y d o u b l e d against the b o d y . At this stage they are kept very moist, b u t a s t h e i r size i n c r e a s e s t h e fluid i n t h e b r o o d p o u c h d e c r e a s e s . T h e y o u n g e m e r g e o v e r a p e r i o d o f t w o o r t h r e e d a y s a n d t h e first moult occurs within 24 h o u r s of liberation. T h e period between the first a n d s e c o n d m o u l t i s t h e m o s t c r i t i c a l i n t h e i r lives, b e c a u s e i f t h e soil i s d r y a t t h i s t i m e t h e y d i e , w h i l e i f i t i s t o o m o i s t t h e y a r e u s u ally k i l l e d b y f u n g i . L a t e r t h e y a r e m o r e r e s i s t a n t a n d t h e i r life m a y b e q u i t e a l o n g o n e , for t h e y s e l d o m b r e e d u n t i l t h e y a r e t w o y e a r s o l d . T h e life c y c l e of Ligia oceanica l a s t s for t h r e e y e a r s a c c o r d i n g to N i c h o l l s ( 1 9 3 1 ) . A t l e a s t five b r o o d s o f y o u n g a r e p r o d u c e d , a n d t h e a v e r a g e n u m b e r o f y o u n g p e r b r o o d i s 8 0 . T h e t i m e t a k e n for the development of the y o u n g varies from 40 days in s u m m e r to 90 in winter, and although the greatest n u m b e r of animals with brood p o u c h e s is found in spring, b r e e d i n g occurs t h r o u g h o u t the year. T h e greatest interval between moults occurs in full-grown males in winter, the shortest in young specimens during the summer. T h e growth rate was observed in a y o u n g specimen to average 1.3 mm increase in length and 0.5 mm in width per m o n t h . Copulat i o n o c c u r s after t h e a p p e a r a n c e o f t h e m a t u r e b r o o d p l a t e s i n t h e f e m a l e . T h e o v a a r e s p a w n e d a b o u t t w o d a y s after t h e c o m p l e t i o n o f t h e m o u l t a n d , i f u n f e r t i l i s e d , r e m a i n v i a b l e for a t l e a s t t h r e e days subsequent to their appearance in the brood pouch. Heeley (1941) found that t h e respective durations of t h e successive stages in t h e b r e e d i n g processes, especially t h e e m b r y o n i c a n d larval p e r i o d s , w h i l s t v a r y i n g i n d i f f e r e n t s p e c i e s a r e m o r e o r less c o n s t a n t for e a c h p a r t i c u l a r s p e c i e s . T h e s e p e r i o d s r a n g e f r o m a n

WOODLICE

13

1/2

a v e r a g e o f 2 1 d a y s e m b r y o n i c a n d 3 d a y s l a r v a l p e r i o d i n Philoscia muscorum t o a n a v e r a g e o f 6 4 d a y s e m b r y o n i c ( i n f i r s t b r o o d ) a n d 9 d a y s l a r v a l p e r i o d i n Porcellio dilatatus. I n t h e s e s p e c i e s t h e b r e e d i n g p h a s e r a n g e s f r o m a n a v e r a g e o f 3 6 d a y s i n P h . muscorum t o 8 4 d a y s i n P . dilatatus. T h e a v e r a g e r a t i o s o f t h e l a r v a l p e r i o d t o t h e e m b r y o n i c p e r i o d of d e v e l o p m e n t in t h e b r o o d p o u c h , in different species, increases approximately in p r o p o r t i o n to t h e average n u m e r i c a l size o f t h e b r o o d s . 1/2

T h e g r a v i d i t y p e r i o d for Armadillidium vulgare i n M i c h i g a n averages 43 days at normal temperatures, according to Hatchett ( 1 9 4 7 ) . F o r Cylisticus convexus i t v a r i e s f r o m 4 4 t o 6 2 d a y s a n d a v e r a g e s 53 d a y s , w h i l e Porcellio scaber c a r r i e s its b r o o d for an a v e r a g e o f 4 4 d a y s . F e m a l e s o f P . (Tracheoniscus) rathkei a r e g r a v i d on t h e a v e r a g e for 39 d a y s . M a n y f e m a l e s of A. vulgare, C. convexus a n d P . scaber h a v e a t l e a s t t w o b r o o d s p e r y e a r , w h i l e P . rathkei u s u a l l y r e p r o d u c e s o n l y o n c e . T h e size o f t h e b r o o d i n C . convexus ranges from 10 to 70 with an average of 33 and the n u m b e r of young in b r o o d s raised in the laboratory was 24. U n d e r similar condit i o n s A. vulgare r a i s e d 2 8 , P. scaber 24 a n d P. rathkei 17 y o u n g . I n c o n t r a s t i n D a l l a s , T e x a s , A . vulgare h a s b e e n f o u n d t o p r o d u c e f r o m 29 to 79 y o u n g , whilst in Scotland, Collinge (1915) r e p o r t e d t h a t i n d i v i d u a l s r a i s e d i n c a p t i v i t y h a d b r o o d s o f 5 0 t o 150 with a m a x i m u m in one instance of 267. In France the n u m b e r v a r i e s f r o m 4 8 t o 156. W h e n t h e y o u n g are ready t o leave t h e b r o o d p o u c h t h e y b e c o m e rather active a n d crawl a b o u t until they are released t h r o u g h an opening between the plates of which the pouch is composed. D u r i n g their departure, the m o t h e r usually remains quiet or moves v e r y s l o w l y , k e e p i n g t h e f i r s t p a i r o f legs i m m o b i l e : t h e y o u n g e m e r g e h e a d first a n d c l i m b d o w n h e r first or s e c o n d pair of legs. T h e majority of t h e y o u n g , after leaving t h e i r p a r e n t , are n o t very active a n d r e m a i n t o g e t h e r in a g r o u p . T o w a r d s t h e e n d of t h e e m e r g e n c e p e r i o d t h e f e m a l e m o v e s a w a y , t h i s t i m e u s i n g all h e r legs, a n d t h e i r m o t i o n f o r c e s t h e f e w r e m a i n i n g y o u n g f r o m t h e m a r s u p i u m . If she is disturbed while carrying young in her brood pouch the female may, by rhythmical contraction of her body, force a p a r t t h e p a i r s o f p l a t e s f o r m i n g t h e m a r s u p i u m a n d r e l e a s e all h e r b r o o d a t o n c e . A full b r o o d p o u c h m a k e s i t n e c e s s a r y for

14

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t h e female to m o v e a r o u n d rather slowly a n d in a h u m p e d position: after t h e release of t h e b r o o d she a s s u m e s h e r n o r m a l position a n d moves about m o r e quickly. BIBLIOGRAPHY Identification E D N E Y , E. B. (1953) T h e woodlice of G r e a t Britain and Ireland. A concise systematic m o n o g r a p h . Proc. Linn. Soc. Lond., 1 6 4 , 4 9 - 9 8 . (1954) Synopses of the British Fauna, No. 9. British Woodlice. L o n d o n : Linn. Soc. SARS, G. O. (1896-9) An Account of the Crustacea of Norway, 2, (Isopoda). Bergen. V A N N A M E , W . G . (1936) T h e American land and freshwater Isopod Crustacea. Bull. Amer. Mus. Nat. Hist., 7 1 , 1 - 5 3 5 . W E B B , W. M. and SILLEM, C. (1906) The British Woodlice. L o n d o n . Biology C L O U D S L E Y - T H O M P S O N , J. L. (1952) Studies in diurnal r h y t h m s , I I . Changes in the physiological responses of the woodlouse Oniscus asellus to environmental stimuli. J. Exp. Biol., 2 9 , 2 9 5 - 3 0 3 . (1955) T h e biology of woodlice. Discovery, 1 6 , 2 4 8 - 5 1 . (1956) Studies in diurnal r h y t h m s , V I I . H u m i d i t y responses and nocturnal activity in woodlice (Isopoda). J. Exp. Biol., 3 3 , 576-82. COLLINGE, W. E. (1915) S o m e observations on the life history and habits of Isopoda (woodlice). Scot. Nat., 2 4 , 299-307. (1935) Woodlice, their folklore and local n a m e s . North w. Nat., 10, 19-21. E D N E Y , E. B. (1954) Woodlice and the land habitat. Biol. Rev., 2 9 , 185-219. (1954) Idem. New Biology, 1 7 , 4 1 - 5 7 . GORVETT, H. (1950) ' W e b e r ' s glands' and respiration in woodlice. Nature, Lond., 1 6 6 , 115. (1956) T e g u m e n t a l glands and terrestrial life in woodlice. Proc. Zool. Soc. Lond., 1 2 6 , 291-314. HATCHETT, S. P. (1947) Biology of the Isopoda of Michigan. Ecol. Monogr., 1 7 , 4 7 - 7 9 . HEELEY, W. (1941) Observations on the life-histories of some terrestrial Isopods. Proc. Zool. Soc. Lond. (B), 1 1 1 , 7 9 - 1 4 9 . H E W I T T , C. G. (1907) Ligia. L.M.B.C. Memoirs, X I V , 1-37. N I C H O L L S , A. G. (1931) Studies on Ligia oceanica, 1. A. H a b i t a t and effect of change of e n v i r o n m e n t on respiration. B. Observation on m o u l t i n g and breeding. J. Mar. Biol. Ass. U.K., 1 7 . 655-74. T H O M P S O N , W. R. (1934) T h e T a c h i n i d parasites of woodlice. Parasitology, 2 6 , 3 7 8 - 4 4 8 . VANDEL, A. (1943) Essai sur l'origine, Involution et la classification des Oniscoidea (Isopodes terrestres). Bull, biol., 3 0 , 1 - 1 3 6 .

CHAPTER

II

MILLIPEDES Classification and distribution T h e D i p l o p o d a , c o m m o n l y called millipedes, w e r e formerly a s s o c i a t e d w i t h t h e C h i l o p o d a , P a u r o p o d a a n d S y m p h y l a i n a class, t h e ' M y r i a p o d a ' , w h i c h c o n t a i n e d all t h e t e r r e s t r i a l A r t h r o p o d s that were not Crustacea, Arachnida or Insecta, b u t they are now

F I G . 5. Examples of millipede families: 1. Glomeridae, 2. Polyzoniidae, 3 . C h o r d e u m i d a e , 4 . Craspedosomidae, 5 . Polydesmidae, 6. Strongylosomidae, 7. Iulidae, 8. Blaniulidae, 9. Spirobolidae, 1 0 . Polyxenidae. (Drawings not to scale.) (After various authors.) 15

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t r e a t e d a s a s e p a r a t e class. T h e n a m e D i p l o p o d a , w h i c h m e a n s 'double-footed', was given to t h e m because in these animals most of the segments of t h e b o d y are provided with two pairs of limbs, a condition arising from t h e confluence of t w o adjacent tergal plates. As in the P a u r o p o d a and Symphyla, the reproductive o r g a n s have their a p e r t u r e s on t h e ventral side of t h e fore p a r t of the body near the head, whereas in the Chilopoda these open on t h e last a b d o m i n a l s o m i t e a s t h e y d o i n i n s e c t s . M i l l i p e d e s h a v e a d i s t i n c t h e a d b e a r i n g a p a i r o f s h o r t , u n b r a n c h e d a n t e n n a e , a t least t w o pairs of j a w s a n d usually eyes. Spiracles leading into t u b u l a r t r a c h e a e o p e n a b o v e t h e c o x a e o f t h e legs a n d t h e d o r s a l p l a t e s o f the segments are greatly developed as c o m p a r e d with the ventral. T h e majority of t h e D i p l o p o d a are included in t h e sub-class Chilognatha and their integument is hard and horny. Each double s e g m e n t is c o m p o s e d typically of a vaulted or nearly circular terg u m , one or two small pleural plates, two sternites and two pairs o f l e g s . T h e t e r g i t e s , p l e u r i t e s a n d s t e r n i t e s m a y all b e m o v a b l e , or they m a y coalesce into a solid ring, t h e significance of w h i c h will b e c o n s i d e r e d l a t e r . T h e r e a r e o n l y t w o p a i r s o f m o u t h p a r t s ; t h e first a r e b i t i n g m a n d i b l e s c o m p o s e d o f t w o o r t h r e e s e g m e n t s ; t h e second pair is fused to form a b r o a d plate or gnathochilarium. I n t h e m a l e s o n e p a i r o f legs i s m o d i f i e d for m a t i n g p u r p o s e s a n d its s t r u c t u r e i s a d i a g n o s t i c c h a r a c t e r i n m a n y s p e c i e s .

F I G . 6. T h e pill-millipede Glomeris marginata. (After CloudsleyThompson,

1956.)

T h e order Oniscomorpha contains millipedes whose body is s h o r t , b r o a d , s t r o n g l y c o n v e x a b o v e a n d flat b e l o w , a n d c a p a b l e o f being rolled into a ball as in s o m e woodlice. T h e r e are from 11 to

MILLIPEDES

17

13 tergal plates of which the second is e n o r m o u s l y e x p a n d e d at t h e s i d e s w h i l e t h e last f o r m s a r o u n d e d s h i e l d w h i c h fits a g a i n s t i t a n d conceals t h e h e a d w h e n t h e animals are coiled u p . I n t h e m a l e s t h e last, o r last t w o p a i r s o f l e g s f o r m c l a s p e r s a n d t h e b a s a l s e g m e n t s o f t h e last p a i r a r e m o d i f i e d a s s p e r m c a r r i e r s . T h e family G l o m e r i d a e contains t h e c o m m o n British pill-millipede, and a n u m b e r of other small species found in E u r o p e , America and Asia; w h i l e t h e S p h a e r o t h e r i i d a e h a v e a s o u t h e r n d i s t r i b u t i o n a n d occur in S o u t h Africa, M a d a g a s c a r , s o u t h e r n Asia a n d Australasia. S o m e o f t h e m a r e o f l a r g e size, s u r p a s s i n g a golf b a l l w h e n r o l l e d up. T h e millipedes of the order L i m a c o m o r p h a resemble the Onisc o m o r p h a i n g e n e r a l s t r u c t u r e b u t a r e o f s m a l l size, m e a s u r i n g not m o r e than about one quarter of an inch in length. T h e two families G l o m e r i d e s m i d a e a n d Z e p h r o n i o d e s m i d a e i n h a b i t tropical A m e r i c a a n d tropical Asia respectively: n o t h i n g is k n o w n of their biology. T h e t h i r d o r d e r , C o l o b o g n a t h a , a n d t h o s e t h a t f o l l o w differ from t h e t w o p r e c e d i n g in t h a t t h e last tergal plate encircles t h e a n u s w h i c h is closed below by a sternite a n d laterally by a pair of v a l v e s . T h e l a s t p a i r o f legs i s u n m o d i f i e d i n t h e m a l e . T h e b o d y is long, spirally coiled w h e n at rest a n d contains a large a n d variable n u m b e r of tergal plates which carry repugnatorial glands usually o p e n i n g on tubercles or larger keel-like o u t g r o w t h s . T h i s o r d e r i s f o u n d i n all t h e w a r m e r c o u n t r i e s o f t h e w o r l d w h e r e i t i s r e p r e s e n t e d by several families, such as t h e P s e u d o d e s m i d a e , Platydesmidae, Polyzoniidae and S i p h o n o p h o r i d a e , w h i c h exh i b i t a p r o g r e s s i v e r e d u c t i o n o f t h e m a n d i b l e s . I n Siphonophora spp. the m o u t h opens at the tip of a long, pointed, sucking and piercing beak formed by the labrum and gnathochilarium, the mandibles within it being greatly reduced. T h e only British m e m b e r of t h e C o l o b o g n a t h a is Polyzonium germanicum w h i c h h a s b e e n found on the chalk d o w n s of K e n t a n d Surrey. It is a bizarre form with semi-suctorial m o u t h p a r t s a n d can be readily identified in c o l l e c t i o n s f r o m t h e fact t h a t w h e n p r e s e r v e d i n a l c o h o l i t i s c o n v e x d o r s a l l y a n d flat o r c o n c a v e v e n t r a l l y . T h e m e m b e r s of the order Ascospermophora have 26 to 32 s e g m e n t s . T h e tergal plates coalesce w i t h t h e pleura, b u t t h e B

S.S.C.M.

18

MILLIPEDES

s t e r n i t e s a r e free. I n t h i s f e a t u r e t h e y c o n t r a s t w i t h all o t h e r Chilognatha except the O n i s c o m o r p h a . T h e tergites are provided with three pairs of symmetrically placed bristles and are usually keel-shaped or carinate at t h e sides, b u t have no stink glands. T h e r e is a pair of s p i n n i n g papillae on t h e last tergal plate. T h e o r d e r is r e p r e s e n t e d by several families, of w h i c h t h e C h o r deumidae, Brachychaeteumidae and Craspedosomidae are found typically in E u r o p e a n d N o r t h A m e r i c a in the n o r t h e r n h e m i s p h e r e , while t h e H e t e r o c h o r d e u m i d a e range from tropical Asia to N e w Zealand in t h e s o u t h e r n h e m i s p h e r e . T h e British forms are small, p a l e a n i m a l s a n d i n c l u d e s p e c i e s of Brachychaeteutna, Microchordeuma, Craspedosoma rawlinsi w h i c h is m o r e r i c h l y c o l o u r e d a n d h a s l a t e r a l t e r g a l e x p a n s i o n s like t h o s e o f t h e P o l y d e s m i d a e , a n d Polymicrodon polydesmoides, w h i c h u s u a l l y i n h a b i t s t h e leafy floor o f d e c i d u o u s w o o d l a n d s . T h e flat-backed millipedes of the order P r o t e r o s p e r m o p h o r a have 19 or 20 tergal plates welded with the pleura and sternites to f o r m solid rings usually p r o v i d e d w i t h lateral shelf-like carinae. I n t h i s , t h e y differ f r o m o t h e r f l a t - b a c k e d f o r m s ( B r a c h y c h a e t u m i d a e ) . T h e r e a r e n o e y e s , n o s p i n n i n g p a p i l l a e o n t h e last t e r g a l plate, a n d t h e pores of t h e repugnatorial glands w h e n these are p r e s e n t are b o r n e on t h e lateral carinae. T h e m e m b e r s of this o r d e r b e l o n g to several families such as t h e P o l y d e s m i d a e , C r y p t o desmidae a n d Strongylosomidae, a n d are referred to a vast n u m b e r o f g e n e r a a n d s p e c i e s f o u n d i n all t h e c o u n t r i e s o f t h e w o r l d . S o m e o f t h e t r o p i c a l s p e c i e s a r e l a r g e r e a c h i n g a l e n g t h o f a b o u t six inches, and may be brightly coloured. T h e British fauna includes a n u m b e r of s p e c i e s of P o l y d e s m i d a e of w h i c h Polydesmus angustus is t h e m o s t c o m m o n , a d o u b t f u l r e c o r d of Eumastigonodesmus bond ( f a m i l y M a s t i g o n o d e s m i d a e ) a n d s o m e r e p r e s e n t a t i v e s o f t h e f a m i l y S t r o n g y l o s o m i d a e . T h e s e i n c l u d e Macrosternodesmus palicola, t h e s m a l l e s t B r i t i s h D i p l o p o d , Ophiodesmus albonanus a n d Oxidus (Paradesmus) gracilis w h i c h is f o u n d in g r e e n h o u s e s all o v e r the country. T h e Lysiopetalidae, w h i c h are usually r e g a r d e d as a separate s u b - o r d e r from t h e p r e v i o u s families w h i c h are g r o u p e d t o g e t h e r in the s u b - o r d e r Polydesmoidea, are not represented in the B r i t i s h f a u n a l list. T h e s e a n i m a l s a r e f o u n d i n E u r o p e , A s i a M i n o r

MILLIPEDES

19

a n d N o r t h Africa a n d have a great a n d variable n u m b e r of tergal plates, m o s t of w h i c h are provided with repugnatorial glands. T h e anterior pair of legs of t h e s e v e n t h s e g m e n t is again modified, as s p e r m carriers however, a n d t h e seminal d u c t s perforate t h e basal s e g m e n t s o f t h e s e c o n d p a i r . S o m e s p e c i e s o f Lysiopetalum m a y r e a c h f o u r o r five i n c h e s i n l e n g t h . T h e last o r d e r of C h i l o g n a t h a is t h e O p i s t h o s p e r m o p h o r a , t h e m e m b e r s of w h i c h have a large a n d variable n u m b e r of cylindrical t e r g a l p l a t e s all o f w h i c h , e x c e p t for a f e w a t t h e a n t e r i o r e n d , a r e provided with repugnatorial glands. In n u m b e r of species, genera a n d f a m i l i e s , t h e o r d e r s u r p a s s e s all o t h e r o r d e r s o f t h e C h i l o g n a t h a . T h e families are usually g r o u p e d into t h r e e s u b - o r d e r s , t h e first o f w h i c h i n c l u d e s t h e S t e m m i u l i d a e w h i c h a r e f o u n d i n t h e tropics of Asia, Africa a n d A m e r i c a . T h e second contains t h e families Iulidae, Blaniulidae, w h i c h are r e p r e s e n t e d in Britain by m a n y species and genera, and t h e Spirostreptidae w h i c h is a b u n dant in t h e tropics and contains some of the largest millipedes in the world. T h e third sub-order includes the Spirobolidae which a r e also w i d e l y d i s t r i b u t e d i n t r o p i c a l r e g i o n s a n d a r e r e p r e s e n t e d b y n u m e r o u s g e n e r a a n d s p e c i e s , s o m e o f w h i c h rival t h e l a r g e s t s p e c i e s of Spirostreptus in size. T h e sub-class P s e l a p h o g n a t h a contains a single widely distributed order, Penicillata, comprising the family Polyxenidae a n d t w o g e n e r a Polyxenus a n d Lophoproctus. T h e s e a r e m i n u t e m i l l i p e d e s h a v i n g a soft i n t e g u m e n t w i t h o u t h o r n y p l a t e s b u t r i c h l y provided with rows a n d tufts of peculiarly shaped bristles. T h e m o u t h p a r t s are complicated and appear to consist of four pairs. T h e b o d y i s c o m p o s e d o f e l e v e n s o m i t e s o f w h i c h t h e first f o u r c a r r y a s i n g l e p a i r o f legs, t h e n e x t f o u r t w o p a i r s a n d t h e n i n t h o n e p a i r , t h e last t w o s e g m e n t s b e i n g l e g l e s s . O f t h e t h i r t e e n p a i r s o f legs n o n e is m o d i f i e d as g o n o p o d s . O n e s p e c i e s , Polyxenus lagurus, occurs in Great Britain.

General behaviour F r o m a study of t h e locomotory m e c h a n i s m s a n d associated s t r u c t u r e s of a series of millipedes r e p r e s e n t i n g t h e major s u b divisions of t h e D i p l o p o d a , M a n t o n (1954) has s h o w n t h a t t h e e v o l u t i o n o f t h e class h a s b e e n r e l a t e d t o t h e d e v e l o p m e n t o f a

20

MILLIPEDES

m a r k e d ability to p u s h by t h e m o t i v e force of t h e legs. By this m e a n s t h e a n i m a l s a c h i e v e e i t h e r h e a d - o n b u r r o w i n g i n t o leaf m o u l d , or p u s h w i t h t h e dorsal surface of the back into splits in wood, spaces u n d e r bark a n d other specialised habitats. T h e habit of curling t h e b o d y into a protective spiral has b e e n a second f a c t o r o f m a j o r e v o l u t i o n a r y i m p o r t a n c e . T h e n e c e s s a r y p o w e r for this p u s h i n g is achieved by the use of gaits in w h i c h the backstroke of the limbs is of very m u c h longer duration than the forward stroke. T h e s e gaits r e q u i r e t h e p r e s e n c e of v e r y m a n y legs to each metachronal wave and this has been achieved by the evolution of numerous diplo-segments. Although moderate fleetness has been evolved m a n y times, particularly in the Colobognatha a n d Polyd e s m o i d e a , fast g a i t s u s u a l l y a p p e a r t o b e o f l e s s e r s i g n i f i c a n c e t o millipedes t h a n t h e slow, powerful gaits. S o m e species of Iulidae can on occasion m a k e use of an u n u s u a l escape reaction. Instead of c u r l i n g u p , t h e y w r i t h e t h e b o d y i n a s e r i e s o f u n d u l a t i n g flexions, wriggling rapidly t h r o u g h the grass or vegetation without using t h e i r feet a t all ( F r y e r , 1 9 5 7 e t c ) . T h i s habit appears to be an incidental accomplishment, however, a n d has n o t b e e n of evolutionary significance. M o r e i m p o r t a n t is t h e ability to climb s m o o t h rock surfaces at any angle f o u n d in Polyzonium germanicum a n d a m o n g t h e o t h e r C o l o b o g n a t h a , w h i c h a r e also a d a p t e d f o r p u s h i n g i n s t o n y p l a c e s . T h i s c l i m b i n g h a b i t necessitates a powerful grip by t h e opposite legs of a pair a n d p o s s i b l y t h e u s e o f a d h e s i v e c o x a l sacs w h e n t h e a n i m a l i s a t r e s t . V a r i o u s s p e c i a l i s a t i o n s e x i s t for s t r e n g t h e n i n g t h e s k e l e t o n a n d for r e s i s t i n g t e l e s c o p i n g a t t h e i n t e r - r i n g j o i n t s ( M a n t o n , 1 9 5 4 ) . T h i s m a y w e l l b e t h e e x p l a n a t i o n for t h e u n u s u a l s o l i d i t y o f t h e millipede cuticle w h i c h is h a r d e n e d not only by phenolic t a n n i n g a s i n i n s e c t s a n d A r a c h n i d s , b u t also b y t h e d e p o s i t i o n o f c a l c i u m as in the Crustacea ( C l o u d s l e y - T h o m p s o n , 1950b). F r o m a physiological point of view d e p e n d e n c e u p o n moist and h u m i d s u r r o u n d i n g s is o n e of t h e m o s t i m p o r t a n t factors in t h e lives o f m i l l i p e d e s , a s o f w o o d l i c e , c e n t i p e d e s a n d o t h e r m y r i a p o d s . F o r e x a m p l e , it h a s b e e n s h o w n t h a t Oxidus (Paradesmus) gracilis, a tropical species widely distributed in glasshouses in t e m p e r a t e r e g i o n s , a n d t h e ' s p o t t e d s n a k e m i l l i p e d e ' Blaniulus guttulatus, a r e stimulated by d r o u g h t a n d c o m e to rest only in moist places

MILLIPEDES

21

( C l o u d s l e y - T h o m p s o n , 1951c). U n d e r t h e influence of desiccation t h e a n i m a l s s h o w p o s i t i v e g e o t a x i s a n d m o v e d e e p e r i n t o t h e soil. A l t h o u g h t h e r e a c t i o n s o f m i l l i p e d e s t o m o i s t u r e a r e far m o r e m a r k e d t h a n are their responses to the h u m i d i t y of the atmosphere, S h e l f o r d ( 1 9 1 3 ) h a s s h o w n t h a t Fontaria corrugata is r e p e l l e d by d r y air a n d m o r e recently P e r t t u n e n (1953) has f o u n d t h a t w h e r e a s O . gracilis i s v e r y s e n s i t i v e t o d i f f e r e n c e s a t t h e h i g h e r e n d o f t h e h u m i d i t y r a n g e , Schizophyllum sabulosum, w h i c h h a s a m u c h l o w e r rate of water-loss, particularly in s u m m e r , t e n d s initially to m o v e t o w a r d s d r y air a n d t h e reaction is g r a d u a l l y reversed to moist as desiccation proceeds. Orientation is entirely 'kinetic' or nondirectional, speed is greater in d r y air t h a n in moist, a n d in an exp e r i m e n t a l c h a m b e r in w h i c h a choice of h u m i d i t i e s is provided, both t h e time spent and the distance covered are greater on the m o i s t side. In this species females that are just a b o u t to start egglaying s h o w a reversal of their h u m i d i t y reaction a n d t h e r e is t h e n a c l e a r a n d i n t e n s e r e s p o n s e t o m o i s t u r e ( P e r t t u n e n , 1955). I n a s i m i l a r w a y , d u r i n g t h e s u m m e r , Polyzonium germanicum w a l k s o n the u n d e r surface of s m o o t h chalk boulders, where it m a y remain for h o u r s o r d a y s h a n g i n g o n ' i n a c h i t o n - l i k e m a n n e r w i t h n e i t h e r h e a d , a n t e n n a e o r legs e x p o s e d ' , b u t d u r i n g t h e w i n t e r i t p e n e t r a t e s i n t o d a m p a n d c o m p a c t v e g e t a b l e m a t t e r a n d leaf m o u l d , f r e q u e n t l y d e e p i n m o s s , w h e r e i t r e m a i n s c u r l e d u p for w e e k s w i t h o u t m o v i n g . I t i s t h e n difficult t o f i n d d e s p i t e its b r i g h t o r a n g e c o l o u r ( M a n t o n 1954). T h e response of millipedes to moisture has some economic imp o r t a n c e for, u n d e r c o n d i t i o n s o f d r o u g h t , t h e y m a y b e f o r c e d t o a t t a c k g r o w i n g c r o p s for t h e s a k e o f w a t e r . A f t e r s o m e y e a r s ' r e search on the physiology a n d ecology of these animals, the writer concluded that outbreaks of the 'spotted snake millipede' tend to b e s t i m u l a t e d b y a d r y spell f o l l o w i n g a p e r i o d s u i t a b l e t o t h e r e p r o d u c t i o n o f t h e s p e c i e s w h e n t h e soil i s d a m p , u n d i s t u r b e d a n d rich i n h u m u s . I t w a s s h o w n e x p e r i m e n t a l l y that h u m u s a n d rotting substances have a texture w h i c h is preferred by millipedes to that of living plant tissues, a n d that the animals are attracted to dilute concentrations of sugars. No d o u b t a moist season combined with the use of farmyard m a n u r e or the growing of some crop producing a considerable

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a m o u n t o f h u m u s , will e n g e n d e r a g r e a t i n c r e a s e i n t h e n u m b e r o f m i l l i p e d e s i n t h e soil, p a r t i c u l a r l y i f t h e g r o u n d i s n o t d i s t u r b e d b y p l o u g h i n g , etc. T h e y m a y be beneficial at this stage in aiding t h e b r e a k d o w n of the h u m u s , b u t if the following season is dry, even for a s h o r t s p e l l , t h e y m a y b e c o m p e l l e d t o a t t a c k c r o p s for t h e sake of moisture. O n c e an attack has been initiated, a return to their n o r m a l diet of h u m u s a n d d e c o m p o s i n g m a t t e r is m o s t u n likely, d u e t o t h e a t t r a c t i o n o f s u g a r s i n t h e p l a n t s a p . I t i s u n likely t h a t d a m a g e b y m i l l i p e d e s t o c r o p s w i t h t o u g h e x t e r i o r s s u c h as p o t a t o e s a n d m a n g o l d s can ever be p r i m a r y , for n o t only do their weak m o u t h p a r t s p r e v e n t t h e m from gaining access, b u t i n addition they are not attracted to u n b r o k e n skins of potatoes, only to cut surfaces. O n c e an entrance has been achieved however, through mechanical damage or the bites of wire-worms and other p e s t s , t h e m i l l i p e d e s will e a t o u t t h e e n t i r e c e n t r e o f a p o t a t o a n d t h e d a m a g e they cause is often followed by fungal attack (CloudsleyT h o m p s o n , 1 9 5 0 a ) . F u r t h e r m o r e , t h e fact t h a t s i n g l e p o t a t o e s h a v e b e e n f o u n d c o n t a i n i n g o v e r a h u n d r e d Blaniulus guttulatus of all a g e s w h i l e t h e r e m a i n d e r o f t h e c r o p w a s u n h a r m e d , s h o w s that they m u s t have been attracted to a damaged tuber and could not have bred there. Millipedes t e n d to avoid t h e light, b u t w i t h t h e exception of a directed response or 'taxis' away from light in those forms that possess eyes a n d a r e s p o n s e to gravity (which of course c a n n o t be other than directed since the stimulus is constant) the behaviour r e a c t i o n s of m i l l i p e d e s a r e e n t i r e l y n o n - d i r e c t i o n a l . Oxidus gracilis a n d Blaniulus guttulatus a r e w i t h o u t e y e s b u t t h e y p o s s e s s a d e r m a l light sense. W h e n i l l u m i n a t e d t h e y crawl a r o u n d until b y c h a n c e they find themselves in darkness w h e r e they c o m e to rest. T h e i r t e m p e r a t u r e r e a c t i o n s fall i n t o t h r e e c a t e g o r i e s . T h e r e i s a g e n e r a l m e t a b o l i c effect u p o n t h e s p e e d o f l o c o m o t i o n a n d d u r a t i o n o f t h e s p i r a l reflex a n d a k i n e t i c ' p r e f e r e n c e ' f o r t e m p e r a t u r e s a b o u t 15° C , while sudden drops of temperature engender intense locomotory activity. A i r b o r n e o d o u r s are apparently not detected, b u t millipedes respond to sugars by m e a n s of taste sense organs on their a n t e n n a e a n d m o u t h p a r t s ( C l o u d s l e y - T h o m p s o n , 1951c). A s they walk about, m i l l i p e d e s steadily t a p t h e surface over w h i c h they are moving with the tips of their antennae and no d o u b t constantly

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t e s t its n a t u r e b y m e a n s o f t h e s e n s o r y h a i r s a n d c h e m o - r e c e p t i v e sensillae referred to. Although to millipedes, as to woodlice and to the other myriapods, h u m i d i t y is t h e m o s t i m p o r t a n t factor of the e n v i r o n m e n t , t h e s e a n i m a l s a r e n o t a b l e t o find t h e i r w a y d i r e c t l y t o d a m p places: instead, they are merely repelled by d r o u g h t . Nevertheless

F I G . 7. Sense organs of the millipede Oxidus gracilis. Left, antenna and below the seventh and eighth segments m o r e highly enlarged to show peg and cone sensillae. Right, gnathochilarium or lower lip with one of the palps m o r e highly magnified to show peg-organs. (After C l o u d s l e y - T h o m p s o n , 1951.) this stereotyped and curiously negative behaviour is surprisingly effective i n p r e v e n t i n g t h e m f r o m w a n d e r i n g a w a y f r o m t h e i r n o r mal habitats: b u t it does raise t h e p r o b l e m of h o w dispersal can take place and n e w habitats b e c o m e colonised. T h e r e are a n u m b e r of cases on record of millipedes, sometimes accompanied by centipedes, a n d woodlice migrating in vast armies.

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Occasionally they have crossed railways and b e e n squashed in such n u m b e r s that locomotives have been impeded and sand has h a d to be strewn on t h e lines before their driving wheels w o u l d grip. At other times cattle have refused to graze on invaded past u r e s , w e l l s h a v e b e e n filled w i t h d r o w n e d c o r p s e s a n d w o r k m e n c u l t i v a t i n g t h e fields h a v e b e c o m e n a u s e a t e d a n d d i z z y f r o m t h e odour of millipedes crushed by their hoes. However, such mass m i g r a t i o n s a r e o f r a r e o c c u r r e n c e a n d local i n e x t e n t , s o t h a t t h e i r n e t effect o n d i s t r i b u t i o n i s p r o b a b l y n e g l i g i b l e . T h e subject of migration in myriapods has been reviewed by C l o u d s l e y - T h o m p s o n (1949b; 1951a) a n d it h a s b e e n suggested t h a t a l t h o u g h c e r t a i n a s p e c t s o f t h e p h e n o m e n o n a r e still n o t e x plained, the evidence lends support to the hypothesis that mass m i g r a t i o n is m e r e l y an e x t r e m e case of t h e m o r e familiar s u d d e n a t t a c k s o n c r o p s d u e t o e x t r e m e l y f a v o u r a b l e local c o n d i t i o n s , followed by drought and possibly accompanied by abnormal physiological c o n d i t i o n s o f r e p r o d u c t i o n . An explanation of the p r o b l e m of h o w dispersal can take place has been suggested as a result of recent w o r k in w h i c h it has been shown that millipedes are markedly nocturnal and show a diurnal c y c l e of r h y t h m i c a c t i v i t y . In O. gracilis a n d B. guttulatus t h i s is p r i m a r i l y a r e s p o n s e t o l i g h t a n d d a r k n e s s , b u t i s also c o r r e l a t e d w i t h t h e s t i m u l u s o f falling t e m p e r a t u r e i n t h e e v e n i n g . A k t o g r a p h experiments on two large W e s t African species of millipedes have demonstrated an endogenous diurnal rhythm independent of fluct u a t i n g l i g h t a n d t e m p e r a t u r e a n d p e r s i s t i n g i n Ophistreptus s p . u p to nineteen days. L o c o m o t o r y activity is stimulated by increases or decreases of t e m p e r a t u r e , and it is probable that in tropical forms t e m p e r a t u r e fluctuations are of p r i m a r y i m p o r t a n c e in the initiation of diurnal r h y t h m s . Perhaps in their natural gloomy habitat in tropical forests, light is an insignificant e n v i r o n m e n t a l factor ( C l o u d s l e y - T h o m p s o n , 1951b). T h u s it is at night that millipedes, like o t h e r m y r i a p o d s a n d w o o d l i c e , a r e a b l e t o d i s p e r s e t h e m s e l v e s and overcome the restrictions inherent in the physiology of their integuments. B l o w e r (in K e v a n , 1 9 5 5 ) * h a s s u g g e s t e d t h a t m i l l i p e d e s a r e d i s t r i b u t e d a t v a r i o u s d e p t h s i n t h e soil a c c o r d i n g t o t h e i r w a t e r relations and b o d y forms. N e m a t o p h o r a and Polydesmoidea w h i c h '

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are m o s t susceptible to desiccation and wetting tend to inhabit thick leaf-litter w h i c h is proof against flood a n d d r o u g h t , while m a n y o f t h e I u l i d a e a n d B l a n i u l i d a e p e n e t r a t e d e e p l y i n t o t h e soil. H e also m a k e s t h e i n t e r e s t i n g s u g g e s t i o n t h a t c a l c i u m i o n s i n t h e soil w a t e r m a y e x e r t a beneficial effect b y l i m i t i n g t h e p e r m e a b i l i t y of the epidermis.

F I G . 8. T w o types of aktograph apparatus suitable for use with millipedes, each consisting of an arena or box pivoted on a knifeedge along its m e d i a n transverse axis. A n y m o v e m e n t of an animal along the longitudinal axis tips the arena and is recorded by a lever balanced by an adjustable counterpoise and writing on a revolving smoked d r u m . (After G u n n and K e n n e d y , 1937, and D'Aguillar, 1952.) S o m e other aspects of the biology of the D i p l o p o d a are w o r t h y of mention. Millipedes not infrequently occur as guests in the n e s t s o f a n t s a n d t e r m i t e s . I n B r i t a i n t h r e e s p e c i e s , Blaniulus guttulatus, Proteroiulus fuscus a n d Polyxenus lagurus, are frequently m y r m e c o p h i l o u s ( D o n i s t h o r p e , 1927)* a n d in t h e tropics several species have b e e n seen a c c o m p a n y i n g c o l u m n s of a r m y ants on t h e m a r c h . A n u m b e r of species are cavernicolous and have b e c o m e a d a p t e d in varying degrees to a troglodytic existence. T h e r e is extensive literature on the subject. R e p o r t s of l u m i n o u s m i l l i p e d e s are few. O n e of t h e m o s t striking e x a m p l e s is Luminodesmus sequoiae, a l a r g e a n d h a n d s o m e s p e c i e s measuring some 40 mm in length, that inhabits the Sequoia National Forest in California. L u m i n e s c e n c e first appears on hatching. It is continuous, u n d e r no voluntary control. Its source

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a p p a r e n t l y lies i n t h e d e e p e r l a y e r s o f t h e i n t e g u m e n t . A t t e m p t s t o d e m o n s t r a t e t h e classical ' l u c i f e r i n - l u c i f e r a s e ' a c t i v i t y i n t h i s species have been unsuccessful ( D a v e n p o r t , W o o t t o n a n d C u s h ing, 1952). Finally t h e r e are a n u m b e r of cases on record of p s e u d o - p a r a s i t ism by millipedes in the alimentary tract of m a n .

Food and feeding habits M i l l i p e d e s are vegetarian a n d feed on a w i d e range of p l a n t s u b stances, although on account of their weak m o u t h p a r t s m a n y s p e c i e s t e n d t o p r e f e r soft o r d e c o m p o s i n g t i s s u e s ( B r a d e - B i r k s , 1 9 3 0 ) . T h e y h a v e also b e e n r e c o r d e d a s e a t i n g d e a d w o r m s , m o l luscs, insects a n d vertebrates. As already m e n t i o n e d , a n u m b e r of species are w e l l - k n o w n agricultural a n d glass-house pests. Of these w i t h o u t d o u b t t h e w o r s t offender in t e m p e r a t e climates is t h e ' s p o t t e d s n a k e m i l l i p e d e ' , Blaniulus guttulatus, w h i c h h a s l o n g b e e n regarded as a pest of sugar beet, potatoes, m a n g o l d s , oats, w h e a t , strawberries a n d o t h e r agricultural c r o p s a n d fruit. It has b e e n s h o w n that outbreaks of this species t e n d often to be stimulat e d b y a d r y spell f o l l o w i n g a p e r i o d s u i t a b l e t o t h e r e p r o d u c t i o n o f t h e s p e c i e s , w h e n t h e soil i s d a m p , u n d i s t u r b e d a n d r i c h i n h u m u s . T h e y u s u a l l y o c c u r o n m e d i u m o r h e a v y soil a n d a r e i n h i b i t e d o r destroyed by extreme drought. Breeding is probably inhibited by m o d e r a t e l y d r y w e a t h e r . T h e species m a y b e beneficial i n aiding the b r e a k d o w n of h u m u s , b u t is a potential danger to growing crops and m a y even attack potatoes and m a n g o l d s if wire-worms a n d o t h e r a g r i c u l t u r a l p e s t s a r e p r e s e n t t o m a k e a n initial e n t r y ( C l o u d s l e y - T h o m p s o n , 1950a). S c h u b a r t (1942) has given a c o m prehensive bibliography of t h e m y r i a p o d s a n d their relation to agriculture, a n d this has b e e n s u p p l e m e n t e d by R e m y (1950a), while Brade-Birks (1930) has studied the economic status of the British Diplopoda. Although it has long been assumed that m y r i a p o d s possess powers of taste and various antennary and gnathochilarial structures have b e e n r e g a r d e d as gustatory sense organs, t h e ability of millipedes to react to contact chemical stimuli has only once or twice been tested experimentally. In 1943, Lyford published an interesting account of his experiments on the palatability of various

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f o r e s t l e a v e s t o Cylindroiulus londinensis. I t w a s f o u n d t h a t t h e p a l a tability of leaves from t h e s a m e tree a n d from adjacent trees of t h e same species showed some variability b u t not e n o u g h to mask the difference in palatability b e t w e e n species. In general, t h e m o s t palatable leaves h a d a high calcium c o n t e n t while t h e u n p a l a t a b l e l e a v e s h a d n o t . M o r e r e c e n t l y i t h a s b e e n f o u n d t h a t lulus a n d Cylindroiulus s p p . e a t q u a n t i t i e s o f n e w l y fallen l e a v e s f r o m t h e s u r f a c e o f a m i x e d b e e c h f o r e s t floor, a n d e v e n m o r e o f t h e l e a v e s t h a t a r e a y e a r o l d e r . Iulus s p p . e a t m o r e oak t h a n o f a n y o t h e r t y p e o f leaf, Cylindroiulus s p p . m o r e p i n e . I t h a s also b e e n s h o w n t h a t Oxidus gracilis a n d Blaniulus guttulatus a r e a t t r a c t e d to g l u c o s e and sucrose with a threshold about 0.5gm/litre: b u t there is no attraction to asparagine or starch. As already mentioned, the antennal a n d gnathochilarial basiconic sensillae are t h e sensory receptors for taste stimuli: millipedes do n o t r e s p o n d to a i r b o r n e o d o u r s ( C l o u d s l e y - T h o m p s o n , 1951c).

Enemies Millipedes, on occasion, are eaten by a wide range of predatory a n i m a l s . T h e s e i n c l u d e s p i d e r s , s o m e s p e c i e s o f w h i c h will f e e d r e l u c t a n t l y on t h e c o m m o n b l a c k Tachypodoiudus niger, Oxidus gracilis a n d o t h e r s m a l l f o r m s ; a n t s , fishes, a m p h i b i a n s , r e p t i l e s , m a m m a l s a n d b i r d s ( C l o u d s l e y - T h o m p s o n , 1949). O f these, only t o a d s a n d b i r d s feed o n m i l l i p e d e s t o a n a p p r e c i a b l e d e g r e e . M i l l i p e d e s f o r m a c o n s t a n t a r t i c l e o f d i e t o f t h e A m e r i c a n t o a d Bufo lentiginosus, a s m a n y a s s e v e n t y - s e v e n h a v i n g b e e n f o u n d i n o n e s t o m a c h , a n d 1 0 % by b u l k of t h e food of this species is c o m p o s e d o f m i l l i p e d e s . T h e B r i t i s h B . vulgaris, w h i c h will e a t a l m o s t a n y t h i n g i t c a n c a t c h , will r e a d i l y d e v o u r m i l l i p e d e s , w h i c h a r e also eaten by frogs a n d s a l a m a n d e r s . M i l l i p e d e s c o m p r i s e a p r o p o r t i o n o f t h e f o o d o f m a n y s p e c i e s o f b i r d s , b u t a s far a s i s k n o w n n o n e equals the starling in their destruction. In America millipedes average up to 1 1 . 7 1 % of this b i r d ' s yearly diet. In April they form 5 4 . 6 9 % , i n M a y 4 2 . 1 9 % a n d i n J u n e 2 3 . 6 6 % . A f t e r a falling off i n t h e l a t e r s u m m e r m o n t h s t h e y a g a i n rise t o 7 . 6 4 % i n O c t o b e r . T h e fact t h a t i n A p r i l 119 o f 1 3 2 a d u l t b i r d s e x a m i n e d , i n M a y 133 o f 140 a n d i n J u n e 146 o f 2 1 5 , h a d e a t e n m i l l i p e d e s , g i v e s a n i d e a o f t h e p e r s i s t e n c e w i t h w h i c h s t a r l i n g s m u s t s e a r c h for s u c h f o o d .

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Fifteen of the birds taken in April were found to have eaten n o t h i n g else, a n d n i n e t e n t h s o f t h e f o o d o f f o u r t e e n o t h e r s w a s c o m p o s e d of millipedes. T o m o s t animals, however, millipedes are r e n d e r e d s o m e w h a t unpalatable on account of their t o u g h i n t e g u m e n t and by t h e irritant exudates secreted by the repugnatorial glands of the Colobognatha, Proterospermophora and Opisthospermophora. T h e struct u r e o f t h e s e g l a n d s i s v e r y s i m i l a r i n all t h r e e o r d e r s . T h e y a r e sac-like in shape a n d each discharges into a l u m e n w h i c h in t u r n leads to t h e foramen or opening. T h o u g h t h e glands themselves c a n n o t b e c o m p r e s s e d , t h e i r o p e n i n g s can b e regulated b y special muscles, while other muscles nearby exert considerable pressure w h e n t h e animal m o v e s s u d d e n l y . In m o s t cases t h e secretion is e x u d e d fairly s l o w l y f r o m t h e p o r e s o f t h e g l a n d s b u t i n s o m e o f the larger tropical forms it can be discharged to a considerable dist a n c e i n t h e f o r m o f a fine j e t o r s p r a y .

F I G . 9. Distribution of repugnatorial glands on the segments of a millipede Oxidus gracilis. Right, section of an individual gland. (After W e b e r , 1882.) T h e m a x i m u m r e c o r d e d a c h i e v e m e n t w a s a d o u b l e salvo from a Rhinocricus lethifer in H a i t i w h i c h s e n t its d i s c h a r g e 28 i n c h e s on o n e s i d e a n d 3 3 o n t h e o t h e r , t h e d r o p l e t s falling f a n w i s e a r o u n d t h e b o d y . T h e r e p u g n a t o r i a l fluid o f t h e l a r g e t r o p i c a l s p e c i e s h a s a strong caustic action and causes blackening on contact with the

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h u m a n s k i n . L a t e r t h e affected p a r t p e e l s , l e a v i n g a w o u n d w h i c h heals only very slowly. It is d a n g e r o u s to t h e eyes a n d is responsible for n u m e r o u s c a s e s o f b l i n d n e s s a m o n g c h i c k e n s i n t h e W e s t I n d i e s a n d elsewhere (Burtt, 1947). I n its s m e l l a n d c o l o u r t h e s e c r e t i o n o f m o s t O p i s t h o s p e r m o p h o r a r e s e m b l e s iodine a n d stains t h e fingers a p u r p l i s h - b r o w n colour i n t h e s a m e m a n n e r a s this s u b s t a n c e . T h e chief c o m p o u n d s of physiological interest in t h e secretions are h y d r o c y a n i c acid, iodine a n d quinine. Small a m o u n t s of chlorine w h i c h give t h e s u b s t a n c e its c h a r a c t e r i s t i c o d o u r h a v e b e e n d e t e r m i n e d e x p e r i mentally. It has been suggested that the disinfecting properties of t h e c h l o r i n e a n d h y d r o c y a n i c a c i d m a y assist i n k e e p i n g t h e a n i m a l free f r o m b a c t e r i a a n d o t h e r m i c r o - o r g a n i s m s . I n contrast t h e P r o t e r o s p e r m o p h o r a rarely secrete visible q u a n tities of odoriferous s u b s t a n c e , a l t h o u g h if a n u m b e r of P o l y desmid millipedes be gathered together, a distinct almond-like smell b e c o m e s discernible. T h e natives of central M e x i c o g r i n d up Polydesmus ricinus w i t h v a r i o u s p l a n t s to m a k e a p o i s o n for t h e i r a r r o w s a n d t h e l a r g e Lysiopetalum foetidissimum t a k e s its n a m e f r o m t h e o b n o x i o u s s m e l l o f t h e s e c r e t i o n f r o m its s t i n k g l a n d s . M a n y of t h e tropical species exhibit patterns of strongly contrasted w a r n i n g colours w h i c h are clearly associated w i t h their poisonous nature. T h e majority of the Colobognatha do not appear t o s e c r e t e r e p u g n a t o r i a l fluids, b u t s p e c i e s o f Polyzonium p r o d u c e a whitish substance that m a y have an odour of c a m p h o r and is p r o b a b l y again a deterrent to p r e d a t o r y enemies. T h e O n i s c o m o r p h a a n d L i m a c o m o r p h a curl u p into a ball w h e n d i s t u r b e d a n d m e m b e r s o f t h e o t h e r o r d e r s f o r m a m o r e o r less compact spiral. T h e s e defensive reactions not only render the a n i m a l s less v u l n e r a b l e t o t h e i r e n e m i e s , b u t also a r e effective i n reducing water-loss by evaporation w h e n the millipedes are in dry s u r r o u n d i n g s . T h e y have b e e n a factor of major evolutionary i m p o r t a n c e ( M a n t o n , 1954). T h e m i n u t e Pselaphognatha are covered with tufts of peculiar h a i r s like s m a l l p i n - c u s h i o n s w h i c h r e s e m b l e t h e u r t i c a t i n g h a i r s o f some L e p i d o p t e r o u s caterpillars. Like t h e m they are hollow, very easily d e t a c h e d f r o m t h e b o d y a n d b e a r a n u m b e r o f r e t r o v e r t e d b a r b s or processes near their tips and along their axes. T h e s e a n d

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t h e s m a l l size o f t h e a n i m a l s c o n s t i t u t e t h e i r o n l y m e a n s o f d e f e n c e . T h e c o m m o n e s t parasites of millipedes are Gregarinidea. T h u s i t h a s b e e n f o u n d t h a t o f 165 lulus a n d Paraiulus s p p . e x a m i n e d , 158 w e r e p a r a s i t i s e d b y G r e g a r i n e s , 2 6 o u t o f 3 2 Polydesmus s p . a n d 6 o u t o f 1 6 Lysiopetalum s p . T h e p a r a s i t e s h a d n o s e a s o n a l c y c l e a n d all s t a g e s w e r e f o u n d t o g e t h e r . N o d o u b t t h e I u l i d a e were so persistently parasitised on account of their gregarious h a b i t s a n d d i e t o f r o t t i n g w o o d a n d v e g e t a b l e m a t t e r . Lysiopetalum s p p . w h i c h live u n d e r s t o n e s i n d r i e r p l a c e s a n d a r e s o m e w h a t s o l i t a r y a r e far less p a r a s i t i s e d . A f t e r G r e g a r i n i d e a , C o c c i d i a a n d Flagellates are the m o s t n u m e r o u s parasites of myriapods. It is probable that a high degree of tolerance has been reached between parasite and host and unlikely that the former do any harm. M o s t of t h e millipedes from t h e A m a z o n basin are infested w i t h n e m a t o d e s a n d these parasites are b y n o m e a n s u n c o m m o n elsewhere: while several D i p l o p o d a are intermediate hosts of cestodes of the related families Dilipididae a n d H y m e n o l i p i d i d a e ( R e m y , 1950b). No doubt phytophagous animals which c o n s u m e a certain a m o u n t o f soil w i t h t h e i r f o o d a r e e s p e c i a l l y l i a b l e t o i n f e c t i o n b y t h e s e animals. N u m e r o u s m i t e s of t w o ecologically separate a n d systematically u n r e l a t e d g r o u p s a r e f o u n d o n m i l l i p e d e s . I n t h e first, w h i c h i n cludes M e s o s t i g m a t a a n d Acaridae, the m y r i a p o d s are u s e d merely for t r a n s p o r t ( p h o r e s y ) w h i l e t h e s e c o n d g r o u p , all M e s o s t i g m a t a , i n c l u d e s m o r e o r less i n t e r m i t t e n t c o m m e n s a l s w h i c h live freely, n o t a t t a c h e d to their h o s t a n d feed on d e t r i t u s . E v a n s (1955) has reviewed the Laelaptidae parasitic on myriapods. Sometimes the b o d y o f a sick m i l l i p e d e m a y b e c o m e c o v e r e d w i t h a m u l t i t u d e o f little m i t e s b u t u s u a l l y t h e s e p a r a s i t e s a r e c o n f i n e d t o t h e h e a d , f r o n t legs a n d g o n o p o d s w h e n c e t h e y c a n n o t easily b e r e m o v e d . T h e adults of one species of m i t e found on Iulidae in Natal and Z u l u l a n d , feed u p o n t h e liquid secreted b y t h e repugnatorial glands of their host. An i n t e r e s t i n g c a s e of a g g r e s s i v e p a r a s i t i s m of a m i l l i p e d e by a fly o f t h e f a m i l y P h o r i d a e w h i c h b a t t l e d w i t h a h u g e b l a c k lulus s p . for s e v e r a l h o u r s h a s b e e n r e c o r d e d , a n d l a r v a e o f a n o t h e r s p e c i e s of P h o r i d a e , Megaselia juli, h a v e b e e n f o u n d in a n u m b e r See discussion of phoresy on p. 103. 1

1

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31

of s p e c i e s of Iulus a n d Spirobolus. P l a n i d i u m l a r v a e of p a r a s i t i c H y m e n o p t e r a h a v e b e e n f o u n d on Gymnostreptus parasitarius in B r a z i l a n d a l a r v a l L a m p y r i d b e e t l e i n t r o d u c e s itself t h r o u g h t h e a n u s i n t o t h e p o s t e r i o r i n t e s t i n e o f Pachyiulus s p p . ( R e m y , 1 9 5 0 b ) . It is p r o b a b l e that parasites play a negligible part in controlling t h e density of m i l l i p e d e p o p u l a t i o n s . O n l y t h r e e classes p a r a sitise t h e m t o a n a p p r e c i a b l e d e g r e e : A c a r i , w h i c h a r e little m o r e t h a n commensals, Sporozoa a n d N e m a t o d a which probably cause little i n c o n v e n i e n c e to t h e i r host. 1

Reproduction and life cycle T h e r e is a M a l a y belief t h a t if t h e v e r t e b r a of a fish is k e p t u n d e r a m a t t r e s s for s o m e t i m e i t b e c o m e s a c e n t i p e d e , a n d t h a t t h e strands which are found b e t w e e n the p u l p a n d t h e rind of a plantain b e c o m e millipedes if they are securely bottled up and kept in a dark corner! T h e paired genital openings of millipedes are situated on the third s e g m e n t j u s t b e h i n d , or on, t h e second pair of legs. In the f e m a l e , t h e orifice i s s u r r o u n d e d b y t w o s c l e r o t i s e d p i e c e s , o n e f o r m i n g t h e b u r s a , a r r a n g e d like t h e t w o s h e l l s o f a m u s s e l w i t h the hinge directed posteriorly and the second, the operculum, covering the gape of the t w o valves of the bursa. T h e whole ensemble is termed the vulva and is of diagnostic value. In the male the genital openings m a y or m a y not be developed into paired or single penes. T h e accessory genitalia consist of one or b o t h a p p e n dages of the seventh segment w h i c h are modified to form introm i t t e n t organs called g o n o p o d s , except in t h e O n i s c o m o r p h a a n d L i m a c o m o r p h a w h e r e t h e h i n d e r m o s t legs s e r v e t h i s f u n c t i o n . T h e s e o r g a n s a r e t h e o n l y c r i t e r i a for a c c u r a t e d i a g n o s i s : i n s o m e species they are retracted within t h e cavity of the seventh segment. Before copulation takes place t h e male, by flexing his anterior segm e n t s , 'charges' his g o n o p o d s from the opening on the third body segment. F r o m the gonopods the spermatic fluid is transferred to the vulvae of t h e female: fertilisation is internal. D u r i n g copulation t h e positions a s s u m e d by t h e male a n d female a r e s o m e w h a t s i m i l a r i n all s p e c i e s . T h e f o l l o w i n g d e s c r i p t i o n ap¬ See discussion of density-dependent and density-independent factors on p . 141. 1

32

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p l i e s t o Oxidus gracilis i n p a r t i c u l a r . T h e v e n t r a l s u r f a c e o f t h e posterior 13 or 14 b o d y somites of t h e male is parallel a n d dorsal to t h e a n t e r i o r 1 0 o r 1 1 b o d y s o m i t e s o f t h e f e m a l e a n d t h e legs o f t h e m a l e o n t h e s e somites are b e n t closely a r o u n d t h e female. I n t h e region of the eighth, n i n t h and tenth somites the body of the male is t w i s t e d half a r o u n d t h e female so t h a t his g o n o p o d s are in c o n tact w i t h her vulvae w h i c h o p e n o n t h e t h i r d b o d y somite. T h e head a n d thorax of t h e male are directed anteriorly a n d b e n t over the head of the female w h i c h is held by his seven anterior pairs of legs. B r i g h t light or h a n d l i n g usually causes a pair to separate: b u t i f u n d i s t u r b e d c o p u l a t i o n m a y o c c u r s e v e r a l t i m e s a n d last for several h o u r s (Causey, 1943).

F I G . 10. Millipedes of the family Polydesmidae in copulation. T h e male is below. (After Seifert, 1932.) T h e m a l e Polydesmus angustus a p p r o a c h e s t h e f e m a l e f r o m b e hind and runs along her back until her head is reached. Suddenly t u r n i n g r o u n d t o w a r d s h e r ventral surface, h e seizes h e r g n a t h o chilarium w i t h his m a n d i b l e s , retaining this hold until her b o d y is for t h e m o s t p a r t o f its l e n g t h e m b r a c e d i n h i s b r o a d e r g r a s p . I t i s interesting to n o t e t h a t a fertilised female, w h e n t o u c h e d on t h e anal s e g m e n t by a male, immediately darts forward a n d refuses to be caught. T h e fertilised females in a collection can be readily recognised by t o u c h i n g lightly on the anal s e g m e n t with a camelh a i r b r u s h ( E v a n s , 1 9 1 0 ) . I n Glomeris marginata t h e m a l e i s m u c h smaller than the female and copulation takes place by apposition o f t h e p a i r i n t h e h e a d t o tail p o s i t i o n . I n c o n t r a s t t o t h e P r o t e r o s p e r m o p h o r a , c o p u l a t i o n i n t h e O n i s c o m o r p h a i s brief, w h i c h m a y

MILLIPEDES

33

b e c o r r e l a t e d w i t h t h e fact t h a t e g g - l a y i n g i s a n i n t e r r u p t e d p r o c e s s a n d t h e female lays h e r eggs in small g r o u p s in several places, u s u a l l y b u r i e d i n l o o s e soil a n d a l w a y s u n d e r c o v e r o f m o s s o r dead leaves. T h e British O p i s t h o s p e r m o p h o r a begin their b r e e d ing rather later in t h e year t h a n do t h e Polydesmids. In s o m e species of millipedes t h e eggs are coated w i t h earth a n d e x c r e m e n t a n d t h e n left i n c r e v i c e s i n t h e soil; i n o t h e r s a n e s t i s c o n s t r u c t e d o f soil p a r t i c l e s t h a t h a v e b e e n m o i s t e n e d w i t h saliva. W h e n completed, the nest has the shape of a hollow sphere. T h e inside is lined with dried excrement a n d is smooth and even, w h e r e a s t h e outside is r o u g h a n d irregular. S o m e t i m e s t h e female d o e s n o t l e a v e t h e n e s t i m m e d i a t e l y , b u t r e m a i n s for s e v e r a l d a y s c u r l e d r o u n d i t s o t i g h t l y t h a t s h e i s difficult t o r e m o v e . W h e n t h e f e m a l e Glomeris marginata i s a b o u t t o lay s h e rolls over on h e r back a n d t h e little egg is passed b a c k w a r d s from segm e n t to segment until it arrives at the end of the body. T h e r e it is held i m m e d i a t e l y over t h e anal region a n d t h e r e c t u m is everted to a c o n s i d e r a b l e e x t e n t so as to f o r m a m o b i l e p a d h o l d i n g a small q u a n t i t y o f v e r y fluid e x c r e m e n t w h i c h i s c a r e f u l l y p l a s t e r e d o v e r the egg. W h e n dry this forms a spherical c h a m b e r in w h i c h t h e e g g lies freely. O c c a s i o n a l l y t w o o r t h r e e e g g s a r e e n c l o s e d i n o n e m a s s , b u t a l w a y s i n s e p a r a t e c o m p a r t m e n t s . I n Polydesmus angustus a n d o t h e r P r o t e r o s p e r m o p h o r a a n d C o l o b o g n a t h a , all t h e e g g s a r e e n c l o s e d i n a c o m m o n c o v e r i n g . T h e n e s t i s like a t h i n - w a l l e d , dome-shaped tent s u r m o u n t e d by a narrow tubular chimney. It is b u i l t o n s o m e f i r m s u b s t r a t u m — a s t o n e , a leaf, t h e i n s i d e o f a n acorn c u p , or t h e inner surface of a piece of b a r k — a n d is constructed with t h e mobile surface of the extroverted rectum. T h e f e m a l e first g n a w s a s m a l l c a v i t y o n t h e s u r f a c e o n w h i c h s h e i n t e n d s t o lay. T h e n s h e b e n d s h e r s e l f i n t o a c i r c l e a n d w a l k s r o u n d and r o u n d , leaving a rapidly drying blob of e x c r e m e n t as she goes, until the concave spot is s u r r o u n d e d by a rampart, the circumference of w h i c h is slightly greater t h a n t h e length of h e r body. W h e n t h e n e s t h a s r e a c h e d a b o u t t w o - t h i r d s its full h e i g h t t h e e g g s a r e l a i d . T h e f e m a l e lies a c r o s s h e r n e s t a n d t h e e g g s d r o p i n o n e after t h e o t h e r , s t i c k i n g t o g e t h e r a s t h e y fall. T h e n e s t i s t h e n roofed over a n d t h e c h i m n e y c o m p l e t e d with t h e aid of t h e everted r e c t u m a n d t h e s u p r a - a n a l p r o c e s s w h i c h p o s s e s s e s six t a c t i l e c

S.S.C.M.

34

MILLIPEDES

hairs. W h e n t h e nest is finished t h e female does n o t leave it i m m e d i a t e l y b u t r e m a i n s c o i l e d a r o u n d i t for a b o u t a w e e k . S h e c o v e r s i t w i t h b i t s o f l e a v e s a n d w i s p s o f g r a s s a n d will r e p l a c e t h e m over a n d over again if t h e y are r e m o v e d ( E v a n s , 1910). Oxidus gracilis f e m a l e s , h o w e v e r , d e p o s i t t h e i r e g g s in s m a l l r o u g h c a v i t i e s f r o m 3 t o 1 5 m m b e l o w t h e s u r f a c e o f t h e soil, b u t d o n o t construct b r o o d i n g c h a m b e r s nor remain with t h e m d u r i n g the incubation period. In contrast, m o s t of the O p i s t h o s p e r m o p h o r a construct a very crude nest which is mainly built from the inside, only the top being laid o n f r o m t h e o u t s i d e . T h e f e m a l e b u r r o w s i n t o l o o s e soil u n t i l she c o m e s to a firm f o u n d a t i o n , usually a s t o n e , w h e r e she p r o ceeds to m a k e a d o m e - s h a p e d clearing, the shaping being done by her jaws. T h i s space is then plastered from t h e inside with liquid excrement by means of the everted rectum, the animal meanwhile having to assume some very awkward positions during the process. On emerging from the recess she p u s h e s her way into a position astride t h e o p e n t o p a n d lays h e r eggs. After closing t h e hole she p a y s no f u r t h e r a t t e n t i o n to h e r nest (Evans, 1910). T h e function of the nest building described above is to protect t h e eggs a n d y o u n g f r o m attack by fungi w h i c h are an ever present m e n a c e , a s t h e y a r e t o t h e y o u n g s t a g e s o f w o o d l i c e , a n d also f r o m the cannibalistic proclivities of t h e males of t h e species. In a simil a r w a y Polymicrodon polydesmoides s p i n s a silk t e n t for t h e p u r p o s e o f m o u l t i n g a n d also t o c o v e r its c l u s t e r o f e g g s . A f t e r a m o u l t i t e a t s t h e silk. T h e B l a n i u l i d a e lay t h e i r l a r g e , e l o n g a t e d e g g s s i n g l y , h o w e v e r . T h e S p i r o b o l i d m i l l i p e d e Arctobolus marginatus o f N o r t h A m e r i c a m a n u f a c t u r e s t h e cases in w h i c h h e r eggs are individually enclosed with material regurgitated from h e r m o u t h . T h e moist l u m p is held by t h e legs of t h e eighth to eleventh pairs a n d s h a p e d with the convex front of the head. A shallow bowl is m a d e into w h i c h an egg is laid. T h e sides of t h e b o w l are t h e n d r a w n up over the egg a n d k n e a d e d together until a perfect sphere is p r o duced. T h e completed pellet i s d r o p p e d b y t h e m o t h e r w h o t h e n starts t h e next ( L o o m i s , 1933). I n m a n y species, o n t h e o t h e r h a n d , the eggs are never covered. T h e n u m b e r of

e g g s laid

by millipedes varies considerably

MILLIPEDES

35

a m o n g different o r d e r s a n d also a m o n g different species of the s a m e o r d e r . T h e r e i s a t e n d e n c y for t h e size o f t h e e g g t o d e c r e a s e in direct proportion as the n u m b e r of y o u n g per b r o o d increases. It follows from this t h a t t h e differences in t h e total a m o u n t of yolk contained in various broods, w h e t h e r they contain a large n u m b e r of small eggs or a smaller n u m b e r of large eggs t e n d s to be evened o u t . Polyxenus lagurus o n l y lays f r o m 10 to 20 e g g s w i t h 4 to 8 p e r n e s t , b u t s p e c i e s of Polydesmus lay b e t w e e n 100 a n d 2 0 0 , Oxidus gracilis u p t o 3 0 0 , Iulus s p p . lay 6 0 t o 100 o r m o r e , a n d s o m e o f t h e S p i r o b o l i d a e m a y a l s o lay u p t o 3 0 0 e g g s . T h e m a x i m u m r e c o r d e d c l u t c h of Arctobolus marginatus in W a s h i n g t o n w a s 2 6 1 . I n c u b a t i o n of t h e eggs m a y take several weeks before h a t c h i n g occurs. T h i s process is assisted by a strong conical egg-tooth situated, in the Opisthospermophora, on the middle of the head. Glomeris marginata s e e k s n o s p e c i a l p r o t e c t i o n d u r i n g m o u l t i n g , b u t does so in s o m e loose e a r t h or on t h e surface u n d e r m o s s or d e a d leaves. T h e case o f b o t h P r o t e r o s p e r m o p h o r a a n d O p i s t h o s p e r m o p h o r a is very different. T h e millipedes of these orders build m o u l t i n g c h a m b e r s w h i c h are essentially similar to their nests. If the moulting chamber is damaged so that other millipedes c a n e n t e r , t h e h e l p l e s s a n i m a l t h a t h a s j u s t s h e d its s k i n i s a l m o s t invariably eaten up by t h e invaders. After m o u l t i n g it is customary for m i l l i p e d e s t o e a t t h e i r c a s t e x u v i u m , t h e r e b y r e s t o r i n g lost supplies of calcium: further development does not proceed normally unless they do so. All D i p l o p o d a are a n a m o r p h i c and the larvae pass t h r o u g h a n u m b e r o f m o u l t s d u r i n g e a c h o f w h i c h t h e n u m b e r o f legs a n d p o s t - c e p h a l i c s o m i t e s i s i n c r e a s e d . A d d i t i o n a l legs a n d s o m i t e s a r e a d d e d in the embryonic region between the anal somite and the o n e t h a t w a s last f o r m e d . C o l o b o g n a t h a , A s c o s p e r m o p h o r a a n d P r o t e r o s p e r m o p h o r a pass t h r o u g h seven larval stadia, in each of w h i c h t h e n u m b e r o f leg p a i r s a n d s o m i t e s i s c o n s t a n t for t h e s p e c i e s o r t h e g r o u p . T h e O p i s t h o s p e r m o p h o r a also n o r m a l l y p a s s t h r o u g h s e v e n l a r v a l s t a d i a b u t a f t e r t h e first o r s e c o n d t h e n u m b e r o f l e g s a n d s o m i t e s i s n o t c o n s t a n t for t h e s p e c i e s . I n t h e O n i s c o m o r p h a , d e v e l o p m e n t is h e m i a n a m o r p h i c : a series of anam o r p h i c m o u l t s is followed by three m o u l t s w h i c h are u n a c c o m p a n i e d b y i n c r e a s e s i n t h e n u m b e r o f l e g s a n d s o m i t e s (Verhoeff,

FIG. 11.

Stages in the development of a millipede Strongylosomidae. (After Seifert, 1932.)

3 6

MILLIPEDES

MILLIPEDES

37

1 9 2 8 ) . T h e y o u n g e s t l a r v a e h a v e t h r e e p a i r s o f legs, t h e n e x t s t a g e usually seven, a n d at each s u b s e q u e n t m o u l t some four m o r e segm e n t s each w i t h eight pairs o f legs are a d d e d on. T h e t i m e r e q u i r e d for m o u l t i n g increases w i t h each s u c c e e d i n g ecdysis from a f e w h o u r s for t h e first t o s e v e r a l w e e k s for t h e last. V e r h o e f f ( 1 9 3 3 b , 1939) h a s s h o w n t h a t i n s o m e s p e c i e s o f I u l i d m i l l i p e d e s t h a t live i n c o l d c l i m a t e s t h e m a t u r e m a l e s m a y r e g r e s s to an interpolated intercalary form lacking t h e highly differentiated g o n o p o d s o f t h e m a t u r e a n i m a l . I n t h e life o f a n i n d i v i d u a l t h e r e m a y be as m a n y as four periods of sexual m a t u r i t y alternating with three interpolated stages. D u r i n g t h e interpolated period, g r o w t h continues with an increase in the n u m b e r of segmental glands. T h i s cycle is related to season, functional m a l e s a p p e a r i n g in late winter a n d the interpolated forms in s u m m e r . It is a m e t h o d of p r o l o n g i n g life t h r o u g h d r y o r c o l d s e a s o n s , a n d e n a b l e s a d u l t m a l e s t o live f o r t w o o r m o r e y e a r s . T h e a c t i v i t y o f t h e t e s t i s automatically declines at the onset of the m o u l t which initiates the i n t e r p o l a t e d s t a g e a n d t h i s a p p e a r s t o b e c o r r e l a t e d w i t h t h e fact that the complicated g o n o p o d s are m o u l t e d only with great difficulty.

BIBLIOGRAPHY Identification ATTEMS, G. ( 1 9 3 7 ) Myriapoda 3, Polydesmoidea 1. Das Tierreich, 6 8 , 1-300. ( 1 9 3 8 ) Idem. 2, Ibid., 6 9 , 1 - 4 8 7 . ( 1 9 4 0 ) Idem. 3, Ibid., 7 0 , 1 - 5 7 7 .

BLOWER, G. ( 1 9 5 2 ) British millipedes with special reference to Yorkshire species. Naturalist, 1 9 5 2 , 1 4 5 - 5 7 . BROLEMANN,

H.

W.

(1935)

Myriapodes.

Diplopodes-Chilognathes

1.

Faune de France, N o . 2 9 , 1 - 3 6 9 , Paris. CHAMBERLIN, R. V. ( 1 9 4 3 ) On Mexican millipedes. Bull. Univ. Utah., 3 4 , (7), 1 - 1 0 3 . L A N G , J . ( 1 9 5 4 ) M n o h o n o z k y — D i p l o p o d a . Fauna C.S.R., 2 , 1 - 1 8 3 .

LATZEL, R. ( 1 8 8 4 ) Die Myriopoden der Oesterreichs-Ungarischen Monarchic, II. Die Symphylen, Pauropoden und Diplopoden. Wien. LOHMANDER, H. ( 1 9 2 5 ) Sveriges Diplopoder. Goteb. Kongl. Vet. Handl, 3 0 , (2), 1 - 1 1 5 .

SCHUBART, O. ( 1 9 3 4 ) Tausendfussler oder Myriapoda, 1. Diplopoda. Tieriv. Deuts.,28, 1 - 3 1 8 .

38

MILLIPEDES

VERHOEFF, K. W. (1926-31) Diplopoda in H. G. BRONN'S Klass. Ordn. Tierreichs, 5, II (2), 1-1072. (See also references under Chilopoda, Chap. III) Biology BRADE-BIRKS, S . G . (1930) N o t e s o n Myriapods, X X X I I I . T h e economic status of Diplopoda and Chilopoda and their allies. J. S-E. Agric. Coll. Wye, N o . 27, 103-46. BURTT, E. (1947) Exudate from millipedes, with particular reference to its injurious effects. Trop. Dis. Bull., 4 4 , 7 - 1 2 . CAUSEY, N. B. (1943) Studies on the life history and the ecology of the hothouse millipede, Orthomorpha gracilis (C. L. K o c h , 1847). Amer. Midl. Nat., 2 9 , 6 7 0 - 8 2 . CLOUDSLEY-THOMPSON, J. L. (1949a) T h e enemies of Myriapods. Naturalist, 1 9 4 9 , 1 3 7 - 4 1 . (1949b) T h e significance of migration in M y r i a p o d s . Ann. Mag. Nat. Hist., (12), 2, 9 4 7 - 6 2 . (1950a) Economics of the 'spotted snake millipede' Blaniulus guttulatus ( B o s c ) . Ibid., (12), 3, 1047-57. (1950b) T h e water relations and cuticle of Paradesmus gracilis (Diplopoda: Strongylosomidae). Quart, J. Micr. Sci., 9 1 , 4 5 3 - 6 4 . (1951a) S u p p l e m e n t a r y notes on M y r i a p o d a . Naturalist, 1 9 5 1 , 16-17. (1951b) Studies in diurnal r h y t h m s — 1 . R h y t h m i c behaviour in millipedes. J. Exp. Biol., 2 8 , 165-72. (1951c) On the responses to environmental stimuli, and the sensory physiology of millipedes (Diplopoda). Proc. Zool. Soc. Lond., 1 2 1 , 253-77. (1954) Problems of dispersal in some terrestrial A r t h r o p o d s . Advanc. Sci., 1 1 , 7 3 - 5 . DAVENPORT, D . , W O O T T O N , D . M . a n d C U S H I N G , J. E . (1952) T h e biology

of the Sierra luminous millipede Luminodesmus sequoiae Loomis and D a v e n p o r t . Biol. Bull., 1 0 2 , 100-10. E A T O N , T. H. Jr., (1943) Biology of a mull-forming millipede, Apheloria coriacea (Koch). Amer. Midi. Nat., 2 9 , 7 1 3 - 2 3 . EVANS, T. J. (1910) Bionomical observations on some British millipedes. Ann. Mag. Nat. Hist., (8), 6, 2 8 4 - 9 1 . EVANS, G. O. (1955) A review of the Laelaptid paraphages of the Myriapoda with descriptions of three new species (Acarina: Laelaptidae). Parasitology, 4 5 , 352-68. FRYER, G. (1957) Observations on some African millipedes. Ann. Mag. Nat. Hist., (12), 1 0 , 4 7 - 5 1 . L O O M I S , H. F. (1933) Egg-laying and larval stages of a millipede, Arctobolus marginatus (Say) Cook, native at Washington. J. Wash. Acad. Sci., 2 3 , 100-9.

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39

LYFORD, W. H . , Jr. (1943) T h e palatability of freshly fallen forest leaves to millipedes. Ecology, 2 4 , 2 5 2 - 6 1 . M A N T O N , S. M. (1954) T h e evolution of A r t h r o p o d a n locomotory m e c h a n i s m s — P a r t 4. T h e structure, habits and evolution of the D i p l o poda. J. Linn. Soc. (Zool), 4 2 , 2 9 9 - 3 6 8 . PALMEN, E. (1949) T h e Diplopoda of Eastern Fennoscandia. Ann. Soc. Zool. Fenn. Vanamo, 1 3 , (6), 1-54. PERTTUNEN, V. (1953) Reactions of Diplopods to the relative h u m i d i t y of the air. Investigations on Orthomorpha gracilis, Iulus terrestris and Schizophyllum sabulosum. Ibid., 1 6 , (4), 1-69. R E M Y , P. (1950a) Les myriapodes et les plantes cultivees (Bibliographic). Bull. Soc. Linn. Lyon., 1 9 , 2 3 2 - 4 . (1950b) On the enemies of M y r i a p o d s . Naturalist, 1 9 5 0 , 1 0 3 - 8 . SCHUBART, O. (1942) Os myriapodes e suas relacoes com a agricultua. C o m u m a bibliografia completa sobre o assunto. Pap. Avul. Dep. Zool. S. Paulo, 2, 205-34. SHELFORD, V. E. (1913) T h e reactions of certain animals to gradients of evaporating power of air. A study in experimental biology. Biol. Bull., 2 5 , 79-120. VERHOEFF, K. W. (1930) Z u r Geographie, Okologie u n d Systematik sudalpenlandischer Chilognathen (116. Diplopoden—Aufsatz). Z. Morph. Okol. Tiere, 1 8 , 575-668. (1933a) Revolution bei D i p l o p o d e n . Zool. Anz., 1 0 4 , 5 9 - 6 4 . (1933b) W a c h s t u m u n d Lebensverlangerung bei Blaniuliden u n d u b e r die Periodomorphose. Z. Morph. Okol. Tiere, 2 7 , 732-49. (1935) Z u r biologie der Spirostreptiden. Zool. Anz., 1 0 9 , 288-92. (1939) W a c h s t u m u n d Lebensverlangerung bei Blaniuliden u n d u b e r die Periodomorphose. I I . T i c l . Z. Morph. Okol. Tiere, 3 6 , 2 1 - 4 0 .

CHAPTER

III

CENTIPEDES Classification and distribution A l t h o u g h t h e C h i l o p o d a a r e a w i d e l y d i s p e r s e d class, t h e b i o l o g y of c e n t i p e d e s has a t t r a c t e d c o m p a r a t i v e l y little a t t e n t i o n from zoologists w h o have t e n d e d to confine their attentions to t h e systematics of the group. In these animals, the b o d y is divided into a variable n u m b e r of somites, each of w h i c h is p r o v i d e d with a pair of l i m b s u s e d for l o c o m o t i o n . T h e h e a d b e a r s a pair of m u l t i s e g m e n t e d a n t e n n a e a n d t h r e e p a i r s o f m o u t h - p a r t s . T h e first o f these post-oral a p p e n d a g e s are toothed mandibles, the second are foliaceous maxillae, while t h e t h i r d are leg-like palps. B e h i n d t h e head is the first s e g m e n t of t h e body, k n o w n as t h e basilar segment. Its appendages are the maxillipedes or taxocognaths. T h e s e are poison-claws w i t h w h i c h t h e prey is c a p t u r e d a n d killed. At t h e t i p s o f t h e i r s t r o n g , p i e r c i n g t e r m i n a l s e g m e n t s a r e t h e orifices o f t h e d u c t s of t h e paired v e n o m - g l a n d s . W h e r e present, t h e eyes are i n t h e f o r m o f c l u s t e r s o f ocelli, e x c e p t i n t h e S c u t i g e r o m o r p h a w h i c h h a v e c o m p o u n d e y e s (see b e l o w ) . T h e n u m b e r o f legs varies from fifteen to over a h u n d r e d pairs, b u t however m a n y there m a y be, t h e n u m b e r is always odd. Each somite of the body is flattened w h e n seen in cross-section a n d is c o m p o s e d externally of a dorsal plate or tergite a n d a ventral sternite u n i t e d by pleural m e m b r a n e s w i t h w h i c h t h e legs articulate a n d u p o n w h i c h t h e spiracles leading into the trachea usually open. T h e class C h i l o p o d a i s s u b - d i v i d e d i n t o f i v e o r d e r s . T h e f i r s t o f these, the G e o p h i l o m o r p h a , includes the long, worm-like centip e d e s w i t h t h e p a i r s o f legs v a r y i n g i n n u m b e r f r o m 3 1 t o 1 7 7 . T h e f o r e p a r t o f e a c h s o m i t e i s m a r k e d off f r o m t h e h i n d e r p a r t b y a distinct joint, t h e r e is a pair of spiracles on each s e g m e n t except t h e f i r s t a n d last, a n d t h e a n t e n n a e a r e a l w a y s c o m p o s e d o f f o u r 40

FIG. 12. Examples of centipede families: 1. Geophilidae, 2. Cryptopidae, 3. Scolopendridae, 4. Lithobiidae, 5, Scutigeridae. (Drawings not to scale.) (After various authors.)

CENTIPEDES 41

42

CENTIPEDES

teen s e g m e n t s . T h e r e are a very large n u m b e r of families in this o r d e r w h i c h h a s a w i d e d i s t r i b u t i o n i n all t h e w a r m a n d t e m p e r a t e c o u n t r i e s of t h e w o r l d . M o s t of t h e m are s u b t e r r a n e a n b u t a few are found u n d e r stones and seaweed below tide marks. T h e l a r g e s t s p e c i e s , like t h e N o r t h A f r i c a n Orya barbarica, m e a s u r e a b o u t six o r s e v e n i n c h e s i n l e n g t h , b u t m o s t a r e o n l y a n i n c h o r two long. T h e writer has recently discovered a smaller species of Orya, O . almohadensis, i n c e n t r a l T u n i s i a w h i c h m e a s u r e s j u s t o v e r two inches w h e n e x t e n d e d a n d is scarcely longer t h a n t h e c o m mon B r i t i s h Haplophilus subterraneus.

F I G . 1 3 . Poison claws of a centipede showing position of poison glands and their ducts.

T h e c e n t i p e d e s o f t h e o r d e r S c o l o p e n d r o m o r p h a differ f r o m t h e G e o p h i l o m o r p h a i n n e v e r h a v i n g m o r e t h a n 2 3 p a i r s o f legs, while the segments of t h e a n t e n n a e vary in n u m b e r from 17 to 30. T h e somites are not m a r k e d l y divided a n d t h e tergal plate of the b a s i l a r s e g m e n t i s f u s e d w i t h t h a t o f t h e first l e g - b e a r i n g s o m i t e . Spiracles are not found on every segment of t h e body. T h i s order i s also w i d e l y d i s t r i b u t e d a n d i n c l u d e s t w o m o s t i m p o r t a n t families, the Scolopendridae and the Cryptopidae, of which the former contains about 16 genera, including m o s t of t h e large tropical and s u b - t r o p i c a l s p e c i e s h a v i n g 2 1 p a i r s o f legs. T h e p o s t e r i o r p a i r o f

CENTIPEDES

43

legs i s u s u a l l y l o n g e r a n d s t o u t e r t h a n t h e o t h e r s , b u t m a y b e modified as antenniform tactile sense-organs as in t h e S o u t h A m e r i c a n g e n u s Newportia. T h e t e r m i n a l legs m a y b e e x p a n d e d a n d leaf-like a t t h e e n d , f o r m i n g a s t r i d u l a t i n g o r g a n a s i n t h e l a r g e t r o p i c a l A f r i c a n g e n u s Alipes, o r s h o r t , t h i c k a n d a r m e d w i t h a p i e r c i n g c l a w u s e d for h o l d i n g f o o d a s i n t h e A m e r i c a n g e n u s Theatops. S o m e o f t h e t r o p i c a l s p e c i e s o f Scolopendra a r e c o m m o n l y six o r e i g h t i n c h e s i n l e n g t h , w h i l e t h e l a r g e s t , S . gigantea f r o m t r o p i c a l A m e r i c a , m e a s u r e s as m u c h as a foot. M a n y of t h e s e are a t t r a c tively c o l o u r e d in t h e living state. F o r e x a m p l e , t h e S o u t h African Rhysida afra is a d e e p a n d s t r i k i n g s h a d e of b l u e or b l u e w i t h a g r e e n i s h t i n g e , S. morsitans h a s g r e e n c r o s s b a r s on a y e l l o w b a c k g r o u n d , w h i l e S. cingulata is a b e a u t i f u l o l i v e g r e e n . T h i s s p e c i e s is distributed widely throughout the Mediterranean regions of E u r o p e , N o r t h Africa a n d t h e M i d d l e East, b u t varies considerably i n size i n different l o c a l i t i e s . A f r i c a n a n d A s i a t i c s p e c i m e n s m a y r e a c h a l e n g t h o f 1 8 c m w h e n fully e x t e n d e d a n d h a v e a y e l l o w b o d y a n d b l u e h i n d l e g s . U n f o r t u n a t e l y t h e y all t e n d t o f a d e t o a u n i f o r m d u l l b r o w n c o l o u r w h e n p r e s e r v e d . S . morsitans a n d S . subspinipes h a v e b e e n t r a n s p o r t e d all o v e r t h e t r o p i c s b y c o m m e r c e , but are unable to establish themselves in temperate latitudes. R e l a t e d g e n e r a a r e Ethmostigmus, w h i c h i s a b u n d a n t i n A f r i c a , a n d Cormocephalus w h i c h i s e q u a l l y a b u n d a n t i n b o t h t h e E t h i o p i a n and Indo-Australasian regions. Only three representatives of the o r d e r o c c u r in t h e B r i t i s h I s l e s , n a m e l y Cryptops hortensis, C. anomalans a n d C . parisi. O f t h e s e t h e m o s t c o m m o n i s t h e o r a n g e c o l o u r e d C . hortensis f r e q u e n t l y f o u n d i n p o t t i n g s h e d s a n d u n d e r t h e bark of trees, etc. T h e o r d e r C r a t e r o s t i g m o m o r p h a h a s b e e n e s t a b l i s h e d for t h e c e n t i p e d e s o f t h e g e n u s Craterostigmus w h i c h i s i n t e r m e d i a t e i n many points between the Scolopendromorpha and the Lithob i o m o r p h a , a n d , like m a n y a n c i e n t arid a n n e c t a n t t y p e s , o c c u r s i n A u s t r a l a s i a . T h e r e a r e o n l y 1 5 p a i r s o f legs a n d s t e r n a a n d t h e spiracles are r e d u c e d to seven pairs as in t h e L i t h o b i o m o r p h a , b u t there are 21 tergal plates representing t h e somites of t h e legbearing segments of the Scolopendromorpha. Unfortunately nothing is k n o w n of the biology of these animals.

44

C E N T I P E D E S

T h e L i t h o b i o m o r p h a are distinguished from t h e S c o l o p e n d r o m o r p h a by having the body composed of 15 leg-bearing somites, of w h i c h o n l y six o r s e v e n p o s s e s s s p i r a c l e s , t h e t e r g a o f t h o s e w i t h o u t s p i r a c l e s b e i n g g r e a t l y r e d u c e d i n size. T h e b a s a l s e g m e n t s o f t h e legs a r e s o m e w h a t e n l a r g e d a n d t h e a n t e n n a l s e g m e n t s n u m b e r from 20 to 50. T h e centipedes of this order are referred to three families: L i t h o b i i d a e , H e n i c o p i d a e a n d C e r m a t o b i i d a e . T h e y are m o s t l y o f s m a l l size, t h e l a r g e s t b e i n g t h e c o n t i n e n t a l Lithobius fasciatus. S e v e r a l s p e c i e s of Lithobius a r e c o m m o n in E n g l a n d , t h e b e s t k n o w n b e i n g t h e l a r g e L. forficatus. N e a r l y as l a r g e is L. variegatus w h i c h i s easily r e c o g n i s e d b y its a t t r a c t i v e v a r i e g a t e d colour pattern. T h i s species is of interest because it is found only in the C h a n n e l Islands and Britain, w h e r e it occurs mostly in s o u t h e r n c o u n t i e s . W e also h a v e o n e s p e c i e s o f H e n i c o p i d a e , Lamyctes fulvicornis, a s m a l l f o r m d i s t i n g u i s h a b l e f r o m Lithobius s p p . b y t h e p r e s e n c e o f a s i n g l e p a i r o f ocelli i n s t e a d o f m a n y , a n d b y t h e p r e s e n c e o f s p i r a c l e s o n t h e first l e g - b e a r i n g s o m i t e . T h e Cermatobiidae resemble the Henicopidae in m a n y characters and a r e n o t e w o r t h y o n a c c o u n t o f t h e a b s e n c e o f p o r e s o n t h e last p a i r o f legs a n d t h e l o n g , t h i n , m a n y - s e g m e n t e d a n t e n n a e . T h e s e characters t e n d to link t h e m with the Scutigeromorpha. T h e g e n u s Cermatobius i s f o u n d i n t h e M o l u c c a s . T h e remaining order, the Scutigeromorpha, is sometimes placed in a separate sub-class, t h e A n a r t i o s t i g m a , r e p r e s e n t e d by a single family, t h e S c u t i g e r i d a e . I t s r e p r e s e n t a t i v e s are r e m a r k a b l e for t h e e x t r a o r d i n a r y l e n g t h o f t h e i r l i m b s a n d for t h e i r e x t r e m e agility. T h e y are m e d i u m - s i z e d c e n t i p e d e s h a v i n g fifteen pairs of legs a n d s t e r n a l p l a t e s , b u t o n l y e i g h t t e r g a l p l a t e s . T h e i r e y e s a r e c o m p o u n d and bulging, the antennae widely separated at the base a n d exceedingly long. T h e spiracles leading into sacular, tufted tracheae are u n p a i r e d a n d o p e n dorsally u p o n t h e first seven terg i t e s . T h e s e a n i m a l s a r e f o u n d i n all w a r m t r o p i c a l a n d t e m p e r a t e c o u n t r i e s , t h e l a r g e s t , Scutigera longicornis a n d S. clunifera, o c c u r ring in India and southern China and reaching two or three inches in length of head a n d body. T h e r e are no indigenous British s p e c i e s , b u t S . coleoptrata, c o m m o n i n s o u t h e r n E u r o p e , w a s o n c e introduced into a paper-mill in A b e r d e e n w h e r e it succeeded in e s t a b l i s h i n g itself.

CENTIPEDES

45

General behaviour C e n t i p e d e s a r e n o c t u r n a l c r e a t u r e s a n d lack a n i m p e r v i o u s c u t i cular wax-layer ( C l o u d s l e y - T h o m p s o n , 1954). T h e i r locomotion h a s l o n g f a s c i n a t e d b i o l o g i s t s , b u t o n l y r e c e n t l y h a s its m e c h a n i c s b e e n analysed in detail by m e a n s of h i g h - s p e e d p h o t o g r a p h y , s h o w i n g it to be of evolutionary a n d functional significance. Ray L a n k e s t e r , w h o s t u d i e d this m a t t e r i n 1889, r e a c h e d t h e conclusion that if t h e animals h a d to settle t h e question themselves they w o u l d n o t g e t o n a t a l l ! H e e n d e d a l e t t e r t o Nature w i t h t h e f o l l o w i n g well-known rhyme: A centipede was h a p p y quite U n t i l a toad in fun Said, 'Pray which leg moves after which ?'. T h i s raised h e r d o u b t s to such a pitch, She fell exhausted in the ditch, N o t knowing how to r u n . H o w e v e r , M a n t o n (1952, 1953) h a s recently s h o w n t h a t t h e long G e o p h i l o m o r p h a have b e c o m e specialised in t h e ability to choose and vary their footholds so that they may or m a y not show a r e g u l a r r e p e t i t i o n o f t h e l o c o m o t o r y p a t t e r n all a l o n g t h e b o d y . At the s a m e time they are adapted to burrowing 'by the earthwormlike m e t h o d o f b e c o m i n g " f a t " , t h e a c t i v e p r e s s i n g o n t h e soil b e i n g done by longitudinal contraction and widening of a segment'. T h e l e g s s e r v e a s a n c h o r i n g p o i n t s , like t h e c h e t a e o f t h e w o r m , a n d w h e n u s e d for w a l k i n g e x e c u t e large angles o f s w i n g t o c o m p e n s a t e for t h e i r s h o r t n e s s . A n i n c r e a s e i n b u r r o w i n g c a p a c i t y i s correlated with the presence of large n u m b e r s of leg-bearing segm e n t s and the burrowing habit explains m a n y of the m o r p h o logical c h a r a c t e r s o f t h e s e a n i m a l s . T h e h e a d e n d o f a c o n t r a c t e d animal can be thrust forward m o r e rapidly by the contraction of the musculature and telescoping of the segments than by walking. A c o m b i n a t i o n of walking m o v e m e n t s in s o m e regions of t h e body with m u s c u l a r contractions and expansions in others results in a thrust or a pull being exerted on parts of the body in which the legs a r e n o t u s e d . T h i s p r o v i d e s a n efficient m e t h o d o f m o v i n g across g a p s or places w h e r e footholds are d i s c o n t i n u o u s or shifting a n d m u s t also b e o f m a j o r i m p o r t a n c e i n w i d e n i n g c r e v i c e s i n t h e soil.

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In contrast, the evolution of the Scolopendromorpha appears to have b e e n associated w i t h acquiring increased speed. F a s t gaits are possible as t h e relative duration of the backstroke of the limbs is shorter than in most other Arthropoda. T h e body may m o m e n tarily be s u p p o r t e d by only t w o or t h r e e legs on each side, b u t excessive sagging of t h e b o d y b e t w e e n these widely separated s u p ports is countered by the body musculature. At the same time alternate-sized tergites appear to contribute an anti-undulation m e c h a n i s m w h i c h b e c o m e s n e c e s s a r y a s t h e legs i n c r e a s e i n l e n g t h a n d t h e gait b e c o m e s faster. T h e s e a c h i e v e m e n t s have b e e n m a d e a t t h e e x p e n s e o f t h e p r i m i t i v e flexibility o f l o c o m o t o r y m o v e m e n t s as are found in t h e O n y c h o p h o r a a n d which have been exploited in relation to the b u r r o w i n g habit of the G e o p h i l o m o r p h a . T h u s t h e gaits of t h e S c o l o p e n d r o m o r p h a are performed with g r e a t e r r e g u l a r i t y t h a n t h o s e o f t h e G e o p h i l o m o r p h a , b u t little choice of footholds is possible. T h e legs o f t h e L i t h o b i o m o r p h a a n d S c u t i g e r o m o r p h a a r e l o n g e r t h a n t h o s e o f t h e o r d e r s s o far c o n s i d e r e d . T h e g a i t s i n these two g r o u p s are essentially similar. O n l y a small range is p o s sible, a n d m o v e m e n t s m u s t b e e x e c u t e d w i t h great precision b e c a u s e t h e fields o f u p t o f o u r s u c c e s s i v e l e g s m a y o v e r l a p . U n dulations of t h e b o d y at faster speeds are partially controlled in Lithobius b y t h e a l t e r n a t e - s i z e d t e r g i t e s , a n d m o r e c o m p l e t e l y b y a r e d u c t i o n i n t e r g i t e n u m b e r i n Scutigera i n w h i c h t h e l e g s a r e o f differential l e n g t h , t h e f o u r t e e n t h p a i r b e i n g a l m o s t d o u b l e t h e l e n g t h o f t h e first. W i t h t h e g r e a t f l e e t n e s s o f t h e S c u t i g e r o m o r p h a are associated several structural advances b e y o n d t h e conditions s e e n i n o t h e r C h i l o p o d a . T h e l o n g legs r e q u i r e a firm g r i p o n t h e g r o u n d to p r e v e n t t h e m from slipping, a n d instead of t h e single or d o u b l e digitigrade s p i n e p r e s e n t in o t h e r c e n t i p e d e s , t h e leg of Scutigera e n d s i n a m u l t i - a r t i c u l a t e p l a n t i g r a d e foot, e a c h j o i n t p o s sessing n u m e r o u s g r i p p i n g hairs. Fast r u n n i n g indicates a high metabolic rate correlated with greater complexity of the maxillary excretory gland, a u n i q u e respiratory system and the presence of a n efficient r e s p i r a t o r y c a r r i e r i n t h e b l o o d . T h e m e c h a n i s m of breathing a n d blood circulation is similar to that of spiders and scorpions since in the Arachnida the blood m u s t traverse the interlamellar spaces before returning to t h e

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h e a r t . I n S . coleoptrata t h e l u n g s a r e d o r s a l a n d s i t u a t e d i n t h e pericardial cavity w h e r e aspiration d u e to systole is strongest. T h e y are bathed by blood in the ventro-lateral lacunae which are c o n n e c t e d w i t h t h e pericardial cavity b y p u l m o n a r y veins. T h u s a n a c t i v e m o d e o f life, s o m e w h a t a n a l a g o u s t o t h a t o f t h e w o l f spiders which h u n t their prey in the open, is associated with analagous morphological structures. At the same time the presence o f c o m p o u n d e y e s i n Scutigera, i n c o n t r a s t t o t h e s i m p l e ocelli o f t h e o t h e r C h i l o p o d a , m a y b e a s s o c i a t e d w i t h fast r u n n i n g a f t e r flies a n d o t h e r i n s e c t s . Of course the G e o p h i l o m o r p h a do not always b u r r o w , particularly t h e s h o r t e r - b o d i e d species w h i c h often seek shelter u n d e r s t o n e s , n o r d o t h e m e m b e r s o f t h e o t h e r o r d e r s r u n fast all t h e time: on the contrary they sprint only occasionally a n d w i t h r e luctance. Nevertheless locomotion appears to be the habit with w h i c h t h e i r e v o l u t i o n h a s b e e n chiefly a s s o c i a t e d ( M a n t o n , 1 9 5 2 , 1953). C e n t i p e d e s a l w a y s live i n d a m p , d a r k a n d o b s c u r e p l a c e s u n d e r s t o n e s , fallen l e a v e s , l o g s , u n d e r b a r k a n d i n c r e v i c e s o f t h e soil, f r o m w h i c h , like w o o d l i c e a n d m i l l i p e d e s , t h e y i s s u e f o r t h a t n i g h t . S i n c l a i r ( 1 8 9 5 ) c l a i m e d t h a t i n M a l t a Scutigera d a r t s a b o u t in t h e h o t s u n s h i n e after its prey, b u t in I n d i a it is said to exhibit a strong 'dislike' of daylight a n d hides d u r i n g the daytime in dark places. Its most c o m m o n habitat is u n d e r m a t t i n g covering the floors o f b u n g a l o w s o r o n w a l l s i n d a r k c o r n e r s a n d u n d e r s t o n e s o u t o f d o o r s . I n I t a l y t o o S . coleoptrata a p p e a r s t o b e p h o t o - n e g a tive ( C l o u d s l e y - T h o m p s o n , 1949). W i t h t h e exception of their eyes w h i c h usually do not seem to be of m u c h importance, t h e sense organs of centipedes take the form of hairs connected with nerve fibres; the animals find their prey by m e a n s o f t h e s e h a i r s w h i c h a r e s e n s i t i v e t o t o u c h . T h e y a r e also very sensitive to moisture and contact stimuli. T h e whole subject has been reviewed by C l o u d s l e y - T h o m p s o n (1952b). According to B a u e r ( 1 9 5 3 ) Lithobius forficatus s h o w s a ' p r e f e r e n c e ' f o r h i g h h u m i d i t i e s a n d a g r o u n d t e m p e r a t u r e o f a b o u t 12° C . A u e r b a c h ( 1 9 5 1 ) h a s f o u n d t h a t t h e d i s t r i b u t i o n o f Bothropolys multidentatus, Lithobius forficatus and Neolithobius voracior in the C h i c a g o a r e a o f N o r t h A m e r i c a d o e s n o t follow a u n i f o r m p a t t e r n .

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T h e first reaches a peak of a b u n d a n c e in wet forest c o m m u n i t i e s , t h e s e c o n d in d r y f o r e s t , w h i l e X. voracior is p l e n t i f u l in t h o s e l o c a l i t i e s i n w h i c h floor m o i s t u r e c o n d i t i o n s a r e i n t e r m e d i a t e : a n d this d i s t r i b u t i o n is related to t h e different t i m e s of survival of t h e t h r e e s p e c i e s w h e n p l a c e d i n d r y air. I t i s o f c o u r s e t r u e t h a t c e r t a i n c e n t i p e d e s s u c h as Scutigera, Scolopendra a n d Dignathodon s p p . , a n d i n o u r o w n c o u n t r y Lithobius calcaratus, t e n d t o i n h a b i t dry places, b u t it is probable that this p h e n o m e n o n is analagous to t h a t f o u n d in woodlice a n d t h a t t h e different species vary m e r e l y in the length of time that they can survive away from dampness. Recently P a l m e n a n d Rantala (1954) have suggested that t h e orient a t i o n of t h e G e o p h i l i d c e n t i p e d e Pachymerium ferrugineum in its n a t u r a l h a b i t a t s , i s chiefly g u i d e d b y r e a c t i o n s t o a i r h u m i d i t y a n d m o i s t u r e and, to a lesser degree, to t e m p e r a t u r e . W h e n t h e relative h u m i d i t y of t h e air decreases in a n i c h e i n h a b i t e d by this species, t h e r e s u l t will b e a n i n c r e a s e i n l o c o m o t o r y a c t i v i t y a n d o r i e n t a tion towards moisture. If high temperature is combined with u n usually low atmospheric humidity, the increased desiccation caused will intensify t h e responses of t h e a n i m a l to m o i s t u r e . M a n y species of centipedes are cave-dwellers a n d a few of the G e o p h i l o m o r p h a are m a r i n e . T w o British species are found on t h e seashore u n d e r stones a n d seaweed a t low t i d e level. T h e s m a l l e r , Scolioplanes maritimus, w a s first d i s c o v e r e d by L e a c h in 1817, w h o w r o t e s o m e w h a t optimistically, ' H a b i t a t i n Britannia inter scopulos ad littora maris vulgissime'. It was re-discovered some fifty years later at P l y m o u t h and has since t u r n e d up in the Isle of M a n , Somerset, Cornwall, Sussex, C o . D u b l i n a n d on the c o a s t o f G a l w a y . I t i s e v i d e n t l y fairly w i d e l y d i s t r i b u t e d o n t h e N o r t h Sea coast o f F r a n c e , D e n m a r k , S w e d e n a n d G e r m a n y . T h e s e c o n d s p e c i e s , Hydroschendyla submarina, is v e r y m u c h less c o m mon. It has nevertheless been found in Cornwall, Jersey and Yorkshire, as well as on t h e coasts of F r a n c e , Italy, Scandinavia, N o r t h A f r i c a a n d B e r m u d a , w h e r e i t lives i n m u d d y s i t u a t i o n s a r o u n d t h e e d g e s o f e r o d e d flat s t o n e s , a n d i n i s o l a t e d h o n e y c o m b e d blocks of limestone about nine inches below m e a n high w a t e r ( C h a m b e r l i n , 1 9 2 0 ) . Pectinunguis americanus o c c u r s u n d e r seaweed, driftwood etc. on t h e coasts of Mexico, including Florida a n d t h e coasts of lower California, a n d other m a r i n e centipedes

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have been collected from the C a p e V e r d e Islands a n d the Galapagos. In t h e f o r m e r case t h e y i n h a b i t crevices in t h e c r u s t of w o r m t u b e s w h i c h c o v e r all r o c k s a t l o w t i d e i n s i d e b a y s , a n d i n t h e l a t t e r l a r g e e m p t y b a r n a c l e s h e l l s also a t l o w t i d e l e v e l . B o n n e l l ( 1 9 3 0 ) o b t a i n e d a n u m b e r of Mixophilus indicus f r o m u n d e r s t o n e s a n d soft m o i s t soil a l o n g w i t h v a r i o u s P o l y c h a e t e w o r m s i n t h e b e d o f the C o o u m River, M a d r a s . As a result of experiments on their r e s i s t a n c e t o s u b m e r s i o n h e c o n c l u d e d t h a t little air i s r e q u i r e d b y t h i s s p e c i e s ; t h e t r a c h e a e s t o r e e n o u g h for 2 4 h o u r s a n d i n addition air is entangled by a loop of t h e posterior e n d of t h e b o d y a n d i n c h i t i n o u s c h a n n e l s i n t h e c o x a e o f t h e last l e g s . I n t h i s l a t t e r r e s p e c t t h e y a p p e a r to differ f r o m H. submarina a n d S. maritimus, b o t h o f w h i c h h o w e v e r c a n s u r v i v e s e v e r a l d a y s i m m e r s i o n i n sea w a t e r w i t h o u t a n y ill effects. T h e l i t e r a t u r e o n marine myriapods has been reviewed by Cloudsley-Thompson (1948, 1951). T h e idea of c e n t i p e d e s living in w a t e r has persisted f r o m classical t i m e s , f o r P l i n y w r o t e of a m a r i n e ' S c o l o p e n d r a ' as a v e r y p o i s o n o u s animal, b u t t h e r e is little d o u b t t h a t he w a s referring to one of the marine w o r m s . T h e G e r m a n naturalist G e s n e r gave an a c c o u n t i n 1569 o f a s i m i l a r ' m a r i n e S c o l o p e n d r a ' w h i c h , s o a k e d i n oil o r p o u n d e d u p w i t h h o n e y , w a s b e l i e v e d t o c a u s e t h e h a i r t o fall. C h a r l e s O w e n , in h i s Essay towards a Natural History of Serpents ( 1 7 5 2 ) w r o t e : ' T h e S c o l o p e n d r a i s a little v e n o m o u s w o r m a n d a m p h i b i o u s . W h e n it w o u n d s any, t h e r e follows a blueness a b o u t t h e affected p a r t a n d a n i t c h all o v e r t h e b o d y like t h a t caused by nettles. Its w e a p o n s of mischief are m u c h t h e same with those of t h e s p i d e r only larger; its bite is very t o r m e n t i n g , a n d p r o d u c e s n o t o n l y p r u r i g i n o u s p a i n i n t h e flesh, b u t v e r y o f t e n d i s traction of t h e m i n d . T h e s e little c r e a t u r e s m a k e b u t a m e a n figure i n t h e r a n k s o f a n i m a l s , y e t h a v e b e e n t e r r i b l e i n t h e i r e x ploits, particularly in driving people o u t of their c o u n t r y . T h u s t h e p e o p l e of R h y t i u m , a city of C r e t e , w e r e c o n s t r a i n e d to leave t h e i r q u a r t e r s for t h e m ( A e l i a n , l i b . X V . , c a p . 2 6 ) . ' T h i s i s t h e only recorded instance of a m a s s migration of centipedes although they have accompanied migrating armies of millipedes. A n u m b e r of cases of p s e u d o p a r a s i t i s m have b e e n r e c o r d e d in which b o t h centipedes a n d millipedes have b e e n f o u n d living in D

S.S.C.M.

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the nasal sinus or t h e a l i m e n t a r y canal of m a n , into w h i c h they have become accidentally introduced. On occasions they have been v o m i t e d u p i n n u m b e r s b y patients w h o alleged t h a t the animals were breeding inside t h e m . T h e r e is a considerable literature on t h e s u b j e c t b u t its b i o l o g i c a l i m p o r t a n c e i s s l i g h t . T h e e x p l a n a t i o n p r o b a b l y lies i n t h e fact t h a t c e n t i p e d e s s e e m t o e x e r t a w e i r d f a s cination on the m o r b i d appetites of the hysterical and insane ( J a c k s o n , 1914; S h i p l e y , 1 9 1 4 ) .

Food and feeding habits Centipedes are primarily carnivorous b u t certain of the G e o p h i l o m o r p h a will o n o c c a s i o n feed u p o n p l a n t t i s s u e s a n d m a y e v e n b e p o s i t i v e l y i n j u r i o u s t o c r o p s i f p r e s e n t i n sufficient n u m b e r s . T h e y also feed u p o n w o r m s , a n d t h e m a r i n e Hydroschendyla submarina i n t h e B e r m u d a I s l a n d s i s s a i d t o e a t L e o d i c i d s , b i t i n g t h e m , l i c k i n g u p t h e i r j u i c e s a n d c a r r y i n g off t h e f r a g m e n t s i n t o w h i c h t h e w o r m s autotomise ( C h a m b e r l i n , 1920). G e o p h i l i d s are n o t easy t o m a i n t a i n i n c a p t i v i t y a n d d o n o t r e a d i l y t a k e f o o d u n d e r laboratory conditions. C o n s e q u e n t l y o u r k n o w l e d g e of their feeding habits is s o m e w h a t scanty, b u t probably they devour a variety of small soil-inhabiting A r t h r o p o d a ( B r a d e - B i r k s , 1929). T h e L i t h o b i o m o r p h a will o c c a s i o n a l l y f e e d o n w o r m s a n d s l u g s t o o , b u t i n s e c t s p r o b a b l y f o r m t h e i r s t a p l e d i e t : Lithobius forficatus r e a d i l y a c c e p t s flies i n c a p t i v i t y . T h i s s p e c i e s h a s b e e n o b s e r v e d o n a w a l l a t n i g h t c a r r y i n g off a w o o d l o u s e i n its j a w s . I t h a s also b e e n k n o w n t o r e s o r t t o e n t o m o l o g i s t s ' s u g a r p a t c h e s for t h e p u r p o s e o f c a p t u r i n g t h e luckless insects w h i c h c o m e for t h e sweets. Small m o t h s have no chance of escape, b u t the larger N o c t u i d s sometimes succeed in tearing themselves away although it is surprising h o w tenaciously the centipedes hold on. T h e S c u t i g e r o m o r p h a are probably entirely insectivorous, b u t study of t h e literature shows that t h e S c o l o p e n d r o m o r p h a have a wide range of diet, a l t h o u g h in m a n y cases t h e precise identification of species is d u b i o u s . A p a r t i c u l a r l y l a r g e s p e c i m e n of S. gigas ( p o s s i b l y S. gigantea) f r o m T r i n i d a d k e p t for o v e r a y e a r i n t h e I n s e c t H o u s e o f t h e Z o o l o g i c a l S o c i e t y o f L o n d o n , fed p r i n c i p a l l y o n s m a l l m i c e w h i c h i t d e v o u r e d w i t h a l a c r i t y . S c o l o p e n d r a s h a v e b e e n k n o w n , i n I n d i a , t o kill a n d e a t s m a l l b i r d s , w h i l e o n e v o r a c i o u s c e n t i p e d e (S. gigantea) w a s

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f o u n d d e v o u r i n g t h e side of a living toad. On t h e o t h e r h a n d , s p e c i m e n s o f S . morsitans f r o m T e x a s r e f u s e d t o b i t e t o a d s . M o r e r e c e n t l y , L a w r e n c e ( 1 9 5 3 ) h a s s e e n S. morsitans s p e e d i l y kill s m a l l g e c k o e s o f t h e g e n u s Pachydactylus b y b i t i n g t h e m i n t h e n e c k . O n e l a r g e u n i d e n t i f i e d S c o l o p e n d r a w a s d i s c o v e r e d o n t h e floor o f a h o u s e at K o k i n e , a s u b u r b of R a n g o o n , w i t h a s m a l l s n a k e w r i t h i n g i n its c l u t c h e s , f r o m t h e tail o f w h i c h t h e s k i n a n d flesh for a b o u t t w o i n c h e s h a d b e e n c o m p l e t e l y r e m o v e d . U n d e r l a b o r a t o r y c o n d i t i o n s S . heros f e e d s freely u p o n t h e agriculturally noxious insects provided: it prefers to remain u n d e r g r o u n d on w a r m days b u t is restless on the surface in cloudy and w e t w e a t h e r . S . viridis r e f u s e s w o o d l i c e a n d e a r t h w o r m s b u t i s p a r t i a l t o flies; t h e p r e y , o f w h i c h t h e h a r d p a r t s a r e r e j e c t e d , i s held firmly to t h e m o u t h by t h e poison claws whilst t h e m a n d i b l e s and maxillae tear it to pieces. L a w r e n c e (1934) observed a large S. subspinipes f e e d i n g on a s l u g (Veronicella leydigi), b u t in c a p tivity t h e s a m e species from B o r n e o does n o t t o u c h r a w meat, w o r m s o r v a r i o u s i n s e c t s . S . subspinipes i s a b u n d a n t i n t h e v i c i n i t y of the town of Tarragona in the Philippine Islands, and Remington (1950) wrote: ' A l m o s t every n i g h t t h e writer saw one or t w o of the great chilopods feeding voraciously on the winged insects which s w a r m e d into his pyramidal laboratory tent, attracted by the elect r i c l i g h t . T h e c e n t i p e d e s c l i m b e d t h e w a l l s o f t h e t e n t easily, fastened their powerful anal legs n e a r t h e ventilator hole of t h e tent peak a n d s w u n g their bodies quickly to one side or t h e other to seize insects w h i c h alighted n e a r b y . ' T h e p r e s e n t w r i t e r k e p t a f e m a l e S . cingulata f o u n d n e a r M a r seilles f o r s e v e r a l m o n t h s in a c r y s t a l l i s i n g d i s h c o v e r e d w i t h a sheet of glass. S h e w a s fed on m e d i u m - s i z e d n y m p h a l cockroaches of which on the average she ate about one per week t h r o u g h o u t the s u m m e r . A d u l t cockroaches had to be disabled before she w o u l d t a c k l e t h e m . S h e fed a l s o o n s p i d e r s , flies, m o t h s a n d o t h e r i n s e c t s a n d c h e w e d u p s o m e w o r m s w h i c h s h e d i d n o t finish. S h e even ate bees and wasps which she caught in mid-air, rearing up t h e fore p a r t o f h e r b o d y t o s n a t c h t h e m w i t h h e r p o i s o n c l a w s a s t h e y flew p a s t . T h e s e s h e d r o p p e d q u i c k l y a n d w a i t e d u n t i l h e r p o i s o n h a d h a d t i m e t o t a k e effect ( C l o u d s l e y - T h o m p s o n , 1955).

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D u r i n g w a r m w e a t h e r she w a s given w a t e r daily w h i c h she d r a n k , s o m e t i m e s for p e r i o d s o f s e v e r a l m i n u t e s , a n d t h e l a p p i n g m o v e m e n t s of her mandibles a n d maxillae could readily be o b s e r v e d t h r o u g h t h e g l a s s o f h e r c o n t a i n e r . I n c o n t r a s t , S . clavipes f r o m C e n t r a l T u n i s i a w e r e p a l e , soft a n d c o m p a r a t i v e l y w e a k c r e a t u r e s w i t h o u t t h e r o b u s t a p p e t i t e o f S . cingulata ( C l o u d s l e y T h o m p s o n , 1955). T h e smaller C r y p t o p i d a e feed u p o n w o r m s , soft-skinned insects or any animal small e n o u g h to be killed by t h e m .

Enemies C e n t i p e d e s a r e c a r n i v o r o u s a n d will e a t o n e a n o t h e r i f a n o p p o r t u n i t y p r e s e n t s itself. Lithobius forficatus m u s t n o t b e o v e r c r o w d e d i n c a p t i v i t y , o r c a n n i b a l i s m will r e s u l t , p a r t i c u l a r l y i f o n e o f t h e animals is smaller than the others or has been injured. It has been suggested too that G e o p h i l i d s form p a r t of t h e natural food of the C r y p t o p i d a e . C e n t i p e d e s are p r o b a b l y distasteful a n d it does not a p p e a r likely t h a t t h e y a r e e a t e n t o a n y d e g r e e b y s p i d e r s a n d o t h e r p r e d a t o r y animals unless o t h e r food is scarce. S c o r p i o n s have b e e n k n o w n to kill a n d e a t S. morsitans b u t t h e b i g Scolopendra o f t e n g e t s t h e b e t t e r o f its a d v e r s a r y . T h e S c u t i g e r o m o r p h a r e a d i l y a u t o t o m i s e t h e i r legs i f a t t a c k e d , a n d i n s o m e s p e c i e s t h e d e t a c h e d limbs continue to stridulate, thereby attracting a predator's attent i o n w h i l e its f o r m e r p o s s e s s o r m a k e s its e s c a p e . On account of their retiring habits, centipedes tend to escape n o t i c e a n d t h e i r p o i s o n also p r o t e c t s t h e m f r o m e n e m i e s . T h e r e a r e n u m e r o u s s c a t t e r e d a c c o u n t s i n t h e l i t e r a t u r e o f t h e effects o f the bite of the larger centipedes, b u t in m a n y the animal has not been adequately identified a n d in t h e r e m a i n d e r the conclusions d r a w n b y t h e a u t h o r s a r e o f t e n m u c h a t v a r i a n c e . T h u s Scolopendra cingulata is s a i d to c a u s e p a i n f u l o e d e m a a n d r e a l d i s c o m f o r t to h u m a n s , b u t S. heros a n d S. viridis p r o d u c e , at m o s t , o n l y t e m p o r a r y s h a r p p a i n . T h e l a r g e S . subspinipes o f B r a z i l p r o d u c e s i n t e n s e p a i n , b l i s t e r i n g , s w e l l i n g , local i n f l a m m a t i o n , b u b o s a n d s u b c u t a n e o u s h a e m o r r h a g e . T h i s species m a y reach a length of 25 cm a n d R e m i n g t o n (1950) w h o was bitten by one while on t h e I s l a n d o f L e y t e i n t h e P h i l i p p i n e s w r o t e t h a t i t c a u s e d a fiery p a i n w h i c h a t first w a s a l m o s t u n b e a r a b l e a n d d i d n o t d i m i n i s h for

CENTIPEDES about t w e n t y m i n u t e s . A swollen, t e n d e r and mildly painful cond i t i o n p e r s i s t e d for a b o u t t h r e e w e e k s . T h e o n l y a u t h e n t i c c a s e r e c o r d e d i n t h e l i t e r a t u r e i n w h i c h a c e n t i p e d e b i t e w a s fatal t o a h u m a n is that of a seven year old child in the Philippines w h o was bitten on t h e h e a d a n d died t w e n t y - n i n e h o u r s later. Bucherl ( 1 9 4 6 ) h a s p u b l i s h e d t h e r e s u l t s o f e x p e r i m e n t s w i t h t h e five c o m m o n e s t a n d largest Brazilian C h i l o p o d s a n d has i n c l u d e d a m o r p h o logical a n d h i s t o l o g i c a l s t u d y o f t h e p o i s o n a p p a r a t u s . H a v i n g experimented with m i c e , guinea-pigs a n d pigeons injected with solutions of the v e n o m at varying concentrations, he reached the conclusion t h a t t h e poison of even the largest of t h e Brazilian s p e c i e s w a s t o o f e e b l e e v e r t o e n d a n g e r t h e life o f m a n o r e v e n young children. Nevertheless, giant centipedes which are so a b u n d a n t in tropical regions are dreaded by the h u m a n inhabitants. In 1798 t h e ren o w n e d n a t u r a l h i s t o r i a n D o n o v a n w r o t e o f Scolopendra morsitans: 'Travellers agree that t h e t e m p e r a t e parts of Asia w o u l d be a terrestrial paradise, w e r e it n o t for t h e m u l t i t u d e of t r o u b l e s o m e insects a n d reptiles w i t h w h i c h t h e y are infested. In a well cultivat e d c o u n t r y , like C h i n a , m a n y o f t h e s e c r e a t u r e s c a n s c a r c e l y find shelter; b u t such as h a r b o u r in t h e walls or furniture of h u m a n d w e l l i n g s a r e a s a b u n d a n t i n t h a t , a s i n a n y o t h e r c o u n t r y t h a t lies within o r near t h e tropics. A m o n g s t t h e latter, n o n e p r o d u c e m o r e t e r r i b l e effects t h a n t h e c e n t i p e d e , w h o s e p o i s o n i s a s v e n o m o u s a s t h a t o f t h e s c o r p i o n , w h i c h also i s a n a t i v e o f C h i n a . ' A s m a l l s p e c i m e n only 85 mm long was found by a zoology student of Exeter University College u n d e r a b o u l d e r at Cassis, near Marseilles, in 1949. It bit h i m on t h e second finger of his r i g h t h a n d as he c a u g h t it. A f t e r a b o u t a q u a r t e r o f a n h o u r t h e b a s e o f t h e f i n g e r h a d s w o l len c o n s i d e r a b l y a n d t h e p a i n w a s similar to t h a t of a h o r n e t sting. W i t h i n a n h o u r t h e w h o l e h a n d h a d s w o l l e n t o t w i c e its n o r m a l size b u t w a s n o t p a i n f u l t o t o u c h . T h e effects h a d q u i t e g o n e t h r e e days later ( T u r k , 1951). T h e refrain of a T r i n i d a d calypso runs: ' M a n centipede bad, bad; w o m a n centipede worse t h a n bad.' Nevertheless, I n d i a n children have been seen to drag h u g e centipedes out of the earth and eat t h e m . T h e African A r a b s d e v o u r S c o l o p e n d r a s alive, often i n c o m p a n y w i t h scorpions, b r o k e n glass, leaves of prickly p e a r a n d

A

CENTIPEDES

other unpleasant things u n d e r the influence of religious excitement. I n S i a m c e n t i p e d e s a r e r o a s t e d a n d g i v e n t o c h i l d r e n suffering from 'thinness a n d swollen belly' (malaria or h o o k w o r m ) : and roasted centipedes p o w d e r e d a n d soaked in alcohol a n d t h e juice of b o r a p e t are u s e d medicinally as a stimulant. F e w t e m p e r a t e species are big e n o u g h to be able to penetrate the human skin with t h e i r p o i s o n - c l a w s . Lithobius forficatus c a u s e s a s h a r p p a i n t h a t i s n o t i c e a b l e for s o m e t i m e , b u t s i g n s of i n j u r y a r e i n s i g n i f i c a n t . T h e l o n g - l e g g e d Scutigera forceps has been recorded as giving a bite that is followed by intense local p a i n . O n t h e w h o l e , a l t h o u g h Buffon, i n a c o n t e m p o r a r y E n g l i s h translation, wrote: 'Of these hideous and angry insects we k n o w little e x c e p t t h e f i g u r e a n d t h e n o x i o u s q u a l i t i e s ' , c e n t i p e d e s a r e for t h e m o s t p a r t c o m p a r a t i v e l y i n n o c u o u s m e m b e r s o f t h e c o m m u n i t y of animals. E v e n t h e large Scolopendras do not bite unless m o l e s t e d a n d will a l w a y s t r y t o e s c a p e r a t h e r t h a n f i g h t . M a n y of the G e o p h i l o m o r p h a , including the c o m m o n British Geophilus electricus, G. carpophagus, Necrophlaeophagus longicornis a n d Scolioplanes crassipes, e x u d e a p h o s p h o r e s c e n t fluid w h e n d i s t u r b e d . T h e phosphorescence m a y be excited at any time of year b y m e c h a n i c a l s t i m u l a t i o n a n d b y i m m e r s i o n i n w a t e r : i t also occurs w h e n the centipedes are attacked by ants a n d similar enemies. In a u t u m n , at t h e time of sexual maturity, centipedes t e n d t o l e a v e t h e i r b u r r o w s a n d for t h i s r e a s o n a n a b u n d a n c e o f luminous specimens is found at that time of year. T h e luminescence is simply a protective reaction a n d is n o t related to sexual b e h a v i o u r as h a s s o m e t i m e s b e e n suggested, for these a n i m a l s are eyeless. In s o u t h e r n C a l i f o r n i a t h e l a r g e g r e e n i s h Scolopendra heros is g r e a t l y f e a r e d , n o t o n l y o n a c c o u n t o f its p o i s o n o u s b i t e b u t b e c a u s e i t also p r o d u c e s a r e d d i s h s t r e a k w h e r e i t h a s c r a w l e d u p o n t h e body. Like m a n y other tropical and subtropical Scolopendrom o r p h a , i t m a k e s t i n y i n c i s i o n s w i t h its n u m e r o u s feet. I n t h e m s e l v e s t h e s e a r e trifling, b u t w h e n a l a r m e d t h e c e n t i p e d e d r o p s i n t o e a c h incision some kind of v e n o m that causes intense irritation so that t h e affected p a r t b e c o m e s i n f l a m e d a n d t h e t w o r o w s o f p u n c t u r e s show white against the flesh. No d o u b t the poisonous and p h o s -

CENTIPEDES

55

p h o r e s c e n t f l u i d s s e c r e t e d n e a r t h e c o x a e o f t h e legs a r e a d d i t i o n a l protective devices that render centipedes dangerous a n d distasteful t o t h e i r e n e m i e s . W i t h r e g a r d t o p a r a s i t e s , t h e c a r n i v o r o u s C h i l o p o d a afford a sharp contrast to t h e vegetarian D i p l o p o d a since few parasitic N e m a t o d a have b e e n recorded from t h e m a l t h o u g h t h e y are s o m e times infested by M e r m i t h i d a e . O t h e r parasites that have occasionally b e e n found include bacteria a n d fungi, Protozoa a n d N e m a t o m o r p h a ( R e m y , 1950). T h o m p s o n (1939) dissected s o m e 3 0 0 s p e c i m e n s o f Lithobius forficatus a n d f o u n d n o p a r a s i t e o t h e r than two species of T a c h i n i d flies. T h e average parasitism was only 7 . 5 % , a n d a l m o s t half t h e parasitised c e n t i p e d e s c o n t a i n e d m o r e t h a n o n e larva: i n m o s t cases b o t h parasite larvae died. O n o n e o c c a s i o n h o w e v e r s o m e l a r v a e o f t h e P r o c t o t r u p i d w a s p Cryptoserphus ater w e r e s e e n i s s u i n g f r o m t h e b o d y of a Lithobius forficatus w h i c h h a d s u c c u m b e d t o t h e i r a t t a c k s ,

Reproduction and life cycle Details of reproduction in centipedes have not often been closely s t u d i e d , b u t i t a p p e a r s t h a t m a n y s p e c i e s s h o w a r e m a r k able degree of parental care. In t e m p e r a t e regions, egg-laying usually takes place t h r o u g h o u t the spring and s u m m e r although copulation m a y have taken place as long before as the previous a u t u m n . In m a n y of the tropical species there seems to be no regular a n n u a l b r e e d i n g season. T h e sexes are very similar a n d can often b e d i s t i n g u i s h e d only b y m i c r o s c o p i c e x a m i n a t i o n . I n t h e L i t h o b i o m o r p h a and Scutigeromorpha the clasping organs at the posterior e n d of t h e b o d y are differently f o r m e d in t h e t w o sexes, that of t h e female b e i n g u s e d for h o l d i n g t h e egg, t h a t of t h e male p r e s u m a b l y for c l a s p i n g t h e f e m a l e . D e m a n g e ( 1 9 5 6 ) h a s r e c e n t l y s h o w n t h a t in Lithobius piceus t h e m a l e c e n t i p e d e d e p o s i t s a s p e r m a t o p h o r e on a small w e b and this is afterwards taken up b y t h e f e m a l e . T h e y o u n g o f all t h e o r d e r s l e a v e t h e e g g - s h e l l w i t h t h e full n u m b e r o f legs w i t h t h e e x c e p t i o n o f t h e L i t h o b i o m o r p h a and Scutigeromorpha, which hatch with seven pairs of legs i n c l u d i n g t h e p o i s o n c l a w s . T h e G e o p h i l o m o r p h a a n d C r y p t o p i d a e u s u a l l y lay 1 5 t o 3 5 e g g s i n a l o o s e m a s s w h i c h i s o f t e n m e r e l y left i n t h e soil. I n t h e

56

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G e o p h i l i d Pachymerium ferrugineum, w h i c h h a s a w i d e g e o g r a p h i cal r a n g e i n E u r o p e , A s i a , A f r i c a a n d A m e r i c a , f e r t i l i s a t i o n t a k e s p l a c e i n t h e s p r i n g i n s o u t h e r n F i n l a n d , b u t m a y also o c c u r b e f o r e h i b e r n a t i o n . T h e m a i n p e r i o d o f e g g - l a y i n g e x t e n d s f r o m t h e last week of M a y to the m i d d l e of July a n d the n u m b e r of eggs per brood varies between 20 a n d 55, a n d is usually 25 to 45. W h e n disturbed d u r i n g b r o o d i n g , t h e female either eats her eggs and y o u n g , o r else a b a n d o n s t h e m , b u t a d o l e s c e n t y o u n g d o n o t s e e m to be attacked. If t h e relative h u m i d i t y d r o p s only 1 - 3 % below saturation, t h e eggs begin to shrink, owing to desiccation. If they are separated from t h e m o t h e r they b e c o m e infected with fungi within a few days: it is p r o b a b l e that w h e n m o u t h i n g a n d touching t h e eggs t h e female coats t h e m w i t h s o m e fungicidal secretion that p r e v e n t s s p o r e s f r o m d e v e l o p i n g . T h e m a x i m u m size o f t h e y o u n g a t t h e e n d o f t h e i r first s u m m e r i s 1 6 m m : s o m e o f t h e i n d i v i d u a l s become mature during their second summer, others not until t h e i r t h i r d . A s t h e size o f t h e m a t u r e f e m a l e s v a r i e s c o n s i d e r a b l y t h e l a r g e s t i n d i v i d u a l s a r e p r o b a b l y a t least f o u r y e a r s o l d ( P a l m e n a n d Rantala, 1954).

F I G . 14. Parental care in a Scolopendra.

I n t h e L i t h o b i o m o r p h a t h e e g g s a r e laid i n d i v i d u a l l y i n t h e soil after b e i n g c o v e r e d w i t h e a r t h b y t h e f e m a l e , b u t i n t h e S c o l o p e n d r o m o r p h a the y o u n g are usually g u a r d e d by their m o t h e r u n t i l t h e y a r e a b l e t o shift f o r t h e m s e l v e s . O f t e n a r o u g h l y h o l l o w e d - o u t c a v i t y i s m a d e i n soft o r r o t t i n g w o o d b y t h e b o d y o f t h e m o t h e r before t h e eggs are laid. T h e p a r e n t c e n t i p e d e t h e n c u r l s h e r s e l f a r o u n d h e r e g g s a n d y o u n g s o t h a t a s s h e lies o n h e r side they are enclosed in a basket-like framework formed by t h e

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v e n t r a l surface o f h e r b o d y a n d t h e i n w a r d l y p o i n t i n g legs. T h e e g g s o r y o u n g a r e t h u s s a f e g u a r d e d f r o m c o n t a c t w i t h t h e soil, a n d t h e m o t h e r c e n t i p e d e m a i n t a i n s t h i s p o s i t i o n for s e v e r a l w e e k s u n t i l t h e d e p a r t u r e o f t h e adolescent y o u n g ( C o r n w e l l , 1934; L a w r e n c e , 1 9 4 7 , 1 9 5 3 * ) . I n t h e c a s e o f S . dalmatica i t a p p e a r s t h a t t h e e a r t h o f t h e ' n e s t ' i s s t u c k t o g e t h e r b y s o m e v i s c o u s fluid. Early writers such as Gervais a n d Lucas believed that Scolopendras w e r e ovoviviparous b u t this error was later corrected by Silvestri w h o suggested t h a t t h e m i s t a k e arose as an e r r o n e o u s i n f e r e n c e f r o m t h e w a y i n w h i c h S . cingulata a s s i d u o u s l y g u a r d s its e g g s a n d y o u n g o n e s . Little exact knowledge of t h e b r e e d i n g habits of S c o l o p e n d r o m o r p h c e n t i p e d e s i s a v a i l a b l e , a n d t h i s i s p a r t l y d u e t o t h e fact that if t h e incubating m o t h e r s are disturbed they react either by devouring the eggs a n d e m b r y o s or by deserting their b r o o d which is t h e n attacked by fungi ( L a w r e n c e , 1947). T h u s w h e n a s p e c i m e n o f S . angulata w a s s e n t w i t h h e r b r o o d f r o m T r i n i d a d t o t h e L o n d o n Z o o i n 1894, o n arrival only o n e y o u n g a n d t h e a d u l t w e r e found, a n d b o t h of t h e m w e r e dead. P a r e n t c e n t i p e d e s feed q u i t e casually on their y o u n g and, at times, even greedily w h e n kept w i t h o u t food. Unlike that of the Diplopoda the development of centipedes proceeds mainly by epimorphosis. It is not k n o w n exactly h o w m a n y m o u l t s a r e p a s s e d t h r o u g h b y t h e y o u n g c e n t i p e d e s after leaving their m o t h e r , b u t t h e r e m u s t be a considerable n u m b e r . After leaving the b r o o d c h a m b e r g r o w t h is c o n t i n u o u s a n d gradual a n d i s chiefly c o n c e r n e d w i t h i n c r e a s e i n size a n d s t r e n g t h e n i n g of t h e chitinous e p i d e r m a l structures, especially t h e m o u t h parts. T h e Lithobiomorpha and Scutigeromorpha at first carry their e g g s , w h i c h a r e laid s i n g l y , i n t h e c l a s p e r s s i t u a t e d o n t h e g e n i t a l somite, a n d d e v e l o p m e n t is initially a n a m o r p h i c a n d later epim o r p h i c . T h e f i r s t s e v e n - l e g g e d s t a g e o f t h e L i t h o b i o m o r p h a lasts o n l y a few h o u r s , after w h i c h t h e r e a r e f o u r e c d y s e s a t t h e last o f w h i c h t h e y o u n g c e n t i p e d e h a s twelve pairs o f legs. T h i s c o m pletes t h e a n a m o r p h i c stage. T h e e p i m o r p h i c phase consists of four s t a g e s , i n all o f w h i c h t h e r e a r e f i f t e e n p a i r s o f legs, a n d t h e s e x u a l l y m a t u r e a d u l t e m e r g e s f r o m t h e last o n e . T h e size o f Lithobius forficatus after l e a v i n g t h e e g g m a y i n c r e a s e f r o m 3 t o 2 4 m m

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58

and the n u m b e r of antennal segments and teeth on the maxillip e d e s also i n c r e a s e s .

T h e time taken to complete the various

s t a g e s differs c o n s i d e r a b l y , t h e s e c o n d b e i n g 1 0 t o 1 4 d a y s , t h e t h i r d 8 0 t o 8 4 days. T h e w h o l e d e v e l o p m e n t from egg t o m a t u r e c e n t i p e d e requires a b o u t t h r e e years, so that larval a n d i m m a t u r e centipedes are usually found together with sexually m a t u r e forms. I n Scutigera

coleoptrata

the

larvae

hatch

with

four pairs

o f legs

a n d t h e r e a r e five m o r e l a r v a l s t a g e s w i t h 5 , 7 , 9 , 1 1 a n d 1 3 p a i r s of legs respectively. T h i s a n a m o r p h i c stage is s u c c e e d e d by an e p i m o r p h i c o n e o f f o u r a d o l e s c e n t s t a g e s e a c h w i t h fifteen p a i r s o f l e g s . T h e first t h r e e l a r v a l s t a g e s r e q u i r e a b o u t t h r e e w e e k s for their completion. Centipedes are long-lived creatures and specim e n s of Lithobius forficatus h a v e b e e n k n o w n to live for up to 5 to 6 y e a r s (Verhoeff, 1 9 3 7 a , b ) . BIBLIOGRAPHY Identification ATTEMS,

C.

G.

(1926) Progoneata,

Chilopoda in

KUKENTHAL, W.

&

KRUMBACH, T . Handbuch der Zoologie, Berlin, 4 , (1-4), 1-402. (1928) T h e M y r i a p o d a of S o u t h Africa. Ann. S. Afr. Mus. 2 6 , 1-431. (1929) Myriapoda, G e o p h i l o m o r p h a . Das Tierreich, 5 2 , 1-388 (1930) Chilopoda, S c o l o p e n d r o m o r p h a . Ibid., 5 4 , 1-308. BLOWER, G. (1955) Yorkshire centipedes. Naturalist, 1 9 5 5 , 1 3 7 - 4 6 . BRADE-BIRKS, S. G. (1939) N o t e s on M y r i a p o d a X X X V I . Sources for description and illustration of the British fauna. J. S-E. Agric. Coll. Wye, N o . 44, 156-79. BROLEMANN, W. H. (1932) Chilopodes. Faune de France, 2 5 , 1 - 4 0 5 . CHAMBERLIN, R. V. (1920) T h e M y r i a p o d a of the Australian region. Bull. Mus. Comp. Zool., 6 4 , 1 - 2 6 9 . CLOUDSLEY-THOMPSON, J. L. (1952) Collecting centipedes and millipedes. Bull. Amat. Ent. Soc, 1 1 , 5 - 8 . LATZEL, R. (1880) Die Myriopoden der Oesterreichish-Ungarischen Monarchic 1. Die Chilopoden. W i e n . VERHOEFF, K. W. (1902-28) Chilopoda in H. G. BRONN'S Klass. Ordn. Tierreichs, 5, II (1), 1-725. W A N G , Y. M. (1951) T h e Myriapoda of the Philippine Islands. Serica 1, 1-80. Biology AUERBACH, S. I. (1951) T h e centipedes of the Chicago area with special reference to their ecology. Ecol. Monogr., 2 1 , 97-124.

CENTIPEDES

59

BAUER, K. (1955) Sinnesokologische U n t e r s u c h u n g e n an Lithobius forficatus. Zool. Jahrb. (Zool.), 6 5 , 2 6 7 - 3 0 0 . BONNELL, B. (1930) Geophilid centipedes from the bed of the C o o u m River ( M a d r a s ) . J. Asiat. Soc. Bengal, ( N . S . ) , 2 5 , 181-4. BUCHERL, W. (1946) Acao do veneno dos Escolopendromorfos do Brasil sobre alguns animais de laboratorio. Mem. Inst. Butanan. S. Paulo, 1 9 , 181-97. CLOUDSLEY-THOMPSON, J. L. (1945) Behaviour of the c o m m o n centipede, Lithobius forficatus. Nature, Lond., 1 5 6 , 5 3 7 - 8 . (1948) Hydroschendyla submarina ( G r u b e ) in Yorkshire: with an historical review of the m a r i n e M y r i a p o d a . Naturalist, 1 9 4 8 , 149-52. (1949) A note on the M y r i a p o d s and Arachnids of n o r t h e r n Italy. Ent.Mon. Mag., 8 5 , 285. (1951) S u p p l e m e n t a r y notes on M y r i a p o d a . Naturalist, 1 9 5 1 , 16-17. (1952a) T h e biology of centipedes and millipedes. Discovery, 1 3 , 18-21. (1952b) T h e behaviour of centipedes and m i l l i p e d e s — 1 . Responses to environmental stimuli. Ann. Mag. Nat. Hist., (12), 5, 4 1 7 - 3 4 . (1954) T h e ecological significance of diurnal r h y t h m s in terrestrial A r t h r o p o d a . Sci. Prog., 4 2 , 4 6 - 5 2 . (1955) S o m e aspects of the biology of centipedes a n d scorpions. Naturalist, 1 9 5 5 , 1 4 7 - 5 3 . CORNWELL, W. S. (1934) N o t e s on the egg-laying and nesting habits of certain species of N o r t h Carolina m y r i a p o d s and various phases of their life histories. J. Elisha Mitchell Sci. Soc, 1 4 9 , 2 8 9 - 9 1 . DEMANGE, J . - M . (1956) C o n t r i b u t i o n a l'etude de la biologie, en captivite, de Lithobius piceus gracilitarsis Brol. ( M y r i a p o d e - C h i l p o d e ) . Bull. Mus. Hist. nat. Paris, (2), 2 8 , 3 8 8 - 9 3 . JACKSON, A. R. (1914) A preliminary list of the M y r i a p o d s of the Chester district. Lanes. Nat., 6, 4 5 0 - 8 . LAWRENCE, R. F. (1947) Some observations on the post-embryonic develo p m e n t of the Natal forest centipede Cormocephalus midtispinus (Kraep.). Ann. Natal. Mus., 1 1 , 139-56. LAWRENCE, T. C. (1934) N o t e s on the feeding habits of Scolopendra subspinipes Leach (Myriapoda). Proc. Hawaii Ent. Soc, 8, 4 9 7 - 8 . M A N T O N , S. M. (1952) T h e evolution of A r t h r o p o d a n locomotory m e c h a n i s m s — P a r t 3. T h e locomotion of the Chilopoda and P a u r o p o d a . J. Linn. Soc. (Zool), 4 2 , 1 1 8 - 6 7 . (1953) L o c o m o t o r y habits and the evolution of the larger A r t h r o podan groups in Evolution. Symp. Soc. Exp. Biol, 7, 339-76. PALMEN, E. (1949) T h e Chilopoda of Eastern Fennoscandia. Ann. Soc. Zool. Fenn. Vanamo, 1 3 , (4), 1-45.

60

CENTIPEDES

PALMEN, E. and RANTALA, M. (1954) On the life-history and ecology of Pachymeriurn ferrugineum (C. L. Koch) (Chilopoda, Geophilidae). Ibid., 1 6 , (3), 1-44. REMINGTON, C. L. (1950) T h e bite and habits of a giant centipede (Scolopendra subspinipes) in the Philippine Is. Amer. J. Trop. Med., 3 0 , 453-5. REMY, P. A. (1950) On the enemies of Myriapods. Naturalist, 1 9 5 0 , 1 0 3 - 8 . SCHUBART, O. (1955) Tausendfiisser als N a h r u n g im T i e r r e i c h . Nach. Nat. Mus. Aschaffenburg, 4 9 , 1 - 2 9 . SHIPLEY, A. E. (1914) Pseudoparasitism. Parasitology, 6, 351-2. SINCLAIR, F. G. (1895) M y r i a p o d s : in HARMER, S. F. and SHIPLEY, A. E.

The Cambridge Natural History, 5, 2 9 - 8 0 . T U R K , F. A. (1951) Myriapodological Notes, I I I . T h e iatro-zoology, biology and systematics of some tropical ' M y r i a p o d s ' . Ann. Mag. Nat. Hist., (12), 4, 3 5 - 4 8 . VERHOEFF, K. W. (1937a) Z u r K e n n t n i s der L i t h o b i i d e n . Arch. Naturgesch. ( N . F . ) , 6, 171-257. (1937b) Z u r Biologie der Scutigera coleoptrata, u n d u b e r die jiingeren Larvenstadien. Z. wiss. Zool., 1 5 0 , 262-82.

CHAPTER

OTHER

IV

'MYRIAPODS'

I T HAS a l r e a d y b e e n p o i n t e d o u t t h a t t h e D i p l o p o d a a n d C h i l o p o d a w e r e f o r m e r l y a s s o c i a t e d w i t h t h e less f a m i l i a r P a u r o p o d a a n d S y m p h y l a a n d r e g a r d e d as o r d e r s of a class ' M y r i a p o d a ' , c o m p o s e d of A r t h r o p o d a possessing bodies formed of m a n y similar somites each p r o v i d e d w i t h at least o n e pair of legs. It is n o w realised, however, that the 'Myriapoda' included an unnatural assemblage of superficially similar b u t u n r e l a t e d g r o u p s w h i c h are n o w considered a s separate classes, h a v i n g n o m o r e relationship t o one

F I G . 1 5 . P a u r o p o d a and Symphyla. Left, Scutigerella sp. (body length 4 m m ) ; right, Pauropus sp. (body length 1 . 5 m m . ) another than to the Crustacea,

Insecta and Arachnida.

Indeed,

there is strong reason to suspect t h a t t h e m o d e r n S y m p h y l a are closely allied to t h e extinct ancestors of insects.

Class

PAUROPODA

T h e P a u r o p o d a r e s e m b l e t h e D i p l o p o d a i n h a v i n g t h e orifice o f t h e r e p r o d u c t i v e o r g a n s o n t h e fore p a r t o f t h e b o d y , t h a t i s t o say in the third somite behind the head, and in the fusion of the two 61

62

OTHER

'MYRIAPODS'

a d j o i n i n g t e r g i t e s t o r e p r e s e n t a s i n g l e s o m i t e ; b u t differ f r o m t h e m in the structure of the two pairs of jaws, in having the end of the antennae b r a n c h e d a n d in the possession of only twelve somites a n d ten pairs of limbs of w h i c h nine have a locomotory function, t h e first p a i r b e i n g r e d u c e d t o m e r e b u d s . I n a d d i t i o n t h e legs a r e v e r y w i d e l y s p a c e d , t r a c h e a e a r e a b s e n t a n d five p a i r s o f l o n g t a c t i l e bristles are attached to the sides of the body. P a u r o p o d s are m i n u t e A r t h r o p o d a m e a s u r i n g only a b o u t o n e t w e n t i e t h o f a n i n c h i n l e n g t h . T h e first w a s d i s c o v e r e d b y L u b bock in 1886. T h e y have since b e e n found in E u r o p e , Asia a n d America where they inhabit d a m p situations beneath decaying l e a v e s , l o g s a n d s o o n . I n s o m e (Pauropus s p p . ) w h i c h a r e m o r e a c t i v e i n t h e i r m o v e m e n t s , t h e b o d y i s n a r r o w , c o m p a r e d w i t h its l e n g t h ; b u t i n t h e m o r e s l u g g i s h f o r m s (Eurypauropus s p p . ) i t i s v e r y w i d e , its s i d e s a n d f r o n t b e i n g p r o d u c e d s o a s t o c o n c e a l t h e legs a n d h e a d . A t t h e p r e s e n t t i m e six f a m i l i e s a r e k n o w n t o s c i e n c e , b u t little i n f o r m a t i o n i s a v a i l a b l e a b o u t t h e i r e c o l o g y a n d d i s t r i b u tion other t h a n that they are believed to be generally distributed except in the arctic, antarctic a n d desert regions of the world. Indeed, owing to their concealed habits they are sometimes b e lieved to be rare, b u t Starling (1944) estimated an a n n u a l average of 1,672,704 p e r a c r e ( t o a d e p t h of 5 i n c h e s ) in o a k s t a n d s on clay soil a n d 2 , 1 7 8 , 0 0 0 i n p i n e s t a n d s o n s a n d y l o a m i n t h e D u k e Forest, N o r t h Carolina. Five times as m a n y Pauropods were found i n oak h u m u s o n clay soil a s i n t h e s a m e level u n d e r p i n e s t a n d s o n s a n d y soil, a n d h i s o b s e r v a t i o n s s u g g e s t e d t h a t m o i s t u r e a n d t e m p e r a t u r e a r e t h e t w o m a i n f a c t o r s t h a t affect t h e d i s t r i b u t i o n o f t h e s e a n i m a l s . T h e g r e a t e s t n u m b e r w a s c o l l e c t e d f r o m s a n d y soil when the moisture percentage of the oven-dry weight was 1 1 - 2 0 % . I n clay soil P a u r o p o d s a p p e a r e d t o p r e f e r 2 1 - 3 0 % o f m o i s t u r e . T h e o p t i m u m range of t e m p e r a t u r e based on activity and mortality rate w h e n P a u r o p o d a were placed in constant t e m p e r a t u r e cabinets w a s f o u n d t o b e 1 6 - 2 0 ° C : t h e o p t i m u m , b a s e d o n field o b s e r v a tions, 17-23° C. S u m m e r appears to be the m o s t favourable season for d e v e l o p m e n t a n d a c t i v i t y , a n d e g g s w e r e o b t a i n e d i n J u n e a n d J u l y . A c o r r e l a t i o n a p p e a r s t o exist b e t w e e n o p t i m u m t e m p e r a t u r e for f u n g a l g r o w t h a n d a h i g h i n c i d e n c e i n P a u r o p o d d i s t r i b u t i o n which m a y be related to their feeding habits.

OTHER

'MYRIAPODS'

63

Little is k n o w n c o n c e r n i n g t h e food of P a u r o p o d s . Speculations have b e e n m a d e t h a t t h e slowly m o v i n g species feed o n decaying p l a n t a n d a n i m a l m a t e r i a l , w h e r e a s t h e m o r e agile t y p e s m a y c o n s u m e m i c r o s c o p i c a n i m a l s ( L a t z e l 1 8 8 4 ) . A s p e c i e s of Pauropus has been seen feeding on dead flies floating in a p u d d l e . No d o u b t m o s t species feed either on fresh sap or t h e s e m i - l i q u i d p r o d u c t s of decaying wood. H a r r i s o n (1914) observed P a u r o p o d s b r o w s i n g ' o n p a r t i c l e s o f soil i n w h i c h n o t h i n g i n t h e w a y o f f o o d c o u l d b e distinguished', and concluded that they were humus-feeders, while S t a r l i n g ( 1 9 4 4 ) o b s e r v e d t h a t P. carolinensis a t e t h e m y c e l i a of m o u l d s g r o w i n g o n d e c a y i n g leaf p a r t i c l e s b u t d i d n o t a p p e a r t o feed o n d e a d a n i m a l m a t e r i a l s u c h a s C o l l e m b o l a , D i p t e r a a n d other P a u r o p o d a that were placed at their disposal. According to T i e g s (1947), P a u r o p o d a are preyed u p o n by carn i v o r o u s m i t e s a n d f a l s e - s c o r p i o n s w h i c h f r e q u e n t l y t a k e toll o f larvae a n d even of adults. N e m a t o d e s have never b e e n found in P a u r o p o d a a n d n o t h i n g else a p p e a r s t o b e k n o w n o f t h e i r e n e m i e s . T h e eggs are deposited singly or in c l u m p s in secluded crevices of d a m p and decomposing vegetation. Like Diplopoda, the young o f P a u r o p o d s h a t c h w i t h t h r e e p a i r s o f legs, after w h i c h t h e y p a s s t h r o u g h four successive larval stages before attaining t h e ninel e g g e d a d u l t c o n d i t i o n . T h e n e w l y h a t c h e d Pauropus huxleyi i s o n e s e v e n t y - s e c o n d o f a n i n c h i n l e n g t h a n d h a s six legs, t h r e e large dorsal plates a n d t w o lateral hairs. D e v e l o p m e n t p r o c e e d s slowly a n d r e s e m b l e s t h a t of t h e D i p l o p o d a in b e i n g a n a m o r p h i c . In P . silvaticus t h e e g g h a t c h e s a f t e r 1 2 - 1 3 d a y s , r u p t u r e b e i n g a s sisted by stout cutting setae of t h e embryological cuticle. A quiescent ' p u p o i d ' stage with t w o pairs of r u d i m e n t a r y limbs emerges w h i c h lasts only 3 - 4 days a n d is followed by four s u c c e s s i v e l a r v a l s t a g e s w h i c h h a v e 3 , 5 , 6 a n d 8 p a i r s o f legs a n d r e q u i r e a p p r o x i m a t e l y 2, 4, 5 a n d 3 weeks respectively to develop. T h e p e r i o d from egg to adult in this species is t h u s a b o u t fourteen weeks in duration, and the adults do not moult again (Tiegs, 1947). T h e life h i s t o r i e s of Pauropus carolinensis, P. amicus a n d Eurypauropus spinosus a p p e a r t o b e s i m i l a r . T h e e g g s a r e l a i d i n g r o u p s o f f r o m 3 t o 12, e a c h e g g b e i n g p e r f e c t l y s p h e r i c a l , p e a r l y w h i t e a n d 0.17 m m i n diameter. T h e o u t e r m e m b r a n e , w h i c h i s o p a q u e .

64

OTHER

'MYRIAPODS'

is covered with m i n u t e pustulations. On the twelfth day the outer m e m b r a n e b r e a k s a n d t h e e m b r y o partially e m e r g e s : its a n t e r i o r e n d b e c o m e s free w h i l e t h e p o s t e r i o r e n d i s still e n c l o s e d i n t h e m e m b r a n e . T h e embryo is covered by one embryonic m e m b r a n e which bears outgrowths that cover the antennae and three pairs o f legs a r e v i s i b l e i n s i d e . T h e e m b r y o r e m a i n s m o t i o n l e s s i n t h i s c o n d i t i o n for t h r e e d a y s a n d t h e n , b y d o r s a l s p l i t t i n g o f t h e s e c o n d cuticle, issues out as an actively m o v i n g h e x a p o d larva w i t h t w o tactile setae ( H a r r i s o n , 1914). T h e r e m a i n i n g instars have 5, 6, 8 a n d 9 legs respectively a n d t h e n u m b e r of tactile bristles are 3, 4, 4 a n d 5. Before m o u l t i n g t h e animals b e c o m e s o m e w h a t rigid b u t remain upright throughout the process. T h e head and antennae are bent ventrally and w h e n the process, w h i c h takes only about twenty-five minutes,

is almost complete, vigorous propulsions,

w h i c h f i r s t free t h e h e a d , e n a b l e t h e w h i t e , m o i s t a n d w e a k a n i m a l t o d r a g itself f r o m its o l d c u t i c l e . Class SYMPHYLA T h e reproductive organs of the Symphyla, Pauropoda,

open upon the third somite

like t h o s e o f t h e

behind the head,

but

o t h e r w i s e t h e t w o classes are very dissimilar. I n t h e S y m p h y l a t h e antennae are very long a n d m a n y jointed, there are four pairs of peculiarly modified j a w s and the head bears a pair of tracheal spiracles. T h e r e are twelve pairs of walking legs, b u t t h e n u m b e r of tergal plates, namely fifteen, the first being very small, is greater t h a n t h e n u m b e r o f l e g s a n d n o t less a s i n t h e D i p l o p o d a a n d P a u r o p o d a . T h e basal s e g m e n t s o f t h e legs o f t h e t h i r d t o twelfth leg-bearing s e g m e n t s are p r o v i d e d w i t h a p r o t r u s i b l e sac t h o u g h t to have a respiratory function, whereas in P a u r o p o d s there is b u t a single pair on the floor of the collum or first post-cephalic segm e n t . W i t h t h e last s o m i t e articulates a pair of tail-like processes u p o n which spinning glands open, and just in front of t h e m is a papilla carrying a tactile hair. S y m p h y l a are small, pallid a r t h r o p o d s r e s e m b l i n g tiny c e n t i p e d e s in a p p e a r a n c e a n d activity, that live i n d a m p p l a c e s u n d e r s t o n e s , d e a d l e a v e s , e t c . T w o f a m i l i e s are k n o w n , Scutigerellidae a n d Scolopendrellidae, b o t h of w h i c h are represented in the British fauna. T h e class S y m p h y l a h a s h e l d t h e i n t e r e s t o f m a n y n a t u r a l i s t s

OTHER

'MYRIAPODS'

65

since a b o u t the m i d d l e of t h e eighteenth century a n d n u m e r o u s a r t i c l e s h a v e b e e n p u b l i s h e d w h i c h d e a l w i t h its m e m b e r s . N e a r l y all o f t h e s e a r e c o n c e r n e d p r i n c i p a l l y w i t h t h e t a x o n o m y , a n a t o m y a n d phylogenetic relationships of t h e g r o u p while a few of t h e later p a p e r s consider its ecological a n d e c o n o m i c aspects. T h e first s p e c i e s w a s d e s c r i b e d in 1 7 6 3 as Scolopendra nivea by S c o p u l i , w h o evidently little realised t h a t t h e o r g a n i s m possessed c h a r a c ters so distinct from those of the Chilopoda that eventually it w o u l d b e p l a c e d i n a c l a s s b y itself. I n 1 8 3 9 G e r v a i s n a m e d t h e s e c o n d s p e c i e s , w h i c h h e c o l l e c t e d n e a r P a r i s , Scolopendrella notacantha a n d i n 1 8 4 7 h e p l a c e d t h i s g e n u s i n t h e G e o p h i l i d a e : b u t M e n g e i n 1851 s u g g e s t e d t h a t Scolopendrella s h o u l d b e c o n s i d e r e d as transitional between the Scolopendridae and the Lepismidae! T h e b e s t - k n o w n s p e c i e s , Scutigerella immaculata, o c c u r s o n b o t h sides of t h e Atlantic, a n d in A m e r i c a has risen to t h e rank of a serious e c o n o m i c pest ( M i c h e l b a c h e r , 1938). Since 1920, n u m e r o u s important papers have been published on this subject. S . immaculata i s w i d e l y d i s t r i b u t e d i n t h e N o r t h e r n H e m i s p h e r e b u t is k n o w n to o c c u r only in a single locality, B u e n o s Aires, south of t h e equator. It does n o t a p p e a r to be w i d e s p r e a d in Africa b u t h a s b e e n r e p o r t e d from several localities i n Algeria a n d T u n i s i a , a n d h a s b e e n f o u n d i n t h e A l p s a t a h e i g h t o f 9 , 8 4 2 ft. T h e r e a r e n o definite r e c o r d s of it f r o m Asia or Australia. N o t h i n g can be said of its s o u t h e r n l i m i t s , b u t i t p r o b a b l y e x t e n d s w e l l i n t o t h e t r o p i c s s i n c e t h e c l i m a t e o f t h e H a w a i i a n I s l a n d s s e e m s w e l l s u i t e d t o its development. O t h e r species of S y m p h y l a are found widespread throughout the world: their northern distribution seems to be limited by expected m i n i m u m temperatures of about 1 5 ° F - . U n d e r e x p e r i m e n t a l c o n d i t i o n s Scutigerella immaculata c a n w i t h s t a n d a t e m p e r a t u r e of 20° C for long periods b u t seems u n a b l e to survive freezing for any l e n g t h of t i m e if previously held at r o o m t e m p e r a t u r e . I f k e p t a t 4 . 5 ° C first h o w e v e r i t m a y w i t h s t a n d 0 ° C for m o n t h s ( M i c h e l b a c h e r , 1 9 3 8 ) . M a n y species are well distributed in none has yet been recorded from China occur there too. S y m p h y l a are negatively phototactic v e r y s t r o n g l y d e v e l o p e d for t h e y a p p e a r E

the tropics and although or Siberia, they probably but the response is not to c o m e to t h e surface of S.S.C.M.

66

OTHER

'MYRIAPODS'

t h e soil t o feed w i t h o u t h e s i t a t i o n a t a n y h o u r o f t h e d a y . I t i s n o t u n c o m m o n to find t h e m lying perfectly motionless on t h e surface o f t h e g r o u n d w h e r e t h e y a r e fully e x p o s e d t o t h e s u n l i g h t . W h e n in motion the antennae are kept constantly moving, b u t while feeding they are, as a rule, held backwards. S y m p h y l a can r u n v e r y r a p i d l y w h e n d i s t u r b e d a n d q u i c k l y r e t r e a t i n t o t h e soil. I f their antennae are t o u c h e d with a camel's hair b r u s h or other instrument they reverse their course with lightning speed. In t u r n i n g r o u n d t h e p o s t e r i o r e n d o f t h e b o d y i s h e l d still a n d a c t s a s a p i v o t (Verhoeff, 1 9 3 4 ) . T h e v e r y y o u n g , h o w e v e r , n e v e r c o m e t o t h e s u r f a c e o f t h e soil a n d a p p a r e n t l y d o n o t f e e d u n t i l t h e y h a v e moulted a second time. Symphyla are not restricted to any part i c u l a r level o f t h e soil, a n d m a y b e f o u n d f r o m t h e s u r f a c e t o a d e p t h o f f o u r feet o r m o r e . M o i s t u r e i s t h e m o s t i m p o r t a n t f a c t o r d e t e r m i n i n g t h e i r v e r t i c a l d i s t r i b u t i o n , b u t t e m p e r a t u r e , soil t e x t u r e , s t r u c t u r e a n d v e g e t a t i o n also i n f l u e n c e t h e m . Symphyla appear to be vegetarians and to prefer decaying and s u c c u l e n t m a t e r i a l s a l t h o u g h t h e y will f e e d o n m a n y k i n d s o f l o w e r p l a n t life. N e w p o r t i n 1845 t h o u g h t t h a t t h e y m u s t b e c a r nivorous, preying perhaps on the microscopic Poduridae to be found in t h e s a m e places, b u t D u b o s c q , s o m e years later, n o t e d the a b s e n c e of a p o i s o n g l a n d in Scolopendrella. Scutigerella immaculata normally feeds u p o n decaying vegetable m a t t e r b u t m a y attack living p l a n t s , often d o i n g v e r y m u c h d a m a g e t o f i e l d a n d glasshouse crops such as y o u n g seedlings, asparagus, lima beans, peas, t o m a t o e s a n d cultivated flowers. It has conical taste sensillae at t h e apex of the second maxillae (considered to be homologous with the gnathochilarium of Diplopoda), but these are simpler in structure and considerably fewer in n u m b e r t h a n those of millipedes. Population studies in the field and greenhouses show that Symphyla m a y be present in large n u m b e r s , s o m e t i m e s as m a n y as 22 million per acre out of doors, a n d 90 million per acre in glassh o u s e s . S u i t a b l e m e t h o d s for c h e c k i n g d a m a g e i n g r e e n h o u s e s consist of using raised benches, steam t r e a t m e n t , insecticides and soil f u m i g a t i o n ( M i c h e l b a c h e r , 1938). A s i n t h e c a s e o f t h e P a u r o p o d a , little i s k n o w n o f t h e p r e d a t o r s of these creatures, b u t C h i l o p o d s are said to be a m o n g t h e m o s t i m p o r t a n t of their natural enemies. A large G a m a s i d m i t e has been

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67

o b s e r v e d t o s e i z e a S y m p h y l i d w i t h its j a w s a n d c a r r y i t r a p i d l y a w a y : v a r i o u s g r e g a r i n e s h a v e b e e n f o u n d i n Scutigerella immaculata, Hanseniella hova a n d H. agilis a n d t h e r e is a s i n g l e r e c o r d of a n e m a t o d e i n t h e first n a m e d s p e c i e s ( R e m y , 1 9 5 0 ) . M a n y S y m p h y l a lay a c l u m p o f e g g s i n a c r e v i c e o r h o l l o w o f t h e soil, a t t a c h i n g t h e m t o its w a l l b y a s h o r t s t a l k s o t h a t t h e e g g s a r e free f r o m c o n t a c t w i t h t h e s i d e s o r floor o f t h e s h e l t e r t h e r e b y o b t a i n i n g s o m e p r o t e c t i o n f r o m f u n g i a n d o t h e r e n e m i e s . I n Scutigerella immaculata, 4 - 2 5 e g g s a r e l a i d ( F i l i n g e r , 1 9 3 1 ) : in Hanseniella agilis 3 - 8 . T h e y o u n g h a t c h w i t h six o r s e v e n p a i r s o f l e g s a f t e r a n a v e r a g e p e r i o d o f a b o u t e l e v e n d a y s : t h e r e a r e five f u r t h e r s t a g e s e a c h h a v i n g o n e m o r e p a i r o f l e g s t h a n t h e last, u p t o t h e n u m b e r of eleven. F r o m this eleven-legged larva, t h e a d u l t e m e r g e s a f t e r a f i n a l m o u l t . A c c o r d i n g t o F i l i n g e r ( 1 9 3 1 ) t h e first m o u l t o c c u r s w i t h i n o n e t o four days, u s u a l l y after 2 4 - 3 6 h o u r s , t h e succeeding ones at intervals of about eight days. Sexual maturity is r e a c h e d after 4 0 - 6 0 days. D u r i n g m o u l t i n g a split o c c u r s b e tween the head and the first body segment, but as the whole c u t i c l e i s soft i t i s n o t u s u a l l y c a s t i n o n e p i e c e a s i n m o s t o t h e r m y r i a p o d s , b u t is m o u l t e d irregularly in strips a n d tattered fragments at various points of the body. M i c h e l b a c h e r ( 1 9 3 8 ) f o u n d t h a t S . immaculata m o u l t s f r o m t i m e t o t i m e d u r i n g i t s e n t i r e life, a n d s i n c e i t m a y l i v e f o r a period of four years or more, t h e m a x i m u m n u m b e r of moults p r o b a b l y exceeds f i f t y . T h e m o u l t i n g characteristics o f different individuals v a r y greatly: a sex factor is p r e s e n t a n d s o m e evidence has b e e n o b t a i n e d w h i c h indicates t h a t a g e n e t i c factor m a y also be involved. O t h e r factors w h i c h influence m o u l t i n g are: t y p e of food, t e m p e r a t u r e , h u m i d i t y a n d mutilation. A b o v e a n d below 28° C t h e m o u l t i n g rate decreases. T h e earliest t h a t egg-laying was observed to begin was between the seventh and eighth moults which w o u l d indicate that this is about the time of sexual maturity. In m o s t cases h o w e v e r eggs are n o t p r o d u c e d until a m u c h later date. Oviposition occurs a short time before moulting. At birth, t h e s p e c i e s o f Scutigerella s o far i n v e s t i g a t e d h a v e b e e n f o u n d t o h a v e s i x p a i r s o f l e g s a n d s i x a n t e n n a l s e g m e n t s , w h e r e a s Hanseniella s p p . h a v e s e v e n p a i r s o f l e g s a n d six a n t e n n a l s e g m e n t s ( T i e g s , 1945). It is s u r p r i s i n g to find t h e s e differences in so h o m o -

68

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geneous a g r o u p as t h e S y m p h y l a . T h e larva slowly a n d laboriously w o r k s its w a y o u t o f t h e e g g t h r o u g h t h e c u t m a d e i n t h e b l a s t o d e r m i c cuticle a n d chorion by t h e t w o pairs of s h a r p spines at t h e bases of the antennae. T h e s e spines are part of the embryonic cuticle a n d are rejected with t h e latter at eclosion. D u r i n g t h e first f e w h o u r s o f f r e e d o m t h e l a r v a e n l a r g e s , e v i d e n t l y b y i n g e s t i o n o f f l u i d f r o m w i t h o u t . F o r t h e first d a y i t c r a w l s s l u g g i s h l y

F I G . 1 6 . Stages in t h e development of Scutigerella immaculata. (After Michelbacher, 1938.)

over the decaying vegetation on w h i c h it feeds, b u t thereafter b e comes m o r e active. After 7 - 1 2 days it retreats to t h e shelter of some secluded crevice a n d there m o u l t s . W i t h the sixth m o u l t t h e o r g a n i s m r e c e i v e s all i t s m o r p h o l o g i c a l p a r t s , b u t c o m p l e t e d i f f e r e n t i a t i o n d o e s n o t o c c u r u n t i l a m u c h l a t e r p e r i o d , t h e lifehistory being rather complex. After each m o u l t m o r e segments are usually a d d e d to the antennae and broken antennae are regenerated. T h i s has been observed in individuals nearly three y e a r s o l d . A s a l r e a d y m e n t i o n e d , t h e t o t a l life s p a n m a y e x c e e d four years.

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69

BIBLIOGRAPHY Identification ATTEMS, C . G . ( 1 9 2 6 ) P r o g o n e a t a , C h i l o p o d a in KUKENTHAL, W .

and

KRUMBACH, T . Handbuch der Zoologie, Berlin, 4 , ( 1 - 4 ) , 1 - 4 0 2 .

BAGNALL, R. S. ( 1 9 1 4 ) A synopsis of the British Symphyla, with descriptions of new species. Trans. Nat. Hist. Soc. Northumb., ( N S ) , 4, 17-41.

H A N S E N , H. J. ( 1 9 0 2 ) On the genera and species of the order Pauropoda. Vidensk. Medd., 1 9 0 2 , 3 2 3 - 4 2 4 . ( 1 9 0 3 ) T h e genera and species of the order Symphyla. Quart. J. micr. Sci., 4 7 , 1 - 1 0 1 .

LATZEL, R. ( 1 8 8 4 ) Die Myriapoden der Osterreichisch-Ungarischen Monarchic 2. Die Symphylen, Pauropoden und Diplopoden. W i e n . MICHELBACHER, A. E. ( 1 9 4 2 ) A synopsis of the genus Scutigerella (Symphyla: Scutigerellidae). Ann. Ent. Soc. Amer., 3 5 , 2 6 7 - 8 8 . REMY, P. ( 1 9 3 8 ) Pauropodes de France, d'Allemagne et des Balkans avec description de quatre formes nouvelles. Bull. Soc. Hist. nat. Metz., 3 5 , 153-78.

STARLING, J. H. ( 1 9 4 3 ) Pauropoda from the D u k e forest. Proc Ent. Soc Wash., 4 5 , 1 8 3 - 2 0 0 . VERHOEFF, K . W . ( 1 9 3 4 ) S y m p h y l a u n d P a u r o p o d a in H . G . BRONN'S

Klass. Ordn. Tierreichs, 5, II ( 3 ) , 1 - 2 0 0 . Biology FILINGER, G. A. ( 1 9 2 8 ) Observations on the habit and control of the garden centipede Scutigerella immaculata N e w p o r t , a pest of greenhouses. J. Econ. Ent., 2 1 , 3 5 7 - 6 0 .

( 1 9 3 1 ) T h e garden centipede Scutigerella immaculata N e w p o r t . Bull Ohio Agr. Exp. Sta., N o . 4 8 6 , 1 - 3 3 . HARRISON, L. ( 1 9 1 4 ) On some Pauropoda from N e w South Wales. Proc Linn. Soc N.S.W., 3 9 , 6 1 5 - 3 4 . K E N Y O N , F . C . ( 1 8 9 5 ) T h e morphology and classification o f the Pauropoda, with notes on the morphology of the Diplopoda. Tufts Coll. Stud., No. 4 , 7 7 - 1 4 6 .

MICHELBACHER, A. E. ( 1 9 3 8 ) T h e biology of the garden centipede Scutigerella immaculata. Hilgardia, 1 1 , 5 5 - 1 4 8 . STARLING, J. H. ( 1 9 4 4 ) Ecological studies of the Pauropoda of the D u k e forest. Ecol. Monogr., 1 4 , 2 9 1 - 3 1 0 . T I E G S , O. W. ( 1 9 4 5 ) T h e post-embryonic development of Hanseniella agilis (Symphyla). Quart. J. Micr. Sci., 8 5 , 1 9 1 - 3 2 8 . ( 1 9 4 7 ) T h e development and affinities of the Pauropoda, based on a study of Pauropus silvaticus. Ibid., 8 8 , 1 6 5 - 2 6 7 , 2 7 5 - 3 3 6 . WILLIAMS, S. R. ( 1 9 0 7 ) Habits and structure of Scutigerella immaculata (Newport). Proc. Boston Nat. Hist. Soc, 3 3 , 4 6 1 - 8 5 .

CHAPTER

V

SCORPIONS Classification and distribution A l t h o u g h d i f f e r e n t i n s i z e , all s c o r p i o n s a r e m o r e o r less a l i k e i n g e n e r a l a p p e a r a n c e a n d a r e easily d i s t i n g u i s h e d f r o m o t h e r A r a c h nida by a c o m b i n a t i o n of characters t h a t are always present. T h e i r m o s t striking features are t h e large pedipalps furnished w i t h stout

F I G . 1 7 . Examples of scorpion families: 1. Buthidae, 2. Scorpionidae, 3. Chactidae. (Drawings not to scale.) (After various authors.) chelae or claws a n d t h e division of the a b d o m e n into two portions: a b r o a d p r e - a b d o m e n consisting of seven s e g m e n t s which are as wide or wider than the cephalothorax or prosoma, and a slender t a i l - l i k e p o s t - a b d o m e n . A t t h e e n d o f t h e tail i s a s t i n g , s o m e w h a t 70

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curved and pointed. Its base is enlarged a n d contains a pair of poison glands which open near t h e tip. On the ventral side of the a b d o m e n , immediately b e h i n d the genital opercula, is situated a pair of comb-like organs k n o w n as 'pectines' which are not found in any other animals. Each pectine articulates with a chitinous plate representing the second sternite and is provided with c o m plex m u s c u l a t u r e . I t s c o m p o n e n t s form t h r e e longitudinal series. Of these the back is composed of three parts, the proximal being t h e longest, while t h e lamellae or teeth c o m p r i s e t h e t h i r d series and are inserted between the constituents of the m e d i a n row.

F I G . 1 8 . Ventral view of a scorpion showing pectines. T h e s e lamellae vary i n n u m b e r from t h r e e t o m o r e t h a n forty d e p e n d i n g u p o n t h e sex a n d species of t h e scorpion, a n d are richly supplied with nerves. T h e dorsal surface of the p r o s o m a is covered by a c o m p a c t a n d u n s e g m e n t e d shield or carapace which bears a pair of m e d i a n and f r o m t h r e e t o five p a i r s o f l a t e r a l s i m p l e e y e s . T h e m o u t h i s v e n t r a l in position a n d is situated b e t w e e n an anterior a n d a posterior lip. In front and above the base of the pedipalps are a pair of short c h e l a t e c h e l i c e r a e u s e d for m a s h i n g a n d s h r e d d i n g t h e f o o d , w h i l e

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t h e f i r s t t w o o f t h e f o u r p a i r s o f w a l k i n g legs h a v e m a x i l l a r y p l a t e s a n d h a r b o u r glands that secrete digestive enzymes. S c o r p i o n s live i n h o t a n d t r o p i c a l c o u n t r i e s . I n E u r o p e s e v e r a l species are found in G r e e c e , Italy, Spain a n d t h e Balkans a n d at least o n e has a r a n g e e x t e n d i n g into s o u t h e r n G e r m a n y . On t h e American continent they are found from Patagonia to the m o r e southern of the U n i t e d States. T h e i r geographical distribution has b e e n m a d e t h e subject of several studies a n d is interesting because scorpions are a very ancient group, are not readily dispersed to new localities a n d c o n s e q u e n t l y are of great i m p o r t a n c e in b i o g e o g r a p h i cal r e s e a r c h . T h e y a r e a b s e n t f r o m m a n y i s l a n d s , i n c l u d i n g N e w Zealand. T h e o r d e r i s d i v i d e d i n t o six f a m i l i e s , o f w h i c h t h e m o s t i m p o r t a n t i s t h e B u t h i d a e w i t h m o r e t h a n 6 0 0 s p e c i e s i n c l u d i n g Buthus occitanus, t h e c o m m o n y e l l o w s c o r p i o n o f F r a n c e a n d t h e M e d i t e r r a n e a n r e g i o n , a n d Androctonus australis t h e f a t - t a i l e d s c o r p i o n of N o r t h Africa, w h i l e t h e species of Centrurus a n d Tityus a r e Neotropical. T h e Diplocentridae are found in the Palaearctic r e g i o n , t h e isle o f S o k o t r a i n t h e G u l f o f A d e n a n d M e x i c o , t h e S c o r p i o n i d a e in Africa, M a d a g a s c a r , Asia a n d Australia, while t h e Vejovidae occur mostly in Asia a n d America. T h e Chactidae have a s o m e w h a t s i m i l a r d i s t r i b u t i o n a n d i n c l u d e t h e s m a l l b l a c k Euscorpius s p p . o f s o u t h e r n E u r o p e a n d t h e M e d i t e r r a n e a n , w h i l e t h e B o t h r i u r i d a e live i n A u s t r a l i a . M o s t s p e c i e s h a v e a v e r y l i m i t e d r a n g e , e x c e p t i n g Isometrus maculatus, w h i c h is u b i q u i t o u s in t h e w a r m e r p a r t s o f t h e g l o b e , a n d Scorpio maurus w h i c h e x t e n d s f r o m the Atlantic to India. F e w are found at high altitudes, b u t S. maurus a n d Buthus occitanus o c c u r i n t h e A t l a s M o u n t a i n s a n d Euscorpius germanus i n t h e T y r o l . O n m o r p h o l o g i c a l g r o u n d s t h e B u t h i d a e can be separated from t h e r e m a i n i n g families of scorpions, and it is believed that t h e two g r o u p s m a y have evolved independently, perhaps even since the Silurian epoch.

General behaviour Scorpions resemble other Arachnida and insects in having an i m p e r v i o u s i n t e g u m e n t a n d efficient p o w e r s o f w a t e r r e t e n t i o n . ( C l o u d s l e y - T h o m p s o n , 1956). T h e y are m a r k e d l y n o c t u r n a l b u t this h a b i t c a n n o t be dictated primarily by t h e n e e d to avoid d r y air.

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I n d e e d , Sergent (1947) has s h o w n t h a t t h e negative reactions to l i g h t of Androctonus australis, Buthus occitanus a n d Scorpio maurus a r e less m a r k e d t h a n a r e t h e i r p o s i t i v e l y t h i g m o t a c t i c r e s p o n s e s , s o it is p r o b a b l e t h a t t h e i r n o c t u r n a l b e h a v i o u r h a s an ecological rather t h a n a physiological significance. S c o r p i o n s are essentially inhabitants of w a r m climates a n d b e c o m e sluggish in cold weather, a l t h o u g h t h e y can w i t h s t a n d freezing for several w e e k s ( V a c h o n , 1953). T h e i r lives a r e c o m p a r a t i v e l y s i m p l e : n o t e v e n t h e m o s t p r i m i t i v e f o r m s o f a n i m a l a s s o c i a t i o n a r e k n o w n a n d all s p e c i e s l e a d s t r i c t l y i n d i v i d u a l lives a n d u s u a l l y e i t h e r a v o i d e a c h o t h e r o r f i g h t t o t h e d e a t h . T h e fact t h a t a g g r e g a t i o n s are s o m e t i m e s f o u n d i n c e r t a i n a r e a s i s n o t d u e t o social i n s t i n c t s — t h e s e a r e c o n s p i c u o u s l y a b s e n t — b u t t o t h e f a c t t h a t t h e y o u n g d o n o t s c a t t e r far from their place of birth. F a b r e ' s (1907) claim t h a t w h e n t w o are f o u n d b e n e a t h t h e s a m e s t o n e t h e y a r e e i t h e r m a t i n g o r else o n e i s devouring the other m a y be an exaggerated generalisation, b u t is probably not entirely without foundation. S o m e s c o r p i o n s ( e . g . Euscorpius s p p . ) n o r m a l l y f r e q u e n t d a m p p l a c e s , o t h e r s ( e . g . Pandinus, Palamnaeus s p p . ) a r e f o r e s t d w e l l e r s w h i l s t p e r h a p s t h e b e s t k n o w n ( e . g . Scorpio, Buthus, Androctonus spp.) are inhabitants of dry and desert regions. M o s t scorpions do n o t d r i n k , b u t m o i s t u r e l o v i n g s p e c i e s s u c h a s Euscorpius italicus are sensitive b o t h to d r o u g h t a n d to excessive m o i s t u r e (Bott, 1951; C l o u d s l e y - T h o m p s o n , 1951). S c h u l t z e (1927) h o w e v e r f o u n d t h a t t h e l a r g e P h i l i p p i n e f o r e s t s c o r p i o n Palamnaeus longimanus h a d t o be given a certain a m o u n t of water every day, a n d it was astonishing w h a t large a m o u n t s of water this creature w o u l d drink. T h e scorpion would take up drops of water from grooves in bark, d r o p s s c a t t e r e d o n its b o d y o r s i p w i t h its m a n d i b l e s w a t e r t h a t h a d a c c u m u l a t e d b e t w e e n t h e c h e l a e — t h a t is, i t w o u l d m o v e t h e l a t t e r close t o t h e m a n d i b l e s ' i n t h e w a y a m a n h o l d s a g l a s s i n h i s h a n d and b r i n g s it t o w a r d s his m o u t h ' . At t h e s a m e t i m e , S e r g e n t (1946) h a s s h o w n t h a t a l t h o u g h A. australis is a s p e c i e s p a r t i c u l a r l y a d a p ted to a d r y climate, it does n o t avoid w a t e r a n d can resist p r o l o n g e d i m m e r s i o n ( 3 1 % s u r v i v e d 2 4 h o u r s ) , w h i l e S . maurus c a n s u r v i v e i m m e r s i o n for u p t o 4 8 h o u r s ( 6 7 % ) . F r o m h i s i n t e r e s t i n g s t u d i e s V a c h o n ( 1 9 5 2 , 1953) h a s r e c e n t l y

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suggested that since m o d e r n scorpions represent t h e remains of an ancient fauna, they originally lived u n d e r q u i t e different conditions of t e m p e r a t u r e and h u m i d i t y . T h e y are very responsive to m i c r o c l i m a t i c v a r i a t i o n s a n d e a c h s p e c i e s s e e m s t o h a v e t o live a n d r e p r o d u c e itself w i t h i n s t r i c t l y l i m i t e d a n d c h a r a c t e r i s t i c e c o l o g i c a l conditions. Nevertheless, scorpions have m a n a g e d to survive in conditions of heat a n d d r o u g h t largely on a c c o u n t of their n o c turnal habits a n d s u b t e r r a n e a n habitats. T h u s t h e B u t h i d a e are usually found in shallow scrapes u n d e r rocks w h i c h they dig with their chelae a n d legs ( L a n k e s t e r 1883). A c c o r d i n g to Pocock (1893) Parabuthus capensis s t a n d s on its first a n d f o u r t h p a i r s of legs u s i n g t h e tips of t h e chelae as p r o p s while it kicks sand b a c k w a r d s with its d i s e n g a g e d l e g s . Euscorpius s p p . d o n o t d i g , b u t h a n g u p s i d e d o w n u n d e r p i e c e s o f w o o d , e t c . o r h i d e u n d e r r o c k s , w h i l e Palamnaeus a n d Scorpio s p p . d i g d e e p h o l e s ( u p t o 7 5 c m i n t h e c a s e o f S . maurus w h o s e e n l a r g e d p e d i p a l p s a r e p r o b a b l y s p e c i a l l y a d a p t e d for t h i s p u r p o s e ) . S c o r p i o n s o f t h e g e n u s Hadrurus i n A r i z o n a f r e q u e n t l y d i g d o w n t w o o r t h r e e feet i n s a n d y w a s t e s a n d r i v e r banks. H e r e they remain even t h o u g h the b u r r o w has collapsed ' a p p a r e n t l y f i n d i n g n o difficulty i n b r e a t h i n g ' ( S t r a h n k e , 1 9 4 5 ) . H o w e v e r , M i l l o t a n d P a u l i a n ( 1 9 4 3 ) h a v e s h o w n t h a t A . australis c a n w i t h s t a n d t h e b l o c k i n g o f s e v e n o f i t s e i g h t l u n g s for m a n y m o n t h s w i t h o u t m u c h ill effect, a n d i t i s e v i d e n t t h a t s c o r p i o n s have considerable respiratory reserves.

Food and feeding habits N o d o u b t t h e a b i l i t y t o s u r v i v e for l o n g p e r i o d s w i t h o u t f o o d i s of great service to scorpions living u n d e r t h e h a z a r d o u s conditions o f d e s e r t r e g i o n s . T h u s a w e l l - f e d Hadrurus s p . m a y r e m a i n b u r i e d for f o u r o r five m o n t h s , a n d i n e x p e r i m e n t s s p e c i m e n s h a v e l i v e d for n i n e m o n t h s w i t h o u t f o o d o r w a t e r ( S t r a h n k e , 1 9 4 5 ) , w h i l e a c c o r d i n g t o W a t e r m a n ( 1 9 5 0 ) t h e W e s t I n d i a n Tityus trinitatis c a n survive t h r e e or four m o n t h s w i t h o u t food p r o v i d e d t h a t w a t e r is a v a i l a b l e . A. australis c a n s u r v i v e six m o n t h s ' s t a r v a t i o n a n d B. occitanus h a s l i v e d for u p t o 3 6 8 d a y s w i t h o u t f e e d i n g . F a b r e ( 1 9 0 7 ) r e m a r k e d t h a t t h e a p p e t i t e o f B . occitanus w a s v e r y s l i g h t a n d L a n k e s t e r ( 1 8 8 3 ) f o u n d g r e a t difficulty in f e e d i n g A. australis. On the other h a n d the writer has found that the same species in

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captivity feeds readily on cockroaches, eating at least o n e p e r week during the summer months, although they do not touch hard b e e t l e s s u c h as Blaps s p p . a n d Akis spinosa u n l e s s s t a r v e d ( C l o u d s l e y - T h o m p s o n , 1955a). M o r e segmental a p p e n d a g e s have b e e n b r o u g h t into service as m o u t h parts in scorpions than in other Arachnids. T h e r e is the usual association of t h e chelicerae, l a b r u m a n d pedipalp coxae, a n d in a d d i t i o n t h e u n d e r lip is c o m p o s e d of e n d i t e lobes of t h e c o x a e o f b o t h t h e first a n d s e c o n d p a i r s o f l e g s . T h e p r e y i s p i c k e d to pieces by alternate m o v e m e n t s of the chelicerae a n d the juices a n d soft t i s s u e s a r e d r a w n i n t o t h e t i n y m o u t h b y t h e p u m p i n g action of the pharynx. In consequence feeding is slow a n d takes several h o u r s . T h e f o o d o f s c o r p i o n s c o n s i s t s chiefly o f s p i d e r s , h a r v e s t m e n , flies, cockroaches, grasshoppers, crickets, m a n t i d s , butterflies, ants, beetles (adult a n d larvae), m y r i a p o d s a n d even small mice. A c c o r d i n g t o S t r a h n k e ( 1 9 4 5 ) Hadrurus s p . will e a t r e a d i l y o f softb o d i e d insects b u t rejects woodlice a n d h a r v e s t m e n ( w h e n h u n g r y t h e y will even tackle h a r d beetles a n d small lizards), w h e r e a s Euscorpius germanus e a t s b l u e b o t t l e s , flies, s m a l l c o c k r o a c h e s , w o o d lice, s p i d e r s a n d c e n t i p e d e s ( P o c o c k , 1 8 9 3 ) . Schultze (1927) f o u n d t h a t various species of Blattidae s e e m e d t o b e f a v o u r e d b y Palamnaeus longimanus b u t t h a t c r i c k e t s , e a r w i g s a n d c e r t a i n l a r v a e o f C o l e o p t e r a w e r e also t a k e n a t t i m e s . T h i s species is usually f o u n d in old or virgin forest u n d e r loose b a r k of d e a d s t a n d i n g trees, u n d e r d e c a y i n g t r u n k s of trees a n d logs, or in cavities of r o t t e n s t u m p s located in t h e j u n g l e , m o s t l y in r a t h e r h u m i d a n d d a m p places, w h e r e such insects a b o u n d . A c c o r d i n g to V a c h o n (1953) it is not entirely clear h o w t h e scorp i o n first d e t e c t s i t s p r e y . T h e e y e s a r e t o o c r u d e t o b e o f m u c h a s s i s t a n c e a n d i n a n y c a s e t h e s c o r p i o n i s a n o c t u r n a l a n i m a l , for w h i c h visual impressions can be of no great significance. O t h e r sense organs m u s t therefore be concerned, notably t h e sensory hairs or trichobothria found only on t h e pedipalps. ' T h e s e are richly s u p p l i e d w i t h nerves, a n d can detect m i n u t e air c u r r e n t s s u c h a s t h o s e c a u s e d b y m o v e m e n t s o f t h e p r e y . T h e y a r e , i n fact like t i n y r e c e i v i n g s e t s , p o i n t i n g i n all d i r e c t i o n s a n d s p r e a d o u t along t h e pedipalpi, w h i c h w h e n e x t e n d e d act as h u g e a n t e n n a e . '

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W h e n h u n g r y , t h e a n i m a l m o v e s s l o w l y f o r w a r d s u p p o r t e d b y its h i n d legs w i t h c l a w s o p e n a n d e x t e n d e d a n d tail r a i s e d a n d p o i n t i n g f o r w a r d s . ' O f t e n t h e s c o r p i o n will t h e n h e s i t a t e a n d t h e f i n a l act of c a p t u r e s e e m s a l m o s t accidental an act of defence r a t h e r t h a n of attack. If the p r e y is active, t h e scorpion m a y even w i t h d r a w for a t i m e , b u t i t w a i t s p a t i e n t l y a n d f i n a l l y a c h i e v e s its a i m . ' S c o r p i o n s p r o b a b l y do n o t usually go to seek t h e i r food. I n s t e a d , t h e y w a i t for t h e i n s e c t s t h a t c o m e t o t h e i r lairs t o h i d e . S o m e s c o r p i o n s s u c h as E. italicus a n d P. longimanus a p p e a r s e l d o m , if e v e r , t o u s e p o i s o n t o kill t h e i r p r e y ( C l o u d s l e y - T h o m p s o n , 1 9 5 1 ; S c h u l t z e , 1927) a n d t h e s t i n g i s u s e d o n l y a s a d e f e n s i v e w e a p o n . On t h e o t h e r h a n d , S. maurus, B. occitanus a n d A. australis will lash o u t w i t h their sting at t h e slightest p r o v o c a t i o n , a l t h o u g h if t h e p r e y i s c o m p a r a t i v e l y q u i e t i t m a y b e d e v o u r e d alive.

Enemies T h e greatest threats to the scorpion's existence are probably food shortage, d r o u g h t a n d h u m a n activities. F r o m ancient times m a n has feared, m a l i g n e d a n d hated t h e animals on account of their poison. N e v e r t h e l e s s , t h e r e are o t h e r e n e m i e s w h i c h also destroy t h e m . In t h e tropical rain forests of Africa a n d A m e r i c a scorpions are sometimes caught by raiding armies of driver ants. Although m a n y t i m e s t h e size o f t h e i r t o r m e n t o r s , t h e s c o r p i o n s r a p i d l y s u c c u m b to their attacks, are overpowered a n d d i s m e m b e r e d . Various centipedes, spiders, Solifugae, lizards, snakes a n d birds have b e e n recorded as predators a n d African b a b o o n s have been observed c a t c h i n g l a r g e s c o r p i o n s , t e a r i n g off t h e i r tail a n d g r e e d i l y d e v o u r i n g t h e r e s t o f t h e b o d y . I t h a s also b e e n r e p o r t e d t h a t c e r t a i n n a t i v e s o f A f r i c a e n j o y e a t i n g live s c o r p i o n s ! I n a d d i t i o n m a n y scorpions are inveterate cannibals. A m o n g the few parasites k n o w n are various mites and n e m a t o d e w o r m s which are unlikely to be very harmful. T h e pectines already m e n t i o n e d are k n o w n to represent the modified a p p e n d a g e s of t h e n i n t h somite of t h e b o d y ( = t h i r d mesosomal segment) b u t their function has long remained problematical. T h e y have been regarded as external respiratory organs and external genitalia, a n d it has been claimed t h a t t h e lamellae of the male a n d female scorpion b e c o m e interlocked and serve to hold

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t h e t w o sexes t o g e t h e r d u r i n g m a t i n g . A n alternative suggestion has been m a d e that their function is to clean the extremities of the p e d i p a l p s , legs a n d t a i l . I n 1 8 8 3 L a n k e s t e r m a d e e x p e r i m e n t s o n the tactile sense of t h e pectiniform appendages, a n d wrote: ' T h e y a p p e a r e d t o m e t o possess n o special sensitiveness. W h e n they were p i n c h e d w i t h forceps, t h e scorpions showed no sign of discomfort. It is quite possible that they m a y acquire a heightened sensibility at the breeding season, a n d serve as guides to t h e male a n d f e m a l e i n effecting c o p u l a t i o n . ' A f e w y e a r s l a t e r , n e r v e t e r minations were discovered in t h e lamellae of the pectines of scorp i o n s b y G a u b e r t , w h o w r o t e : T l est incontestable q u e leur richesse e n n e r f s e n fait d e s o r g a n e s s e n s i t i f s . ' Pocock (1893) suggested t h a t t h e pectines w e r e tactile organs of some importance. He pointed out that their situation near the g e n i t a l a p e r t u r e , t h e i r l a r g e r size i n m a l e s a n d t h e m o d i f i c a t i o n o f their basal portion in females of the same species indicated some sexual function. A p a r t from this he considered t h a t it was highly probable that they were useful organs of t o u c h in other aspects of life, e n a b l i n g t h e i r p o s s e s s o r t o l e a r n t h e n a t u r e o f t h e s u r f a c e o v e r which it was walking. He added: In favour of this view m a y be a d d u c e d t h e fact t h a t t h e s e a n i m a l s h a v e b e e n s e e n t o t o u c h t h e g r o u n d with their combs. Moreover, it is a very noticeable circums t a n c e t h a t s c o r p i o n s w h i c h , l i k e Euscorpius, c r e e p a l o n g w i t h t h e i r bellies close to t h e g r o u n d , have very s h o r t c o m b s w h i l e in others w h i c h , like Parabuthus, s t a n d h i g h u p o n t h e i r l e g s , t h e c o m b s a r e e x c e e d i n g l y l o n g . I o n c e n o t i c e d a Parabuthus m a r c h i n g o v e r a p i e c e o f d e a d c o c k r o a c h . W h e n s h e h a d h a l f c r o s s e d it, i n s t e a d o f going straight ahead as was expected, she halted abruptly, backed a little a n d s t o o p i n g d o w n s t a r t e d t o d e v o u r t h e f r a g m e n t . F r o m the height at which the body was being carried, I am persuaded that no portion of t h e lower surface, except t h e c o m b s , could have c o m e i n t o c o n t a c t w i t h t h e p i e c e o f food; s o t h e r e c a n b e little d o u b t t h a t its p r e s e n c e w a s d e t e c t e d b y t h e o r g a n s i n q u e s t i o n . ' Shortly afterwards it was suggested that the pectines of scorp i o n s , l i k e t h e s p e c i a l s e n s e o r g a n s of Limulus, a n d of Galeodes a n d other Arachnids were probably to be accredited with the functions o f e q u i l i b r a t i o n a n d a u d i t i o n , b u t W a r b u r t o n (in H a r m e r a n d Shipley, 1909)* s u p p o r t e d Pocock's (1893) view.

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F r o m a detailed histological s t u d y of the pectines, S c h r o d e r concluded that they were chemotactic organs and had a double funct i o n a s r e c e p t o r s f o r t a s t e a n d s m e l l a n d w e r e p e r h a p s also u s e d d u r i n g m a t i n g a s a s t i m u l a t o r y o r g a n (Wollustorgane) i n t h e r e c o g n i t i o n o f t h e s e x e s . W i t h still m o r e i m a g i n a t i o n , U b i s c h a t t r i b u t e d to t h e m an auxiliary role in respiration. S h e suggested that with their c o m p l e x m u s c u l a t u r e , t h e pectines could be used as fans to b l o w f r e s h a i r a c r o s s t h e l u n g - b o o k s w h i l e t h e s c o r p i o n w a s i n its stuffy r e t r e a t , a n d t h a t t h e y s e r v e d t o v e n t i l a t e t h e l u n g - b o o k s w h e n t h e a n i m a l r e s t e d o n t h e g r o u n d b y lifting t h e p r e - a b d o m e n a n d t h u s p e r m i t t i n g a i r t o p a s s freely b e n e a t h t h e b o d y . On t h e o t h e r h a n d , S c h u l t z e (1927) o b s e r v e d in t h e case of t h e l a r g e P h i l i p p i n e f o r e s t s c o r p i o n Palamnaeus longimanus t h a t w h i l e giving birth to young the pectines of the m o t h e r scorpion 'were carried in a vertical position pointing d o w n w a r d s , seemingly to serve as holders or bracers'. Finally, L a w r e n c e (1953)* wrote: ' T h e pectines of scorpions have b e e n interpreted either as tactile or stimulatory organs d u r i n g courtship, or as organs of smell. T h e latter seems to be t h e m o r e likely e x p l a n a t i o n e x c e p t t h a t t h e i r p o s i t i o n i s p e c u l i a r i n t h e a r t h r o poda, w h e r e these organs are generally located on the antennae or legs'. After reviewing some of the functions that have been attribut e d t o t h e p e c t i n e s , M i l l o t a n d V a c h o n (in G r a s s e , 1 9 4 9 ) * c o n c l u d e d w i t h j u s t i f i a b l e c a u t i o n : ' T o u t e s ces h y p o t h e s e s n e f o n t q u e masquer notre complete ignorance.' As a r e s u l t of e x p e r i m e n t s c a r r i e d o u t on Buthus occitanus, Androctonus australis a n d Euscorpius germanus, in w h i c h it w a s f o u n d t h a t t h e r e s p o n s e o f t h e s c o r p i o n s t o a v i b r a t i n g t u n i n g fork d e c r e a s e d m a r k e d l y after t h e p e c t i n e s h a d b e e n p a i n t e d o v e r , i t h a s r e c e n t l y b e e n s u g g e s t e d t h a t t h e f u n c t i o n o f t h e s e o r g a n s lies i n t h e perception of g r o u n d vibrations ( C l o u d s l e y - T h o m p s o n , 1955b). P r o b a b l y they are used m o r e as a w a r n i n g of danger t h a n in the detection of prey. It is a w e l l - k n o w n fact t h a t a n u m b e r of t h e larger species s u c h as t h e g r e e n i s h - b l a c k Palamnaeus swammerdami of s o u t h e r n I n d i a will frequently e m i t a u d i b l e s o u n d s u n d e r t h e s t i m u l u s of fear or of anger. T h e s o u n d is said to be almost as l o u d as, a n d very similar to that m a d e by briskly and continuously drawing the tip of the

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index ringer b a c k w a r d s and forwards in a direction transverse to its c o a r s e e d g e s o v e r t h e e n d s o f t h e t e e t h o f a v e r y f i n e - t o o t h e d c o m b . T h e s t r i d u l a t o r y a p p a r a t u s c o n s i s t s o f a s c r a p e r o n t h e flat o u t e r face of t h e basal s e g m e n t of t h e p e d i p a l p s a n d a rasp on t h e e q u a l l y flat i n n e r face o f t h e c o r r e s p o n d i n g s e g m e n t o f t h e f i r s t pair of legs. T h e scraper is tolerably thickly, b u t regularly, beset w i t h s t o u t c o n i c a l s h a r p s p i n u l e s like a t i g e r ' s c a n i n e , o n l y m o r e curved t o w a r d s t h e points, s o m e of w h i c h t e r m i n a t e in a long, limp hair, while the rasp is s t u d d e d with m i n u t e tubercles shaped like t h e t o p s o f m u s h r o o m s . T h e r e is no evidence that scorpions or large spiders can hear t h e sounds that their own stridulating organs produce, and Pocock (1896) points out that m a n y poisonous animals including wasps and snakes are frequently rendered conspicuous by bright and staring colours or by s o u n d - p r o d u c i n g organs which, w h e n in action, serve as a danger signal to m e d d l e s o m e intruders, w a r n i n g t h e m to beware of hostile interference. In this way t h e poisonous forms a r e n o t d e s t r o y e d b y c a r n i v o r o u s c r e a t u r e s i n m i s t a k e for o t h e r harmless a n d edible species. T h e existence of stridulatory organs implies t h e existence of an auditory sense, not necessarily in the performers themselves, b u t only in the enemies that might other-

F I G . 1 9 . Stridulatory apparatus of a scorpion. 1. Coxa of claw with rasp. 2. Coxa of first leg w i t h scraper. (After Pocock, 1 8 9 6 . ) w i s e d e s t r o y t h e m . T h e fact t h a t m o n k e y s , w h i c h a r e p a r t i a l t o a d i e t o f s c o r p i o n s a n d skilful e n o u g h t o h a n d l e t h e m w i t h o u t d a m a g e , p a y n o h e e d t o t h e hissing w h e n s e a r c h i n g for t h e s e a n i m a l s b e neath stones does not detract from the theory. Despite their warning colours, bees are d e v o u r e d by frogs a n d t o a d s a n d t h e c o b r a is

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killed by t h e m o n g o o s e — i n d e e d , few species are devoid of p r e datory enemies. Nevertheless, the existence of poison, coupled w i t h t h e p r e s e n c e o f a p o s e m a t i c s o u n d p r o d u c t i o n , will d e t e r m a n y potential enemies, thereby imparting an evolutionary advantage to their possessors.

Poison T h e p o i s o n of s c o r p i o n s h a s attracted a t t e n t i o n since earliest t i m e s a n d o b s e r v a t i o n s a s t o its effects o n m a n a n d o t h e r v e r t e brates have often b e e n m a d e . U n f o r t u n a t e l y these have b e e n s o m e w h a t c o n f l i c t i n g a n d scientifically a c c u r a t e d a t a h a s b e e n o b t a i n e d o n l y c o m p a r a t i v e l y r e c e n t l y . O n e s o u r c e o f e r r o r h a s b e e n lack o f knowledge of the physiological state of the animal on w h i c h the observation was m a d e , of the quantity of poison injected by the s c o r p i o n i n t o t h e w o u n d a n d its r e l a t i o n t o t h e t o t a l w e i g h t o f t h e victim. Another has been inaccurate and uncertain determinations of t h e species of scorpion, for it is k n o w n t h a t different species vary greatly in the degree of virulence and type of their poison. Exact k n o w l e d g e can be o b t a i n e d only u n d e r carefully controlled l a b o r a t o r y e x p e r i m e n t s w h i c h m a y b e s u p p l e m e n t e d b y field o b servations p r o v i d e d t h a t t h e scorpion is identified by an expert. S u c h observations h a v e led to t h e conclusion t h a t at least t w o t y p e s o f p o i s o n e x i s t . O n e o f t h e s e i s local i n effect a n d c o m p a r a t i v e l y h a r m l e s s t o m a n : i t i s e x e m p l i f i e d b y t h e E u r o p e a n Euscorpius italicus a n d t h e A m e r i c a n Centruroides vittatus. T h e o t h e r type is neurotoxic resembling some kinds of snake v e n o m and can be e x t r e m e l y d a n g e r o u s . It is f o u n d in Buthus occitanus a n d Androctonus australis in N o r t h A f r i c a a n d in Centruroides sculpturatus a n d C . gertschi i n N o r t h A m e r i c a . P o i s o n f o r e x p e r i m e n t s m a y b e o b t a i n e d in p u r e f o r m w i t h o u t injury to t h e scorpion by electrical s t i m u l a t i o n . I t h a s b e e n f o u n d t h a t B . occitanus o f s o u t h e r n F r a n c e p r o d u c e s a t o n e t i m e a b o u t 8 m g o f fluid p o i s o n : c u r i o u s l y e n o u g h t h e s a m e species from N o r t h Africa is said to be m u c h m o r e d a n g e r o u s , w h i l e t h e s t i n g of A. australis h a s b e e n k n o w n to kill a m a n in a b o u t four h o u r s , a dog in seven m i n u t e s a n d has a toxicity a l m o s t equal to t h a t of a cobra. T h e s y m p t o m s c a u s e d b y s c o r p i o n p o i s o n o f t h e less v i r u l e n t type consist mostly of s u d d e n sharp pain followed by n u m b n e s s of

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81

t h e l i m b a n d local s w e l l i n g : t h e s e p a s s a w a y w i t h i n a n h o u r o r t w o . Certain scorpions have reduced poison glands and their venom m a y h a v e n o effect w h a t s o e v e r . N o t s o w i t h s p e c i e s w h o s e p o i s o n is neurotoxic. Here the symptoms resemble poisoning with strychn i n e . I n t h e c a s e o f t h e A m e r i c a n C . sculpturatus t h e v e n o m d o e s n o t p r o d u c e a s w e l l i n g o r d i s c o l o r a t i o n a t t h e site o f t h e s t i n g . First, a feeling of tightness develops in t h e t h r o a t so t h a t t h e victim tries to clear his t h r o a t of an i m a g i n a r y p h l e g m . T h e t o n g u e d e v e l o p s a f e e l i n g o f t h i c k n e s s a n d s p e e c h b e c o m e s difficult. T h e v i c t i m n e x t b e c o m e s restless a n d t h e r e m a y b e slight, involuntary twitching of t h e muscles. Small children at this stage will n o t b e still: s o m e a t t e m p t t o c l i m b u p t h e w a l l o r t h e s i d e s o f t h e i r cot. A series of sneezing s p a s m s is a c c o m p a n i e d by a c o n t i n u o u s flow o f fluid f r o m n o s e a n d m o u t h w h i c h m a y f o r m a c o p i o u s froth. Occasionally t h e rate of heart-beat is considerably increased. C o n v u l s i o n s f o l l o w , t h e a r m s a r e flailed a b o u t a n d t h e e x t r e m i t i e s become quite blue before death occurs. T h i s complex pattern of reactions m a y last f r o m 45 m i n u t e s to 10 or 12 h o u r s . In those a d u l t s a n d c h i l d r e n w h o r e c o v e r , t h e effects o f t h e v e n o m p e r s i s t l o n g e s t a t t h e o r i g i n a l site o f t h e s t i n g , w h i c h m a y b e h y p e r s e n s i t i v e for s e v e r a l d a y s , s o t h a t o n l y a s l i g h t b u m p will s e n d p a i n f u l o r tingling sensations t h r o u g h o u t t h e i m m e d i a t e s u r r o u n d i n g area. T h e effect o f s c o r p i o n p o i s o n o n d i f f e r e n t a n i m a l s v a r i e s a g o o d deal. H e d g e h o g s , j e r b o a s a n d f e n n e c foxes are practically i m m u n e , b u t guinea-pigs a n d dogs are especially susceptible. Birds are quite s e n s i t i v e a s a r e f r o g s a n d fishes. T h e p o i s o n h a s a h a e m o l y t i c a c t i o n d e s t r o y i n g r e d b l o o d c o r p u s c l e s a n d also c o n t a i n s a d e n o s i n e tri-phosphatase in large quantities. Anti-scorpion s e r u m s are p r o d u c e d in various centres i n c l u d i n g Algeria, M e x i c o , Brazil, Arizona and London.

Mating habits In scorpions t h e t w o sexes are distinct a n d s h o w slight b u t visible differences in t h e relative p r o p o r t i o n s of t h e b o d y . T h e m a l e i s m o r e s l e n d e r a n d h a s a l o n g e r tail. I t also h a s a p a i r o f organs u s e d in copulation, b u t visible only w h e n t h e animal is t u r n e d o n its b a c k . I n a d d i t i o n t o t h e n o w t h o r o u g h l y d i s c r e d i t e d legend of their suicidal tendencies, scorpions appear to arouse F

S.S.C.M.

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p o p u l a r i n t e r e s t for a n u m b e r o f r e a s o n s , n o t t h e least b e i n g t h e i r curious m a t i n g habits. C o u r t s h i p takes the form of a dance ('prom e n a d e a d e u x ' ) first o b s e r v e d b y M a c c a r y i n 1 8 1 0 a n d l a t e r described by F a b r e (1907), Serfat and V a c h o n (1950) and T h o r n ton (1956). On finding a female, the male grasps her pedipalpal c l a w s w i t h h i s a n d w a l k s s i d e w a y s o r b a c k w a r d s w h i l e s h e follows,

F I G 20. Courtship dance of scorpions. (After Vachon, 1 9 5 3 . ) u s u a l l y w i t h o u t r e l u c t a n c e . I n Buthotus alticola t h e p r o m e n a d e i s p r e c e d e d b y a m a n o e u v r e d u r i n g w h i c h t h e t w o a n i m a l s face e a c h other, forcibly straighten t h e back parts of their bodies a n d c o m p r e s s t h e i r a b d o m e n s t o t h e g r o u n d , w h i l s t t h e i r tails, e x t e n d e d u p w a r d s , are continuously entwined and t h e n disengaged. T h e p r o m e n a d e w h i c h f o l l o w s i s s o m e w h a t less e n e r g e t i c a n d t h e t a i l s of the two animals are raised b u t supple. T h e male directs operations while his m a t e follows placidly as he leads t h e dance. T h e p r o c e s s m a y last s e v e r a l h o u r s a n d i n t h e c a s e o f Buthus occitanus t h e tails m a y a g a i n b e e n t w i n e d b u t o f c o u r s e w i t h o u t h o s t i l e i n t e n t .

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83

At length the male either digs a hole without entirely quitting its h o l d o f t h e f e m a l e , o r else l e a d s h e r t o a s u i t a b l e r e t r e a t i n t o which b o t h disappear. T r u e copulation takes place, which is rare in t h e A r a c h n i d a . In t h e course of this act t h e m a l e p r o t r u d e s certain special organs already referred to a n d these form a t e m p o r a r y p e n i s w i t h w h i c h h e i n s e r t s t h e s p e r m a n d finally p l a c e s i n p o s i t i o n a vaginal p l u g — a k i n d of p o s t n u p t i a l h y m e n ( V a c h o n , 1953). Afterwards t h e female not infrequently eats h i m . I n t h e S o u t h A f r i c a n Opisthopthalmus latitnanus t h e classical ' a r b r e d r o i t ' is either a b s e n t or only fleetingly p r e s e n t , while t h e ' p r o m e n a d e a d e u x ' d o e s n o t u s u a l l y last l o n g e r t h a n a n h o u r . T h e male holds t h e chelicerae of t h e female a n d not, as in o t h e r species, her pedipalps. T h e p r o m e n a d e takes place in a limited area a n d if t h e g r o u n d i s r o u g h t h e m a l e c l e a r s t h e soil p a r t i c l e s f r o m t h e s p a c e i n w h i c h t h e p a i r a r e d a n c i n g . S h o r t l y after t h e s t a r t , t h e g e n i t a l o p e r c u l a o f t h e f e m a l e o p e n s a n d a little l a t e r t h a t o f t h e m a l e also o p e n s a s t h e e x t r u s i o n o f a s p e r m a t o p h o r e b e g i n s . A s soon as this is clear of t h e genital a p e r t u r e of t h e m a l e he m o v e s b a c k s l i g h t l y s o t h a t i t lies freely o n t h e g r o u n d . H e t h e n j e r k s t h e f e m a l e v i o l e n t l y , d r a w i n g h e r o v e r t h e s p e r m a t o p h o r e a n d half lifting h e r a t t h e s a m e t i m e . S h e l o w e r s h e r b o d y o v e r t h e c a p s u l e of the spermatophore, which becomes inserted in her genital aperture. T h u s i n O . latimanus t h e r e i s n o t r u e c o p u l a t i o n b u t a fertilisation m e c h a n i s m similar to that found in false-scorpions. T h e ' p r o m e n a d e a deux' results in the female being jerked back a n d forth until she is in the correct position over the s p e r m a t o p h o r e which she t h e n picks up (Alexander, 1956). 1

Reproduction and life cycle T h e fertilised eggs develop inside t h e m o t h e r a n d t h e y o u n g are b o r n alive. T h e course o f d e v e l o p m e n t varies a c c o r d i n g t o w h e t h e r t h e eggs are rich in yolk, as in t h e B u t h i d a e , or lacking in yolk, as 1

Since this account was written, similar information has been o b tained on the m a t i n g habits of the Chactidae, Bothriuridae and Buthidae as well as the Scorpionidae. It therefore seems likely that insemination by m e a n s of s p e r m a t o p h o r e s occurs t h r o u g h o u t t h e o r d e r and that true copulation m a y not take place as previously s u p p o s e d (Alexander, 1957).

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in t h e Scorpionidae. In t h e first case t h e eggs pass quickly into t h e oviduct a n d develop there, t h e e m b r y o s c o n s u m i n g t h e yolk with w h i c h they are filled; in t h e second, t h e fertilised egg r e m a i n s in place a n d b e c o m e s closely c o m m i n g l e d w i t h t h e m a t e r n a l tissues. A t t h e e n d o f its d e v e l o p m e n t e a c h e m b r y o lies i n a d i v e r t i c u l u m w h i c h p o s s e s s e s a t u b u l a r e x t e n s i o n like a n u m b i l i c a l c o r d a l o n g

F I G . 2 1 . Developing embryos of scorpion (family Scorpionidae) showing 'bottle and teat'. (After Vachon, 1 9 5 3 . ) w h i c h pass n u t r i e n t fluids from t h e wall of t h e m o t h e r ' s intestine. T h e s e are t r a n s f o r m e d b y g l a n d u l a r secretions a n d t h e n led t h r o u g h the tube to the m o u t h of the embryo which has a well-developed p h a r y n x w i t h w h i c h it sucks t h e m a t e r n a l fluid ( V a c h o n , 1950a). T h e chelicerae of the e m b r y o scorpion end in contractile vesicular organs which actually take hold of t h e teat a n d carry it to the mouth! In m a n y species the y o u n g are b o r n d u r i n g the night, s o m e times in two batches separated by an interval of a day, b u t in Buthotus alticola b i r t h h a s b e e n o b s e r v e d f r o m 7.0 t o 9.0 a . m . (Serfat a n d V a c h o n , 1950). A c c o r d i n g to F a b r e (1907) a n d W a t e r m a n (1950) t h e y o u n g , w h i c h are b o r n enveloped in their chorion, are freed by their m o t h e r , b u t this unlikely hypothesis has been d i s p r o v e d in B. occitanus, a n d in B. alticola by S e r f a t a n d V a c h o n ( 1 9 5 0 ) w h o s t a t e t h a t t h e y o u n g free t h e m s e l v e s w i t h o u t p a r e n t a l a s s i s t a n c e , w h i l e i n Euscorpius f l a v i c a u d i s t h e y o u n g e s c a p e b y l a c e r ating t h e c h o r i o n w i t h their stings ( C l o u d s l e y - T h o m p s o n , 1955a). T h e process of m o u n t i n g the m o t h e r ' s back m a y take up to two h o u r s a s t h e little s c o r p i o n s a r e v e r y p l u m p a n d w e a k ( C l o u d s l e y T h o m p s o n , 1 9 5 1 ; S c h u l t z e , 1 9 2 7 ) . H e r e t h e y r e m a i n u n t i l after t h e i r f i r s t m o u l t . I n P . longimanus t h i s p e r i o d l a s t s a b o u t t e n d a y s

SCORPIONS

85

( S c h u l t z e , 1 9 2 7 ) . in E. carpathicus f o u r t e e n d a y s ( B e r l a n d , 1 9 3 2 ) * , in E. italicus t e n to t w e l v e d a y s ( C l o u d s l e y - T h o m p s o n , 1 9 5 1 ) , w h i l s t in E. germanus it t a k e s a b o u t s i x t e e n d a y s ( C l o u d s l e y T h o m p s o n , 1955a). N o d o u b t h o w e v e r t h e length o f t i m e d e p e n d s m u c h u p o n the season and t e m p e r a t u r e at w h i c h t h e animals are living. T h e m o t h e r scorpion carries her y o u n g a r o u n d b u t does n o t feed t h e m : t h e y exist o n t h e n o u r i s h m e n t w h i c h t h e y derive from digesting t h e e m b r y o n i c yolk. Q u i t e w h i t e a n d m e a s u r i n g only a few millimetres in length, they remain placidly on her back, often c o m p l e t e l y h i d i n g h e r b o d y from view so t h a t only t h e a p p e n d a g e s a n d tail r e m a i n v i s i b l e . I f t h e y s h o u l d h a p p e n t o fall off, t h e y m a k e b u t f e e b l e efforts t o c l i m b b a c k a n d t h e s t i m u l u s for this is of short duration a n d inhibited by light. T h e i r tarsi possess a specially modified p a d w h i c h enables t h e m to climb to their m o t h e r ' s back. A f t e r t h e first m o u l t t h e y o u n g a c q u i r e t h e t y p i c a l s c o r p i o n - l i k e a p p e a r a n c e a f t e r w h i c h t h e y r e m a i n w i t h t h e i r m o t h e r for a d a y o r t w o l o n g e r b e f o r e finally s c a t t e r i n g . G r o w t h i s a c c o m p a n i e d b y m o u l t i n g a s i n all A r t h r o p o d a ; t h e o l d s k i n c r a c k s a r o u n d t h e c a r a pace a n d is shed completely, including the lining of the m i d g u t and hindgut and of the four pairs of lung-books situated on the ventral side of t h e t h i r d to sixth p r e - a b d o m i n a l s e g m e n t s . T h e total n u m b e r of m o u l t s of m o s t species is not exactly k n o w n and m a y vary s o m e w h a t even in t h e s a m e species, b u t it is believed t h a t t h e r e a r e e i g h t s t a d i a i n Palamnaeus longimanus a n d s e v e n i n Androctonus australis.

BIBLIOGRAPHY Identification G O U G H , L . H . a n d H I R S T , S. ( 1 9 2 7 ) K e y to identification of E g y p t i a n

scorpions. Min. Agr. Egypt Tech. Sci. Bull., N o . 7 6 , 1 - 8 . KRAEPELIN, K . ( 1 8 9 9 ) S c o r p i o n e s u n d P e d i p a l p i . Das Tierreich., 8, 1 - 2 6 5 . MELLO-LEITAO

(1945)

Escorpioes

Sul-Americanos.

Arq.

Mus.

Nac.

Brasil, 4 0 , 1 - 4 6 8 .

POCOCK, R. I. ( 1 9 0 0 ) The Fauna of British India, including Ceylon and Burma. Arachnida. L o n d o n . VACHON, M. ( 1 9 5 2 ) Etudes sur les Scorpions. Alger. WERNER, F . ( 1 9 3 5 ) S c o r p i o n e s , in H . G . BRONN'S Klass.Ordn. Tierreichs,5, IV (4), 1 - 3 1 6 .

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Biology ALEXANDER, A. J. (1955) M a t i n g in scorpions. Nature, Lond., 1 7 8 , 8 6 7 - 8 . (1957) T h e c o u r t s h i p a n d m a t i n g of t h e scorpion Opisthophthahnus latimans. Proc. Zool. Soc. Lond., 1 2 8 , 5 2 9 - 4 4 . BERLAND, L. (1945) Les Scorpions. Paris. B O T T , R. (1951) Beobachtungen am sudeuropaischen Skorpion (Euscorpius italicus). Natur. u. Volk., 8 1 , 2 9 0 - 3 . C L O U D S L E Y - T H O M P S O N , J. L. (1951) N o t e s on Arachnida, 1 6 . — T h e behaviour of a scorpion. Ent. Mon. Mag., 8 6 , 1 0 5 . (1955a) S o m e aspects of the biology of centipedes and scorpions. Naturalist, 1 9 5 5 , 1 4 7 - 5 3 . (1955b) On the function of the pectines of scorpions. Ann. Mag. Nat. Hist., (12),8, 556-60. (1956) Studies in diurnal r h y t h m s , V I . Bioclimatic observations in T u n i s i a and their significance in relation to the physiology of the fauna, especially woodlice, centipedes, scorpions and beetles. Ann. Mag. Nat. Hist.,(12), 9, 3 0 5 - 2 9 . FABRE, J. H. (1907) Souvenirs entomologiques, Ser. 9, Paris. LANKESTER, E. R. (1883) Notes on the habits of the scorpions Androctonus funestris Ehr. and Euscorpius italicus Roes. J .Linn. Soc. (Zool.), 1 6 , 4 5 5 - 6 2 . M I L L O T , J. and PAULIAN, R. (1943) Valeur fonctionelle des p o u m o n s des scorpions. Bull. Soc. zool. Fr., 5 8 , 9 7 - 8 . PETRUNKEVITCH, A. (1947) Scorpion. Encyclopaedia Britannica. POCOCK, R. I. (1893) N o t e s u p o n t h e habits of some living scorpions. Nature, Lond., 4 8 , 1 0 4 - 7 . (1896) H o w and w h y scorpions hiss. Nat. Sci., 9, 1 7 - 2 5 . SCHULTZE, W. (1927) Biology of the large Philippine forest scorpion. Philippine J. Sci.. 3 2 , 3 7 5 - 8 9 . SERFAT, A. and V A C H O N , M. (1950) Quelques r e m a r q u e s sur la biologie d ' u n scorpion de l'Afghanistan: Buthotus alticola (Pocock). Bull. Mus. Hist. Nat. Paris, (2), 2 2 , 2 1 5 - 1 8 . SERGENT, E. (1946) L e s scorpions et Teau. Arch. Inst. Pasteur d'Algerie, 2 4 , 76-9; 304-5. (1947) Abris des scorpions. Ibid., IS, 2 0 6 - 9 . STRAHNKE, H. L. (1945) Scorpions of t h e g e n u s Hadrurus T h o r e l l . Amer. Mus. Nov., No. 1298, 1-9. T H O R N T O N , I. W. B. (1956) N o t e s on the biology of Leiurus quinquestriatus ( H . E . , 1929) (Scorpiones, B u t h i d a e ) . Brit. J. Anim. Behav., 4, 9 2 - 3 . VACHON, M. (1950) R e m a r q u e s preliminaires sur l'alimentation les organes cheliceriens le biberon et la tetine de l ' e m b r y o n du scorpion: Ischnurus ochropus C. L. K o c h (Scorpionidae). Arch. Zool. exp. gen., 8 6 , 137-56. (1953) T h e biology of scorpions. Endeavour, 1 2 , 8 0 - 9 . WATERMAN, J. A. (1950) Scorpions in t h e W e s t Indies with special reference to Tityus trinitatis. Caribbean Med. J., 1 2 , 167-77.

CHAPTER

VI

SOLIFUGAE Classification and distribution T h e A r a c h n i d s of t h e O r d e r Solifugae or Solpugida, s o m e t i m e s k n o w n as 'false-spiders' or 'wind-scorpions', are a m o n g the most f o r m i d a b l e of t h e terrestrial i n v e r t e b r a t e s . A superficial r e s e m blance to true spiders is belied by the segmented a b d o m e n without s p i n n e r e t s , w h i l s t t h e legs o f t h e f o u r t h p a i r c h a r a c t e r i s t i c a l l y b e a r five ' m a l l e o l i ' o r ' r a c q u e t o r g a n s ' w h o s e f u n c t i o n i s u n k n o w n , a l t h o u g h it has been suggested that they m a y serve to s u p p o r t the

F I G . 22. Examples of Solifugid families: 1. Rhagodidae, 2. Hexisopodidae, 3. Galeodidae, 4. Eremobatidae, 5. Ammotrechidae. (Drawings not to scale.) (After various authors.) 87

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a b d o m e n . I t i s m o r e likely h o w e v e r t h a t t h e y a r e s e n s e o r g a n s analogous with the pectines of scorpions. T h e hairy body is divided into two parts, a prosoma or cephalothorax and an opisthosoma or a b d o m e n which are segmented and united to one another without a n a r r o w pedicle as is found in spiders. T h e chelicerae are ext r e m e l y well developed, f o r m i n g t w o powerful pincers w i t h w h i c h the prey is destroyed. S o m e t i m e s these are as long as t h e entire p r o s o m a a n d t h e y a r e p o s s i b l y for t h e i r size t h e m o s t f o r m i d a b l e j a w s i n t h e a n i m a l w o r l d . T h e p e d i p a l p s h a v e t h e n o r m a l six s e g m e n t s a n d end, not in a claw, b u t in a peculiar suctorial organ to be discussed below. T h e legs o f t h e S o l i f u g a e a r e q u i t e c h a r a c t e r i s t i c . T h e first p a i r are long a n d r a t h e r feeble. T h e y are n o t used for walking b u t are carried stretched o u t in front a n d u s e d as additional tactile organs, a h a b i t f o u n d also i n t h e ' w h i p - s c o r p i o n s ' . T h e r e m a i n i n g legs a r e true ambulatory limbs, those of the fourth pair, which are the s t r o n g e s t o f all, b e a r i n g t h e m a l l e o l i . T h e r e a r e o n l y t h r e e o f t h e s e t o e a c h h i n d leg i n t h e f a m i l y H e x i s o p o d i d a e , w h i c h i n c l u d e s t h e c u r i o u s , s h o r t - l e g g e d Chelypus s p p . T h e size o f t h e b o d y v a r i e s f r o m o n e t o five c e n t i m e t r e s i n l e n g t h , a n d t h e l a r g e r s p e c i e s s u c h as Galeodes arabs a n d G. araneoides w h o s e f o r m i d a b l e a p p e a r a n c e i s e n h a n c e d b y t h e i r u n u s u a l h a i r i n e s s a n d b u l k , c a n w i t h t h e i r l i m b s s p a n a w i d t h o f five i n c h e s . M o s t species are uniformly yellow or b r o w n in colour while those of t h e g e n e r a Rhagodes a n d Dinorhax a r e b l a c k . A few, h o w e v e r , have a p a t t e r n of l o n g i t u d i n a l black stripes on a yellow b a c k g r o u n d , or t h e reverse with occasional reddish tints. P r e d o m i n a n t l y inhabitants of hot, dry and desert areas, the Solifugae are almost entirely confined to tropical a n d subtropical r e g i o n s . I n E u r o p e o n l y six s p e c i e s o c c u r a n d t h e s e a r e f o u n d i n warmer parts such as south-east Spain, Greece, the Balkans and t h e v i c i n i t y o f t h e Black S e a . T e n f a m i l i e s a r e k n o w n t o s c i e n c e o f which two, t h e E r e m o b a t i d a e a n d A m m o t r e c h i d a e , are uniquely Nearctic, while the r e m a i n d e r are restricted to t h e Old W o r l d . Of these t h e C e r o m i d a e a n d H e x i s p o d i d a e are f o u n d in Africa south of t h e E q u a t o r , t h e Solpugidae in Africa a n d Iraq, while the D a e s i i d a e are d i s t r i b u t e d t h r o u g h o u t Africa, A r a b i a , Asia M i n o r , Persia and southern E u r o p e . T h e Rhagodidae and Galeodidae are

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restricted to an area n o r t h of the E q u a t o r ranging from M o r o c c o to India a n d T u r k e s t a n : t h e r e m a i n i n g families, t h e K a r s c h i i d a e and Melanoblossiidae, have a s o m e w h a t discontinuous distribution in Africa a n d Asia. Solifugae are particularly a b u n d a n t in Africa, b u t n o n e are f o u n d i n M a d a g a s c a r a n d t h e y a r e also a b s e n t f r o m A u s t r a l i a a n d N e w Zealand.

General behaviour T h e s e animals are lovers of w a r m t h a n d are n e v e r f o u n d in cold o r t e m p e r a t e c o u n t r i e s , a l t h o u g h o n e s p e c i e s , Gylippus rickmersi, inhabits t h e 10,000 foot plateau of t h e P a m i r in C e n t r a l Asia, north of the H i n d u K u s h M o u n t a i n s . Even where they thrive, they hide away or hibernate t h r o u g h o u t the winter season. T h e y avoid fertile oases a n d seem to prefer utterly neglected regions w h e r e t h e soil i s b r o k e n a n d b a r e , b u t t h i s i s n o t b e c a u s e t h e y c a n n o t exist i n p r o x i m i t y w i t h m a n . O n t h e c o n t r a r y , t h e y frequently enter t h e tents of travellers to catch flies and other insects. A c c o r d i n g t o A e l i a n , a n a r e a o f E t h i o p i a w a s d e s e r t e d b y its i n h a b i tants on account of the appearance of an incredible n u m b e r of scorpions a n d P h a l a n g i u m s ' b u t Pliny, in quoting the same story, r e p l a c e d P h a l a n g i u m ' by ' S o l f u g a ' . Gluvia dorsalis is s a i d to be a f a m i l i a r s i g h t i n t h e s t r e e t s o f M a d r i d a n d t h e s p e c i e s Mummucia variegata a n d Pseudocleobis morsicans o f t e n r u n a b o u t in t h e s t r e e t s of Santiago w h e r e they are k n o w n as ' A r a n h a s del Sol' (sunspiders). T h e majority of Solifugae, as their n a m e indicates, are however, n o c t u r n a l a n d hide away u n d e r stones or in crevices of t h e soil d u r i n g t h e d a y t i m e . I t h a s b e e n s u g g e s t e d t h a t t h i s h a b i t m a y be correlated with a low t e m p e r a t u r e tolerance, b u t t h e m a t t e r has not been tested experimentally. H i n g s t o n (1925) has described t h e process of b u r r o w i n g in a P e r s i a n s p e c i e s of Galeodes (G. arabs or G. araneoides). No g r e a t skill i s e x h i b i t e d , a n d t h e p r o c e d u r e i s l a b o r i o u s e v e n i n f r i a b l e soil. W h e r e t h e s a n d i s l o o s e , a f u r r o w i s p l o u g h e d w i t h t h e p o i n t e d m a n d i b l e s , t h e soil b e i n g r a k e d b a c k w i t h t h e h a i r y l e g s . T h e a n i m a l faces its e x c a v a t i o n w i t h o u t s t r e t c h e d l i m b s ; t h e l o n g p e d i p a l p s a r e t h r u s t f o r w a r d t o e x p l o r e t h e w a y ; t h e first p a i r o f l e g s a l s o i s a d v a n c e d , b u t i t i s t h e s e c o n d p a i r t h a t fulfils t h e p u r -

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pose of rakes. T h e s e are p u s h e d into t h e loose sand, their e n d s being t u r n e d inwards so as to gather it in armfuls. T h e rakings are repeated in such rapid succession that the sand comes spouting from b e n e a t h the a b d o m e n in a r h y t h m i c a l series of jets. F r o m t i m e t o t i m e t h e S o l i f u g i d r e v e r s e s its p o s i t i o n , l o w e r s itself i n t o t h e excavation, t h r u s t s its b o d y into t h e place w h e r e it previously r a k e d , a n d s h o v e l s u p t h e d e b r i s w i t h its b r o a d h e a d , e s p e c i a l l y a n y o f t h e l a r g e r f r a g m e n t s w h i c h i t c a n n o t s o easily d i s l o d g e w i t h its r a k e s . T h e n i t a g a i n t u r n s a b o u t a n d r e s u m e s t h e scuffling w i t h its s e c o n d p a i r o f l e g s . S o m e t i m e s t h e f e m a l e s m e r e l y c u t a c i r c l e i n t h e soil w i t h t h e i r j a w s a n d k i c k t h e l o o s e n e d f r a g m e n t s a w a y ( P o c o c k , 1 8 9 8 ) . Eremobates formicaria c o n s t r u c t s its b u r r o w in t h e s a m e m a n n e r a s Galeodes, b u t i n s t e a d o f u s i n g a c o m m o n b u r r o w t h r o u g h o u t the breeding season, a n e w one is constructed almost every n i g h t ( T u r n e r , 1916).

Food and feeding habits Solifugae are exclusively p r e d a t o r y a n d carnivorous, h a v i n g an e x t r a o r d i n a r y v o r a c i t y . T h e y will c o n t i n u e f e e d i n g u n t i l t h e i r a b d o m e n s are so distended that they can scarcely m o v e . A y o u n g Galeodes s c a r c e l y 5 m m l o n g h a s b e e n s e e n t o d e v o u r o v e r 100 flies in 24 hours. A l t h o u g h insects, including even h a r d beetles, form t h e i r s t a p l e d i e t , S o l i f u g a e will kill a n d e a t l a r g e s p i d e r s , s c o r p i o n s a n d l i z a r d s . T h e y h a v e also b e e n o b s e r v e d t o kill m i c e a n d s m a l l b i r d s . S e v e r a l s p e c i e s s u c h as Solpuga sericea a n d S. lineata b u r r o w into the g r o u n d to catch termites while a Californian species of Eremobates kills b e e s , e n t e r i n g t h e h i v e s i n s e a r c h o f p r e y . T h e s m a l l n o c t u r n a l s p e c i e s E . pallipes f r o m C o l o r a d o i s s a i d t o h u n t bed-bugs. T h e p r e y i s p r o b a b l y f o l l o w e d b y s i g h t i n s o m e s p e c i e s , for a b l i n d Galeodes h a s difficulty i n l o c a t i n g its v i c t i m s , b u t t h e n o c t u r n a l S o u t h A f r i c a n Solpugyla globicornis s e a r c h e s a t r a n d o m w i t h its p e d i p a l p s a n d first p a i r o f legs s t r e t c h e d f o r w a r d , a n d s i g h t i s n o t u s e d . I t i s p o s s i b l e t h a t t h e o l f a c t o r y s e n s e m a y also b e u s e d i n orientation, as one specimen was observed trying to get hold of a s n a i l t h a t h a d r e t r e a t e d i n t o its s h e l l ( B o l w i g , 1 9 5 2 ) . T h e l o n g legged forms can r u n at great speed so that they resemble balls of yellow thistledown blown over the desert. Often w h e n going at

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full s p e e d , t h e y s t o p a b r u p t l y a n d b e g i n h u n t i n g a b o u t like a d o g checked in mid-course by the scent of game. W h e n gorged with f o o d o r w h e n p r e g n a n t , h o w e v e r , t h e y a r e fat a n d s l u g g i s h . S o m e species have been k n o w n to climb trees in search of insects a n d other prey. It is p r o b a b l e that t h e ability to m o v e is t h e m a i n attrib u t e b y w h i c h l i v i n g p r e y i s d i s t i n g u i s h e d f r o m n o n - l i v i n g , for i n c a p t i v i t y a d e a d i n s e c t will b e a t t a c k e d o n l y i f s u i t a b l y m o v e d ( T u r n e r , 1916). T h e r e has been m u c h controversy as to the poisonous properties with which these creatures have been widely credited. Lichtenstein (1797) h a s e n d e a v o u r e d t o s h o w t h a t t h e mice w h i c h p l a g u e d t h e Philistines (1 Sam. v. 6) w h e n they captured the 'ark of the Coven a n t ' m a y h a v e b e e n Galeodes arabs, a n d i t i s c e r t a i n l y t r u e t h a t their hairy bodies a n d rapid m o v e m e n t s give to m a n y species a m o u s e - l i k e a p p e a r a n c e . T h i s a u t h o r also s u g g e s t e d t h a t t h e ' e m e r o d s ' with w h i c h they w e r e plagued referred to t h e sores c a u s e d b y t h e b i t e s o f t h e s e a n i m a l s , for S o l i f u g a e h a v e b e e n k n o w n to attack travellers asleep in the desert at night. Olivier (1807) disbelieved t h e awful r e p o r t s of t h e A r a b s , w h o w e r e terrified a t t h e s i g h t o f t h e w i n d - s c o r p i o n s , w h i c h a p p e a r e d i n t h e t e n t s a t n i g h t a n d w h o t o l d y a r n s , e a c h m o r e h o r r i b l e t h a n t h e last, a s t o t h e i r d a n g e r o u s b i t e s . H e d i d a d m i t , h o w e v e r , t h a t w i t h such j a w s the results would probably be m o s t painful. People have been bitten accidentally by the animals getting u n d e r their clothes a n d the effect i s s o m e t i m e s s e v e r e . T h e i n h a b i t a n t s o f B a k u o n t h e C a s p i a n S e a b e l i e v e t h a t a local s p e c i e s is e s p e c i a l l y p o i s o n o u s after its winter sleep, a n d they r u b t h e w o u n d with t h e carcass of the animal after first s t e e p i n g i t i n b o i l i n g oil, i n o r d e r t o n e u t r a l i s e t h e effects of the venom. On the other hand, the Somalis do not regard t h e m as n o x i o u s — i n d e e d , t h e y h a v e n o n a m e i n t h e i r l a n g u a g e for a n y t h i n g so u n i m p o r t a n t ! H u t t o n (1843) r e c o r d s t h e case of a lizard b i t t e n b y a Galeodes w h i c h r e c o v e r e d i n t h r e e d a y s , a n d o t h e r a u t h o r s h a v e s e a r c h e d i n v a i n for p o i s o n g l a n d s s u c h a s t h o s e i n t h e j a w s o f spiders.* B e r n a r d ( 1 8 9 7 ) s u g g e s t e d t h a t p o i s o n i n g m i g h t r e s u l t f r o m a s i m p l e e x u d a t i o n o f t o x i c e x c r e t o r y m a t t e r t h r o u g h t h e setal p o r e s which, he believed, could be traced along the tips of the jaws. Phisalix (1922)* r e c o r d s a n u m b e r of cases of Solifugae biting m e n a n d c o n c l u d e s t h a t i n v i e w o f t h e s e v e r i t y o f t h e effects w h i c h

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m a y occasionally result in death, t h e possibility of poison c a n n o t b e e n t i r e l y e l i m i n a t e d . A l t h o u g h t h e m a t t e r h a s n o t y e t b e e n fully tested experimentally, it is n o w generally a s s u m e d t h a t Solifugae are not v e n o m o u s since a n u m b e r of people have allowed t h e m s e l v e s t o b e b i t t e n w i t h o u t a n y ill effects. O n t h e few o c c a s i o n s that poisoning does occur, it is m o s t probably d u e to infection of the wound. In t h e silence of t h e night, t h e desert Solifugae race about, conduct their a m o u r s and glut themselves on i n n u m e r a b l e insects to supply their r e q u i r e m e n t s during the winter sleep. T h e S o u t h A f r i c a n Solpuga caffra is a l a r g e s p e c i e s w i t h m a s s i v e p o w e r f u l j a w s set i n a v e r y w i d e h e a d - p l a t e . T h e m e t h o d o f c a t c h i n g i n s e c t s s e e m s t o d e p e n d o n c o n t a c t a n d w i t h i n a c e r t a i n critical distance t h e prey is seized with a short spring a n d lightning snap of t h e j a w s . A cricket is seldom missed, b u t m o r e active grassh o p p e r s s o m e t i m e s e s c a p e t h e first a t t e m p t t o c a t c h t h e m . W h i l e being eaten the crackling sound of the harder parts of an insect's cuticle as they are c r u s h e d in the chelicerae can be heard from a distance of several feet! T h e p o i n t e d extremities of t h e j a w s are o f t e n u s e d t o p i e r c e t h e b o d y o f t h e p r e y ( L a w r e n c e , 1949) a n d I h a v e o b s e r v e d t h e s a m e w h e n Rhagodes s p . f e e d s o n l a r g e M y g a l o m o r p h spiders. T h e prey w h e n caught is usually held cross-ways by both jaws. M a s t i c a t i o n a n d m a c e r a t i o n i s a fairly c o m p l i c a t e d p r o c e d u r e s i n c e there are simultaneous m o v e m e n t s of the jaws in two planes; first t h e r e i s t h e o p e n i n g a n d c l o s i n g o f t h e j a w s a l t e r n a t e l y , a m o v e m e n t in the vertical plane; at the same time the prey is g r o u n d b e t w e e n t h e c h e l i c e r a e , t h e left a n d r i g h t s i d e s m o v i n g alternately backwards and forwards p r o d u c i n g a horizontal m o v e m e n t . T h e p r e y i s s p e e d i l y r e d u c e d t o a soft p u l p a n d p r e s s e d against t h e m o u t h opening w h e r e m o s t of it is absorbed in a semifluid c o n d i t i o n . E v e n h a r d , c h i t i n o u s p a r t s , a l t h o u g h u s u a l l y r e jected, may at times be devoured. M o s t victims are o v e r p o w e r e d w i t h ease, b u t occasionally Solifugae e n c o u n t e r a m o r e powerful adversary s u c h as a c e n t i p e d e , s c o r p i o n o r a n o t h e r S o l i f u g i d w h i c h will n o t s u b m i t w i t h o u t a s t u b b o r n fight. H i n g s t o n ( 1 9 2 5 ) g i v e s a g r a p h i c a c c o u n t o f s u c h c o m b a t s in Galeodes arabs a n d G. araneoides. He b e l i e v e s t h a t t h e s e

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species have n o t m u c h faculty of vision, taste or hearing, b u t his e x p e r i m e n t s are o p e n to the objection that he was testing the responses of the animals to unnatural stimuli which they do not e n c o u n t e r i n t h e i r n o r m a l life. T h e c h i e f s e n s e i s t h a t o f t o u c h , which is located in the i n n u m e r a b l e hairs with which the b o d y is covered. T h e contest is usually m o r e an exhibition of swiftness t h a n o f a n y p a r t i c u l a r s t r a t e g i c a l skill, t h e v i c t i m b e i n g q u i c k l y m a c e r a t e d b y t h e j a w s o f its f e r o c i o u s e n e m y . D u e l s b e t w e e n rival S o l i f u g i d s a r e u s u a l l y m o r e p r o l o n g e d . T h e combatants rush at each other, their pedipalps taking the imm e d i a t e s h o c k a n d w a r d i n g off t h e p o n d e r o u s j a w s . A f t e r t h i s t h e contest becomes very variable. Sometimes the animals rock from side to side, their bodies kept apart by their projecting pedipalps like w r e s t l e r s a t a r m ' s l e n g t h w a i t i n g f o r a c h a n c e t o s e c u r e a g r i p . At o t h e r s they c o m e quickly in to closer apposition a n d their j a w s interlock as t h e y struggle to get a vital g r i p . G i v e n t h e slightest o p p o r t u n i t y o n e will d r i v e i t s c h e l i c e r a e i n t o t h e soft p a r t s o f its opponent and the struggle ends. N o t infrequently however the interlocking jaws are disengaged and the wrestlers spring apart only to charge again, w h e n one m a y o v e r w h e l m t h e other. Savory (1928)* writes that d u r i n g t h e G r e a t W a r Solifugae b e came familiar to the troops in E g y p t a n d the N e a r East where Galeodes arabs i s c o m m o n . T h e s o l d i e r s n a m e d t h e m g e r r y m a n d e r s ' a n d a d m i r e d t h e m for t h e i r ferocity. A t o n e t i m e t h e m e n stationed a t A b o u k i r k e p t pet Solifugae a n d m a t c h e d t h e m like f i g h t i n g c o c k s . E a c h C o m p a n y h a d its c h a m p i o n a n d b e t s w e r e freely laid o n t h e r e s u l t s o f t h e f i g h t s . S i z e i s n o t a l w a y s a decisive factor a n d it s o m e t i m e s h a p p e n s t h a t a smaller individual s e i z e s its o p p o n e n t b e t w e e n its t o o w i d e l y - o p e n e d j a w s a n d c o n quers by holding on in a position in which the big creature is quite helpless. C o m b a t s with scorpions usually result in the death of the latter before t h e y h a v e t i m e to use t h e i r stings. In 1942 in L i b y a , my t r o o p c o r p o r a l k e p t a s h o r t - l e g g e d , b l a c k Rhagodes in a b i s c u i t tin on t h e back of his tank a n d fed it almost entirely on scorpions. In a d d i t i o n to their use as buffers in t h e h o u r of battle, w h e n they are of s u p r e m e importance, t h e pedipalps are used as i m p l e m e n t s o f f e e d i n g . T h e y a r e s t r e t c h e d f o r w a r d like l o n g a r m s t o seize p i e c e s o f f o o d w i t h t h e i r t e r m i n a l s u c k e r s . T h e m o r s e l s a r e

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t h e n transferred to t h e j a w s . W h e n drinking, t h e tips are b r o u g h t t o g e t h e r , t h r u s t i n t o t h e f l u i d a n d t h e n e m p l o y e d like a p a i r o f h a n d s t o lift t h e l i q u i d i n t o t h e m o u t h ( H i n g s t o n , 1 9 2 5 ) . T h e p a l p a l organs w e r e originally described by L i c h t e n s t e i n (1797) as organs of scent, b u t later it was claimed that they were suckers. T o w a r d s t h e e n d o f t h e last c e n t u r y h o w e v e r , i t w a s s u g g e s t e d o n m o r p h o logical g r o u n d s t h a t t h e e a r l i e r v i e w w a s t h e c o r r e c t o n e a n d H e y m o n s (1902) claimed t h a t t h e male Solifugae recognised t h e females b y t h e s e n s e o f s m e l l , t h e r e c e p t o r o r g a n s for w h i c h lay i n t h e tarsi of t h e pedipalps. After a m p u t a t i o n of these organs, males invariably fled w h e n i n t r o d u c e d into t h e presence of a female. It is not surprising, however, that the mating instinct should be destroyed by this crippling treatment. Solifugae can c l i m b up glass or out of a b u c k e t by m e a n s of their pedipalps whose organs are u n d o u b t e d l y suckers (CloudsleyT h o m p s o n , 1954).

Enemies Little is k n o w n of t h e e n e m i e s of Solifugae, b u t D i s t a n t (1892) in t h e T r a n s v a a l s a w a w a g t a i l a t t a c k a Solpuga hostilis a n d P o c o c k (1898) suggests t h a t t h e y are p r o b a b l y eaten by insectivorous birds, small m a m m a l s a n d reptiles. T h e y have recently been found i n t h e s t o m a c h c o n t e n t s o f a n A f r i c a n S t e p p e B u z z a r d . E n e m i e s also i n c l u d e l a r g e l i z a r d s , o t h e r r e p t i l e s a n d o t h e r S o l i f u g a e t o o , for cannibalism is by no means unknown. T h e n i n t h somite of Solifugae is suppressed in t h e adult and the p r o s o m a i s j o i n e d t o t h e o p i s t h o s o m a a c r o s s its w h o l e w i d t h . Nevertheless, there is a great flexibility b e t w e e n t h e two parts of t h e b o d y a n d the a b d o m e n can be raised until it is almost vertical. T h i s a c t i o n i s c o m m o n i n life a n d r e s u l t s i n a s c o r p i o n - l i k e a p pearance, particularly in the short-legged black Rhagodidae. It h a s b e e n suggested ( C l o u d s l e y - T h o m p s o n , 1949) t h a t this b e haviour m a y be a form of mimicry; at any rate, that raising the a b d o m e n in this fashion m a y be an asset in d e t e r r i n g an attacker. At the same time this vulnerable m e m b e r is kept away from danger a n d t h e foe i s p r e s e n t e d w i t h a p a i r o f g a p i n g j a w s s u r r o u n d e d b y five pairs of strong limbs a r m e d with long bristles, short spines a n d s h a r p claws.

SOLIFUGAE

95

Solifugae can stridulate a n d m a k e g r u n t i n g s o u n d s b y r u b b i n g together a pair of h o r n y ridges on t h e inner surface of t h e chelic e r a e . A n e n r a g e d Galeodes h a s b e e n s a i d t o ' s c r e e c h ' a n d t h i s , like

F I G . 23. Galeodes arabs in defensive attitude. (After Millot and Vachon, 1949.) t h e hissing of scorpions a n d snakes, is p r o b a b l y a f o r m of advertisem e n t and a warning to enemies. T h e o n l y p a r a s i t e o f S o l i f u g a e s o far r e c o r d e d i s t h e I n d i a n P o m p i l i d w a s p Salius sycophanta w h i c h h a s b e e n s e e n , after a p r o l o n g e d s t r u g g l e , to s t i n g a Galeodes a n d d r a g it to a h o l e in w h i c h w e r e a f t e r w a r d s f o u n d n o less t h a n f i v e Galeodes all d e p r i v e d o f t h e i r legs a n d w i t h a s i n g l e e g g a t t a c h e d t o t h e h a i r o n t h e u n d e r side of t h e i r s t o m a c h s . All w e r e q u i t e d e a d e x c e p t for t h e last w h i c h w a s still m o v i n g feebly.

Mating habits Sexual differences in Solifugae are n o t striking. T h e m a l e is smaller a n d of lighter b u i l d t h a n t h e female, b u t his legs are longer.

96

SOLIFUGAE

T h e y probably stand h i m in good stead at mating time w h e n the f e m a l e i s a l l e g e d t o kill a n d d e v o u r h e r less p o w e r f u l m a t e i f s h e c a n ! T h e j a w s o f t h e m a l e a r e less b u l k y t h a n t h o s e o f t h e f e m a l e w h i c h are u s e d to dig b u r r o w s in w h i c h t h e eggs are laid. T h e y are less s t r o n g l y t o o t h e d a n d b e a r o n t h e i r u p p e r s i d e a p e c u l i a r w h i p like s t r u c t u r e o f u n k n o w n f u n c t i o n k n o w n a s t h e f l a g e l l u m . M a t i n g takes place at dusk or during the night: it is rapid and b r u t a l . A c c o r d i n g t o H e y m o n s ( 1 9 0 2 ) w h o o b s e r v e d i t i n Galeodes caspius d u r i n g a j o u r n e y a c r o s s t h e s t e p p e s o f T u r k e s t a n , t h e m a l e courts his m a t e by stroking her, t h u s r e d u c i n g her to a state of lethargy. H e t h e n seizes h e r w i t h his chelicerae, p e d i p a l p s a n d legs, u s u a l l y w i t h o u t h a r m i n g h e r , c a r r i e s h e r for s o m e little d i s t a n c e a n d lays h e r o n h e r s i d e . A f t e r m a s s a g i n g h e r v e n t r a l s u r f a c e for s o m e t i m e w i t h h i s j a w s , h e o p e n s h e r g e n i t a l orifice w h o s e e d g e s h a v e b e c o m e s w o l l e n f r o m t h e s e a t t e n t i o n s , lifts h i s a b d o m e n a n d e m i t s a m a s s o f s p e r m a t o z o a w h i c h falls t o t h e g r o u n d . G a t h e r i n g t h i s w i t h h i s c h e l i c e r a e , h e f o r c e s i t i n t o t h e v a g i n a o f t h e fem a l e , c l o s e s t h e s i d e s a n d h o l d s t h e m s h u t for a w h i l e . T h e n h e b o u n d s off a n d flees b e f o r e s h e c a n c a t c h h i m . A m a l e c a n effect s e v e r a l c o p u l a t i o n s i n s u c c e s s i o n b u t after t h e first t h e s p e r m a t i c mass is comparatively small and he dies shortly afterwards. T h e s e a c t i o n s a r e p u r e l y reflex, b e c a u s e i f t h e a n i m a l s a r e s e p a r a t e d d u r i n g c o p u l a t i o n t h e m a l e will c o n t i n u e h i s m a s s a g i n g m o v e m e n t s against the h a n d of the observer, just as t h o u g h the female w e r e still t h e r e . A l t h o u g h t h e t o t a l a c t m a y last for s e v e r a l m i n u t e s , c e r t a i n d e t a i l s a r e e x t r e m e l y r a p i d a n d i t i s difficult t o see e x a c t l y w h a t i s o c c u r r i n g ; for e x a m p l e , i t i s n o t q u i t e c l e a r h o w t h e m a s s of spermatozoa is gathered up and introduced into the genital orifice of t h e f e m a l e .

Reproduction and life cycle A f t e r f e r t i l i s a t i o n t h e f e m a l e d e v e l o p s a n e n o r m o u s a p p e t i t e for t w o or t h r e e weeks. T h e r e follows a period of intense t u n n e l l i n g operations during which a deep b u r r o w is constructed, mostly at n i g h t . I n Solpuga caffra e g g - l a y i n g lasts f o r s o m e 3 - 4 hours ( L a w r e n c e , 1949), s o m e 200 eggs b e i n g p r o d u c e d . I n t h e smaller S . hostilis t h e n u m b e r i s u n d e r 100. D u r i n g l a b o u r t h e f e m a l e lies o n h e r s i d e r a t h e r listlessly w h i l e t h e e g g s slip f r o m h e r a t r e g u l a r 1/2

1/2

PLATE la. A group of woodlice. T o p row: Ligia oceanica, Ligidium hypnorum, Hemilepistus reaumtiri and Armadillidium vulgare. Bottom row: Oniscus asellus, Porcellio scaber, Androniscus dentiger and Philoscia muscorum. T h e halfpenny gives the scale. (Photo: J. L. C l o u d s l e y - T h o m p s o n . )

PLATE lb. Ligia oceanica (length 2-3 cm), Platyarthrus hoffmannseggi (length 3 m m ) and Oniscus asellus (length 16 m m ) . ( F r o m W e b b and Sillem, 1906.)

PLATE

PLATE

IVb.

IVA.

Giant

Flat-backed

tropical

millipede

millipede

(Polydesmus angustus).

(Spirostrephis

graphs.)

sp.).

(Shell

photo-

PLATE

VA.

American

house

centipede

(Scutigera

forceps).

(Photo:

Hugh

Spencer.)

PLATE

Vb.

The

common

centipede

(Lithobius

has lost s o m e legs. (Shell

forficatus).

photograph.)

The

specimen

PLATE

PLATE

VIb.

Head of

S.

VIa.

cingulata.

Scolopendra

(Photos:

J.

cingulata

L.

Cloudsley-Thompson.)

PLATE

VIIA.

Fat-tailed

gives

PLATE

VIIb.

the

scale.

scorpion {Photo:

(Androctonus J.

Newly born scorpions

L.

australis).

The

halfpenny

Cloudsley-Thompson.)

escaping

E. A. Robins.)

from their

c h o r i o n s . (Photos:

PLATE V I I I a . Euscorpius italicus with newly b o r n young.

PLATE V I I I B . E. italicus, the same female protecting her young just after their first moult. T h e cast skins can be seen on the m o t h e r ' s back. (Photos: J. L. C l o u d s l e y - T h o m p s o n . )

PLATE IXa. Left, Androctonus australis, one of the most deadly species in the world. Right, ignoring a h a r d desert beetle (Akis spinosa). (Photos: J. L. C l o u d s l e y - T h o m p s o n . )

PLATE 1X6. Left, black scorpion (Androctonus aeneas). (Photo: J. L. Cloudsley-Thompson.) Right, pectine of scorpion m u c h enlarged. (Photo: E. A. Robins.)

PLATE X « .

PLATE

Xb.

Left,

Solpuga

racquet organs of Solifugid;

caffra,

A.

right, pectine of scorpion.

{Photos:

E.

Robins.)

female

depositing eggs.

(Photo:

R.

A.

Holliday.)

PLATE X I A . Solifugids fighting. (Photo: Richard L. Cassell.)

PLATE Xlb.

Whip-scorpion (Thelyphomis candatus). (Photo: E. A. Robins.)

PLATE

XIIa.

Left,

Mygalomorph

spider;

right,

False-scorpion

(Toxochernes

panzeri).

PLATE

XIIb. toma

Harvest chrysomelas.

spiders. (Photos:

Left,

Trogulus

copyright,

J.

tricarumtus; H.

P.

right,

Sankey.)

Nemas-

PLATE

PLATE

XI116.

XIIIA.

The

jumping

spider

Jumping

spider

(Phidippus

audax)

line.

(Photos:

Walker

van

(Phidippus

climbing Riper.)

audax).

up

the

safety-

PLATE

PLATE

XlVb.

(female

XlVa.

Left, carrying

Wolf

spider

(Lycosa

Amaurobius egg

s a c ) . (Photos:

ferox J.

sp.)

with

(male);

egg

right,

sac.

Scytodes

thoracica

L. C l o u d s l e y - T h o m p s o n . )

PLATE X V 7 . Argiope bruennichi female on web. Left, ventral; right, dorsal view. T h e n a r r o w ribbons of silk or stabilimentum help to camouflage the spider. (Photos: J. L. C l o u d s l e y - T h o m p s o n . )

PLATE XVb.

Brown tick (Rhipicephalus appendiculatus). Male left; female right. (Shell photograph.)

PLATE

XVIa.

Bont

tick

(Amblyomma hebraeum).

Close

up

view

of h e a d

and mouthparts of male.

PLATE

XVIb.

Red

spider

mites

(Paratetranychus pilosus).

a n d h a t c h e d e g g c a s e s o n u n d e r s i d e o f a p p l e leaf.

Adults,

eggs

(Shell photographs.)

PLATE

XVIIa.

Big b u d mite

(Eriophiyes

normal

PLATE

XVIIb.

Big

bud

bud

m i t e (EriopJiyes

bud.

(Shell

ribis).

Infected

bud

on top

with

underneath.

ribis)

removed

photographs.)

from

blackcurrant

SOLIFUGAE i n t e r v a l s : s h e i s l i m p a n d m o t i o n l e s s e x c e p t for r h y t h m i c c o n t r a c tions of her b o d y at a rate of approximately one per two seconds. T h e e g g s o f Galeodes m a y n u m b e r m o r e t h a n 2 0 0 . T h e y a r e i n t h e f o r m o f w h i t e a n d g l i s t e n i n g s p h e r e s t h a t reflect t h e s u n l i g h t w i t h a beautiful metallic lustre as if m a d e of mother-of-pearl: they adhere t o o n e a n o t h e r i n c o m p a c t h e a p s . I n Solpuga caffra t h e e g g s a r e o f a l i g h t , b u t d i r t y y e l l o w c o l o u r , w h i l e i n S . hostilis t h e r e a r e d a r k e r m a r k i n g s . W i t h i n a day or t w o after oviposition t h e female b e g i n s t o t a k e a n i n t e r e s t i n f e e d i n g . Eremobates formicaria l a y s m o r e t h a n one b a t c h of small w h i t e spherical eggs p e r season, b u t closes t h e m o u t h o f t h e b u r r o w a n d l e a v e s t h e m t o t h e i r fate. T h e appearance and detailed structure of the newly hatched first l a r v a a p p e a r s t o v a r y c o n s i d e r a b l y i n d i f f e r e n t g e n e r a . I n Galeodes t h e y o u n g l a r v a e e m e r g e f r o m t h e e g g s w i t h i n a d a y o r t w o a f t e r t h e y a r e l a i d . A t first t h e y a r e soft, w h i t e a n d h e l p l e s s . T h e y are u n a b l e t o m o v e , b u t after t w o o r t h r e e weeks, d u r i n g w h i c h t h e y a r e c l o s e l y g u a r d e d b y t h e i r m o t h e r , t h e first m o u l t takes place and from t h e n on the y o u n g creatures rapidly become m o r e active. T h e i r i n t e g u m e n t h a r d e n s a n d progressively assumes the various external characters of the m a t u r e animal. Eventually they disperse. T h e n u m b e r of moults and the length of time required to reach the adult condition is not k n o w n with certainty in a n y species of t h e o r d e r Solifugae.

BIBLIOGRAPHY Identification KRAEPELIN, Tierreich,

K.

(1901)

Arachnoidea:

Palpigradi

und

Solifugae.

Das

12,1-159.

M U M A , M . H . ( 1 9 5 1 ) T h e Arachnid O r d e r Solpugida i n the United States. Bull. Amer. Mus. Nat. Hist., 9 7 , ( 2 ) , 3 1 - 1 4 2 . ROEWER, C. F. ( 1 9 3 4 ) Solifugae, in H. G. BRONN'S Klass. Ordn. Tierreichs, 5 , i v ( 4 ) , 1 - 6 0 8 .

(1941)

Solifugen

1934-46.

Veroff.

deuts.

Kolon.-Ubersee-Mus., 3 ,

97-192.

Biology BERNARD, A. ( 1 8 9 7 ) 'Wind-scorpions', a brief account of the Galeodidae. Sci. Prog. (N.S.), 1 , 3 1 7 - 4 3 . BOLWIG, N. ( 1 9 5 2 ) Observations on the behaviour and m o d e of orientation of h u n t i n g Solifugae. J. Ent. Soc. S. Afr., 1 5 , 2 3 9 - 4 0 . G

S.S.C.M

SOLIFUGAE

98

CLOUDSLEY-THOMPSON, J . L . ( 1 9 4 9 ) Notes o n Arachnida, 9 . — D o Solifugae m i m i c scorpions? Ent. Mon. Mag., 8 5 , 4 7 . ( 1 9 5 4 ) Notes on Arachnida, 2 2 . — T h e function of the palpal organ of Solifugae. Ibid., 9 0 , 2 3 6 - 7 . DISTANT, W . L . ( 1 8 9 2 ) A r e t h e Solpugidae poisonous? Nature, Lond., 46, 247.

HEYMONS, R . ( 1 9 0 2 ) Biologische Beobachtungen a n asiatischen Solifugen. Abh.preuss. Akad. Wiss., 1 9 0 , 1 - 6 5 . HINGSTON, R. W. ( 1 9 2 5 ) Nature at the Desert's Edge. L o n d o n . 1 9 2 - 2 6 1 . H U T T O N , T. ( 1 8 4 3 ) Observations on the habits of a large species of Galeodes. Ann. Mag. Nat. Hist., 1 2 , 8 1 - 5 . LAWRENCE, R. F. ( 1 9 4 9 ) Observations on the habits of a female Solifuge, Solpuga caffra Pocock. Ann. Transvaal Mus., 2 1 , 1 9 7 - 2 0 0 . LICHTENSTEIN, A . A . H . ( 1 7 9 7 ) G a t t u n g e n Solpuga u n d Phalangium i n HERBST, J. F. W. Natursystem der ungefliigelten Insekten, Berlin. LONNBERG, E. ( 1 8 9 9 ) Some biological observations on Galeodes and Buthus. K. vetensk. Akad. Forh., 5 6 , 9 7 7 - 8 3 . OLIVIER, G. A. ( 1 8 0 7 ) Voyage dans l' Empire Ottoman, l' Egypte et la Perse, 3, Paris. POCOCK, R. I. ( 1 8 9 8 ) T h e nature and habits of Pliny's Solpuga. Nature, Lond.,

57,618-20.

TURNER, C . H . ( 1 9 1 6 ) Notes o n the feeding, behaviour and oviposition o f a captive A m e r i c a n false-spider {Eremobates formicaria). J. Anim. Behav.,

6,160-8.

CHAPTER

VII

FALSE-SCORPIONS Classification and distribution T h e order Pseudoscorpiones, Chelonethi or Chernetes comprises small A r a c h n i d s w h i c h resemble scorpions in the form of their pedipalps and of their body, except that the hind part of the abd o m e n is not n a r r o w as is the p o s t - a b d o m e n or m e t a s o m a of scor-

F I G . 24. Examples of False-scorpion families: 1. Chthoniidae, 2. Neobisiidae, 3. Cheiridiidae, 4. Chernetidae, 5. Cheliferidae. (After various authors.) pions a n d they have no caudal sting. T h e dorsal surface of the p r o s o m a or c e p h a l o t h o r a x is f o r m e d of a large sclerite bearing t h e e y e s , w h e n t h e s e a r e p r e s e n t , a n d six p a i r s o f a p p e n d a g e s : t h e 99

100

FALSE-SCORPIONS

chelicerae, p e d i p a l p s a n d four pairs of legs. T h e chelicerae are p r e oral in position a n d are c o m p o s e d of t w o s e g m e n t s . T h e i r fingers bear a series of c o m p l i c a t e d s t r u c t u r e s k n o w n as t h e serrulae a n d l a m i n a e . T h e s e r r u l a e x t e r i o r i s k e e l - l i k e , s e t w i t h fine t e e t h a n d attached for varying degrees of its l e n g t h to t h e m o v a b l e finger while the serrula interior, attached to the base of the fixed finger, is even m o r e variable in form. A flagellum, f o r m e d of setae w h o s e n u m b e r a n d s h a p e are valuable t a x o n o m i c characters, is also attached to the fixed finger. T h e m o u t h is situated b e t w e e n t h e basal s e g m e n t s of t h e sixs e g m e n t e d pedipalps. T h e s e are e n o r m o u s l y developed a n d resemble the claws of scorpions. T h e y serve as prehensible organs to c a p t u r e a n d kill t h e p r e y a n d b e a r s e n s o r y h a i r s o r s e t a e . T h e i m m o v a b l e finger of t h e chelae h a s a r o w of c u t t i n g t e e t h along its i n n e r edge, t h e last of w h i c h is c o n s i d e r a b l y enlarged. T h r o u g h t h i s p a s s e s t h e d u c t o f t h e e l o n g a t e d p o i s o n g l a n d w h i c h itself i s e m b e d d e d in t h e s u b s t a n c e of t h e finger. In certain families b o t h fingers are equipped with poison glands. T h e coxae of the pedipalps are extended forward so as to form masticatory plates, or they m a y bear distinct endites with which the prey is held in front o f t h e m o u t h d u r i n g f e e d i n g . T h e f o u r p a i r s o f w a l k i n g l e g s differ from those of other A r a c h n i d a in that t h e tibia is u n d i v i d e d so that there is no patella. At t h e same t i m e in m a n y species t h e f e m u r is d i v i d e d i n t o t w o m o r e o r less d i s t i n c t s e g m e n t s . T h e n u m b e r o f tarsal joints is of great systematic i m p o r t a n c e a n d is t h e chief character u p o n which the three sub-orders of the Pseudoscorpiones are differentiated. T h e opisthosoma or abdomen is broadly attached to the cephalot h o r a x a n d consists of 12 s e g m e n t s , t h e last of w h i c h is small a n d f o r m s a c i r c u m a n a l r i n g . T h e g e n i t a l orifice i s s i t u a t e d b e t w e e n the second and third sternites, the second forming an o p e r c u l u m while the first sternite is m u c h reduced. T h e o r d e r P s e u d o s c o r p i o n e s c o n t a i n s o v e r 1,500 s p e c i e s b e l o n g i n g t o t h r e e s u b - o r d e r s all o f w h i c h a r e r e p r e s e n t e d i n t h e B r i t i s h f a u n a . F a l s e - s c o r p i o n s a r e d i s t r i b u t e d all o v e r t h e w o r l d w i t h t h e exception of the arctic and antarctic regions. At present, nineteen f a m i l i e s h a v e b e e n d e s c r i b e d , b u t t h e o r d e r i s still b y n o m e a n s well k n o w n a n d o t h e r s m a y yet be discovered. S o m e g e n e r a h a v e a

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101

w o r l d - w i d e d i s t r i b u t i o n , o t h e r s are r a r e a n d local. As a rule t h e y are sober-coloured animals, their livery consisting of various shades of yellow a n d b r o w n . A w i d e variety of habitats are colonised, t h e majority of species inh a b i t i n g soil a n d d e c a y i n g v e g e t a t i o n w h i l e o t h e r s live u n d e r s t o n e s a n d t h e b a r k o f t r e e s . N o n e i s p a r a s i t i c : Chelifer cancroides h a s o c casionally b e e n r e c o r d e d on m a n b u t it is p r o b a b l y m e r e l y p h o r e t i c (see b e l o w ) . T h i s s p e c i e s , Allochernes italicus, Cheiridium museorum, e t c . , f r e q u e n t l y live in h u m a n h a b i t a t i o n s . Microbisium femoratum lives e x c l u s i v e l y i n m o s s a n d m e m b e r s o f t h e g e n u s Neobisium a r e n e a r l y a l w a y s f o u n d i n m o s s a n d h u m u s : t h e s p e c i e s o f Chthonius a r e n e a r l y a l w a y s f o u n d u n d e r s t o n e s w h i l e t h e g e n u s Chernes i n c l u d e s b a r k - i n h a b i t i n g f o r m s . S p e c i e s s u c h as Microbisium dumicola a n d Neobisium sylvaticum t h a t w a l k i n t h e o p e n o n p l a n t s a n d b u s h e s are extremely rare, b u t cavernicolous false-scorpions are relatively n u m e r o u s , a l t h o u g h they b e l o n g almost exclusively to t h e g e n e r a Neobisium, Roncus a n d Chthonius. Q u i t e a n u m b e r of s p e c i e s a r e m y r m e c o p h i l o u s a n d live i n t h e n e s t s o f a n t s : D o n i s t h o r p e (1927)* records t h e following a m o n g s t t h e British fauna, Chthonius ischnocheles, Neobisium muscorum, Roncus lubricus, Microcreagris cambridgei, Pselaphochernes scorpioides and Allochernes wideri. Neobisium maritimum, Chthonius halberti and the large Garypus beauvoisi h a v e a l i t t o r a l d i s t r i b u t i o n a n d a r e f o u n d in c r a c k s i n r o c k s b e t w e e n t i d e - m a r k s o n t h e sea s h o r e w h i l e Neobisium muscorum a n d s e v e r a l o t h e r s p e c i e s o c c u r i n d a m p s e a w e e d a t t h e water's edge. A n u m b e r of s p e c i e s s u c h as Withius subruber, Cheiridium museorum a n d Toxochernes panzeri a r e o f t e n a s s o c i a t e d w i t h s t o r e d f o o d products in warehouses, where they inhabit extremely dry environm e n t s : t h e y also o c c u r i n b i r d s ' n e s t s i n h o l l o w t r e e s . I n v i e w o f t h e i r s m a l l size i t i s o b v i o u s t h a t t h e i r p o w e r s o f w a t e r - r e t e n t i o n m u s t b e e x t r e m e l y efficient. A n u m b e r o f o t h e r s p e c i e s a r e p a r t i a l t o h e a p s o f m a n u r e a n d o n e o r t w o c l i n g t o t h e legs o f flies a n d o t h e r a r t h r o p o d s a s a m e a n s o f d i s p e r s a l (see b e l o w ) . T h e w e l l k n o w n ' b o o k - s c o r p i o n ' Cheiridium museorum, a l r e a d y m e n t i o n e d , h a s b e e n k n o w n t o live i n h u m a n h a b i t a t i o n s s i n c e t h e t i m e o f Aristotle, for he w r o t e : In b o o k s o t h e r small a n i m a l s are found, s o m e o f w h i c h a r e like s c o r p i o n s w i t h o u t t a i l s , ' a n d i n t h i s c o u n t r y

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H o o k e (1664) d r e w a picture possibly of t h e same species in his f a m o u s b o o k Micrographia.

General behaviour A l l false s c o r p i o n s a r e o f s m a l l size, s e l d o m e x c e e d i n g 7 o r 8 m m i n l e n g t h . T h e g i a n t Garypus beauvoisi o f C o r s i c a a n d t h e M e d i terranean is only a q u a r t e r of an inch in length, a n d t h e largest B r i t i s h s p e c i e s , t h e h a n d s o m e Dendrochernes cyrneus, is o n l y 3.6 mm long. Because they are so small a n d have shy, retiring habits, p s e u d o s c o r p i o n s are little k n o w n a n d s e l d o m f o u n d unless specially sought. T h i s is a pity, for t h e y are interesting creatures a n d m a n y aspects of their biology w o u l d provide suitable subjects for study by b o t h a m a t e u r a n d professional zoologists. M o s t pseudoscorpions are markedly photo-negative and do not often v e n t u r e into t h e o p e n . T h e y m a y b e collected b y h a n d from rotting leaves a n d from u n d e r t h e bark of trees, b u t this m e t h o d t e n d s t o b e l a b o r i o u s for t h e y are b y n o m e a n s plentiful. T h e m o s t effective m e t h o d e n t a i l s t h e u s e o f t h e B e r l e s e F u n n e l , b u t a s i m p l e r w a y i s t o s c a t t e r fallen l e a v e s , m o s s a n d o t h e r v e g e t a b l e d e b r i s o n t o a s h e e t o f n e w s p a p e r o r a w h i t e t a b l e t o p . D e s p i t e t h e i r s m a l l size, t h e c r e a t u r e s c a n t h e n b e easily r e c o g n i s e d b y t h e i r s q u a r i s h s h a p e : t h e y g e n e r a l l y c r o u c h m o t i o n l e s s , t h e i r legs a n d c h e l a e d r a w n i n until they are touched, w h e n they at once proclaim their nature by r u n n i n g b a c k w a r d s . F a l s e - s c o r p i o n s walk slowly w i t h an air of i m pressive dignity and calm deliberation which distinguishes t h e m from m o s t of the other small a r t h r o p o d s that inhabit the same type of locality, t h e i r e n o r m o u s p e d i p a l p s s p r e a d o u t in front of t h e m like t h e a n t e n n a e o f a n i n s e c t . If, a s t h e y p r o c e e d , t h e y h a p p e n t o t o u c h s o m e o t h e r animal w i t h t h e long setae on their extended palps, they dart sideways or backwards with surprising speed, l o o k i n g r a t h e r like a s t a r t l e d c r a y f i s h . T h i s s u d d e n r e t r e a t i s h i g h l y c h a r a c t e r i s t i c for n o t m a n y a n i m a l s c a n g o b a c k w a r d s a s easily a s forwards, and very few m o r e rapidly. It has b e e n p o i n t e d out t h a t a few species inhabit a c o m p a r a tively d r y e n v i r o n m e n t , b u t t h e m a j o r i t y a r e e x t r e m e l y s u s c e p t i b l e to desiccation and m u s t be provided with moisture if kept in c a p t i v i t y . S o m e s p e c i e s a r e l i g h t - s h y , b u t i n Chelifer cancroides n o negative phototaxis has been observed although the animals tend

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to prefer a r o u g h surface to walk on. T h a n k s to t h e arolium, a t r u m p e t - s h a p e d m e m b r a n o u s sucker beneath t h e claws of the w a l k i n g legs, f a l s e - s c o r p i o n s a r e a b l e t o c l i m b v e r t i c a l l y a n d w a l k u p s i d e - d o w n on t h e u n d e r surfaces of stones a n d logs. If they s h o u l d h a p p e n t o fall o n t h e i r b a c k s , h o w e v e r , t h e y c a n o n l y r i g h t t h e m s e l v e s w i t h difficulty b y a r c h i n g t h e i r b o d i e s a n d r o c k i n g from side to side, or by grasping s o m e n e a r b y object w i t h their claws. T h e p h e n o m e n o n o f t h e utilisation o f a n o t h e r a n i m a l for t r a n s port, to which the n a m e 'phoresy' is c o m m o n l y applied, is perhaps a particular t y p e of c o m m e n s a l i s m . An e x a m p l e is afforded by Limosina sacra, a B o r b o r i d fly, n u m b e r s of w h i c h c o n s t a n t l y r i d e o n t h e b a c k s o f d u n g b e e t l e s i n N o r t h A f r i c a , a p p a r e n t l y for t h e purpose of ovipositing in the particularly choice assemblage of faecal m a t t e r t h a t t h e b e e t l e s c o l l e c t a n d c o n s o l i d a t e . I n a s i m i l a r way, bird-lice (Mallophaga) are frequently conveyed from one h o s t t o a n o t h e r b y t h e H i p p o b o s c i d fly Ornithomyia avicularia. A b o u t twenty-five species of pseudoscorpion are k n o w n to obtain transport from one place to another on other animals such as Diptera, Hymenoptera, Coleoptera, Hemiptera, Orthoptera and other insects, harvest-spiders a n d birds. Beier (1948) provides a useful s u m m a r y of t h e extensive literature n o t only on p h o r e s y b u t also o n o t h e r t y p e s o f a s s o c i a t i o n i n w h i c h f a l s e - s c o r p i o n s a r e . c o n c e r n e d . H e lists t h e s p e c i e s t h a t h a v e b e e n f o u n d i n h a b i t i n g the nests of birds and mammals, termites, ants and other H y m e n optera, and tabulates the Chernetes that have been recorded as attached to the extremities of the limbs a n d to the bodies of insects and other a r t h r o p o d s . T h e m o s t i m p o r t a n t phoretic species in E u r o p e is Lamprochernes nodosus w h i c h is n o t i n f r e q u e n t l y f o u n d a t t a c h e d t o t h e legs o f h o u s e f l i e s i n s u m m e r a n d a u t u m n a l t h o u g h i t also c l i n g s t o h o v e r - f l i e s a n d o t h e r i n s e c t s . F a l s e - s c o r p i o n s o c casionally ride on t h e backs of beetles, sheltering u n d e r their e l y t r a . Cordylochernes scorpioides is a w e l l - k n o w n e x a m p l e f r e q u e n t l y p h o r e t i c o n t h e b e e t l e Acrocinus longimanus i n t r o p i c a l America. Various explanations of the phoretic habit have been suggested, b u t in m o s t cases it s e e m s t h a t this b e h a v i o u r is either accidental or motivated by h u n g e r . O n l y female false-scorpions are phoretic,

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a n d t h e s p e c i e s i n v o l v e d a r e t h o s e t h a t i n h a b i t fallen l e a v e s a n d d e b r i s , n o t t h o s e t h a t live u n d e r s t o n e s a n d b e n e a t h b a r k ( V a c h o n , 1947a). T h e ability of false-scorpions to spin was denied by s o m e of t h e earlier writers, b u t it is n o w k n o w n t h a t they c o n s t r u c t nests p a r t l y o r w h o l l y o f silk f r o m t h e i r o w n b o d i e s . T h e a n i m a l s u s u a l l y e n c l o s e t h e m s e l v e s i n t h e s e n e s t s f o r m o u l t i n g , for b r o o d p u r p o s e s a n d , i n s o m e c a s e s , for h i b e r n a t i o n . S u c h n e s t s a r e c l o s e d cells o f s p u n t i s s u e w i t h o r w i t h o u t a n e x t e r n a l c o v e r o f e x t r a n e o u s matter. T h e y are roughly circular in shape and may be attached above a n d b e l o w to t h e solid surfaces of n a r r o w crevices. W h e n t h e y a r e a t t a c h e d o n o n e s i d e o n l y t h e y h a v e a free, c o n v e x r o o f a n d m a y b e fixed h e r e a n d t h e r e t o s u r r o u n d i n g o b j e c t s . T h e e x ternal covering, if p r e s e n t , consists of e a r t h or vegetable fibres w h i c h a r e n o t b o u n d t o t h e s t r u c t u r e b u t a r e f i r m l y a t t a c h e d t o it, b u t t h e i n t e r i o r i s s m o o t h a n d a l w a y s free f r o m f o r e i g n m a t t e r . T h e s p u n tissue is thin and dense, composed of i n n u m e r a b l e threads, crossed a n d recrossed a n d coalesced in irregular confusion w i t h o u t interspaces. T h e silk i s d e r i v e d f r o m g l a n d s i n t h e c e p h a l o t h o r a x w h o s e d u c t s t r a v e r s e t h e chelicerae to t h e a p e x of t h e m o v a b l e finger. T h e y o p e n at t h e tips of t h e b r a n c h e s of t h e galea or on or near the margin of a tubercle which replaces that structure in some groups. T h e spinning is done with the chelicerae b u t the presence or absence of t h e galea does n o t a p p e a r to be associated w i t h differences of m e t h o d or in t h e tissue: t h e serrulae, etc. are not concerned. Nest building is carried out from within. T h e cons t r u c t i o n o f a n e x t e r n a l f r a m e w o r k i s t h e first t a s k , a n d w h e r e t h i s has a coating of extraneous materials, t h e animal frequently goes o u t t o collect t h e m . T h e y are picked u p i n t h e p e d i p a l p s , t r a n s ferred to t h e chelicerae and attached to the nest by the application o f silk t o t h e i r i n n e r s u r f a c e s . T h e silk i s d r a w n f r o m t h e g a l e a o r t u b e r c l e i n s e v e r a l v i s c i d a n d v e r y fine t h r e a d s w h i c h m a y r e m a i n separate or m a y coalesce, a n d t h e s p i n n i n g is a c c o m p a n i e d by continuous forward and backward movements of the body and b y l a t e r a l m o v e m e n t s o f t h e c h e l i c e r a e . A t first, w h e n a t t a c h m e n t s are being m a d e from place to place, t h e t h r e a d s usually do coalesce, b u t afterwards t h e animal settles d o w n to long c o n t i n u e d spinning

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a n d t h e silk i s r a p i d l y b r u s h e d o n t o t h e i n t e r i o r o f t h e n e s t , first i n one place, t h e n in another. T h e animal continues at work gradually i m p r i s o n i n g itself, f o r d a y s o r e v e n w e e k s u n t i l a d e n s e t i s s u e i s p r o d u c e d o v e r e v e r y p a r t o f t h e i n s i d e o f its a b o d e ( K e w , 1 9 1 4 ) .

Food and feeding habits P s e u d o s c o r p i o n s are exclusively c a r n i v o r o u s a n d feed on living or recently killed p r e y s u c h as Collembola, Psocids, T h y s a n u r a , Diptera, other small insects, S y m p h y l a a n d Arachnids. Unlike spiders, they are not usually cannibalistic if food is available b u t an injured or ailing individual has a p o o r c h a n c e of survival. It is d o u b t f u l i f t h e p r e y i s a c t i v e l y s o u g h t after, b u t r a t h e r t h a t falses c o r p i o n s lie i n w a i t , w i t h t h e i r c l a w s o p e n , u n t i l s o m e s u i t a b l e animal accidentally brushes against their sensory hairs, w h e n it is seized w i t h e x t r e m e rapidity. It is said t h a t s o m e species of Chthonius c a n a c t u a l l y l e a p u p o n t h e i r p r e y . T h e r o l e o f t h e p o i s o n g l a n d s in t h e p a l p s is n o t entirely clear. S o m e t i m e s t h e p r e y is paralysed immediately b u t not infrequently it is conveyed to the c h e l i c e r a e w h i l s t still s t r u g g l i n g . O c c a s i o n a l l y o n e f a l s e - s c o r p i o n h a s b e e n o b s e r v e d t o r o b a n o t h e r o f its f o o d a f t e r a s h o r t s t r u g g l e ( V a c h o n in G r a s s e , 1 9 4 9 ) . * T h e p r o t o n y m p h is t h e m o s t active instar a n d is quite b o l d a n d f e a r l e s s i n its b e h a v i o u r : i t will e v e n t a k e f o o d d i r e c t l y f r o m a p r o b e . T h e later stages do n o t feed so readily a n d a d u l t s m a y eat only o n c e o r t w i c e a m o n t h . L e v i ( 1 9 4 8 ) f o u n d t h a t i n Chelifer cancroides, a d u l t s fed o n c e a w e e k i n c a p t i v i t y s e e m e d t o b e i n b e t t e r condition than those caught in the woods. D u r i n g feeding the pedipalps may be vibrated, possibly by the action of the pharyngeal p u m p ( C h a m b e r l i n , 1931). T h e A r g e n t i n e f a l s e - s c o r p i o n Sphenochernes schulzi r e c e n t l y d e s cribed by T u r k (1953) is very c o m m o n in t h e nests of a leaf-cutting a n t , Acromyrmex lundi. T h e s e p s e u d o s c o r p i o n s live b u r i e d i n t h e material of the nest and seemingly do not normally emerge except for t h e i r p r e y . T h e y h o l d t h e i r p e d i p a l p s o p e n a l m o s t c o n t i n u o u s l y , c a t c h i n g a t t h e legs o f t h e a n t s a s t h e y r u n p a s t , a n d h o l d i n g fast u n t i l t h e a n t d i e s f r o m t h e effect o f t h e i r p o i s o n . T h e a t t a c k e r s , and there are usually m o r e than one, then probe their victim with their chelicerae, and proceed to suck the b o d y fluids. It is a curious

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fact t h a t t h e s e a t t a c k s t a k e p l a c e o n l y i n d a y l i g h t . I f a v e s s e l c o n taining C h e r n e t i d s and captured ants is darkened t h e ants are released, whereas in t h e light t h e hold of t h e C h e r n e t i d s is so s t r o n g a n d p e r s i s t e n t t h a t t h e y will n o t let g o e v e n w h e n w h i r l e d about. T h e attacks of the pseudoscorpion are m o s t clumsy, and this is t h o u g h t to be the reason that the ant species continues to survive. T h e ants never succeed in freeing themselves from their attackers by biting. M o r e recently V a c h o n (1954) has r e c o r d e d an e x t r a o r d i n a r y a s s o c i a t i o n b e t w e e n Ellingsenius hendrickxi a n d b e e s in the Belgian Congo. T h i s curiously o r n a m e n t e d and sculptured species is very c o m m o n at T s h i b i n d a a n d K a t a n a w h e r e it passes its w h o l e life c y c l e i n b e e h i v e s . T h e f a l s e - s c o r p i o n s o f t e n a t t a c h t h e m s e l v e s t o t h e legs o f t h e b e e s a n d s o m e t i m e s n u m b e r s c o m b i n e t o a t t a c k b o t h w o r k e r s a n d q u e e n s , w h i c h a r e k i l l e d a n d e a t e n like o r d i n a r y p r e y . The Ellingsenius f o r c e s its c h e l i c e r a e i n t o t h e a r t i c u l a t i o n s o f t h e legs o f t h e b e e a t i n t e r s e g m e n t a l m e m b r a n e s a n d

F I G . 25. Ellingsenius hendrickxi. (After Vachon, 1954.) f e e d s u p o n it, h o l d i n g o n b y its c h e l i c e r a e o n l y . I f t h e s e b e c o m e unfixed, however, the pedipalps are used to regain control. A f t e r a m e a l a f a l s e - s c o r p i o n c a n o f t e n be s e e n to c l e a n its m o u t h - p a r t s and chelicerae. T h i s habit it shares with spiders and h a r v e s t m e n , w h i c h s i m i l a r l y p a s s t h e i r p a l p s o r legs t h r o u g h t h e i r jaws. Since the prey is digested externally by m e a n s of enzymes a n d t h e n sucked in in solution, it is essential t h a t t h e several channels a n d g r o o v e s i n t h e m o u t h - p a r t s s h o u l d b e k e p t free f r o m solid

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particles. In addition to this however, false-scorpions are remarka b l e i n t h a t t h e y also c l e a n t h e i r c h e l i c e r a e b e f o r e a m e a l ( V a c h o n , 1 9 4 8 ) . F o r e x a m p l e , w h e n Dactylochelifer latreillei s e n s e s its p r e y i t b e g i n s t o c l e a n its c h e l i c e r a e w i t h its p e d i p a l p s . O n c a p t u r e , the prey is grasped by t h e pedipalps. Often b o t h are used, b u t the h o l d o f o n e o f t h e m i s s o o n r e l i n q u i s h e d a n d t h e p r e y i s h e l d aloft b y t h e o t h e r . T h e free p a l p t h e n c o n t i n u e s t o c l e a n t h e m o u t h p a r t s . After a few m i n u t e s t h e prey, w h i c h by n o w m a y well be inactive, is applied to the chelicerae w h i c h by their c o m b i n e d action make a small w o u n d . T h e m o u t h - p a r t s are inserted until the l a b r u m appears t o penetrate slightly into t h e w o u n d . W h e n fixation t o t h e c h e l i c e r a e i s c o m p l e t e t h e p e d i p a l p s r e l e a s e t h e i r g r i p a n d t a k e u p a c h a r a c t e r i s t i c flexed a t t i t u d e . D u r i n g f e e d i n g it can be seen t h a t liquid is flowing b o t h in a n d o u t of t h e prey. A s s u c k i n g p r o c e e d s a s o f t - s k i n n e d i n s e c t b e c o m e s q u i t e flaccid, only to become suddenly turgid due to the exudation from the false-scorpion of a liquid p r e s u m a b l y containing digestive e n z y m e s . T h e m e a l m a y l a s t f o r a n h o u r o r m o r e b e f o r e t h e p r e y i s finally discarded a n d t h e m o u t h - p a r t s again cleaned (Gilbert, 1951). T h e f e e d i n g b e h a v i o u r of Neobisium muscorum a n d N. maritimum i s s i m i l a r , e x c e p t t h a t t h e f o o d i s a c t i v e l y k n e a d e d b y t h e c h e l i c e r a e , w h i c h r e m a i n c o m p a r a t i v e l y still i n D . latreillei, a n d considerable use is m a d e of t h e pedipalps in food capture. In Chthonius ischnocheles, h o w e v e r , t h e p r e y i s d i s a b l e d b y t h e c h e l i cerae. T h i s m a y be correlated with the unusually large chelicerae a n d t h e a b s e n c e o f a p a l p a l v e n o m a p p a r a t u s i n t h e g e n u s Chthonius. T h e chelicerae, by a chewing action, m a k e a w o u n d and this is quickly extended so that the prey becomes immobilised within two or three minutes. Feeding is accompanied by an incessant kneading of the prey, one chelicera being clenched in the w o u n d w h i l e t h e o t h e r i s c l o s e d r o u n d it, a t t h e s a m e t i m e d i g g i n g f u r t h e r inwards. T h i s alternate insertion of each chelicera continues at intervals of about one second: at times the clenching of the chelicerae is n o t alternate, o n e of t h e m o p e n i n g a n d closing several times in succession. C h a m b e r l i n (1931) m e n t i o n s that t h e modification of the serrulae seems to parallel t h e prehensile or n o n prehensile functions of t h e chelicerae, a n d G i l b e r t (1951) suggests that there m a y be a correlation b e t w e e n genera in w h i c h t h e ser-

FALSE-SCORPIONS

108

r u l a e a r e fixed t h r o u g h o u t t h e i r l e n g t h t o t h e c h e l i c e r a l f i n g e r s a n d those whose chelicerae are inactive during feeding. At the same t i m e i t i s p o s s i b l e t h a t t h e p o s s e s s i o n o f p a r t i a l l y free s e r r u l a e i n Xeobisium a n d Chthonius is a s s o c i a t e d w i t h t h e m a i n t e n a n c e of a l i q u i d film b e t w e e n t h e f a l s e - s c o r p i o n a n d its p r e y , d e s p i t e t h e fact t h a t t h e c h e l i c e r a e a r e m o v i n g .

Enemies O w i n g to their secretive habits, false-scorpions have few enemies although Levi (1948) has r e c o r d e d that they m a y be eaten by ants. T h e y do not

o f t e n fall v i c t i m t o

spiders: their poison-bearing

pedipalps help t h e m to hold their o w n against species of their o w n size, w h i l s t t h e y a r e likely t o r e m a i n u n n o t i c e d b y m a n y s p i d e r s o f a larger size. T h e y do n o t a p p e a r to be distasteful h o w e v e r , a n d Bristowe

(1941)*

h a s fed

Chthonius ischnocheles a n d Lamprochernes

nodosus t o a n u m b e r o f s p i d e r s p e c i e s . T h e y m a y also b e e a t e n b y harvest-spiders ( C l o u d s l e y - T h o m p s o n , 1955). W i t h t h e e x c e p t i o n o f six n e m a t o d e w o r m s o f t h e g e n u s Hexameris f o u n d in a f e m a l e Roncus s p . w h o s e o v a r i e s w e r e a t r o p h i e d , no parasites of pseudoscorpions are known.

Mating habits In m a l e false-scorpions t h e galea or spinneret on t h e m o v a b l e finger of t h e chelicerae is poorly d e v e l o p e d c o m p a r e d w i t h t h a t of the female; the abdominal tergites m a y be provided with strong l a t e r a l k e e l s a s i n Chelifer cancroides a n d t h e c l a w s o f t h e p e d i p a l p s are m o r e r o b u s t a n d h a v e a w i d e r g a p e . L a t e r a l genital sacs are p r e s e n t u n d e r t h e genital o p e r c u l u m close t o t h e genital a p e r t u r e . In some species these are capable of being extruded. T h e y reach their highest development in the Cheliferidae where they can be completely evaginated and constitute the 'ram's-horn organs' of many authors, a term proposed by Menge. T h e p a i r i n g of Dendrochernes cyrneus a n d Dactylochelifer latreillei h a s b e e n d e s c r i b e d b y K e w ( 1 9 1 4 ) . T h e m a l e s a r e d i f f e r e n t l y e q u i p p e d : D . latreillei h a s a n e l a b o r a t e g e n i t a l a r e a , l o n g r a m ' s h o r n o r g a n s a n d m u c h m o d i f i e d legs o f t h e first p a i r , w h i l e D . cyrneus h a s a less e l a b o r a t e g e n i t a l a r e a , n o r a m ' s - h o r n o r g a n s a n d no modified legs. B o t h are destitute of i n t r o m i t t e n t o r g a n s of

FALSE-SCORPIONS

109

c o p u l a t i o n a n d f e r t i l i s a t i o n i s effected b y m e a n s o f a s p e r m a t o p h o r e . T h e m a l e a n d f e m a l e face o n e a n o t h e r i n w a l k i n g p o s i t i o n , the male grasping one or b o t h of t h e pedipalps of t h e female with one or b o t h of his own. T h e r e is a forced courtship d u r i n g w h i c h t h e m a l e m a k e s display of definite character. At l e n g t h he e x t r u d e s a s p e r m a t o p h o r e w h i c h is attached to t h e substrate in front of the female w h e r e it stands erect or obliquely. T h e male t h e n retires and the female moves forward until her genital opening comes into contact w i t h t h e s p e r m a t o p h o r e w h i c h is received w i t h o u t delay. C o u r t s h i p varies in the two species correlated w i t h their m o r p h o logical d i f f e r e n c e s . D . latreillei h o l d s t h e f e m a l e w i t h b o t h p a l p s and makes display with his r a m ' s - h o r n organs, releasing her just before extruding a spermatophore. W h e n she comes forward he

F I G . 26. Courtship dance of false-scorpions. (After Vachon, 1938.) s e i z e s h e r b y t h e g e n i t a l o p e n i n g w i t h h i s first p a i r o f legs a n d executes a series of pulling m o v e m e n t s by w h i c h t h e reception of t h e m a l e p r o d u c t i s facilitated. T h e a n i m a l s t h e n separate a n d g o t h e i r d i f f e r e n t w a y s . I n D . cyrneus t h e m a l e h o l d s h i s m a t e w i t h o n e p e d i p a l p o n l y , t h e o t h e r b e i n g s h a k e n i n h e r face, a n d h i s first legs a r e m o v e d r a p i d l y , b e i n g lifted a n d r e p l a c e d i n a p e c u l i a r fashion. T h e female, w h o is apparently ' m u c h impressed' by these actions, is not released d u r i n g extrusion of t h e s p e r m a t o p h o r e w h i c h she takes quickly w i t h o u t t h e m a l e seizing her genital o p e n ing. After a period of repose the whole process m a y be repeated a

110

FALSE-SCORPIONS

n u m b e r of times a n d a large n u m b e r of s p e r m a t o p h o r e s are t h u s p r o d u c e d and received in quick succession. In Chelifer cancroides, a c c o r d i n g to V a c h o n ( 1 9 3 8 ) , a n u p t i a l dance takes place during which the male vigorously displays and r e t r a c t s h i s r a m ' s - h o r n o r g a n s a n d w a v e s h i s p e d i p a l p s i n t h e air like t h e a r m s o f a s w i m m e r . T h e d a n c e c o n s i s t s o f a t l e a s t t h r e e s e t f i g u r e s w h i c h a r e r e p e a t e d r h y t h m i c a l l y for s o m e m i n u t e s o r l o n g e r if t h e female is u n r e s p o n s i v e . Still d a n c i n g , he a p p r o a c h e s his m a t e , deposits a s p e r m a t o p h o r e a n d t h e n retreats, slowly m o v i n g his palps. O b e d i e n t to this signal, t h e female advances until she stands above the spermatophore which she introduces into her spermathecae. T h e male t h e n lowers his head b e n e a t h that of his mate, grips t h e femurs of her palps w i t h his o w n claws a n d taps her genital region w i t h his anterior legs, t h u s e n s u r i n g that t h e s p e r m a tozoa from t h e s p e r m a t o p h o r e are properly secured.

Reproduction and life cycle I t h a s b e e n k n o w n s i n c e t h e t i m e o f F a b r i c i u s i n 1793 t h a t t h e e g g s o f Chelifer w e r e r e t a i n e d b e n e a t h t h e a b d o m e n o f t h e m o t h e r , b u t L u b b o c k i n 1861 w a s t h e f i r s t t o o b s e r v e t h a t t h e y w e r e e n closed in a transparent, structureless m e m b r a n e attached to t h e a b d o m e n a n d that large motionless y o u n g similarly retained were n o u r i s h e d b y a m i l k y fluid p r o v i d e d b y t h e m o t h e r . T e n y e a r s l a t e r Metschnikoff discovered that development involved a m e t a m o r phosis including immobile larvae w h i c h w e r e provided anteriorly with a strongly muscular sucking-apparatus and Barrois showed that the larvae u n d e r w e n t t w o distinct periods of embryogenesis. T h e eggs a n d later t h e larvae m a y be arranged in a flat disc in those species w h e r e t h e female continues an active existence d u r i n g g e s t a t i o n , for e x a m p l e i n m o s t o f t h e C h e l i f e r i d a e ; b u t w h e r e t h e f e m a l e c o n s t r u c t s a n e s t i n w h i c h s h e seals h e r s e l f u p a n d r e m a i n s inactive until t h e development of the y o u n g is complete, they are usually in a mulberry-like mass. A c c o r d i n g to K e w (1929) in these false-scorpions the enormously distended females imprison t h e m selves i n b r o o d n e s t s w h e r e t h e y r e m a i n h i d d e n f r o m v i e w . A f e w h o u r s before t h e eggs are laid an i n c u b a t i o n c h a m b e r or b r o o d - s a c m a k e s its a p p e a r a n c e a c c o m p a n i e d b y peculiar m u s c u l a r m o v e m e n t s of t h e m o t h e r ' s b o d y . It is a delicate, t r a n s p a r e n t m e m b r a n e

FALSE-SCORPIONS

111

a n d l o o k s like a m i n u t e m u s h r o o m , its s t a l k j o i n e d t o t h e o v i d u c t , a n d t h e e g g s a r e l a i d i n t o it. T h e i r n u m b e r m a y v a r y f r o m five t o forty or m o r e . After a few days t h e y o u n g escape from t h e eggm e m b r a n e b u t stay inside the brood-sac. T h e s e first l a r v a e h a v e a s u c k i n g b e a k a n d r e m a i n a t t a c h e d t o t h e g e n i t a l orifice o f t h e f e m a l e t h r o u g h w h i c h t h e y a r e f e d o n a k i n d of uterine milk secreted by the transformed ovaries of the m o t h e r , w h o s e a b d o m e n gradually s h r i n k s a s t h e larvae g r o w . T h e y swell so m u c h t h a t V a c h o n describes t h e m as 'larvae gonflees' a n d t h e brood-mass becomes more bulky than the mother's body whence it projects b r o a d l y on each side a n d often also posteriorly. By d e g r e e s a n d w i t h o u t m u c h f u r t h e r i n c r e a s e i n size t h e s e d e u t e m b r y o s c o m p l e t e their d e v e l o p m e n t . B e h i n d t h e old larval s t r u c t u r e s the chelicerae appear anteriorly a n d wide apart while dorsally the a b d o m i n a l segments with their setae b e c o m e distinct. Laterally a n d ventrally t h e p a l p s a n d legs b e c o m e clearly differentiated. F o u r o r five w e e k s a f t e r t h e e x t r u s i o n o f t h e e g g s s o m e p o w e r o f movement is attained and the young emerge from the brood-mass, the debris of which remains attached to their mother. T h e young, or protonymphs, emerge within about a day. In s o m e s p e c i e s s u c h as Garypus minor a n d t h e B r i t i s h Chthonius ischnocheles, Neobisium carpenteri, N. maritimum, N. muscorum, Toxochernes panzeri, Chernes cimicoides a n d Dendrochernes cyrneus, 2 0 o r m o r e y o u n g a r e p r o d u c e d , i n Chelifer cancroides, 7 t o 3 9 , b u t t h e f a m i l i e s of t h e s m a l l e r Cheiridium museorum n u m b e r o n l y 2 to 5 individuals. In some species the p r o t o n y m p h s ride on their m o t h e r s ' backs like y o u n g s c o r p i o n s a n d w o l f s p i d e r s , b u t t h e y a r e a c t i v e , g r e e d y little c r e a t u r e s a n d s o o n disperse. W h e n young pseudoscorpions emerge from the brood-mass they resemble miniature copies of their parents. T h e y moult three times o n l y , for w h i c h p u r p o s e t h e y u s u a l l y e n c l o s e t h e m s e l v e s i n m o u l t ing nests, before reaching t h e adult stage. D u r i n g this t i m e t h e y increase t h e i r l e n g t h by a b o u t o n e a n d a half t i m e s , t h e special structures of the chelicerae develop and the n u m b e r of hairs with which t h e b o d y is covered increases considerably. A period of q u i e s c e n c e l a s t i n g s o m e t e n t o fifteen d a y s p r e c e d e s t h e a c t u a l m o u l t i n g process a n d t h e animals do n o t leave their nests until

FALSE-SCORPIONS

112

t h e y a r e a l m o s t fully c o l o u r e d ; t h a t i s t o say, w i t h i n t e n o r t w e l v e days.

P a i r i n g m a y o c c u r w i t h i n a b o u t a f o r t n i g h t o f t h e final

moult. According

to Vachon (1947b)

the

different

instars

of false-

scorpions can be recognised as follows: t h e p r o t o n y m p h always has four trichobothria (or long sensory hairs) on t h e chelae of t h e p e d i p a l p s ( o n e o n t h e m o v a b l e finger, t h r e e o n t h e fixed f i n g e r ) , t h e d e u t o n y m p h h a s e i g h t ( t w o o n t h e m o v a b l e finger, six o n t h e fixed), t h e t r i t o n y m p h h a s t e n ( t h r e e o n t h e m o v a b l e finger, s e v e n o n t h e fixed) w h i l e t h e a d u l t h a s t w e l v e t r i c h o b o t h r i a ( f o u r o n t h e m o b i l e f i n g e r a n d e i g h t o n t h e fixed f i n g e r ) . T h i s r u l e h o l d s g o o d f o r all s p e c i e s i n w h i c h t h e a d u l t h a s t w e l v e t r i c h o b o t h r i a o n e a c h of its c l a w s . I n Chernes cimicoides f e m a l e s p r o d u c e t h e i r e g g s i n t h e s u m m e r , b u t y o u n g m a y b e f o u n d t h r o u g h o u t t h e year. T h e larval stages are passed t h r o u g h in t h e a u t u m n a n d t h e y o u n g usually h i b e r n a t e b e f o r e o r after t h e i r s e c o n d m o u l t . T h e y r e a p p e a r t h e f o l l o w i n g s p r i n g a n d t h e final m o u l t t a k e s p l a c e i n e a r l y s u m m e r , t h e e n t i r e life c y c l e l a s t i n g f o r a y e a r . L e v i ( 1 9 4 8 ) f o u n d t h a t i n W i s c o n s i n t h e life c y c l e of Chelifer cancroides also o c c u p i e s a y e a r , b u t V a c h o n (1938) f o u n d t h a t in F r a n c e t h e s a m e species took t w o years to r e a c h m a t u r i t y . A p s e u d o s c o r p i o n h a s b e e n k n o w n t o live i n c a p tivity for a p p r o x i m a t e l y 3

1/2

years (Strebel, 1937).

BIBLIOGRAPHY Identification BEIER, M . ( 1 9 3 2 ) P s e u d o s c o r p i o n i d e a . Das Tierreich, 57, 1 - 2 5 8 ; 58, 1 - 2 9 4 .

CHAMBERLIN, J . C . ( 1 9 3 1 ) T h e Arachnid order Chelonethida. Publ. Stanf. Univ. (Biol.), 7 , 1 - 2 8 4 . EVANS, G . O . a n d B R O W N I N G , E .

( 1 9 5 4 ) Synopses of the British Fauna,

No. 10—Pseudoscorpiones. L o n d o n : Linn. Soc. K E W , H. W. ( 1 9 1 1 ) A synopsis of the false-scorpions of Britain and Ireland. Proc. R. Irish Acad. ( B ) , 29, 3 8 - 6 4 . ( 1 9 1 6 ) Idem. S u p p l e m e n t . Ibid. ( B ) , 33, 7 1 - 8 5 . ROEWER, C . F . ( 1 9 3 7 - 4 0 ) C h e l o n e t h i o d e r P s e u d o s k o r p i o n e in

H.

G.

BRONN'S Klass. Ordn. Tierreichs, 5, IV ( 6 ) , 1 - 3 5 4 .

Biology BEIER, M . ( 1 9 4 8 ) P h o r e s i e u n d P h a g o p h i l i e bei P s e u d o s c o r p i o n e n . Ost. Zool. Z., 1 , 4 4 1 - 9 7 .

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CLOUDSLEY-THOMPSON, J. L. (1956) N o t e s on Arachnida, 25.—An u n usual case of phoresy by false-scorpions. Ent. Mon. Mag., 9 2 , 7 1 . GILBERT, O. (1951) Observations on t h e feeding of some British falsescorpions. Proc. Zool. Soc. Lond., 1 2 1 , 5 4 7 - 5 5 . K E W , H. W. (1911) On the pairing of Pseudoscorpiones. Proc. Zool. Soc. Lond., 1 9 1 1 , 3 7 6 - 9 0 . (1914) On the nests of Pseudoscorpiones: with historical notes on the s p i n n i n g organs and observations on the building and s p i n n i n g of nests. Ibid., 1 9 1 4 , 9 3 - 1 1 1 . (1929) On the external features of the development of the P s e u d o scorpiones: with observations on t h e ecdyses and notes on the> i m m a t u r e forms. Ibid., 1 9 2 9 , 3 3 - 8 . LEVI, H. W. (1948) N o t e s on the life history of the Pseudoscorpion Chelifer cancroides (Linn.) (Chelonethida). Trans. Amer. Micr. Soc, 6 7 , 290-8. STREBEL, O. (1937) Beobachtungen am einheimischen Biicherskorpion Chelifer cancroides L. (Pseudoscorpiones). Beitr. naturh. Forsch. Sudzu. Dtsch., 2, 1 4 3 - 5 5 . T U R K , F. A. (1953) A n e w genus and species of pseudoscorpion with some notes on its biology. Proc Zool. Soc Lond., 1 2 2 , 9 5 1 - 4 . VACHON, M. (1938) La reproduction et le developpement des P s e u d o scorpions. Ann. Sci. nat. Zool., (11), 1 , 1 - 2 0 9 . (1947a) Nouvelles r e m a r q u e s a p r o p o s de la phoresie des P s e u d o scorpions. Bull. Mus. Hist. nat. Paris, (2), 1 9 , 8 4 - 7 . (1947b) C o m m e n t reconnaitre Page chez les Pseudoscorpions (Arachnides). Ibid., (2), 1 9 , 2 7 1 - 4 . (1948) Q u e l q u e s r e m a r q u e s sur la 'nettoyage des pattes machoires' et les glandes salivaires, chez les Pseudoscorpions (Arachnides). Ibid., (2), 2 0 , 1 6 2 - 4 . (1954) R e m a r q u e s sur un Pseudoscorpion vivant dans les ruches d'Abeilles au C o n g o Beige, Ellingsenius hendrickxi n. sp. Ann. Mus. Congo. Tervuren, 1, 2 8 4 - 7 .

H

S.S.C.M

CHAPTER

WHIP-SCORPIONS

VIII

AND

OTHERS

I N THE p r e s e n t c h a p t e r , f i v e s m a l l o r d e r s o f A r a c h n i d a a r e c o n s i d e r e d w h o s e affinities h a v e l o n g b e e n d i s p u t e d , a n d w h o s e n a t u r a l h i s t o r y a n d w a y o f life a r e still l a r g e l y u n k n o w n . T h e t h r e e o r d e r s T h e l y p h o n i d a , S c h i z o m i d a a n d P h r y n i c h i d a w e r e for m a n y years recognised as sub-orders of the order Pedipalpi and were known as

F I G . 27. Examples of Palpigradi, T h e l y p h o n i d a and Schizomida. (Drawings not to scale.) (After various authors.)

Uropygi Holopeltidia, Uropygi Schizopeltidia and Amblypygi or T a r a n t u l i d a e respectively. H o w e v e r , in 1948, P e t r u n k e v i t c h raised t h e m to ordinal rank and thus they are here treated, although M i l l o t (in G r a s s e , 1 9 4 9 ) * still r e g a r d s t h e S c h i z o m i d a a s a s u b order of the Uropygi. 114

WHIP-SCORPIONS

Order

AND

OTHERS

115

PALPIGRADI

Classification and distribution T h e Palpigradi or Microthelyphonida are tiny creatures resembling, as their alternative n a m e suggests, miniature whip-scorpions. T h e p r o s o m a appears to consist of only two segments w h e n seen from above, the t e r g u m of t h e s e g m e n t bearing the fourth pair of appendages forming part of the carapace; b u t ventrally there are four sternites. T h e chelicerae are t h e only chelate a p p e n d a g e s as t h e p e d i p a l p s are leg-like a n d t e r m i n a t e in a pair of claws. Eyes a r e a b s e n t a n d t h e m o u t h i s a m e r e slit b e t w e e n t h e b a s e s o f t h e chelicerae. T h e a b d o m e n is distinctly segmented a n d is t e r m i n a t e d by a slender flagellum consisting of 15 segments. T h e external reproductive organs of the adults are quite complicated and are borne on the second and third abdominal segments. T h e o r d e r comprises b u t a single family, t h e K o e n e n i i d a e , containing about twenty species in four genera. T h e s e m i n u t e A r a c h nida are widely d i s t r i b u t e d in s o u t h e r n E u r o p e , Africa, A m e r i c a from California to Chile, Siam a n d Australia.

Biology Palpigradi show a m a r k e d avoidance of light a n d are usually found u n d e r half-buried stones and in other d a m p and sheltered places in

company with spring-tails,

myriapods, woodlice and

o t h e r r e t i r i n g a n i m a l s . A f e w s p e c i e s s u c h as Koenenia spelaea, K. draco a n d K . pyrenaica a r e t r o g l o d y t e s a n d h a v e p a r t i c u l a r l y e l o n g a ted limbs with abundant sensory hairs. Micro-whip-scorpions appear to be dependent u p o n moist conditions and are extremely susceptible to desiccation. D u r i n g periods of d r o u g h t they make t h e i r w a y d e e p i n t o t h e soil. P a l p i g r a d i can m o v e w i t h g r e a t agility, t h e i r p e d i p a l p s assisting the other limbs in locomotion while their flagellum is held horizontally b e h i n d t h e b o d y . F r o m t h e s t r u c t u r e of t h e i r chelicerae it is evident that these animals are carnivorous, b u t in view of their m i n u t e size t h e r e c a n b e few o t h e r a n i m a l s small e n o u g h t o b e suitable as prey. W h e e l e r (1900) f o u n d t h a t t h e alimentary canal of Koenenia mirabilis,

a

species occurring

in

Texas,

contained

only

material resembling yolk particles and concluded that it was ad-

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m i r a b l y c o n s t r u c t e d for s u c k i n g t h e e g g s o f o t h e r m i n u t e a r t h r o pods such as S y m p h y l a and Pauropods, b u t this hypothesis has been contested. No predators have yet been recorded, although the same a u t h o r found attached to the ventral surface of the p r o s o m a of certain individuals, an ecto-parasite of u n k n o w n nature, the y o u n g forms of which were u n i - s e g m e n t e d and the adults three-segmented. O f t h e m a t i n g h a b i t s a n d life c y c l e o f t h e P a l p i g r a d i v e r y l i t t l e i s known, t h o u g h it is believed that individuals can recognise one another by scent. In certain species the males appear to o u t n u m b e r t h e f e m a l e s , w h i l e i n o t h e r s , s u c h a s K . mirabilis, m a l e s a r e e x tremely rare.

I n t h e y o u n g s t a g e s o f Prokoenenia wheeleri t h e r e a r e

f e w e r h a i r s , f e w e r c h e l i c e r a l t e e t h a n d f e w e r flagellar s e g m e n t s t h a n in t h e a d u l t s . In c e r t a i n species, a p a i r of eversible sacs h a v e been described on each of the fourth to sixth abdominal sternites. T h e s e vary in n u m b e r and position during growth and m a y represent a primitive and very simple type of breathing organ.

Order

THELYPHONIDA

Classification and distribution In their general form, t h e T h e l y p h o n i d a bear s o m e slight resemb l a n c e t o s c o r p i o n s . T h e y can easily b e d i s t i n g u i s h e d , h o w e v e r , b y t h e f o r m o f t h e p e d i p a l p s , t h e first p a i r o f legs a n d t h e a b d o m e n , which bears a slender caudal appendage from which the n a m e ' w h i p - s c o r p i o n ' is derived. T h e s e strange A r a c h n i d s are generally o f large size, v a r y i n g f r o m 2 5 t o 7 0 m m i n l e n g t h . T h e e l o n g a t e d p r o s o m a is covered by a dorsal carapace and has three thoracic sternites. T h e chelicerae are c o m p o s e d of two segments and are n o t c h e l a t e , w h i l e t h e p e d i p a l p i a r e p o w e r f u l l i m b s o f six s e g m e n t s . T h e i r coxae are fused below t h e m o u t h and have no masticating function, b u t each trochanter has a large semicircular process on its i n n e r s i d e a r m e d

with sharp

teeth.

The

processes can be

pressed against each other a n d are well a d a p t e d to crushing the prey, w h i c h is detected by t h e long a n t e r i o r legs. T h e s e are n o t u s e d for w a l k i n g b u t are h e l d s t r e t c h e d o u t in front as tactile organs. T h e r e is one pair of m e d i a n a n d t h r e e pairs of lateral eyes b u t these are feeble a n d serve only to distinguish b e t w e e n light and darkness.

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T h e a b d o m e n i s c o m p o s e d o f 1 2 s e g m e n t s , o f w h i c h t h e last three are small and annular, forming a p y g i d i u m which bears the long, whip-like telson. Representatives of the order are dispersed somewhat unevenly t h r o u g h o u t t h e t r o p i c s : t h e g e n u s Hypoctonus i s f o u n d i n M a l a y a , Typopeltis i n C o c h i n c h i n a a n d J a p a n , w h i l e Thelyphonus h a s a n I n d o - o c e a n i c distribution. T h e largest species belong to t h e g e n u s Mastigoproctus which, appropriately enough, is exclusively American.

General behaviour T h e T h e l y p h o n i d a are nocturnal predators and usually spend t h e d a y - t i m e h i d i n g u n d e r logs a n d stones or sheltering in their b u r r o w s . A c c o r d i n g t o P e r g a n d e ( 1 8 8 6 ) , Mastigoproctus giganteus a p p e a r s to select a place for d i g g i n g w h e r e t h e r e is already a small d e p r e s s i o n i n t h e soil. W i t h i t s f r o n t legs laid b a c k w a r d s , i t t h e n s c r a p e s a q u a n t i t y o f s a n d i n t o a h e a p w i t h its p o w e r f u l p e d i p a l p s , g r a s p s t h i s w i t h b o t h p e d i p a l p s a n d , m o v i n g b a c k w a r d s for s o m e d i s t a n c e f r o m its b u r r o w , t u r n s r o u n d a n d d e p o s i t s its l o a d . A f t e r p a t t i n g a n d s m o o t h i n g i t s o m e w h a t w i t h o n e o r o t h e r o f its p a l p s , i t r e s t s f o r a m o m e n t w i t h o n l y t h e a n t e n n a e - l i k e first legs p l a y i n g , 'as if in t h o u g h t ' . T h e n , t u r n i n g r o u n d , it retraces its w a y to t h e o p e n i n g , a l w a y s u s i n g its l o n g , s l e n d e r legs c a u t i o u s l y t o d i s cover its p a t h . O n r e a c h i n g t h e b u r r o w i t goes t h r o u g h t h e s a m e performance as before. T h e channel w h e n d u g reaches a length o f 7.5 t o 1 0 c m a n d t a k e s s e v e r a l d a y s t o c o m p l e t e , a s t h e a n i m a l often rests m o t i o n l e s s for h o u r s , or goes o u t on a h u n t i n g expedition. A s m a l l s p e c i e s , Labochirus proboscideus is fairly a b u n d a n t in the low-lying jungles of t h e K a n d y district of Ceylon and is k n o w n to extend to a considerably higher altitude. It is found u n d e r stones a n d logs of decaying w o o d in t h e n e i g h b o u r h o o d of w a t e r c o u r s e s a n d i n o t h e r p a r t s o f t h e j u n g l e w h e r e t h e soil i s t h o r o u g h l y moistened by the rains, b u t does not occur on marshy ground. T h i s s p e c i e s d i g s a b u r r o w f o r itself b e n e a t h t h e s t o n e s u n d e r w h i c h it lives ( G r a v e l e y , 1 9 1 1 , 1 9 1 5 ) . Thelyphonus sepiaris, w h i c h also i n h a b i t s C e y l o n is, h o w e v e r , m u c h b e t t e r a b l e t o w i t h s t a n d d r o u g h t . I t lives i n d r i e r s i t u a t i o n s a n d will s u r v i v e i n a d r y c a g e y

118

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OTHERS

w i t h o u t w a t e r for several weeks w i t h o u t a p p a r e n t discomfort. It a p p e a r s , t o o , t o b e o f a s o m e w h a t less t i m i d d i s p o s i t i o n .

Food and feeding habits W h i p - s c o r p i o n s f e e d chiefly o n i n s e c t s s u c h a s c o c k r o a c h e s , grasshoppers, caterpillars a n d termites, as well as w o r m s a n d slugs, w h i c h they seize quickly w i t h t h e i r s h a r p p e d i p a l p s . A c c o r d i n g t o Graveley (1915) it is almost impossible to observe t h e feeding of t h e n o c t u r n a l C e y l o n s p e c i e s Labochirus proboscideus in its n a t u r a l h a u n t s . E v e n i n c a p t i v i t y i t i s v e r y s h y o f a n y l i g h t after e m e r g i n g f r o m its h i d i n g p l a c e i n s e a r c h o f f o o d , b u t will e a t a s o f t e n a s suitable p r e y is p r o v i d e d . It will accept w i n g e d t e r m i t e s , small locusts a n d roaches, especially w h e n these are disabled, b u t is easily ' f r i g h t e n e d ' b y l a r g e r i n s e c t s a n d b y v e r y a c t i v e o n e s . T h e prey is seized b e t w e e n t h e p e d i p a l p s a n d held b e t w e e n t h e m and t h e p r o s o m a : little u s e a p p e a r s t o b e m a d e o f t h e chelae. T h e chelicerae are provided with b r u s h e s of hairs which m a y serve to filter t h e b l o o d o f t h e d i s m e m b e r e d p r e y . T h e y a r e also u s e d i n c l e a n i n g t h e t e r m i n a l s e g m e n t s o f t h e l e g s . T h e a n t e n n i f o r m first legs a r e g e n e r a l l y h e l d d i r e c t e d f o r w a r d s a n d u s u a l l y s o m e w h a t outwards in an arched position. As the animal moves along they are lowered alternately from t i m e to t i m e until t h e tip c o m e s in c o n t a c t w i t h t h e g r o u n d , a n d t h e n raised again. I t i s n o t k n o w n for certain w h e t h e r this species drinks water as so m a n y others do, b u t it is highly probable. W h e n hunting, t h e l a r g e A m e r i c a n Mastigoproctus giganteus m o v e s s l o w l y a n d c a u t i o u s l y w i t h its f o r m i d a b l e p a l p s o u t s t r e t c h e d a n d o p e n , f e e l i n g a n d t o u c h i n g all o b j e c t s a b o u t i t w i t h i t s s e n s o r y first legs, u n t i l i t d i s c o v e r s a n i n s e c t w h i c h i t g r a s p s . T h e p r e y i s t h e n carried into t h e b u r r o w as a cat carries a m o u s e . A l t e r n a t e striking and grappling m o v e m e n t s of the palps carry the attached prey firmly t o w a r d s t h e chelicerae. T h i s large species has b e e n k n o w n t o eat small frogs a n d t o a d s , b u t o n t h e w h o l e T h e l y p h o n i d a are very timid creatures. Nevertheless, w h e n i n t r o d u c e d to one a n o t h e r in close q u a r t e r s , t h e y e n g a g e in fierce battles in w h i c h one or b o t h of t h e c o n t e s t a n t s is frequently killed or m u t i l a t e d . In c a p t i v i t y , s p e c i m e n s of Thelyphonus skimkewitchii feed r e a d i l y on dead insects, first carefully a n d slowly e x a m i n i n g t h e object

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AND

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119

before taking it up in their chelae. Live insects are rarely caught and they do not a t t e m p t to interfere with beetles and grasshoppers l a r g e r t h a n t h e m s e l v e s . O n t h e o t h e r h a n d a m o t h will b e d e v o u r e d a l m o s t c o m p l e t e l y a n d a d r a g o n f l y e a t e n all b u t t h e w i n g s . B e s i d e s i n s e c t s , t h e y will e a t s m a l l p i e c e s o f o v e r - r i p e b a n a n a ( F l o w e r , 1901). M a r x ( 1 8 9 2 ) f o u n d t h a t v e r y y o u n g M . giganteus w o u l d n o t e a t f l i e s b u t fed o n s m a l l c o c k r o a c h e s . T h e a n t e r i o r legs o f T h e l y p h o n i d a s e r v e a s f e e l e r s : t h e y a r e sensitive n o t only t o t o u c h , b u t also t o chemicals a n d m o i s t u r e . T h e delicacy of their response can be illustrated by breathing on t h e m w h e n they are at r e s t — e v e n this slight s t i m u l u s in t h e case o f Mastigoproctus i s e n o u g h t o s e n d t h e m i n t o r e s t l e s s a c t i v i t y . I f an animal which is aimlessly wandering about should h a p p e n to g e t t h e t i p o f o n e o f t h e s e l i m b s i n t o a d i s h o f w a t e r , i t will i m m e d i a t e l y s w i n g a b o u t , t h r u s t its o t h e r feeler i n t o t h e w a t e r , c l a m b e r h a l f i n t o t h e d i s h a n d b e g i n g r e e d i l y t o s c o o p w a t e r i n t o its m o u t h w i t h its c h e l i c e r a e . I f v e r y d i l u t e h y d r o c h l o r i c a c i d i s s u b s t i t u t e d for w a t e r , a c l e a r - c u t a v o i d a n c e r e a c t i o n i s o b t a i n e d (Patten, 1917). A l t h o u g h it is believed that n o n e of the 'Pedipalps' is poisonous, and no poison glands have been found in any of these orders, M. giganteus i s g r e a t l y f e a r e d i n s o m e o f t h e s o u t h e r n U n i t e d S t a t e s o n a c c o u n t o f its s u p p o s e d l y v e n o m o u s p o w e r s . I t i s g i v e n t h e local n a m e o f ' g r a m p u s ' a n d c a n inflict w o u n d s i n t h e h u m a n s k i n w i t h t h e s h a r p s p i n e s o n its p e d i p a l p s . T h e l y p h o n i d a p r o t e c t t h e m s e l v e s w h e n disturbed by discharging from the anal region a dust-like c l o u d h a v i n g a s t r o n g o d o u r o f a c e t i c a c i d i n s p e c i e s s u c h a s Thelyphonus caudatus, T. sepiaris a n d Hypoctonus oatesi, w h i l e t h e o d o u r of t h e r e p u g n a t o r i a l fluid f r o m T. linganus is s a i d to r e s e m b l e t h a t of c h l o r i n e gas. If a w h i p - s c o r p i o n be m o l e s t e d w i t h a finger b e a r i n g a c u t o r r a w s c r a t c h , t h i s c u t o r s c r a t c h will p r o b a b l y b e g i n t o s m a r t v i o l e n t l y f r o m a c i d e j e c t e d f r o m n e a r t h e b a s e o f t h e tail, b u t this is the worst they can do. T h e n a m e 'vinegarone' b y which T h e l y p h o n i d a are k n o w n i n parts of t h e s o u t h e r n U n i t e d States was originally bestowed on t h e m by settlers from the F r e n c h W e s t Indies, a n d arose from the vinegar-like, acid secretion they e x u d e w h e n a p p r o a c h e d . A blacks m i t h i n 1 8 7 7 i s r e p o r t e d t o h a v e c r u s h e d o n e t o h i s u p p e r left

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breast. Blisters resulted from the acid secretion w h i c h e x t e n d e d over t h e w h o l e of his chest. F l o w e r (1901) also h a d a c u r i o u s exp e r i e n c e w i t h a s p e c i m e n of Thelyphonus skimkewitchii in B a n g k o k . T h i s s p e c i e s i s k n o w n i n S i a m e s e a s ' M e n g p o n - m e n n ' (i.e. s t i n k i n g s c o r p i o n ) : i t i s chiefly t o b e s e e n d u r i n g t h e r a i n y s e a s o n a n d g i v e s off a f a i n t a n d c h a r a c t e r i s t i c s m e l l . H e w r o t e : ' S e e i n g a Thelyphonus o f t h i s s p e c i e s r u n n i n g o n t h e g r o u n d , I p i c k e d i t u p b y t h e c e p h a l o t h o r a x b e t w e e n t h e first finger a n d t h u m b o f m y left h a n d ; i t a t o n c e b e n t its t h r e a d - s h a p e d tail o v e r its b a c k (as a s c o r p i o n d o e s ) a n d also s c r a t c h e d a b o u t m y f i n g e r s w i t h its legs, b u t t h e p i n c e r s d i d n o t t o u c h m e ; I t h o u g h t n o t h i n g o f its tail, e t c . u n t i l I felt a s h a r p p a i n a n d f o u n d t h e a n i m a l had s o m e h o w s t u n g m e . I w e n t s t r a i g h t i n t o m y h o u s e , a n d a l r e a d y t h e first j o i n t o f m y finger w a s v e r y s w o l l e n a n d i n f l a m e d , t h e r e b e i n g a r a p i d l y g r o w ing w h i t e l u m p , a n d t h e rest w a s red; at o n e spot w a s a fresh p u n c t u r e as if a n e e d l e h a d b e e n d r i v e n in, in a h o r i z o n t a l direction, a n d g o n e s o m e little w a y u n d e r t h e skin. After c u t t i n g a n d s q u e e z i n g t h e w o u n d , I p u t m y finger i n t o a s t r o n g s o l u t i o n o f p e r m a n ganate of potash, which at once relieved the pain and stopped the s w e l l i n g , b u t t h e little w o u n d c o n t i n u e d t o s m a r t for s o m e h o u r s . S i n c e t h e n I h a v e b e e n c a r e f u l n e v e r to let a Thelyphonus t o u c h me.' Graveley (1915) h o w e v e r could hardly believe that this sting w a s r e a l l y d u e t o t h e T . skimkewitchii a s h e h a d f r e q u e n t l y h a n d l e d other species w i t h o u t receiving any h a r m a n d it is probable that the animal was b l a m e d unfairly.

Mating habits and life cycle T h e external a p p e a r a n c e of t h e sexes is almost identical a n d they can often be distinguished only by m e a n s of small differences in t h e s t r u c t u r e o f t h e g e n i t a l s t e r n i t e s . T h e c o u r t s h i p o f Thelyphonus sepiaris h a s b e e n d e s c r i b e d b y G r a v e l y ( 1 9 1 5 ) . I t c o n s i s t s o f a curious sexual parade reminiscent of that of t h e scorpions. T h e m a l e g r i p s t h e a n t e n n i f o r m first legs o f t h e f e m a l e i n h i s p e d i p a l p s and holds their extremities in his chelicerae. He t h e n walks backw a r d s , t h e female following. Before long she raises h e r a b d o m e n i n t h e air a n d t h e m a l e c o m m e n c e s t o s t r o k e h e r g e n i t a l s e g m e n t with his elongated front legs. T h e s e are usually passed b e t w e e n

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t h e t h i r d a n d f o u r t h legs o f t h e female, b u t s o m e t i m e s p a s s b e h i n d h e r back legs. T h e i r tips are generally crossed. A t t h e s a m e t i m e the chelae of the male are held o p e n a n d are m o v e d slightly over the dorsal surface of t h e a b d o m e n of t h e female. When

the female

is

pregnant,

she

seeks

shelter.

Thelyphonus

caudatus d i g s a b u r r o w s o m e 4 0 c m i n d e p t h a n d s l i g h t l y e n l a r g e d a t its e x t r e m i t y . T h e e n t r a n c e i s concealed w i t h leaves a n d o t h e r debris. T h e female installs herself at t h e b o t t o m of t h e b u r r o w w h e r e she lays s o m e 20 to 35 yellowish eggs. T h e s e are r e t a i n e d in a t r a n s p a r e n t m e m b r a n e fixed b e n e a t h h e r g e n i t a l s t e r n i t e . T h e y are comparatively large, m e a s u r i n g a b o u t 3 mm in diameter, and are protected from desiccation by a quantity of liquid p r o d u c e d at the time of their emission. T h e f e m a l e r e m a i n s m o t i o n l e s s i n h e r r e t r e a t for s e v e r a l w e e k s . T h e exact incubation period is not k n o w n however, as captive f e m a l e s u s u a l l y d e v o u r t h e i r e g g s . T h e y o u n g free t h e m s e l v e s b y c u t t i n g t h e egg-sac w i t h special spines o n their legs. T h e y are yellowish-white in colour a n d very different in a p p e a r a n c e from the adults. After a while they climb slowly on to their m o t h e r ' s b a c k a n d c l i n g t o h e r o p i s t h o s o m a a n d t h e b a s e o f h e r b a c k legs by m e a n s of t h e adhesive discs w i t h w h i c h their tarsi are furnished. H e r e t h e y r e m a i n u n t i l a f t e r t h e first m o u l t w h e n t h e y a c q u i r e t h e typical form a n d r e s e m b l e m i n i a t u r e adults. N o w t h e y leave their m o t h e r w h o has become so thin and weak as a result of her p r o l o n g e d v i g i l t h a t s h e falls i n t o a s t a t e o f l e t h a r g y f r o m w h i c h s h e does not recover. T h e d e v e l o p m e n t of t h e y o u n g is e x t r e m e l y slow. T h e y u n d e r g o three m o r e moults at yearly intervals before b e c o m i n g adult (Strubell, 1926).

Order

SCHIZOMIDA

Classification and distribution Schizomida, sometimes known as Schizonotidae or Tartaridae, differ f r o m t h e T h e l y p h o n i d a , w i t h w h i c h t h e y a r e o f t e n g r o u p e d , in their small size—they m e a s u r e from 5 to 7 mm in l e n g t h — a n d in having the carapace subdivided into three u n e q u a l divisions, the

propeltidium,

mesopeltidium

and

metapeltidium.

The

last

122

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t w o a r e p r e s e n t a s free t e r g i t e s , a p r i m i t i v e c o n d i t i o n , a n d b e l o n g t o t h e s e g m e n t s b e a r i n g t h e t h i r d a n d f o u r t h p a i r s o f legs r e s p e c tively. M e d i a n eyes are lacking b u t a p a i r of lateral eyes m a y be present w h i c h are reduced to small pale areas of cuticle in some forms. T h e pedipalps are clawless, raptatory, r a t h e r r o b u s t a n d o f t e n a r m e d w i t h c h a r a c t e r i s t i c s p i n e s a n d s e t a e , w h i l e t h e legs o f t h e first p a i r a r e l o n g a n d s l e n d e r a n d u s e d l i k e a n t e n n a e a s t a c t i l e sense organs. T h e a b d o m e n is again c o m p o s e d of twelve segments, t h e last t h r e e b e i n g small, a n n u l a r a n d f o r m i n g a p y g i d i u m w h i c h bears a short caudal appendage m a d e up of one to three, or occasionally four, s e g m e n t s . In t h e males it is often fused into a single r o u n d e d or elongate k n o b . T h r e e g e n e r a o n l y a r e f o u n d i n t h e o r d e r : Schizomus a n d Trithyreus h a v e a w i d e t r o p i c a l a n d e q u a t o r i a l d i s t r i b u t i o n , w h i l e Stenochrus c o n t a i n s a s i n g l e s p e c i e s f r o m P o r t o R i c o . O n e o r t w o s p e c i e s have been described from specimens introduced into hot-houses i n t e m p e r a t e c o u n t r i e s ( C l o u d s l e y - T h o m p s o n , 1949). T h e genera Schizomus a n d Trithyreus c a n b e d i s t i n g u i s h e d b y t h e fact t h a t t h e p o s t e r i o r free s e g m e n t o f t h e p r o s o m a i s d i v i d e d b y a l o n g i t u d i n a l s u t u r e in t h e latter.

Biology Schizomida are absolutely nocturnal in their habits and spend t h e day in d a m p , dark retreats u n d e r leaves, stones a n d logs, or d e e p i n t h e soil w h e r e t h e g r o u n d i s m o i s t . I n C e y l o n , Schizomus crassicaudatus i s f o u n d o n l y u n d e r b r i c k s , e t c . , o n o r c l o s e t o o p e n g r o u n d m o r e o r less s h a d e d b y t r e e s , w h i l e S . vittatus a n d Trithyreus paradenigensis o c c u r a m o n g d e a d l e a v e s e s p e c i a l l y w h e r e t h e s e form a layer of considerable d e p t h and are m a t t e d together by fungal h y p h a e . A l t h o u g h t h e y m a k e no a t t e m p t to drink, t h e y are very susceptible to desiccation. In addition, they are strongly photo-negative a n d are very sensitive to tactile a n d vibratory s t i m u l i . T h e y c a n r u n s u r p r i s i n g l y fast a n d , w h e n t o u c h e d i n front, escape by a s u d d e n j u m p backwards. A p p r o a c h i n g objects a p p e a r often to be p e r c e i v e d — p r o b a b l y by m e a n s of v i b r a t i o n s — before t h e y a r e actually t o u c h e d . T h e elongated front p a i r o f legs, h i g h l y s e n s i t i v e t a c t i l e s e n s e o r g a n s , a r e c a r r i e d aloft a n d n o t u s e d in walking. Little is k n o w n of the biology of Schizomida. T h e y pro-

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b a b l y feed on small a r t h r o p o d s s u c h as Collembola, T h y s a n u r a , S y m p h y l a a n d p o s s i b l y s m a l l a n t s s u c h a s Monomorium pharaonis with which they are frequently associated ( C l o u d s l e y - T h o m p s o n , 1949). In captivity t h e y s h o w cannibalistic proclivities. A n a l stink glands p r o d u c e acetic acid, or similar c o m p o u n d s , w h i c h are u s e d i n d e f e n c e . T h e a n i m a l s h a v e n o f i x e d a b o d e , b u t live i n n a t u r a l h o l e s a n d c r e v i c e s i n t h e soil. M a l e s o f Schizomus latipes h a v e n o t y e t b e e n f o u n d , a l t h o u g h the writer has examined over forty specimens of this species. P o s s i b l y t h e y h a v e a s h o r t life a n d d i e s o o n after m a t i n g . T h e b r e e d i n g h a b i t s o f S c h i z o m i d a a r e little k n o w n a n d a p p e a r t o h a v e b e e n o b s e r v e d o n l y i n t h e c a s e o f S . crassicaudatus. A c c o r d i n g t o G r a v e l e y ( 1 9 1 5 ) a c a p t i v e s p e c i m e n c o n s t r u c t e d a little

F I G . 2 8 . Schizomus crassicaudatus, female guarding her eggs. (After Gravely, 1915.)

c a v i t y a b o u t 1 5 m m b e l o w t h e s u r f a c e o f t h e soil. T h e n e s t h a d n o o p e n i n g a n d t h e Schizomus n e v e r left i t u n t i l t h e e g g s d i s a p p e a r e d t h r e e w e e k s l a t e r . I t w a s l i n e d w i t h soil c e m e n t e d t o g e t h e r . T h e eggs w e r e seven in n u m b e r , flattened at their poles, glistening white and not enclosed in a brood pouch. T h e y were arranged in a spherical mass attached to the a b d o m e n of the female in the region of her genital aperture. As a rule she rested on the side of the nest,

WHIP-SCORPIONS

124

AND

OTHERS

her b o d y b e n t at right angles, with thorax vertical and a b d o m e n horizontal.

Order

PHRYNICHIDA ( = AMBLYPYGI)

Classification and distribution T h e P h r y n i c h i d a differ f r o m o t h e r T e d i p a l p s ' i n l a c k i n g a n y caudal appendage and in having the opisthosoma joined to the cephalothorax by a slender pedicel. T h e carapace is entire with a pair of m e d i a n , a n d t h r e e pairs of lateral eyes, a n d t h e r e are t h r e e

F I G . 2 9 . Phrynichida ( = A m b l y p y g i ) , Charon grayi (after K a n o , 1 9 3 7 ) and Charinus milloti (after Millot, 1 9 4 9 . ) (Body lengths, 2 cm.)

thoracic sternites. T h e pedipalps are stout raptatory organs armed w i t h s t r o n g s p i n e s a n d t e r m i n a t i n g i n a m o v a b l e h o o k . T h e flexible t i p o f t h e l e g s o f t h e first p a i r i s v e r y l o n g a n d c o m p o s e d o f m a n y segments: it is used as a tactile sense organ. W i t h their flattened bodies a n d s o m b r e colours, these animals b e a r a superficial r e s e m blance to crab spiders. T h e a b d o m e n is c o m p o s e d of twelve segm e n t s , t h e last o n e f o r m i n g a p y g i d i u m . T h e size v a r i e s f r o m 8 t o 45 mm in length. T h e d i s t r i b u t i o n of t h e tailless w h i p - s c o r p i o n s is largely c o n ditioned by their water r e q u i r e m e n t s and they are found only in the m o r e h u m i d regions of the tropics and sub-tropics. T h e r e are t w o families, t h e C h a r o n t i d a e a n d t h e T a r a n t u l i d a e . T h e f o r m e r

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125

is c o m p o s e d m o s t l y of smaller, cavernicolous f o r m s having a dist r i b u t i o n i n s o u t h e r n a n d e a s t e r n A s i a a n d t h e Pacific i s l a n d s , while the latter contains three sub-families: the Phrynicinae which are f o u n d i n Africa, I n d i a a n d Ceylon, t h e D a m o n i n a e w h i c h occur in Africa a n d S o u t h America, a n d t h e T a r a n t u l i n a e w h i c h are entirely A m e r i c a n .

Biology A s a l r e a d y m e n t i o n e d , m o s t o f t h e P h r y n i c h i d a live i n h u m i d regions u n d e r logs a n d stones, or in crevices a m o n g rocks, w h e r e t h e y c a n m o v e freely. U n l i k e t h e T h e l y p h o n i d a w h i c h r e s t o n t h e g r o u n d i f t h e o b j e c t u n d e r w h i c h t h e y a r e s h e l t e r i n g i s lifted u p , t h e y are usually t o b e f o u n d clinging t o its u n d e r surface. T h e y will d a r t r o u n d t h e s t o n e b e n e a t h w h i c h t h e y w e r e h i d i n g i n o r d e r to evade capture, b u t seldom try to escape to other stones. T h e tailless w h i p - s c o r p i o n s a r e a g a i n n o c t u r n a l c a r n i v o r e s a n d s p e n d the day hiding in their dark retreats. W h e n suddenly exposed to the light, t h e y do n o t at once flee, b u t freeze into i m m o b i l i t y . If touched, however, they can r u n with surprising speed. T h e i r m o v e m e n t s are s o m e w h a t unpredictable; they usually move sidew a y s like c r a b s p i d e r s , w a l k i n g w i t h t h e six p o s t e r i o r l e g s e x t e n d e d s i d e w a y s w h i l e t h e first p a i r a r e w a v e d like a n t e n n a e a n d explore the surface over which t h e animals are travelling. W h e n , t h e creatures are at rest, however, these legs m a y be slowly rotated, one forwards a n d the other backwards, so as to sweep a large area r o u n d the body. T h e y resemble the writhing of tentacles rather t h a n the m o r e typical m o v e m e n t s of a r t h r o p o d antennae. T h e extreme tip is used to touch the surface which is being investigated and this is done with t a p p i n g m o v e m e n t s of extreme delicacy. T h a n k s to their tarsal pulvilli, t h e C h a r o n t i d a e can climb vertical surfaces a n d r u n a b o u t u n d e r n e a t h t h e ceilings of caves. Charinides bengalensis, for e x a m p l e , c a n c l i m b a v e r t i c a l s h e e t of polished glass a n d even walk across t h e lower surface of a horizontal sheet while t h e T a r a n t u l i d a e , lacking pulvilli, c a n n o t do this. A n u m b e r o f s p e c i e s h a v e b e c o m e d o m e s t i c a t e d a n d live i n d a r k corners of houses in tropical regions. E x a m p l e s are afforded by

126

WHIP-SCORPIONS

AND

OTHERS

Phrynichus ceylonicus in I n d i a , Paracharon caecus in P o r t u g u e s e G u i n e a , Masicodamon allanieus in M o r o c c o a n d Damon medius a n d D . variegatus i n F r e n c h W e s t A f r i c a a n d S o u t h A f r i c a r e s p e c tively. A c c o r d i n g to L a w r e n c e (1949) t h e last species p r o b a b l y o c c u r s i n all b u i l d i n g s i n P i e t e r m a r i t z b u r g i n t h e v e n t i l a t i o n a r e a s b e l o w f l o o r - l e v e l . S p e c i m e n s a r e also v e r y c o m m o n i n o u t h o u s e s , b e n e a t h stored furniture, p a c k i n g cases a n d o t h e r large w o o d e n s t r u c t u r e s w h i c h h a v e b e e n left u n d i s t u r b e d . I n p a r k s a n d g a r d e n s t h e y o f t e n live u n d e r o l d t r e e s t u m p s o r f a l l e n t r u n k s o f t r e e s , while in m o r e open country they are c o m m o n u n d e r stones and in crevices of rocks. It is p r o b a b l e that t h e m o r e domesticated species a r e b e t t e r a b l e t o w i t h s t a n d d r y c o n d i t i o n s , a n d Phrynichus ceylonicus, a s p e c i e s t h a t d o e s n o t b u r r o w , c a n live f o r t w o o r t h r e e w e e k s i n a b a r e c a g e , w h i l e t h e v a r i e t y pusillus a p p e a r s t o b e c o n f i n e d t o m o i s t j u n g l e s of t h e lower hills of C e y l o n a n d dies in a few days if n o t s u p p l i e d w i t h m o i s t soil ( G r a v e l e y , 1 9 1 5 ) . All P h r y n i c h i d a are p r e d a t o r y , feeding on a varied selection of insects such as cockroaches, crickets, grasshoppers, termites, w o o d lice a n d t h e like. T h e y a r e v e r y ' n e r v o u s ' a n i m a l s , a p p r o a c h t h e i r p r e y cautiously a n d t h e n seize it s u d d e n l y , g r i p p i n g it w i t h t h e i r p e d i p a l p s . I n Phrynichus ceylonicus b o t h p a l p s a r e s h o t f o r w a r d i n a n y a t t e m p t t o c a t c h t h e p r e y , b u t c a p t u r e i s u s u a l l y effected between the terminal claw a n d t h e spine near t h e e n d of the tibia of t h e pedipalp on one side only. Spines are arranged to form a very effective ' h a n d ' , t h e t e r m i n a l c l a w b e i n g a p p o s a b l e t o t h e p r o x i m a l of t w o long dorsal spines at t h e distal e n d of t h e tibia a n d t h e spine o n t h e p e n u l t i m a t e j o i n t t o t h e d i s t a l o f t h e s e . A s t h e c l a w a n d all three spines are rigid a n d sharply p o i n t e d it m i g h t be s u p p o s e d that once the prey is grasped, escape w o u l d be quite impossible. T h e strength necessary to retain the prey appears to be lacking, however, a n d even a soft-bodied cricket m a y be attacked u n s u c c e s s f u l l y , t i m e after t i m e . B u t o n c e w i t h i n r e a c h o f t h e c h e l i c e r a e , all c h a n c e o f e s c a p e v a n i s h e s . T h e p r e y , w h i c h f r e q u e n t l y r e m a i n s alive for a t i m e , i s h e l d b e t w e e n t h e pedipalps, often w i t h t h e t e r m i n a l finger e m b e d d e d in its t i s s u e s , w h i l s t p a r t s o f i t a r e s c o o p e d i n t o t h e m o u t h b y t h e terminal segments of the chelicerae w h o s e saw-like a r m a t u r e m a y b e o f u s e i n s e v e r i n g p i e c e s o f s u i t a b l e size f r o m t h e m a i n m a s s .

WHIP-SCORPIONS AND

OTHERS

127

S u c h pieces are masticated by c o m b i n e d vertical a n d longitudinal m o v e m e n t s of these appendages which r u b it against the gnathobases of the pedipalps. U n l i k e Phrynichus ceylonicus, Charinides bengalensis c a p t u r e s its prey b e t w e e n t h e two second appendages as the terminal claw of t h e palp cannot be closed against t h e spines at t h e end of t h e tibia. T h e capture is extremely s u d d e n and can only be observed with difficulty. W h e n d r i n k i n g , d r o p s o f w a t e r a r e c o n v e y e d b y t h e palps to t h e chelicerae, or these organs m a y be inserted directly i n t o t h e w a t e r w h i c h i s t a k e n u p w i t h m o v e m e n t s like t h o s e e m ployed in mastication. T h e a p p e n d a g e s a r e o f t e n c l e a n e d b y t h e c h e l i c e r a e a s i n falses c o r p i o n s a n d g r e a t c a r e i s t a k e n t o k e e p t h e i r t i p s free f r o m d i r t . I n t h e case o f t h e p e d i p a l p s this m a y b e correlated w i t h t h e presence on the terminal segments of an elaborate system of spines, clubbed hairs and pits which m a y perhaps constitute an organ of taste. It is n o t u n l i k e l y t o o t h a t t h e p u l v i l l u s o n t h e t a r s i o f C . bengalensis a n d t h e p a d i n P . ceylonicus m u s t b e k e p t p e r f e c t l y c l e a n i f t h e y a r e t o b e u s e d effectively a n d t a c t i l e o r g a n s m a y b e c o n c e n t r a t e d i n t h i s r e g i o n . T h a t t h e a n t e n n i f o r m first l e g s s h o u l d b e k e p t c l e a n is clearly necessary on a c c o u n t of t h e i r f u n c t i o n as feelers. T h e extent to w h i c h vision is used in seeking prey is uncertain ( G r a v e l e y , 1 9 1 5 ) . P h r y n i c h i d a u s u a l l y fast f o r s e v e r a l d a y s a f t e r each meal. T h e s e c o n d a r y sex differences of t h e P h r y n i c h i d a are e x t r e m e l y s m a l l , a n d i n m o s t s p e c i e s t h e r e i s little t o d i s t i n g u i s h t h e m a l e s f r o m t h e f e m a l e s . I n Charon grayi, h o w e v e r , w h i c h h a s a w i d e d i s tribution in eastern Asia, t h e f e m u r of t h e pedipalp in t h e male i s l o n g e r t h a n t h o s e o f t h e s e c o n d , t h i r d a n d f o u r t h w a l k i n g legs, while in the female it is shorter. M a t i n g habits have not yet been observed in any of t h e P h r y n i c h i d a . D u r i n g t h e b r e e d i n g season, the females of t h e species carry an egg sac on their a b d o m e n s . T h e n u m b e r of eggs m a y vary from 7 to 80 or m o r e , d e p e n d i n g on t h e size o f t h e m o t h e r ( T a k a s h i m a , 1 9 5 0 ) . T h e e g g s a r e q u i t e l a r g e , m e a s u r i n g 2 t o 3 m m i n d i a m e t e r a n d p r o b a b l y i n all s p e c i e s are carried by t h e m o t h e r in a capsule attached to t h e ventral surface o f h e r a b d o m e n . B o t h e g g s a n d e m b r y o s a r e c l o s e l y p a c k e d i n t h i s e g g sac, t h e p r e s s u r e i n t h e c o n f i n e d a r e a g i v i n g a s u b a n g u l a r

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outline t o s o m e o f t h e c o n t i g u o u s eggs. T h e c o n t e n t s o f t h e sac are n o t a r r a n g e d in regular rows, either longitudinally or t r a n s v e r s e l y , b u t i n t h e S o u t h A f r i c a n Damon variegatus a r e t w o l a y e r s d e e p ( L a w r e n c e , 1949). According to

Graveley (1915)

all t h e

Indian and Ceylonese

species appear to b r e e d at a b o u t the same t i m e of year.

The

e m b r y o s are carried u n d e r t h e a b d o m e n w h e r e they are s u p p o r t e d b y a m e m b r a n e s e c r e t e d for t h e p u r p o s e . T h e n u m b e r o f e g g s varies

from

15

to

60

or

more.

Charinides bengalensis

breeds

in

July a n d A u g u s t a n d s o m e t i m e s earlier. T h e newly h a t c h e d y o u n g are entirely w h i t e : like y o u n g s c o r p i o n s t h e y cling t o t h e dorsal s u r f a c e a n d t h e s i d e s o f t h e a b d o m e n o f t h e i r m o t h e r u n t i l after t h e i r f i r s t m o u l t . I m m e d i a t e l y after t h e f i r s t m o u l t t h e c a r a p a c e i s a little over 1 mm in w i d t h , b u t d u r i n g t h e first y e a r its w i d t h is doubled. D u r i n g the second year it increases to about 2.5 mm and d u r i n g t h e t h i r d t o 3 m m o r m o r e . T h e a d u l t size i s a p p r o x i m a t e l y 3.5 m m .

F I G . 3 0 Ricinulei. (After Berland, 1 9 5 5 , and Millot, 1 9 4 9 . )

Order

RICINULEI

T h e Ricinulei or P o d o g o n a t a are small Arachnids, 4 to 10 mm in length with a short massive b o d y a n d a remarkably hard, thick and deeply granulated integument. T h e prosoma is covered by a

W H I P - S C O R P I O N S

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n o n - s e g m e n t e d carapace at t h e front edge of w h i c h is a mobile h o o d o r c u c u l l u s w h i c h fits d o w n t i g h t l y o v e r t h e c h e l i c e r a e . N o t r u e eyes are present, b u t vague pale spots on each side of t h e carap a c e m a y w e l l r e p r e s e n t v e s t i g i a l e y e s . T h e p e d i p a l p s a r e o f six s e g m e n t s a n d are r e m a r k a b l e in t h a t their coxal s e g m e n t s are fused in the mid-line: they are chelate as are the t w o - s e g m e n t e d chelicerae. T h e p r o s o m a is j o i n e d to t h e opisthosoma by a n a r r o w pedicel, b u t this is h i d d e n from view by expansions of t h e base of t h e a b d o m e n w h i c h fits v e r y c l o s e l y a g a i n s t t h e p r o s o m a , t h e j u n c t u r e f o r m i n g a coupling device. T h e living animal is able to disengage the carapace from the a b d o m e n so that t h e genital orifice i s e x p o s e d d u r i n g m a t i n g a n d o v i p o s i t i o n . T h e o p i s t h o s o m a i s c o m p o s e d o f n i n e s e g m e n t s o f w h i c h o n l y t h e first f o u r a r e w e l l d e n n e d , w h i l e t h e last t h r e e f o r m a small p y g i d i u m . T h e legs are short and stout, the third pair being modified as copulatory organs in m a t u r e males, a character otherwise found only in certain mites. T h e o r d e r is limited to a single family, t h e Ricinoididae (or C r y p t o s t e m m i d a e ) a n d c o n t a i n s o n l y t w o g e n e r a , Ricinoides a n d Cryptocellus. O f t h e s e t h e first i s r e p r e s e n t e d b y six W e s t A f r i c a n species, t h e second by seven species having a distribution from T e x a s to t h e A m a z o n basin. After t h e discovery in 1838, of t h e first s p e c i m e n s o f t h e s e v e r y r a r e a n i m a l s , o n l y 3 2 w e r e f o u n d u n t i l , n e a r l y a c e n t u r y l a t e r i n t h e B r i t i s h C a m e r o o n s n o less t h a n 3 1 7 s p e c i m e n s o f Ricinoides sjostedti w e r e o b t a i n e d . I t i s n o t e n tirely surprising, therefore, t h a t t h e biology of these peculiar creatures is practically u n k n o w n , although specimens have been k e p t alive a t t h e B r i t i s h M u s e u m ( N a t u r a l H i s t o r y ) f o r o v e r a y e a r ( F i n n e g a n , 1935). R i c i n u l e i a p p e a r g e n e r a l l y t o live u n d e r d a m p , fallen l e a v e s i n equatorial forests. Certain M e x i c a n species are cavernicolous a n d s p e c i m e n s of Cryptocellus dorotheae h a v e b e e n f o u n d s h o r t l y after r a i n s i n t h e s a n d y soil o f t h e R i o G r a n d e R i v e r V a l l e y . T h e y w e r e taken f r o m u n d e r slabs of concrete, h e a v y sheet i r o n a n d roofing material w h i c h h a d n o t b e e n d i s t u r b e d for several y e a r s . T h e creatures are very sluggish a n d h a v e a slow a n d c u r i o u s gait. T h e y m o v e w i t h c o n s i d e r a b l e d e l i b e r a t i o n a n d s e e m t o feel t h e i r w a y a l o n g w i t h t h e i r f r o n t p a i r o f legs, t h e i r m o v e m e n t s r e s e m bling those of a tick crawling over t h e g r o u n d , S u d d e n illuminI

S.S.C.M.

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a t i o n o r s l i g h t v i b r a t i o n s o f t h e soil s e n d t h e m i n t o a c a t a l e p t i c state. N o t h i n g i s k n o w n o f t h e life h i s t o r y a n d d e v e l o p m e n t o f t h e s e r a r e A r a c h n i d s b e y o n d t h e fact t h a t t h e y a r e o v i p a r o u s , t h e e g g s h a t c h i n g into a six-legged larval f o r m as in Acari.

BIBLIOGRAPHY Identification E W I N G , H. E. ( 1 9 2 9 ) A synopsis of the American Arachnids of the primitive order Ricinulei. Ann. Ent. Soc. Amer., 2 2 , 5 8 3 - 6 0 0 . GRAVELEY, F . H . ( 1 9 1 6 ) T h e evolution and distribution o f the I n d o Australian T h e l y p h o n i d a e , with notes on the distinctive characters of various species. Rec. Ind. Mus., 1 2 , 5 9 - 8 9 . KASTNER, A . ( 1 9 3 2 ) P e d i p a l p i Latreille in KUKENTHAL, W . a n d KRUMBACH,

T. Handbuch der Zoologie, Berlin, 3, ( 2 ) , 1 - 7 6 . ( 1 9 3 2 ) Palpigradi T h o r e l l . Ibid., 7 7 - 9 8 . ( 1 9 3 2 ) Ricinulei T h o r e l l . Ibid., 9 9 - 1 1 6 . KRAEPELIN, K . ( 1 8 9 9 ) S c o r p i o n e s u n d P e d i p a l p i . Das Tierreich, 8 , 1 - 2 6 5 . ( 1 9 0 1 ) P a l p i g r a d i . Ibid., 1 2 , 1 - 3 .

POCOCK, R. I. ( 1 9 0 0 ) The Fauna of British India, including Ceylon and Burma. Arachnida. L o n d o n . ROEWER, C. F. ( 1 9 3 4 ) Palpigradi in H. G. BRONN'S Klass. Ordn. Tierreichs, 5, IV (8), 6 4 0 - 7 2 3 . WERNER, F . ( 1 9 3 5 ) P e d i p a l p i . Ibid., 3 1 7 - 4 9 0 .

Biology CLOUDSLEY-THOMPSON, J . L . ( 1 9 4 9 ) Notes o n Arachnida, 1 1 . — S c h i zomida in E n g l a n d . Ent. Mon. Mag., 8 5 , 2 6 1 . FINNEGAN, S. ( 1 9 3 5 ) Rarity of the archaic Arachnids Podogona (Ricinulei). Nature, Lond., 1 3 6 , 1 8 6 . FLOWER, S. S. ( 1 9 0 1 ) Notes on the millipedes, centipedes, scorpions etc of the Malay Peninsula and Siam. J. Straits Brit. Asiat. Soc, 3 6 , 1 - 4 8 . GRAVELEY, F. H. ( 1 9 1 1 ) Pedipalpi of Ceylon. Spolia Zeylandica, 7, 4 3 - 7 . ( 1 9 1 5 ) N o t e s on the habits of Indian insects, myriapods and arachnids. Rec. Ind. Mus., 1 1 , 4 8 3 - 5 3 9 .

LAWRENCE, R. F. ( 1 9 4 9 ) Notes on the whip-scorpions (Pedipalpi) of S o u t h Africa. Trans. Roy. Soc. S. Africa, 3 2 , 2 7 5 - 8 5 . MARX, G. ( 1 8 9 2 ) Contributions to the life-history of Arachnida. Proc. Ent. Soc.

Wash., 2, 2 5 2 - 4 .

PATTEN, B. M. ( 1 9 1 7 ) Reactions of the whip-tail scorpion to light. J. Exp. Zool, 2 3 , 2 5 1 - 7 5 .

PERGANDE, T. ( 1 8 8 6 ) [Habits of a specimen of Thelyphonus}. Proc. Ent. Soc.

Wash.,

1,42-4.

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STRUBELL, A. ( 1 9 2 6 ) Thelyphonus caudatus L., Eine biologische Skizze. Verh. Nat. Ver. Bonn., 8 2 , 3 0 1 - 1 4 . TAKASHIMA, H. ( 1 9 5 0 ) Notes on Amblypygi found in territories adjacent to Japan. Pacific Sci., 4, 3 3 6 - 8 . WHEELER, W. M. ( 1 9 0 0 ) A singular Arachnid (Koenenia mirabilis Grassi) occurring in T e x a s . Amer. Nat., 3 4 , 8 3 7 - 5 0 .

CHAPTER

IX

HARVEST-SPIDERS Classification and distribution T h e order Opiliones or Phalangidea includes the harvestmen, t h e m a j o r i t y o f w h i c h c a n b e r e c o g n i s e d b y t h e i r l o n g , s l e n d e r legs and segmented abdomen which is joined to the cephalothorax across t h e whole b r e a d t h and not by a n a r r o w pedicel as in spiders. T h e c e p h a l o t h o r a x i s c o m p o s e d o f six s e g m e n t s a n d i s o f t e n s e p a r a t e d f r o m t h e a b d o m e n b y a fairly d e e p g r o o v e . T h e c a r a p a c e i s usually s m o o t h and, in m o s t species, bears t w o eyes, a l t h o u g h these m a y occasionally be absent. T h e eyes are nearly always situated on a p r o m i n e n t ocular tubercle near the middle of the cephalothorax, one looking out at each side. N e a r t h e anterior m a r g i n of t h e p r o s o m a o p p o s i t e t h e a t t a c h m e n t o f t h e first p a i r o f l e g s t h e r e a r e t w o small openings leading to a pair of odoriferous glands: t h e glands themselves can, in s o m e species, be seen t h r o u g h the carapace w h e n t h e y l o o k like a n e x t r a p a i r o f e y e s . T h e c h e l i c e r a e a r e t h r e e s e g m e n t e d , t h e last t w o s e g m e n t s f o r m i n g p i n c e r s , w h i l e t h e p e d i p a l p s a r e o f six s e g m e n t s . T h e i r c o x a e b e a r g n a t h o b a s e s w h i c h form p a r t of a c o m p l e x m o u t h . T h e pedipalps are short a n d leglike; t h e y a r e chiefly s e n s o r y o r g a n s f o r u s e i n c o n t a c t w i t h o b j e c t s c l o s e t o t h e b o d y , a n d t h e y also h e l p i n g r a s p i n g t h e f o o d a n d bringing it to the jaws. In some genera they e n d in a claw which m a y be s m o o t h or toothed, b u t in others no claw is found. T h e bodies of harvest-spiders are usually covered with spines, pointed tubercles a n d bristles. T h e r e is often a d o u b l e r o w along the centre of the ocular tubercle and in some genera of Palpatores (see b e l o w ) a g r o u p f o r m s a t r i d e n t i n t h e m i d d l e o f t h e f o r e - e d g e of the cephalothorax and is an important diagnostic character. On t h e u n d e r s i d e of t h e b o d y t h e coxae of t h e legs almost m e e t in t h e middle so that there is no s t e r n u m as in spiders. 132

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T h e a b d o m e n is composed of ten segments, but these can be distinguished only in the most primitive sub-order, the C y p h o p h t h a l m i : in other Opiliones not m o r e t h a n nine tergites are a p p a r e n t . A u n i q u e p e c u l i a r i t y o f h a r v e s t - s p i d e r s lies i n t h e fact that t h e tergite a n d sternite of t h e same segment are not always placed vertically opposite one another. T h e a n u s has b e e n b r o u g h t f o r w a r d v e n t r a l l y s o t h a t t h e t e r g i t e p r i m i t i v e l y a b o v e i t n o w lies behind, and the sternite primitively below is n o w placed i m m e d iately i n f r o n t . C o n s e q u e n t l y m o s t O p i l i o n e s h a v e s h o r t a n d r o u n d e d bodies. T h e majority of species have cryptic, or concealing coloration, b e i n g usually b r o w n or grey, often w i t h a central dark b a n d w h i c h serves to break up the outline of the animal's s h a p e a n d r e n d e r s i t i n c o n s p i c u o u s a g a i n s t its n a t u r a l b a c k g r o u n d .

F I G . 3 1 . Examples of harvest-spider families: 1. (Suborder) Cyp h o p h t h a l m i , 2 . Phalangodidae, 3 . Gonyleptidae, 4 . Trogulidae, 5 . N e m a s t o m i d a e , 6 . Ischyropsalidae, 7 . Phalangiidae. (Drawings not to scale.) (After various authors.)

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T h e size o f t h e b o d y v a r i e s f r o m a b o u t 1 t o 2 0 m m i n l e n g t h , b u t the majority are between 5 and 10 mm long. T h e Opiliones are divided into three s u b - o r d e r s , of which the C y p h o p h t h a l m i is t h e m o s t primitive. It comprises s o m e forty mite-like species varying in length between 1 and 3 m m , with s h o r t legs a n d r e p u g n a t o r i a l g l a n d s o p e n i n g a t t h e e n d s o f l a t e r a l prosomatic tubercles. T h e genitalia are not covered by an operc u l u m but the b o d y is protected by a shield resulting from the fusion of t h e cephalothorax a n d t h e a b d o m i n a l tergites, excepting t h e last. T h e a b d o m i n a l s t e r n i t e s a r e also f u s e d i n a s i m i l a r m a n n e r a n d eyes are often absent. T h e Cyphophthalmi have a very discontinuous distribution, species occurring in Corsica, Dalmatia, central F r a n c e , parts of tropical Africa, Ceylon, J a p a n , t h e E a s t I n d i e s a n d t h e U n i t e d States of Florida and Oregon. T h e y are generally to be found in h u m i d s i t u a t i o n s u n d e r m o r e o r less d e e p l y b u r i e d s t o n e s . T h e g e n u s Siro is r e p r e s e n t e d in F r a n c e by S. rubens, a s p e c i e s first d i s c o v e r e d b y L a t r e i l l e a t B r i v e a n d l o n g m i s t a k e n for a m i t e u n t i l E . S i m o n e s t a b l i s h e d its t r u e n a t u r e . Siro duricorius i s k n o w n f r o m t h e c a v e s o f C a r n i o l a i n Y u g o s l a v i a a n d t h e r e l a t e d Parasiro corsicus f r o m t h e n e i g h b o u r h o o d o f P o r t o V e c c h i o i n C o r s i c a . T h e g e n u s Stylocellus o c c u r s in t h e E a s t I n d i e s , Ogivea a n d Paragovia i n E q u a t o r i a l A f r i c a a n d Purcellia o n t h e C a p e o f G o o d H o p e , w h e r e t h e g e n u s Speleosiro i s r e p r e s e n t e d b y a s i n g l e t r o g l o d y t i c species. T h e second sub-order, the Laniatores, is more important than t h e p r e c e d i n g o n e a n d s o m e 1,500 s p e c i e s h a v e s o f a r b e e n d e scribed, principally from southern latitudes. T h e y are characterised b y great d e v e l o p m e n t o f t h e p e d i p a l p s w h i c h are a r m e d w i t h s t o u t s p i n e s a n d s t r o n g c l a w s a n d a r e u s e d a s r a p t a t o r y o r g a n s for t h e c a p t u r e of prey. T h e Laniatores have an almost exclusively tropical d i s t r i b u t i o n , o n e family, t h e P h a l a n g o d i d a e , h a v i n g a few r e p r e s e n t a t i v e s i n E u r o p e (Scotolemon s p p . ) a n d i n N o r t h A m e r i c a (Phalangodes s p p . ) . T h e s e a r e t r o g l o d y t e s i n h a b i t i n g , a m o n g s t others, the M a m m o t h Cave in K e n t u c k y . In addition, several g e n e r a o c c u r i n t h e t r o p i c s o f t h e O l d W o r l d , A u s t r a l i a , t h e Pacific i s l a n d s a n d m o s t o f S o u t h A m e r i c a . T h e r e m a i n i n g families o f Laniatores are entirely tropical: the O n c o p o d i d a e are found in

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I n d i a , t h e A s s a m i i d a e i n I n d i a , a n d o t h e r p a r t s o f A s i a a n d Africa excluding Madagascar, the Cosmetidae in the southern United States and the Triaeonychidae in Madagascar, Australia and America. T h e largest family is t h e G o n y l e p t i d a e w h i c h is almost e n t i r e l y c o n f i n e d t o S o u t h A m e r i c a w h e r e s p e c i e s live i n d a m p f o r e s t s u n d e r s t o n e s a n d fallen t r e e s . T h e y h a v e p a r t i c u l a r l y l a r g e , d e f e n s i v e s p i n e s o n t h e last p a i r o f l e g s . T h e most important sub-order of the Opiliones is the Palpat o r e s , t o w h i c h all t h e B r i t i s h s p e c i e s b e l o n g . F o u r f a m i l i e s a r e known, of which the T r o g u l i d a e are considered to be the most primitive. T h e s e are sluggish, short-legged, ground-living species to be found a m o n g grass roots, moss and even m u d in chalky districts o f E u r o p e , Asia M i n o r , N o r t h Africa a n d N o r t h A m e r i c a . T h e fore e d g e o f t h e p r o s o m a f o r m s a b i f u r c a t e d h o o d c o v e r i n g t h e m o u t h parts, there is no ocular tubercle and the body is dark coloured and habitually covered with particles of dirt and earth w h i c h r e n d e r t h e a n i m a l s e x t r e m e l y difficult t o s e e . T h e N e m a s t o m i d a e a r e also s m a l l , s h o r t - l e g g e d , d a r k , g r o u n d - l i v i n g f o r m s usually f o u n d a m o n g m o s s a n d d e a d leaves while t h e I s c h y r o p s a l i d a e a r e a s m a l l f a m i l y l i m i t e d t o c e n t r a l E u r o p e , w h e r e t h e y live i n d a m p m o s s in woods, m o u n t a i n torrents a n d t h e caves of t h e P y r e n e e s . T h e l a r g e s t f a m i l y i s t h e P h a l a n g i i d a e w h i c h i n c l u d e s all t h e w e l l - k n o w n long-legged h a r v e s t m e n of E u r o p e , N o r t h Africa and. N o r t h America. T h e s e animals have typically r o u n d e d bodies, the p a l p a l t a r s u s i s l o n g e r t h a n t h e t i b i a a n d its c l a w i s w e l l d e v e l o p e d . T h e y a r e t o b e f o u n d a m o n g l i t t e r a n d fallen l e a v e s o n t h e g r o u n d , on t h e t r u n k s of trees a n d in vegetation ( T o d d , 1949). T h e distribution of harvest-spiders in t h e British Isles has b e e n described by Bristowe (1949) a n d Sankey (1949b), while t h e E u r o pean forms have been studied by S t i p p e r b e r g e r (1928).

General behaviour T h e n a m e Opilio m e a n s , in L a t i n , a ' s h e p h e r d ' a n d m a y refer to t h e fact t h a t i n s o m e c o u n t r i e s s h e p h e r d s w a l k a b o u t o n s t i l t s , t h e b e t t e r t o c o u n t t h e i r flocks. I n o u r o w n l a n d h a r v e s t m e n w e r e k n o w n as ' s h e p h e r d spiders' four centuries ago, b u t T. Muffett ( 1 6 3 4 ) in h i s Theatre of Insects e x p l a i n e d t h i s by s a y i n g ' t h e 1

1

Insectorum sive minimorum animalium

theatrum. L o n d o n .

HARVEST-SPIDERS E n g l i s h call i t S h e p h e r d e i t h e r b e c a u s e i t i s p l e a s e d w i t h t h e C o m p a n y o f S h e e p o r b e c a u s e S h e p h e r d s t h i n k t h o s e fields t h a t a r e full of t h e m to be e o o d w h o l e s o m e S h e e p - p a s t u r e . . .' H o o k e (1658) i n h i s Micrographia g a v e t h e a l t e r n a t i v e n a m e s ' s h e p h e r d o r c a r t e r spider' and Bristowe (1949) quotes an old Essex superstition that i t w a s u n l u c k y p u r p o s e l y t o kill a h a r v e s t m a n b e c a u s e o f t h e belief t h a t t h e s e c r e a t u r e s h e l p e d f a r m e r s w i t h t h e s c y t h e , r a k e a n d sickle w h i c h they w e r e alleged to possess. In F r a n c e they are k n o w n as faucheurs ( r e a p e r s ) b e c a u s e t h e y g i v e t h e a p p e a r a n c e o f r e a p i n g a s t h e v walk, while t h e G e r m a n Weber-knechte m a y refer to t h e j e r k y m o v e m e n t s m a d e b y t h e legs o f t h e s e a n i m a l s after t h e y h a v e become detached from the bodies of their owners. O n l v t w o s p e c i e s , Phalangium opilio a n d Leiobunum rotundum, a r e a t all c o n s p i c u o u s i n o u r fields a n d a r e m o s t n o t i c e a b l e a t t h e harvest season, w h e n t h e y r e a c h maturity-. C o n s e q u e n t l y these, p a r t i c u l a r l y P . opilio, a r e p r o b a b l y r e s p o n s i b l e for t h e n a m e ' h a r v e s t m e n ' . B r i s t o w e ( 1 9 4 9 ) b e l i e v e s t h a t 'Phalangium" w h i c h i s of eighteenth century origin, is derived from the Greek 'phalanx' and that t h e h a r v e s t - s p i d e r was likened to a formidable soldier in a phalanx because it was confused with the very poisonous ' M a l m i g n a t t e ' , Latrodectus 13-guttatus, 2, r e l a t i v e of t h e n o t o r i o u s ' b l a c k - w i d o w ' s p i d e r w h i c h o c c a s i o n a l l y b i t e s r e a p e r s i n t h e fields o f southern E u r o p e . On the other hand, Sankey (1949b) has suggested t h a t t h e n a m e m a y b e d e r i v e d f r o m phalange, a h e a d o r t o e s e g m e n t , for l o n g l i m b s a r e o n e o f t h e m o s t c o n s p i c u o u s f e a t u r e s o f most harvest-spiders. T h e biology of the Laniatores, so c o m m o n in tropical regions, is p r a c t i c a l l y u n k n o w n b e y o n d t h e fact t h a t t h e y l e a d r e t i r i n g lives i n d a m p f o r e s t s b e n e a t h b a r k , fallen t r e e s a n d m o s s , a n d o c c a s i o n a l l y i n caves. In N e w Zealand t h e h a r v e s t m e n of the s u b - o r d e r Laniatores are a l w a y s f o u n d i n f o r e s t e d c o u n t r y o r i n a r e a s w h i c h h a v e i n r e c e n t t i m e s b e e n f o r e s t e d b u t w h e r e t h e b u s h h a s b e e n felled a n d c l e a r e d , l e a v i n g d e c a y i n g logs a n d s m a l l p o c k e t s o f f o r e s t w h i c h p r o v i d e a favourable habitat. T h e great majority of species r e q u i r e a high and even relative h u m i d i t y . T h e y are n o c t u r n a l and are to be f o u n d d u r i n g t h e d a y s h e l t e r i n g b e n e a t h logs a n d s t o n e s , i n t h e d e b r i s o n t h e f o r e s t floor, i n m o s s g r o w i n g i n s i m i l a r s i t u a t i o n s o r o n t h e t r u n k s a n d b r a n c h e s o f t r e e s i n t h e w e t t e r a r e a s . T h e leaf-

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m o u l d fauna consists mainly of t h e smaller species of N u n i a and s p e c i e s of Pristobunus. T h e s p e c i e s of Synthetonychia are r o u n d o n l y in l e a f - m o u l d a n d m o s s , w h i l e Muscicola pitta a n d Algidia viridata a p p e a r t o b e r e s t r i c t e d t o m o s s a n d a r e d i s t i n g u i s h e d b y their striking green coloration. No altitudinal speciation has been o b s e r v e d : o n l y a few s p e c i e s h a v e b e e n f o u n d a b o v e b u s h - l i n e a n d then only in small n u m b e r s in sub-alpine scrub. T h e y are m o r e n u m e r o u s n e a r sea level a n d p r o g r e s s i v e l y d i m i n i s h i n n u m b e r a t h i g h e r a l t i t u d e s . V e r y f e w a r e e n c o u n t e r e d a b o v e 2 . 5 0 0 ft. a n d o n l y Palpatores are f o u n d u n d e r alpine conditions ( F o r s t e r . 1954). T h e C y p h o p h t h a l m i a r e r a r e a n d e q u a l l y o b s c u r e , l i v i n g like m i t e s u n d e r stones, etc. in d a m p places, a n d are usually to be found only after r a i n h a s fallen. T h e o n l y s u b - o r d e r w h o s e b i o l o g y i s k n o w n a t all a d e q u a t e l y i s t h e P a l p a t o r e s . t h a n k s l a r g e l y t o t h e w o r k o f British naturalists. T h e T r o g u l i d a e a n d N e m a s t o m i d a e are inhabitants of the surface l a y e r s o f t h e soil a n d a p p e a r t o r e q u i r e a b a l a n c e d m i c r o c l i m a t e a s t h e y a r e p a r t i c u l a r l y s u s c e p t i b l e t o d e s i c c a t i o n . T h e first n a m e d family is conrined to chalky districts w h e r e t h e y rind t h e snails on w h i c h t h e y feed, b u t m e m b e r s o f b o t h f a m i l i e s a v o i d t h e l i g h t a n d c r a w l s l o w l y i n t o c o v e r i f e x p o s e d . V i b r a t i o n s o f t h e soil u s u a l l y i n d u c e a d e a t h - f e i g n i n g reflex. T h e B r i t i s h s p e c i e s Tropdus r n carinatus a n d Anelasmocephalus cambridgei a r e r a r e f o r m s r o u n d o n l y b y c a r e f u l s e a r c h i n g i n s o u t h e r n c o u n t i e s , b u t N e m a s t o m a lugubre a n d N . chrysomelas a r e q u i t e c o m m o n a n d w i d e l y d i s t r i b u t e d . ' T h e s t u d y of h a r v e s t m e n is a s t u d y of legs,' w r o t e Savon* 1938) a n d legs a r e i n d e e d a f e a t u r e t h a t i s b o u n d t o i m p r e s s a n y o n e o b serving the Phalangiidae. Although autotomy is frequently practised as an escape reaction, no regeneration of the limbs occurs in h a r v e s t m e n . A m i n i m u m o f f o u r legs, p r o v i d e d o n e o r t h e s e c o n d p a i r r e m a i n s , e n a b l e s m o s t s p e c i e s t o l e a d a m o r e o r less n o r m a l life, b u t i f b o t h o f t h e s e c o n d p a i r a r e lost d e a t h s o o n f o l l o w s . T h e s e s e c o n d legs s e e m t o b e u s e d for t a c t i l e p u r p o s e s a n d p o s s i b l y for s m e l l r e c e p t i o n a n d t h e s e n s o r y h a i r s o n t h e first legs m a y also serve t h e latter p u r p o s e . It is interesting to note that the longlegged Phalangiidae possess two small spiracles on t h e tibia of each leg i n a d d i t i o n t o t h e u s u a l s p i r a c l e s w h i c h o p e n n e a r t h e c o x a e of t h e f o u r t h p a i r of legs ( S a n k e y , 194°>b).

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Like o t h e r A r a c h n i d s , h a r v e s t m e n carefully clean their l i m b s . A leg i s h e l d i n t h e c h e l i c e r a e w h i c h o p e n a n d s h u t a s t h e l o n g s e g m e n t s are pulled t h r o u g h t h e m . By the t i m e the tarsus is reached, t h e leg i s b e n t a l m o s t i n t o a c i r c l e , a n d finally s h o o t s o u t like a n u n b e n t spring. T h e pedipalps are cleaned in the same way and the chelicerae are w a s h e d while drinking. A few species are able to stridulate b u t t h e s o u n d is p r o b a b l y too faint to be audible to t h e h u m a n ear. T o t h e l y r i f o r m o r g a n s — b u t t o n - s h a p e d slits f o u n d s i n g l y o r together in a lyre-shaped g r o u p — h a v e been attributed the function of smell. T h e y occur especially on t h e first s e g m e n t s of t h e chelicerae a n d on t h e coxae of t h e legs. E a c h is s u p p l i e d w i t h a n e r v e and they m a y well be p r o p r i o c e p t o r s analagous to t h e chordotonal sensillae of insects w h i c h serve to detect strains a n d stresses in t h e integument. H a r v e s t m e n respond to touch and chemical stimuli, a n d b u n c h t o g e t h e r i n captivity. T h e i r eyes are simple a n d p r o b a b l y s e r v e m a i n l y for d i s t i n g u i s h i n g l i g h t f r o m d a r k n e s s . I t i s doubtful if there is m u c h form-vision in any of the Opiliones b u t some perception of m o v e m e n t may occur. Although harvestspiders are susceptible to changes of t e m p e r a t u r e and humidity, the organs w h i c h serve these functions are not yet k n o w n . T o d d (1949) has w o r k e d o u t t h e t e m p e r a t u r e a n d h u m i d i t y preferences for s o m e B r i t i s h s p e c i e s a n d f o u n d a s t r o n g c o r r e l a t i o n b e t w e e n t h e h u m i d i t y preference of the species tested in the laboratory and their stratification in oak w o o d l a n d . At t h e s a m e t i m e it was n o t e d that those species with the highest t e m p e r a t u r e preference app e a r e d t o h a v e a s o u t h e r n d i s t r i b u t i o n o r t o live i n d r i e r o r w a r m e r habitats than others. British harvest-spiders can be divided into various groups according to their vertical distribution. T h u s t h e species w h i c h u s u a l l y live o n t h e g r o u n d u n d e r s t o n e s , logs a n d i n m o s s o r p l a n t d e b r i s i n c l u d e t h o s e w i t h s h o r t legs a n d s m a l l e y e s s u c h a s Trogulus tricarinatus, Anelasmocephalus cambridgei, Nemastoma lugubre, N. chrysomelas, Homalenotus quadridentatus, Oligolophus meadii a n d Opilio saxatilis. T h e s e c o n d g r o u p i n c l u d e s s p e c i e s w h i c h live mainly a m o n g s t low vegetation (the field layer) of grass a n d o t h e r herbaceous plants, b u t w h o s e y o u n g stages occur on the g r o u n d , s u c h as Nelima silvatica, Leiobunum blackwalli, L. rotundum, Mito-

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pus morio, Oligolophus tridens, Lacinius ephippiatus, Platybunus triangularis, Megabunus diadema and Phalangium opilio. Finally c e r t a i n s p e c i e s t e n d t o live a s a d u l t s a b o v e t h e field l a y e r o n b u s h e s , trees, walls a n d fences while their y o u n g stages are found nearer t h e g r o u n d . T h e s e i n c l u d e Oligolophus agrestis O. hansenii, Odiellus spinosus a n d Opilio parietinus, b u t t h e r e is s o m e o v e r l a p b e t w e e n all three groups and most species migrate u p w a r d s as they m a t u r e . T h i s a p p e a r s t o b e a s s o c i a t e d w i t h t h e n e e d for b i g g e r p r e y , m o r e space t o m o v e in, m a t i n g a n d p r o b a b l y different t e m p e r a t u r e a n d m o i s t u r e r e q u i r e m e n t s (Sankey, 1949b). I n addition, T o d d (1949) has s h o w n t h a t m a n y species of h a r v e s t m e n are m o s t active at night w h e n they show a tendency to migrate u p w a r d s on to trees w h e r e t h e air is d a m p e r . T h i s activity is correlated w i t h t h e d e crease in light intensity, increase in relative h u m i d i t y a n d decrease i n t e m p e r a t u r e t h a t o c c u r s after d a r k . T h u s i n W y t h a m W o o d s , some 4 m i l e s n o r t h - w e s t of O x f o r d , Leiobunum rotundum h u n t s o n t h e u n d e r s i d e o f Mercuralis perennis l e a v e s d u r i n g t h e d a y b u t passes t h e night on the t r u n k s of trees. 1/2

A s i m i l a r v e r t i c a l m i g r a t i o n w a s f o u n d t o o c c u r i n Oligolophus tridens, a n d m a n y o t h e r s p e c i e s s h o w a v e r t i c a l m i g r a t i o n d u r i n g t h e i r life h i s t o r i e s , a s a l r e a d y m e n t i o n e d . A t t h e s a m e t i m e t h e r e i s usually a microhabitat separation in space and time, or both, b e t w e e n a l l i e d s p e c i e s of t h e s a m e g e n u s . L. rotundum a n d L. blackwalli r e s e m b l e e a c h o t h e r v e r y c l o s e l y b u t d u r i n g t h e i r life h i s t o r i e s there is no habitat overlap in time until they both appear on tree t r u n k s at t h e a g e of six m o n t h s . L. rotundum h a t c h e s a b o u t a m o n t h i n a d v a n c e o f L . blackwalli a n d r e t a i n s t h i s l e a d a s i t a s c e n d s f r o m o n e p l a n t l a y e r t o t h e n e x t . L . blackwalli i s n e v e r a b u n d a n t a n d i s f o u n d o n t h e l o w e r p a r t s o f t h e t r e e t r u n k s w h i l e L . rotundum i s m u c h m o r e p l e n t i f u l a n d i s u s u a l l y t o b e s e e n u p t o s e v e n feet a b o v e g r o u n d level. S i m i l a r l y Oligolophus tridens is a d o m i n a n t f i e l d - l a y e r f o r m w h i l e t h e less a b u n d a n t O. agrestis a n d O. hansenii are f o u n d p r e d o m i n a n t l y o n tree t r u n k s a n d a m o n g s t t h e b r a n c h e s .

F o o d a n d f e e d i n g habits H a r v e s t - s p i d e r s a r e p r i m a r i l y c a r n i v o r o u s a n d u s u a l l y feed o n f r e s h o r r e c e n t l y d e a d a n i m a l t i s s u e s , b u t t h e y will also e a t a v a r i e d a s s o r t m e n t o f m a t t e r s u c h a s b r e a d , fat, t h e gills o f Chanterelle a n d

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other fungi, seeds a n d even c h e w pellets of miscellaneous vegetable matter which they have carried to a suitable feeding g r o u n d s u c h a s t h e t o p o f a leaf. T h e y h a v e b e e n r e c o r d e d s c a v e n g i n g o n bird droppings and dead animal material such as w o r m s , millip e d e s , c e n t i p e d e s , a n t s , s p i d e r s , flies, b e e t l e s a n d v e r t e b r a t e s : i n deed it s e e m s t h a t little organic m a t e r i a l c o m e s amiss to these o m n i v o r o u s creatures (Sankey, 1949a). M o r e often h o w e v e r t h e y are seen to p r e y on woodlice, millipedes, centipedes, false-scorpions, spiders, m i t e s a n d a w i d e variety of insects. A n u m b e r of s p e c i e s , s u c h as Mitopus morio, a r e h a b i t u a l l y c a n n i b a l i s t i c w h i l e t h e T r o g u l i d a e feed o n s n a i l s s u c h a s Cepaea a n d Oxychilus s p p . and are mainly found in the chalky districts w h e r e these are most n u m e r o u s . T h e I s c h y r o p s a l i d a e also f e e d o n G a s t e r o p o d m o l l u s c s and have extra long chelicerae with w h i c h the prey is d r a w n from its s h e l l . W h e n t h e s n a i l i s c o m p l e t e l y r e t r a c t e d t h e h a r v e s t - s p i d e r s o m e t i m e s b r e a k s off p i e c e s o f t h e s h e l l u n t i l i t c a n r e a c h t h e b o d y o f t h e a n i m a l . T h e c a v e r n i c o l o u s Scotolemon s p p . a r e p a r t i c u l a r l y ferocious a n d h u n t o t h e r a r t h r o p o d s , particularly beetles, w h i c h t h e y d e v o u r i n g r e a t n u m b e r s . T h e s e n s i t i v e s e c o n d legs a r e o f prime importance in the recognition of prey. W h e n e a t i n g , t h e c h e l i c e r a e , p e d i p a l p s a n d legs m a y all b e b r o u g h t into use. L e g s a n d palps help in s u b d u i n g living p r e y a n d the pincers of t h e chelicerae serve to tear it to bits. Sometimes two or m o r e Phalangids m a y be seen pulling and tearing at the same morsel of food. W a t e r is of special i m p o r t a n c e in t h e e c o n o m y of h a r v e s t - s p i d e r s a n d m o s t s p e c i e s d o n o t s u r v i v e for l o n g w i t h o u t it. T h e y m a y fast f o r a f o r t n i g h t o r m o r e w i t h o u t a p p a r e n t d i s c o m fort b u t m a n y will d i e i n a c o u p l e o f d a y s i f u n a b l e t o d r i n k . A f t e r rain m a n y species, b o t h diurnal and nocturnal, m a y be found a b r o a d , b u t d u r i n g p e r i o d s o f d r o u g h t a l m o s t all will a v o i d d i r e c t light a n d forage only at twilight or early in t h e m o r n i n g (Bishop, 1949b). A c c o r d i n g to Savory (1938) a very thirsty h a r v e s t m a n is stiff a n d t o r p i d b u t i f p l a c e d o n t h e s u r f a c e o f t h e w a t e r r e m a i n s t h e r e s u c k i n g u p t h e l i q u i d like b l o t t i n g p a p e r .

Enemies A d u l t h a r v e s t - s p i d e r s s e e m to have few e n e m i e s a n d m o s t of t h e i r difficulties i n life a r e p r o b a b l y o f a p h y s i c a l n a t u r e s u c h a s

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changes of t e m p e r a t u r e and humidity: b u t according to one school of t h o u g h t t h e r e m u s t be s o m e biological d e n s i t y - d e p e n d e n t factor to keep their n u m b e r s in check. F o r if a particular c o m p o n e n t of the e n v i r o n m e n t is to regulate t h e p o p u l a t i o n density of a species, it m u s t be able to destroy a greater fraction of the population of that species w h e n t h e density is high t h a n w h e n it is low. If destruction w e r e m e r e l y p r o p o r t i o n a l to p o p u l a t i o n density, t h e factor causing it would not be a regulatory one. Parasites and predators are exa m p l e s o f t h e first c a t e g o r y ( d e n s i t y - d e p e n d e n t f a c t o r s ) , climatic conditions of the second. Other writers suggest that natural c o n t r o l i s a c h i e v e d chiefly b y c l i m a t i c a n d e d a p h i c f a c t o r s a n d t h a t it is unnecessary to invoke d e n s i t y - d e p e n d e n t factors to explain either the m a x i m u m or the m i n i m u m n u m b e r occurring in a n a t u r a l p o p u l a t i o n . P e r h a p s t h e t r u t h m a y lie s o m e w h e r e b e t w e e n these extremes. 1

T h e f o l l o w i n g p r e d a t o r s h a v e b e e n r e c o r d e d : fish ( w h e n h a r v e s t m e n h a v e b e e n c a u g h t b y t h e s u d d e n flooding o f s t r e a m s ) , frogs, t o a d s , l i z a r d s , b i r d s , s h r e w s , b a d g e r s , foxes a n d o t h e r m a m m a l s , c e n t i p e d e s , s p i d e r s , p r e d a c e o u s flies, b e e t l e s , e a r w i g s , d r a g o n f l i e s , b u g s a n d o t h e r insects, as well as cannibalistic Opiliones (Sankey, 1949a). H o w e v e r , t h e g r o u n d - l i v i n g forms are exceedingly inconspicuous and probably seldom found by their potential enemies, whilst t h e long-legged species generally have cryptic coloration and can often stride o u t of h a r m ' s way. If caught they m a y escape by a u t o t o m i s i n g a l i m b . T h e leg b r e a k s at t h e articulation b e t w e e n the coxa and trochanter a n d there is no bleeding. T h e detached portion may make spontaneous rhythmical movements which persist for a n h o u r o r m o r e a n d s e r v e t o d i s t r a c t t h e p r e d a t o r ' s a t t e n t i o n f r o m its p r e y . L o s t a p p e n d a g e s a r e n o t r e g e n e r a t e d h o w e v e r , a n d h a r v e s t - s p i d e r s a p p e a r t o lack t h e a b i l i t y t o r i d t h e m s e l v e s o f d a m a g e d m e m b e r s b u t c o n t i n u e to d r a g a c r i p p l e d leg u n t i l it s e v e r s itself. I t i s i n t e r e s t i n g t o n o t e h e r e t h a t a u t o t o m y d o e s n o t appear to occur in the Trogulidae. S h o u l d a h a r v e s t m a n c o m e t o g r i p s w i t h a n a g g r e s s o r a fluid i s e x t r u d e d f r o m its r e p u g n a t o r i a l g l a n d s t h a t i s d i s t a s t e f u l t o m o s t i n v e r t e b r a t e p r e d a t o r s . T h u s few spiders will sustain a n attack o n 1

I have recently discussed these points; 1957, Entomologist, 1 9 5 - 2 0 3 . See also; M I L N E , A. (1957) Canad. Ent. 8 9 , 1 9 3 - 2 1 3 .

90,

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HARVEST-SPIDERS

a d u l t h a r v e s t m e n : u s u a l l y t h e y r e t r e a t after o n e b i t e a n d w i p e t h e i r m o u t h s o n a leaf. I n n o B r i t i s h s p e c i e s i s t h e o d o u r d i s c e r n i b l e t o m a n : t h e fluid i s c o l o u r l e s s a n d d o e s n o t a p p e a r t o h a v e a n y m a r k e d flavour, b u t various G o n y l e p t i d a e in Brazil p r o d u c e a strong, nauseating o d o u r if handled, a n d in addition can deliver a sharp p i n c h by firmly d r a w i n g their h i n d femora together b e h i n d t h e m . O d o r i f e r o u s g l a n d s a r e f o u n d i n b o t h s e x e s o f all s p e c i e s o f h a r v e s t spider and in their nature are very similar to those of millipedes. As already m e n t i o n e d , there is a single pair of glands w h i c h opens at t h e m a r g i n of t h e cephalothorax above t h e coxa of t h e second l e g . I n t h e l a r g e r S o u t h A f r i c a n L a n i a t o r e s s u c h a s Larifugella natalensis, t h e o p e n i n g i s p r o t e c t e d a n d p a r t l y c o v e r e d b y a l a r g e flattened tubercle or process of t h e coxa. In s o m e species t h e g l a n d ular secretion can be discharged in t h e form of a fine jet to a dist a n c e o f m o r e t h a n a n i n c h from t h e a n i m a l ( L a w r e n c e , 1937), b u t in most it merely flows from the gland opening. T h e colour of the secretion in the Laniatores is bright yellow or reddish b r o w n : it is highly volatile w i t h an acrid smell a n d m a y cause a s m a r t i n g sensation in t h e eyes if a d r o p is b r o u g h t too close to t h e m . T h e i r r e p u g n a t o r i a l f l u i d m a y b e r e s p o n s i b l e f o r t h e fact t h a t i f a n u m b e r of phalangids are confined in a limited space they seem to b e a n a e s t h e t i s e d o r n a r c o t i s e d b y e a c h o t h e r a n d r e m a i n for a l o n g p e r i o d i n a s t a t e o f i n s e n s i b i l i t y . W h e n t h r o w n o u t u p o n t h e floor of a cage t h e y p r o m p t l y recover a n d r u n a b o u t normally (Savory, 1938). T h e s a m e p h e n o m e n o n has b e e n o b s e r v e d b y Bishop ( 1 9 4 9 b ) : t h e s p e c i m e n s lie i n a t a n g l e d m a s s o f legs a n d b o d i e s , a p p a r e n t l y w i t h o u t life, b u t w h e n d i s t u r b e d b y s h a k i n g t h e y r e cover a n d a s s u m e their n o r m a l activities. T h e parasites of Opiliones include nematode w o r m s and gregarines, while several species have b e e n f o u n d w i t h larval m i t e s s u c h as Erythraeus p h a l a n g i o i d e s , Belaustium nemorum, Leptus s p p . and other T h r o m b i d i i d a e w h i c h are a conspicuous bright red colour, attached to t h e m . Phoretic false-scorpions are occasionally to be seen clinging t o their legs. A c c o r d i n g t o F o r s t e r (1954) t h e N e w Zealand Laniatores are not attacked by spiders b u t infestation by n e m a t o d e s a n d Chalcid wasps has b e e n n o t e d . S p e c i m e n s are often heavily infested with mites w h i c h cling to intersegmental m e m branes of abdomen and appendages.

HARVEST-SPIDERS

143

Mating habits M a t i n g in harvest-spiders is as casual as eating or drinking. M a t u r e males a n d females that encounter one another in the field o r d i n a r i l y m a t e briefly, s e p a r a t e a n d c o n t i n u e t h e i r w a n d e r i n g s . A short t i m e later they m a y m a t e again with one a n o t h e r or with d i f f e r e n t i n d i v i d u a l s . T h e n e c e s s i t y for f r e q u e n t m a t i n g s m a y p e r h a p s b e c o r r e l a t e d w i t h t h e fact t h a t t h e e g g s m a t u r e a f e w a t a time a n d are deposited at intervals t h r o u g h o u t , and in most British species, towards t h e e n d of s u m m e r . Secondary sexual differences are very slight. N o t r u e c o u r t s h i p has b e e n o b s e r v e d i n O p i l i o n e s , b u t s o m e c u r i o u s b e h a v i o u r s o m e t i m e s o c c u r s i n Mitopus morio, o n e o f t h e d o m i n a n t A r a c h n i d s i n I c e l a n d ( C l o u d s l e y T h o m p s o n , 1948a, b ) . T h i s species i s p a r t i c u l a r l y e v i d e n t o n s u n n y d a y s . T h e m a l e , r e c o g n i s a b l e b y h i s s m a l l e r b o d y , l o n g e r legs a n d paler colour, r u n s towards a m o v i n g female a n d takes up a position w i t h h i s b o d y j u s t a b o v e a n d legs s t r a d d l i n g h e r s . T h e t w o r u n i n t h i s p o s i t i o n for s e v e r a l i n c h e s b e f o r e s t o p p i n g . T h e m a l e t h e n moves forward slightly so that his b o d y is n o w in front of that of t h e f e m a l e a n d t u r n s a b o u t t o face h e r . H i s l o n g e x t e r n a l g e n i t a l i a are n o w t h r u s t forward a n d m a t i n g takes place. In t h e majority of species, however, it is p r o b a b l e t h a t copulation takes place at night. F o r s t e r (1954) has observed m a t i n g in t h e N e w Zealand L a n i a t o r e s o f b o t h Nuncia a n d Algidia s p p . C o p u l a t i o n i s d i r e c t w i t h little p r e n u p t i a l b e h a v i o u r . T h e m a l e a p p r o a c h e s t h e f e m a l e rapidly, t o u c h i n g h e r w i t h t h e tarsi of t h e second pair of legs. W h e n face t o face h e c l a s p s h e r p e d i p a l p s w i t h h i s o w n . B o t h bodies are t h e n raised, bringing t h e genital openings in line. T h e long penis of the male is t h e n exserted and placed directly into the genital o p e n i n g of t h e female: in no case observed has t h e female exserted her ovipositor to receive the penis. In Leiobunum calcar, a c o m m o n , w i d e l y d i s t r i b u t e d s p e c i e s of P a l p a t o r e s i n N o r t h A m e r i c a , t h e m a l e s a r e easily r e c o g n i s e d b y the presence on the f e m u r of t h e pedipalp of a large, ventro-lateral spur. T h e patella is short, strongly arched above a n d curved vent r a l l y a n d its s w o l l e n b a s e i s a r m e d w i t h s h o r t d a r k d e n t i c l e s . Because of the shortness of the patella the s p u r on the femur m a y b e a p p o s e d t o t h e s w o l l e n b a s e o f t h e t i b i a t o f o r m a n efficient grasping organ. W h e n a male encounters a female he rushes at her

144

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w i t h o u t p r e l i m i n a r y c o u r t s h i p , a n d grasps h e r firmly, h o l d i n g t h e t r o c h a n t e r s o f h e r f i r s t legs w i t h t h e s p u r o n h i s f e m u r w h i l e copulation takes place (Bishop, 1949a). In the short-legged Trogulidae the male hangs beneath the female clasping h e r w i t h his legs, w h o s e claws g r i p t h e r o u g h s u r face o n h e r b a c k s o t h a t t h e v e n t r a l s u r f a c e s o f t h e t w o a r e o p p o s e d (Pabst, 1953). It has often b e e n r e p o r t e d t h a t at t h e b r e e d i n g season male harvest-spiders fight 'bloodless battles' with one another, but Bristowe (1941)* has suggested that the explanation of these fights h a s a s its b a s i s s e x u a l e x c i t e m e n t a n d m i s t a k e n i d e n t i t y . T h e m a l e ' s c h e m o - t a c t i c s e n s e i s s t i m u l a t e d n o t o n l y b y a f e m a l e b u t also b y a m a l e o f its o w n k i n d a s i s s h o w n b y t h e e x t r u s i o n o f t h e p e n i s .

Reproduction and life cycle Female harvest-spiders have very long ovipositors and generally lay t h e i r e g g s i n c r e v i c e s i n t h e soil, u n d e r s t o n e s , w o o d a n d i n other moist places. A m o n g the N e w Zealand Palpatores mating usually takes place in O c t o b e r a n d N o v e m b e r a n d eggs are laid b e t w e e n late O c t o b e r a n d D e c e m b e r . N o eggs a p p e a r t o b e laid i n t h e a u t u m n for o v e r - w i n t e r i n g a s i s t h e c a s e i n s o m e B r i t i s h P a l p a t o r e s . I n Hendea myersi a n d o t h e r T r i a e o n y c h i d a e t h e e g g s a r e d e p o s i t e d i n s m a l l g r o u p s n u m b e r i n g f r o m o n e t o f i v e a m o n g leafm o u l d or m o r e c o m m o n l y in rotting wood, a n d these receive no f u r t h e r a t t e n t i o n . F r o m 2 0 t o 6 0 e g g s m a y b e laid i n t h i s w a y d u r i n g t w o w e e k s . T h e s p e c i e s o f Soerensella, b y c o n t r a s t , select t h e u n d e r s u r f a c e of a l o g or o c c a s i o n a l l y a s p a c e b e n e a t h a l o o s e f i t t i n g r o c k for o v i p o s i t i o n . A s m a l l g r o u p o f e g g s , f r o m 1 0 t o 2 0 , i s laid a n d t h i s i s t h e n g u a r d e d b y t h e f e m a l e . A t i n t e r v a l s o f a f e w days or a week further eggs are d e p o s i t e d so t h a t in s o m e cases egg m a s s e s o f s o m e 6 0 t o 100 e g g s m a y b e f o u n d , s o m e o f w h i c h a r e h a t c h i n g , w h i l e o t h e r s a r e f o u n d i n all s t a g e s o f d e v e l o p m e n t , o f t e n i n c l u d i n g n e w l y laid e g g s . I t i s p r o b a b l e t h a t h a t c h i n g n o r m a l l y takes a b o u t 20 days (Forster, 1954). I n Phalangium opilio a m o n g t h e P a l p a t o r e s t h e f i r s t o v i p o s i t i o n u s u a l l y t a k e s p l a c e a b o u t 1 8 d a y s after t h e f i n a l m o u l t , t h e s e c o n d 2 t o 2 2 d a y s l a t e r a n d a t h i r d i n a n o t h e r w e e k . V i r g i n f e m a l e s c a n lay eggs, b u t do n o t usually do so ( G u e u t a l , 1944). T h e eggs are

145

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usually white, devoid of s c u l p t u r i n g a n d a d h e r e loosely together. T h e i r n u m b e r v a r i e s f r o m o v e r 2 0 0 i n Odiellus spinosus a c c o r d i n g t o S a n k e y ( 1 9 4 9 b ) a n d 2 7 5 i n Platybunus pinetorum ( S t i p p e r b e r g e r , 1 9 2 8 ) t o 4 0 0 t o 6 0 0 i n Phalangium opilio a c c o r d i n g t o G u e u t a l ( 1 9 4 4 ) . H o l m ( 1 9 4 7 ) f o u n d t h a t Opilioparietinus l a i d f r o m 2 0 t o 6 0 eggs at 20° C, a n d t h a t t h e r e w a s no f u r t h e r d e v e l o p m e n t after an early b l a s t o d e r m stage unless t h e eggs w e r e transferred to a refrige r a t o r , w h e r e t h e y w e r e k e p t a t 6 ° C for t w o w e e k s a n d t h e n , for a f u r t h e r week, at - 6 ° C . I n Leiobunum blackwalli, h o w e v e r , t h e p e r c e n t a g e of eggs h a t c h i n g w a s n o t significantly h i g h e r after cold t r e a t m e n t according to T o d d (1949). A faint m o t t l i n g indicates t h e o n s e t of d e v e l o p m e n t ; t h e eyes appear at one pole and just before hatching the b o d y segments and limbs can be seen neatly tucked away inside the egg. H a t c h i n g is a quick process, the y o u n g breaking the egg m e m b r a n e by means of a powerful egg-tooth in front of the ocular tubercle. E u r o p e a n Palpatores are about 1 mm in length on emergence. T h e newly hatched y o u n g resemble the adults in general, b u t are distinguished by the absence of a n u m b e r of detailed characters which are gradually a s s u m e d w i t h each m o u l t . T h e first of these occurs almost i m m e d i a t e l y a f t e r e c l o s i o n a n d i s f o l l o w e d b y six o r s e v e n o t h e r s a t i n t e r v a l s o f a b o u t t e n d a y s e x t e n d i n g o v e r a p e r i o d o f six t o n i n e m o n t h s . T h e y o u n g are at first soft-bodied and sluggish in their m o v e m e n t s b u t there is a progressive hardening of the integument with each ecdysis. In those Laniatores and Palpatores which have n u m e r o u s t a r s a l s e g m e n t s i n t h e m a t u r e f o r m s , t h e n u m b e r i s far fewer in t h e y o u n g stages a n d increases as they g r o w older. W h e r e k n o w n , t h e soft-skinned, delicate eggs of t h e T r o g u l i d a e are laid in t h e shells of snails in w h i c h t h e y are sealed by a p r o tective m e m b r a n e secreted by the ovipositor of the female. T h e n u m b e r varies from one to eight in each batch, b u t as m a n y as 25 e g g s m a y b e laid b y a s i n g l e f e m a l e d u r i n g t h e y e a r . M a x i m u m activity takes place in t h e s p r i n g a n d a u t u m n b u t eggs are p r o d u c e d during every m o n t h except D e c e m b e r and January. T h e duration o f o n t o g e n y d e p e n d s u p o n t h e s e a s o n a t w h i c h t h e e g g s a r e laid, and development is slow between October and M a r c h , coming almost to a standstill between N o v e m b e r and February, b u t in the s u m m e r m o n t h s i t lasts f i v e t o eight w e e k s . P o s t - e m b r y o n i c develK

S.S.C.M.

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146

o p m e n t is c o m p l e t e d after a c o n s t a n t n u m b e r of ecdyses of w h i c h t h e first a g a i n t a k e s p l a c e i m m e d i a t e l y after h a t c h i n g . I n Anelasmocephalus cambridgei a n d t h e moults

respectively.

Trogulus

T h e animals

s p p . t h e r e a r e five a n d six do

n o t m o u l t after r e a c h i n g

m a t u r i t y w h i c h i n A . cambridgei i s r e a c h e d i n o n e t o t w o m o n t h s a n d t a k e s f o u r t o five m o n t h s i n Trogulus s p p . , a l t h o u g h t h e a d u l t s m a y c o n t i n u e t o live for a n o t h e r t w o y e a r s o r m o r e ( P a b s t , 1 9 5 3 ) . T h r e e t y p e s o f life c y c l e c a n b e r e c o g n i s e d i n t h e B r i t i s h O p i l i o n e s . T h e T r o g u l i d a e a n d N e m a s t o m i d a e , w h i c h live i n s h e l t e r e d habitats, can be found b o t h as y o u n g and adults t h r o u g h o u t the year. T h e n there are t h e species that pass t h e winter as eggs and m a t u r e a t t h e e n d o f t h e f o l l o w i n g s u m m e r , s u c h a s Oligolophus a n d Odiellus s p p . Megabunus diadema,

F i n a l l y a few, s u c h as Platybunus triangularis a n d mature

in

early s u m m e r a n d lay eggs

from

which hatch y o u n g that s p e n d t h e following winter in an i m m a t u r e stage (Sankey, 1949b; T o d d , 1949). BIBLIOGRAPHY Identification FORSTER, R. R. (1954) T h e N e w Zealand H a r v e s t m e n (sub-order L a n i a tores). Canterbury Mus. Bull., N o . 2, 1-329. KASTNER, A. (1928) Spinnentiere oder Arachnoidea I I I . Opiliones in D A H L , F. Tierw. Deuts., 8, 1-51. PICKARD-CAMBRIDGE, O. (1890) M o n o g r a p h of the British Phalangidea or harvestmen. Proc. Dorset Field Club., 1 1 , 163-216. ROEWER, C. F. (1923) Die Weberknechte der Erde, J e n a (with several supplements). SAVORY, T. H. (1948) Synopses of the British Fauna. No. 1. Opiliones (Arachnida) or Harvestmen. 2ND E d . L o n d o n : Linn. Soc. S I M O N , E. (1879) Les Arachnides de France, Paris, 7, 116-332. T O D D , V. (1948) K e y to the determination of the British harvestmen (Arachnida, Opiliones). Ent. Mon. Mag., 8 4 , 1 0 9 - 1 3 . Biology BISHOP, S. C. (1949a) T h e function of the s p u r on the femur of the palpus of t h e male Leiobunum calcar (Wood) (Arachnida: Phalangida). Ent. NewsPhilad., 60,10-11. (1949b) T h e Phalangida (Opiliones) of N e w York. Proc. Rochester Acad. Sci., 9 , 1 5 9 - 2 3 5 . BRISTOWE, W. S. (1949) T h e distribution of harvestmen (Phalangida) in G r e a t Britain and Ireland, with notes on their names, enemies and food. J. Anim. Ecol. 1 8 . 1 0 0 - 1 4 .

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C L O U D S L E Y - T H O M P S O N , J. L. (1948a) N o t e s on Arachnida, 4. Courtship behaviour of t h e harvester Mitopus morio. Ann. Mag. Nat. Hist., (11), 14,809-10. (1948b) Observations on t h e ecology of A r a c h n i d s in N o r t h - w e s t Iceland. Ibid., (12), 1, 4 3 7 - 4 7 . GUEUTAL, J. (1944) La p o n t e chez un Opilion: Phalangium opilio L i n n e . Rev. fr. Ent. Paris, 1 1 , 6 - 9 . KASTNER, A. (1931) Biologische B e o b a c h t u n g e n an Phalangiiden. Zool. Anz., 9 5 , 2 9 3 - 3 0 2 . LAWRENCE, R. F. (1937) T h e odoriferous glands of some S o u t h African harvest-spiders. Trans. R. Soc. S. Africa, 2 5 , 3 3 3 - 4 2 . H O L M , A. (1947) On the d e v e l o p m e n t of OpilioparietinusDeg. Zool. Bidr. Uppsala, 2 5 , 4 0 9 - 2 2 . PABST, W. (1953) Z u r Biologie der mitteleuropaischen T r o g u l i d e n . Zool. J. (Syst.), 8 2 , 1 - 4 6 . ROTERS, M. (1944) Observations on British H a r v e s t m e n . J. Qnek. Micr. Club., (4), 2, 2 3 - 5 . SANKEY, J. H. P. (1949a) Observations on food, enemies and parasites of British harvest-spiders (Arachnida, Opiliones). Ent. Mon. Mag., 8 5 , 246-7. (1949b) British harvest-spiders. Essex Nat., 2 8 , 1 8 1 - 9 1 . SAVORY, T. H. (1938) N o t e s on t h e biology of h a r v e s t m e n . J. Quek. Micr. Club., (4), 1, 8 9 - 9 4 . (1949) N o t e s on the biology of Arachnida. Ibid., (4), 3 , 1 8 - 2 4 . STIPPERBERGER, H. (1928) Biologie u n d V e r b r e i t u n g der Opilioniden N o r d - T i r o l s . Arb. Zool. Inst. Univ. Innsbruck, 3 , 1 2 - 7 9 . T O D D , V. (1949) T h e habits and ecology of the British h a r v e s t m e n (Arachnida, Opiliones), w i t h special reference to those of the Oxford district. J. Anim. Ecol., 1 8 , 2 0 9 - 1 6 .

CHAPTER

X

SPIDERS Classification and distribution W i t h o u t d o u b t spiders are the best k n o w n and in m a n y ways the m o s t i n t e r e s t i n g o f all t h e A r a c h n i d a . T h e d i v e r s i t y o f t h e i r w e b s and the various and intricate m e t h o d s used in their construction have always attracted attention. Indeed, m a n y people seem to notice only those species that capture their prey in w e b s such as

F I G . 32. Examples of spider families: 1. Liphistiidae, 2. T h e r a phosidae, 3. Gnaphosidae, 4. Sparassidae, 5. T h o m i s i d a e , 6 .Salticidae, 7 . Lycosidae, 8 . Agelenidae, 9 . Theridiidae, 1 0 . Argiopidae, 1 1 . Linyphiidae. (Drawings not to scale.) (After various authors and original.) 148

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t h e m u c h m a l i g n e d , l o n g - l e g g e d h o u s e s p i d e r s (Tegenaria s p p . ) which spin cobwebs in the corners of rooms and outhouses; and t h e g a r d e n s p i d e r s (Araneus s p p . ) w h o s e d e w - s p a n g l e d o r b w e b s glistening in the sunlight lend their beauty to the a u t u m n morning. A l l s p i d e r s s p i n silk, b u t b y n o m e a n s all o f t h e m live s e d e n t a r y lives i n w e b s : i f t h e y d i d , a l a r g e a m o u n t o f p o t e n t i a l f o o d i n t h e f o r m o f i n s e c t s w o u l d n o t b e e x p l o i t e d . I n fact t h e m o r e p r i m i t i v e s p e c i e s t e n d t o u s e silk o n l y f o r b u i l d i n g t h e i r r e t r e a t s a n d for w e a v i n g t h e c o c o o n s i n w h i c h t h e y lay t h e i r e g g s . I n d e e d , i t h a s been suggested that predation by primitive hunting spiders u p o n early wingless insects m a y have b e e n o n e of t h e m a i n factors that engendered the evolution of insect wings. W h e n their prey took to t h e air to escape, spiders evolved aerial w e b s as a m e a n s of t r a p p i n g it in flight. T h e Araneae or spiders resemble the whip-scorpions in having the cephalothorax (prosoma) and a b d o m e n (opisthosoma) separated by a waist formed by the constriction of the pregenital somite; in having t h e a b d o m e n in primitive forms c o m p o s e d of eleven segments, in the presence of two pairs of lung-books opening behind t h e s t e r n i t e s o f t h e first a n d s e c o n d a b d o m i n a l s e g m e n t s ; a n d i n h a v i n g m e d i a n a n d l a t e r a l e y e s i n t h e c a r a p a c e . T h e y differ f r o m them in that the appendages of the third and fourth abdominal somites have been retained as t h e so-called spinning m a m m i l l a e for t h e m a n i p u l a t i o n o f silk s e c r e t e d b y c o m p l i c a t e d g l a n d s i n t h e a b d o m e n ; in the presence of a poison gland in the mandibles or chelicerae, t h e second s e g m e n t of w h i c h forms a sharp, piercing f a n g w i t h a s i n g l e orifice a t t h e t i p for t h e e x i t o f t h e p o i s o n ; i n t h e simple leg-like n o n - p r e h e n s i l e palpi; a n d t h e conversion of t h e terminal segment of the palp of t h e male into a sperm-carrier. Although the order is a homogeneous one, the phylogenetic and systematic p r o b l e m s involved in d i s t i n g u i s h i n g t h e various families are often c o m p l e x a n d several different classificatory s c h e m e s h a v e b e e n p r o p o s e d (e.g. Bristowe, 1938; P e t r u n k e v i t c h , 1933, 1939, e t c . ) . T h r e e s u b - o r d e r s a r e n o w g e n e r a l l y r e c o g n i s e d . T h e first, L i p h i s t i o m o r p h a , i s c h a r a c t e r i s e d b y t h e fact t h a t t h e a b d o m e n h a s r e t a i n e d its p r i m i t i v e s e g m e n t a t i o n , b e i n g p r o v i d e d w i t h e l e v e n tergal plates a n d o t h e r atavistic qualities. T h e spiders of this s u b order belonging to t h e family Liphistiidae, of w h i c h t h e best

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k n o w n g e n u s i s Liphistius, a r e r e s t r i c t e d t o B u r m a , t h e M a l a y Peninsula a n d n e i g h b o u r i n g countries. Several of t h e species such as L. desultor r e a c h a fair size b u t v e r y little is k n o w n of t h e i r h a b i t s . S o m e live e x c l u s i v e l y i n c a v e s ; all i n b u r r o w s i n t h e g r o u n d . I n the s u b - o r d e r M y g a l o m o r p h a , w h i c h includes t h e so-called 'bird-eating' spiders of the tropics, the articulation of the m a n d ibles w i t h t h e p r o s o m a is vertical so t h a t t h e y project forward, t h e fang or s e c o n d s e g m e n t closing straight b a c k w a r d or nearly so. T h e spiders of this group are confined to t e m p e r a t e and tropical regions of the world where they are represented by large n u m b e r s of genera a n d species b e l o n g i n g to several families. T h e best k n o w n of these are t h e T h e r a p h o s i d a e , often erroneously spoken of as ' T a r a n t u l a s ' , w h i c h include t h e largest species k n o w n , the C t e n i z i d a e o r t r a p - d o o r s p i d e r s w h i c h a r e f a m o u s for t h e p e r f e c tion of their b u r r o w s , and the Atypidae w h i c h include the pursew e b s p i d e r Atypus affinis t h e s o l e B r i t i s h r e p r e s e n t a t i v e o f t h e s u b order. T h i s , one of o u r largest species, has a shining r e d d i s h black colour and is provided with e n o r m o u s chelicerae. In the steaming j u n g l e s o f S o u t h A m e r i c a live t h e l a r g e s t s p i d e r s o f all. A m a l e Theraphosa s p . f r o m F r e n c h G u i a n a m a y m e a s u r e t h r e e i n c h e s i n length w i t h a leg s p a n e x c e e d i n g ten inches, while an e n o r m o u s f e m a l e Lasiodora s p . f r o m B r a z i l is r e c o r d e d as h a v i n g a b o d y 3 inches long a n d a w e i g h t of a l m o s t 3 oz. ( G e r t s c h , 1949).* y

1/2

Bristowe (1947) relates t h a t t h e h e r o of M i l a n is claimed to have s l a i n a m o n s t r o u s s p i d e r w h i c h h a d b e e n l a p p i n g u p t h e l a m p oil of the Cathedral C h u r c h in 1751. 'After death, we are told, it weighed 4 lb. or s o m e w h a t m o r e t h a n a large Pekinese! A n o t h e r , w i t h s i m i l a r o i l - d r i n k i n g h a b i t s , m a d e its h o m e i n S t . E u s t a c e ' s C h u r c h in Paris, and I suspect the sexton was u n d e r grave susp i c i o n o f b o r r o w i n g t h e oil h i m s e l f u n t i l h e r e p o r t e d s e e i n g " a spider of enormous dimensions come down the chain by which the l a m p w a s s u s p e n d e d , d r i n k u p t h e oil, a n d w h e n g o r g e d t o s a t i e t y s l o w l y r e t r a c e i t s s t e p s " . ' T h e l a r g e s t B r i t i s h h o u s e s p i d e r , Tegenaria parietina, h a s a b o d y l e n g t h of a b o u t i n c h a n d a l e g s p a n of a b o u t five inches. It has b e e n r e c o r d e d that, in 1936, a p o l i c e m a n o n p o i n t d u t y a t L a m b e t h B r i d g e h e l d u p t h e L o n d o n traffic for s o m e m i n u t e s to allow an outsize e x a m p l e to cross t h e road in safety—which it did, m u c h to the delight of passers-by. T h e r e is 3/4

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an obscure legend that Cardinal Wolsey, who simply could not abide spiders, had a particular aversion to this species which was all t o o p l e n t i f u l a t H a m p t o n C o u r t a n d i s still p o p u l a r l y k n o w n a s the 'cardinal spider'. T h e third sub-order, A r a n e o m o r p h a , includes the most specialised spiders a n d c o m p r i s e s t h e majority of living species w h i c h exhibit a greater range in structural variation and in habits than any other order of Arachnida except, perhaps, the Acari. In the elaboration of complex instincts a n d habits they are unexcelled. T h e plane of articulation of the chelicerae to the cephalothorax is horizontal so that t h e m a n d i b l e s point d o w n w a r d , t h e fangs closing o b l i q u e l y i n w a r d . T h e s e s p i d e r s a r e classified i n f a m i l i e s a c c o r d i n g to structural characters w h i c h are often correlated w i t h the methods employed in the capture of prey. T h u s the Dictynidae and U l o b o r i d a e coat their m e s h e d w e b s w i t h a bluish, sticky sheet o f f l o c c u l e n t silk p r o d u c e d b y a f l a t s p i n n i n g o r g a n o r ' c r i b e l l u m ' l y i n g c l o s e i n f r o n t o f t h e u s u a l six s p i n n e r e t s . T h e c r i b e l l u m m a y be likened to t h e fused s p i n n i n g fields of t w o spinnerets lying nearly flat against the ventral surface of the a b d o m e n a n d is always a c c o m p a n i e d by an accessory c o m b of hairs called t h e 'calam i s t r u m ' u p o n t h e m e t a t a r s i o f t h e h i n d l e g s . T h e s p i d e r s p i n s its composite hackled b a n d by rubbing the calamistrum back and forth over the cribellum, drawing out two ribands that are attached t o t w o l i n e s o f n o r m a l silk c o m i n g a t t h e s a m e t i m e f r o m t h e spinnerets. T h e O o n o p i d a e , D y s d e r i d a e a n d Scytodidae are sixeyed nocturnal h u n t i n g spiders. A l t h o u g h t h e n u m b e r of eyes is n o t s u c h a f u n d a m e n t a l c h a r a c t e r a s w a s o n c e t h o u g h t , i t i s still a convenient diagnostic feature. T h e m e m b e r s of the G n a p h o s i d a e and Clubionidae are mostly n o c t u r n a l s p e c i e s t h a t m o v e s t e a l t h i l y a s t h e y feel for t h e i r p r e y w i t h front legs o u t s t r e t c h e d . T h e G n a p h o s i d a e are g r o u n d s p i d e r s of s o m b r e coloration w i t h few c o n t r a s t i n g m a r k i n g s , t h e dull greys, b r o w n s a n d blacks deriving from a covering of short hairs that gives t h e m a velvety a p p e a r a n c e . M o r e flattened t h a n t h e C l u b i o n i d a e , t h e y differ f r o m t h e l a t t e r i n h a v i n g t h e a n t e r i o r l a t e r a l spinnerets widely separated. T h e Anyphaenidae and some Clubi o n i d a e live o n p l a n t s , h a v e w e l l - d e v e l o p e d c l a w t u f t s a n d a r e g o o d climbers. M o s t l y whitish or b r o w n i s h in colour, they dwell in flat

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t u b u l a r nests o p e n at b o t h e n d s , in rolled leaves or u n d e r bark. S o m e a l s o live a m o n g v e g e t a b l e d e b r i s a n d n e s t u n d e r s t o n e s . T h e C l u b i o n i d a e t h a t h a b i t u a l l y live o n t h e soil e x h i b i t far m o r e d i v e r s i t y i n size, a p p e a r a n c e a n d c o l o r a t i o n t h a n d o t h e c o n s e r v a tive p l a n t - d w e l l i n g f o r m s . M a n y smaller species s u c h as t h e British Phrurolithus festivus a r e m y r m e c o p h i l o u s a n d m i m i c a n t s . Crab spiders or T h o m i s i d a e are sedentary animals that wait on t h e g r o u n d o r i n f l o w e r s a n d v e g e t a t i o n for p a s s i n g i n s e c t s w h i c h are seized b y t h e p o w e r f u l o u t s t r e t c h e d legs: t h e y f r e q u e n t l y possess markedly cryptic (concealing) coloration. T h e English n a m e for t h i s f a m i l y d e r i v e s f r o m t h e i r h a b i t o f r u n n i n g s i d e w a y s like c r a b s . T h e S a l t i c i d a e o r j u m p i n g s p i d e r s a r e s m a l l , r a t h e r squat animals w i t h b r o a d s q u a r e h e a d s , extremely large eyes a n d short, s t o u t legs. T h e y h a v e v e r y k e e n sight a n d stalk t h e i r p r e y f r o m afar. T h i s i s o n e o f t h e l a r g e s t s p i d e r f a m i l i e s a n d i n c l u d e s several t h o u s a n d species w h i c h are found m a i n l y in tropical countries w h e r e t h e y almost rival t h e insects in t h e brilliance of t h e i r h u e s . O n l y t h i r t y - t w o s p e c i e s a r e o n t h e B r i t i s h list a n d m o s t of these are rare and unlikely to be found, except by the most energetic collector. O u r c o m m o n e s t species is t h e little 'zebra s p i d e r ' , Salticus scenicus, so n a m e d b e c a u s e it is c o n s p i c u o u s l y m a r k e d w i t h b l a c k a n d w h i t e s t r i p e s . T h o u g h less b r i l l i a n t l y c o l o u r e d t h a n s o m e o f its e x o t i c r e l a t i v e s , i t i s a n a t t r a c t i v e c r e a t u r e often to be seen w a l k i n g on walls a n d fences in t h e s u n s h i n e . Wolf spiders of t h e family Lycosidae have longer bodies a n d limbs a n d moderately large eyes a n d overcome their prey by sheer strength. L i k e t h e related Pisauridae, t h e y are essentially g r o u n d living forms a n d t h e majority of t h e m h u n t in t h e o p e n by day. T w o o t h e r families o f h u n t i n g spiders, t h e O x y o p i d a e a n d t h e laterigrade Sparassidae, contain species w h i c h are usually found in low herbage w h e n c e they leap d o w n on to their u n s u s p e c t i n g prey. T h e y a r e r e p r e s e n t e d i n t h e B r i t i s h f a u n a b y Oxyopes heterophthalmus a n d Micrommata virescens, r e s p e c t i v e l y , a n d a r e m o r e n u m e r o u s in the w a r m e r regions of the world where the giant c r a b s p i d e r , Heteropoda venatoria, is w i d e l y d i s t r i b u t e d . T h e r e m a i n i n g f a m i l i e s a r e all w e b - b u i l d e r s , t h e A g e l e n i d a e constructing f u n n e l - s h a p e d c o b w e b s consisting of a triangular s h e e t w i t h its a p e x r o l l e d i n t o a t u b e i n w h i c h t h e s p i d e r w a i t s for

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its p r e y . T h e t h r e a d s o f w h i c h t h e w e b i s c o n s t r u c t e d are n o t adhesive, b u t a tangled m a s s of scaffolding above trips passing i n s e c t s w h i c h fall o n t o t h e s h e e t . B e f o r e t h e y h a v e t i m e t o r e c o v e r , t h e o w n e r o f t h e w e b h a s d a r t e d f r o m its t u b e a n d g a t h e r e d t h e m in. T h e c o m b - f o o t e d s p i d e r s o f t h e f a m i l y T h e r i d i i d a e a r e for t h e most part thickset, sedentary types that h a n g upside d o w n from their irregular maze-like webs. M o s t are small spiders suspending t h e i r s n a r e s o n p l a n t s w i t h l i n e s s o fine t h a t t h e y a r e o f t e n u n n o t i c e d , o r h i d i n g t h e m i n b u r r o w s o r f i s s u r e s i n t h e soil a n d u n d e r litter. T h e two-dimensional orb web of the Argiopidae is the crowning a c h i e v e m e n t of t h e aerial s p i d e r s : it is t h e last stage in a series t h a t has resulted in a circular design. Finally, the Linyphiidae build a horizontal platform u p o n w h i c h d r o p flying a n d j u m p i n g insects, usually after b e i n g h a l t e d in m i d - a i r by a s u p e r s t r u c t u r e of crisscrossed lines g u y e d t o adjacent vegetation. T h e s p i d e r clings u p s i d e d o w n b e n e a t h it, r u n s o v e r t h e s u r f a c e w i t h s u r p r i s i n g r a p i d i t y a n d pulls its p r e y t h r o u g h t h e w e b b i n g . A s e c o n d sheet is often present b e n e a t h t h e h a n g i n g spider a n d p r o b a b l y serves as a barrier to attack from below. In n u m b e r s of individuals, genera a n d s p e c i e s t h e L i n y p h i i d a e far e x c e e d t h e t o t a l o f a n y o t h e r family o f s p i d e r s i n t h e t e m p e r a t e z o n e s w h e r e t h e y are t h e d o m i n a n t aerial t y p e s . T h e majority of t h e s e s p i d e r s are small, even m i n u t e , a n d t h e y o c c u r i n v a s t , l i t t l e n o t i c e d n u m b e r s u n d e r soil debris. M o s t of t h e m are reddish or black creatures with somewhat e l o n g a t e d b o d i e s a n d l e g s s e t w i t h fine s p i n e s , b u t t h e r e a r e n o t a b l e e x c e p t i o n s . T h e p r e s e n c e o f a s t r i d u l a t i n g file o n t h e s i d e of the chelicerae and a scraping spine on the femur of the pedipalp serves to differentiate t h e m from t h e orb weavers. T h e s p i d e r fauna of t h e British Isles c o m p r i s e s s o m e 24 families with over 570 species, nearly half of w h i c h are L i n y p h i i d a e . T h e population in late s u m m e r has b e e n conservatively estimated by Bristowe (1939)* at some 2 millions per acre. He has calculated t h a t i f all t h e s p i d e r s f r o m a n a c r e o f l a n d w e r e t o c o m b i n e t o b u i l d one c o n t i n u o u s thread, t h e y w o u l d p r o d u c e a s t r a n d in a single day's s p i n n i n g t h a t w o u l d j u s t a b o u t circle t h e w o r l d a t t h e e q u a t o r : after t e n d a y s i t w o u l d b e l o n g e n o u g h t o r e a c h t h e m o o n . 1/4

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T h e weight of insects destroyed each year by spiders in E n g l a n d and Wales m u s t well exceed the total weight of the h u m a n population!

General behaviour S p i d e r s are seen in different lights by different people, b u t t h e s u p e r s t i t i o n s r e g a r d i n g t h e m , i n b o t h p r i m i t i v e a n d civilised countries, are extremely n u m e r o u s . Bristowe (1945), w h o has w r i t t e n an i n t e r e s t i n g review of s p i d e r folklore, c o n c l u d e s t h a t on the w h o l e t h e y are v e n e r a t e d a n d for a n u m b e r of reasons. T h e s e i n c l u d e a d m i r a t i o n for t h e s p i d e r s ' skill a s s p i n n e r s o f silk, a d m i r a t i o n for t h e i r w i s d o m a n d c u n n i n g , f e a r o f t h e i r v e n o m o u s and sinister qualities, association of spiders w i t h religious beliefs— in particular, that in spiders reside the spirits of the dead—belief in their ability to foretell a n d influence t h e w e a t h e r , in their m e d i cinal p r o p e r t i e s , a n d in t h e k n o w l e d g e of t h e p a r t t h e y play in destroying insects. N o t all o f t h e s e h a v e g i v e n r i s e t o s u p e r s t i t i o n s , b u t t h e first f o u r i n p a r t i c u l a r p r o v i d e t h e r a w m a t e r i a l s for folk t a l e s a s a r e s u l t o f w h i c h t h e s p i d e r ' s p o w e r for g o o d a n d evil h a s b e c o m e t r a d i tional t h r o u g h o u t a large part of t h e world. In particular there is a widespread legend of a fugitive w h o escaped his p u r s u e r s because a spider built a w e b across t h e m o u t h of his hiding place so that they t h o u g h t he could not possibly be concealed therein. A m o n g others this story has been told of the Infant Christ, w h o was thus saved from H e r o d , David, w h o escaped from the w r a t h of Saul, M o h a m m e d from the Coreishites, and Yoritomo, a twelfthcentury Japanese hero, w h o hid in a hollow tree and was saved by a spider in similar fashion. A n o t h e r and m o r e famous m y t h is the ancient Greek story of Arachne, who, although deprived of her h u m a n f o r m b y A t h e n e ( M i n e r v a ) for d a r i n g t o c h a l l e n g e t h e G o d d e s s o f W i s d o m t o a s p i n n i n g c o n t e s t , w a s n e v e r t h e l e s s left w i t h h e r skill a s a s p i n n e r . T h i s s t o r y i s p r o b a b l y t h e o r i g i n o f m a n y superstitions which have survived in European countries although t h e m y t h itself h a s b e e n f o r g o t t e n . T h u s t h e r e i s a w i d e s p r e a d belief t h a t a s p i d e r f o u n d r u n n i n g o v e r o n e ' s c l o t h e s h a s c o m e t o s p i n n e w o n e s : a s a n a t u r a l c o n s e q u e n c e o f t h i s i t i s u n l u c k y t o kill a spider. W h e t h e r the t e r m 'money spider' should be applied to

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small scarlet mites or t h e small s h i n y - b o d i e d black L i n y p h i i d spiders, b o t h of w h i c h are not infrequently found r u n n i n g over one's clothes on s u n n y days, is uncertain. As the mites do not spin silk, h o w e v e r , a n d t h e L i n y p h i i d s a r e r e s p o n s i b l e for t h e s i l v e r sheets of g o s s a m e r w h i c h cloak o u r fields in a u t u m n it is a p p r o priate t h a t t h e y a n d n o t t h e mites, s h o u l d b e a w a r d e d t h e title. ( F o r a n u m b e r o f R e d I n d i a n s u p e r s t i t i o n s a n d m y t h s , see G e r t s c h , 1949*). A m o n g the m a n y remarkable traits of spiders, n o n e has excited greater interest nor p r o d u c e d m o r e fantastic speculation t h a n that of 'ballooning'. T h e ancients were familiar w i t h s o m e of the p h e n o m e n a a t t e n d i n g t h e f l i g h t o f s p i d e r s , for A r i s t o t l e b e l i e v e d that spiders could shoot out their threads, and Pliny wrote: 'In the year that L. Paulus and C. Marcellus were consuls, it rained wool.' Often d u r i n g t h e late s u m m e r a n d a u t u m n m o n t h s o n quiet, hazy days, t h e air is filled w i t h s h i n i n g s t r a n d s a n d t h r e a d s of g o s s a m e r , t h e silk p r o d u c e d b y t h e s p i d e r s t h a t h a v e a t t e m p t e d t o f l y a n d failed. S o m e t i m e s o n e s e e s a f i e l d o r m e a d o w c a r p e t e d w i t h silk a n d a h o s t o f little s p i d e r l i n g s s p r e a d i n g t h e i r l i n e s i n v a i n a t t e m p t s t o f l y . O n t h e o t h e r h a n d m a n y are s u c c e s s f u l — D a r w i n , i n 1839, r e c o r d e d t h e a r r i v a l o n H . M . S . Beagle o f ' v a s t n u m b e r s o f a s m a l l spider, a b o u t o n e - t e n t h of an inch in length, and of a dusky red colour' w h e n t h e ship was sixty miles from t h e coast of S o u t h A m e r i c a — a n d ballooning is w i t h o u t d o u b t an i m p o r t a n t factor in t h e d i s t r i b u t i o n o f m a n y s p e c i e s all o v e r t h e w o r l d . N o r i s i t c o n fined to any particular season. In Britain, aeronautic dispersal of i m m a t u r e spiders takes place mainly in s u m m e r , of adult L i n y p h i i d a e chiefly d u r i n g t h e c o l d e r m o n t h s w h e n t e m p e r a t u r e i s t h e m o s t i m p o r t a n t m i c r o - c l i m a t i c factor, a n d b a l l o o n i n g is i n h i b i t e d d u r i n g u n f a v o u r a b l e w e a t h e r (Duffey, 1956). T h e prosaic translate 'gossamer' as 'goose s u m m e r ' in reference t o t h e fanciful r e s e m b l a n c e o f t h e fragile s k e i n s o f silk t o t h e d o w n of geese w h i c h t h e thrifty housewife causes to fly w h e n she r e n o vates her feather b e d s and pillows; b u t gossamer translated as ' G o d ' s s u m m e r ' r e f e r s t o t h e l e g e n d t h a t t h i s g o s s a m e r 'is t h e r e m n a n t o f O u r L a d y ' s w i n d i n g s h e e t w h i c h fell a w a y i n t h e s e lightest fragments as she was a s s u m e d into heaven' (Bishop, 1945).

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M u c h o f t h e a d v e n t u r e a n d r i s k i n t h e life o f t h e s p i d e r i s c r o w d e d i n t o t h e first f e w d a y s o f f r e e d o m w h e n t h e y o u n g s p i d e r l i n g s , h a v i n g first left t h e i r e g g s a c , c l i m b o v e r t h e s t e m s o f p l a n t s a n d up t h e leaves of grasses, stringing their t h r e a d s as t h e y go.

F I G . 33. Ballooning by y o u n g spiders.

S o o n a t a n g l e o f w e b s s p r i n g s u p , c r o s s i n g i n all d i r e c t i o n s a n d covering the vegetation. W h e n the young spider has reached the s u m m i t of the nearest p r o m o n t o r y — a weed, a b u s h or a fence—it t u r n s t o face t h e w i n d , e x t e n d s i t s l e g s s o t h a t i t a p p e a r s t o b e s t a n d i n g o n t i p t o e a n d l e t s a i r c u r r e n t s c a r r y t h e silk f r o m its spinnerets. W h e n t h e friction of t h e c u r r e n t s against the t h r e a d s e x e r t s sufficient p u l l , t h e s p i d e r l o o s e n s its h o l d a n d u s u a l l y sails a w a y : a t t h e t a k e off, a t least, i t i s d r a g g e d b a c k w a r d s . S o m e t i m e s , a f t e r take-off, t h e s p i d e r c l i m b s r a p i d l y t o t h e m i d d l e o f its t h r e a d , which then sweeps forward and becomes doubled. Less frequently the spider makes a forward start. T h i s m e t h o d is employed by small spiders w h i c h m a k e a weak a t t a c h m e n t to a s u p p o r t a n d allow themselves t o b e b l o w n o u t w a r d a n d u p w a r d until t h e t h r e a d s n a p s n e a r its h o l d ( B r a e n d e g a a r d , 1 9 3 8 ) . T h e m o d e s o f life a n d t h e h a b i t a t s o f s p i d e r s a r e m o s t v a r i e d : s o m e a r e w a n d e r e r s t h r o u g h o u t t h e i r lives, o t h e r s a r e a l m o s t e n t i r e l y s e d e n t a r y ; s o m e live i n s u n n y , a i r y p l a c e s , o t h e r s a r e found in o b s c u r e caverns w h e r e the light never penetrates. A

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n u m b e r of species inhabit desert regions, others are aquatic or s e m i - m a r i n e . I n d e e d , t h e r e are few p a r t s of t h e w o r l d w h e r e spiders do not thrive. A n u m b e r of generalisations can, however, be m a d e . S o m e spiders such as the M y g a l o m o r p h a , Salticidae and Sparassidae flourish in t h e tropics a n d diminish progressively t o w a r d s the cooler regions; t h e G n a p h o s i d a e , Dysderidae, Agelenidae a n d various cribellate families thrive m o s t successfully in t h e w a r m e r t e m p e r a t e o r s u b - t r o p i c a l a r e a s , while* o t h e r s , i n c l u d i n g the Lycosidae and particularly the Linyphiidae, reach their greatest d o m i n a n c e in t h e arctic or s u b - a r c t i c r e g i o n s . E v e n in s u c h a small area as that covered by t h e British Isles there are m a r k e d differences b e t w e e n t h e spiders f o u n d i n t h e n o r t h a n d south, differences w h i c h d e m o n s t r a t e t h e s a m e t r e n d a s t h a t o u t l i n e d a b o v e . S c o t l a n d lacks M y g a l o m o r p h a , O x y o p i d a e , P h o l c i d a e , Scytodidae, Sparassidae etc., whilst the Linyphiidae a n d Salticidae r e p r e s e n t 5 0 % a n d 4 % o f its fauna respectively, c o m p a r e d w i t h 4 2 % a n d 6 % for E n g l a n d (Bristowe, 1939).* Some plants harbour more spiders than others. For example, the f a u n a o f b r a c k e n , b l u e b e l l s , m i n t , l a u r e l , w i l l o w a n d b e e c h i s far less r i c h t h a n t h a t o f g r a s s , h e a t h e r , g o r s e , h o l l y , y e w , c o n i f e r s a n d oak. I t m a y b e t h a t t h e scents o f certain p l a n t s are avoided, b u t t h e d e n s i t y o f t h e foliage i s a l s o a n i m p o r t a n t f a c t o r a s i t affects t h e h u m i d i t y o f t h e e n v i r o n m e n t . A g a i n , t h e a b u n d a n c e o f i n s e c t life, l i v i n g o n , o r c o m i n g t o d i f f e r e n t p l a n t s a l s o affects t h e n u m b e r o f s p i d e r s t h a t c a n live t h e r e . B r i s t o w e ( 1 9 3 9 ) * h a s c o n s i d e r e d i n detail t h e spider fauna of sandhills, m a r s h e s , m o u n t a i n s , caves, m i n e s a n d cellars, houses, t o w n s , sewage w o r k s , a n t s ' a n d t e r m i t e s ' nests, beehives, birds' and m a m m a l s ' nests, and other spiders' webs. A n u m b e r of authors have stressed the importance of moisture on t h e d i s t r i b u t i o n of s p i d e r s , a n d N e m e n z (1954) h a s discussed its p h y s i o l o g i c a l s i g n i f i c a n c e . T h e conflict b e t w e e n t h e i n c o m p a t i b l e requirements of respiratory exchange and the prevention of waterloss h a s r e c e n t l y b e e n d e m o n s t r a t e d b y t h e w r i t e r b y a c o m p a r i s o n of t w o c o m m o n B r i t i s h s p e c i e s , Amaurobius ferox a n d A. similis* b o t h of w h i c h have a cuticular wax-layer w i t h a critical t e m p e r a t u r e a t a b o u t 3 0 ° C , a b o v e w h i c h t h e y q u i c k l y lose w a t e r b y e v a p o r a t i o n i n d r y air. A t l o w e r t e m p e r a t u r e s , h o w e v e r , t h e r a t e o f w a t e r - l o s s

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in A. ferox is a l m o s t d o u b l e t h a t of A. similis. A. similis ' t i r e s ' v e r y r a p i d l y w h e n f o r c e d t o r u n a t full s p e e d w i t h o u t s t o p p i n g a n d i s almost always overcome in fights b e t w e e n evenly m a t c h e d indiv i d u a l s o f t h e t w o s p e c i e s . B o t h s p e c i e s c a n r u n for l o n g p e r i o d s when supplied with oxygen and it is suggested that the greater s t a m i n a of A. ferox d e p e n d s u p o n a p r o p o r t i o n a t e l y l a r g e r r e s p i r a tory surface acquired at t h e expense of greater d e p e n d e n c e u p o n e n v i r o n m e n t a l h u m i d i t y ( C l o u d s l e y - T h o m p s o n , 1957). I n B r i t a i n , a n d i n fact i n t h e w h o l e o f t h e n o r t h e r n h e m i s p h e r e , there is only one spider that is truly aquatic. T h i s is the well-known Argyroneta aquatica, o n e o f o u r l a r g e s t s p e c i e s a n d s o m e w h a t e x c e p t i o n a l i n t h a t t h e m a l e i s b i g g e r t h a n its m a t e . I t s w i m s u n d e r w a t e r c l o t h e d i n a b u b b l e o f a i r t h a t s h i n e s like q u i c k s i l v e r , a n d c o n s t r u c t s a r e t r e a t in t h e f o r m of a d i v i n g b e l l of silk filled w i t h air w h i c h is carried d o w n in b u b b l e s from t h e surface. T h e r e are, h o w e v e r , s e v e r a l o t h e r s p e c i e s w h i c h live, like f i s h e r m e n , b y a n d o n t h e water. A l t h o u g h m o s t wolf spiders frequent d r y a n d stony places a n d are particularly n u m e r o u s in spring a n d early s u m m e r , t h e m e m b e r s o f t h e g e n u s Pirata a r e s e m i - a q u a t i c , l i v i n g a t t h e margins of rivers and p o n d s , and are able to r u n on t h e surface of t h e w a t e r . P . piscatorius s p i n s a s i l k e n t u b e i n m o s s a t t h e w a t e r ' s e d g e a n d will r u n b e n e a t h t h e w a t e r i f i t i s a l a r m e d . A s t h e i n c o m i n g t i d e c r e e p s o v e r t h e m u d flats, Lycosa purbeckensis, a n i n h a b i t a n t o f salt m a r s h e s , t o u c h e s t h e w a t e r 'like a b a t h e r f e e l i n g t h e t e m p e r a t u r e with his toe before taking the plunge', and then deliberately walks d o w n the stem of a sedge or other halophytic plant, t a k i n g w i t h it a b u b b l e of air c a u g h t by m e a n s of t h e hairs on its b o d y ( B r i s t o w e , 1 9 2 3 ) . V a r i o u s T h e r i d i i d a e , s u c h a s Oedothorax fuscus a n d s p e c i e s of Desis ( A g e l e n i d a e ) f r o m t h e s h o r e s of t h e I n d i a n o c e a n , also live u n d e r s e m i - m a r i n e c o n d i t i o n s . T o e s c a p e c a p t u r e , t h e l a r g e Dolomedes fimbriatus ( P i s a u r i d a e ) will r u n d o w n a p l a n t s t e m b e n e a t h t h e s u r f a c e o f t h e w a t e r . T h i s s p e c i e s , w h i c h lives i n s w a m p s a n d d i t c h e s , i s s o m e t i m e s c a l l e d t h e ' r a f t - s p i d e r ' on a c c o u n t of a p o p u l a r fallacy t h a t it m a k e s a raft of fallen l e a v e s o n w h i c h t o f l o a t d o w n s t r e a m . S o m e o f its f o r e i g n relations catch tadpoles a n d even small fishes to eat. No obvious features indicate that t h e Pisauridae are spiders of t h e water, b u t they can r u n on t h e surface with a grace almost equalling that of a

SPIDERS water-skater necessary.

and

can

remain

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159 for

long

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T o s u m m a r i s e , a q u a t i c s p i d e r s are k n o w n from several families including the Agelenidae, Lycosidae, Pisauridae, Argiopidae, Clubionidae, Linyphiidae, Salticidae and T h o m i s i d a e . T h e ext e n t t o w h i c h t h e y live b e n e a t h t h e s u r f a c e v a r i e s a n d s o m e c a n w a l k a b o u t c o m f o r t a b l y w i t h a b u b b l e o f air s u r r o u n d i n g t h e i r bodies whilst o t h e r s rely on finding s o m e c r a n n y c o n t a i n i n g air or e n c l o s e t h e m s e l v e s a n d a s u p p l y o f air i n a s i l k e n cell. T h e s u b j e c t has been reviewed by Bristowe (1930b). T h e m a j o r i t y o f s p i d e r s live o n t h e s u r f a c e o f t h e soil, s o m e i n b u r r o w s , o t h e r s s h e l t e r i n g u n d e r s t o n e s , logs o r b e n e a t h t h e d e b r i s o f fallen l e a v e s i n f o r e s t s . M o s t o f t h e T h e r a p h o s i d a e c h o o s e a n y kind of retreat, living u n d e r stones or r u b b i s h on t h e g r o u n d a n d i n c r a c k s i n t r e e s . S o m e d i g a s i m p l e cell w h i c h t h e y l i n e w i t h a s l i g h t w e b o f silk. F o r t h e m o s t p a r t t h e y a r e a c t i v e f o r m s a n d w a n d e r about at night in search of prey. T h e most perfectly constructed b u r r o w s are those of the Ctenizidae, which dig with the aid o f a c o m b - l i k e r a k e o f l a r g e s p i n e s o n t h e m a r g i n s o f t h e i r c h e l i c e r a e . T h e w a l l s o f t h e t u b e i n w h i c h t h e s p i d e r lives a r e l i n e d w i t h a w a t e r p r o o f c o a t i n g o f e a r t h a n d saliva t o w h i c h a l a y e r o f silk i s a p p l i e d : a s t h e s p i d e r g r o w s , i t e n l a r g e s its b u r r o w , t h e e n t r a n c e t o w h i c h i s c l o s e d w i t h a t r a p - d o o r . T h e first d e s c r i p t i o n o f t h i s i n t e r e s t i n g d e v i c e w a s g i v e n b y P a t r i c k B r o w n i n h i s Civil and Natural History of Jamaica, L o n d o n ( 1 7 5 6 ) . S e v e n y e a r s l a t e r t h e careful observations of t h e A b b e S a u v a g e s on t h e nests of Nemesia caementaria, w h i c h h e d i s c o v e r e d n e a r M o n t p e l l i e r , w e r e published. Although trap-door spider nests attracted popular attention thereafter, it was not until M o g g r i d g e (1873) p u b l i s h e d his studies on t h e habits of these animals t h a t a n y c o m p r e h e n s i v e treatment was accorded them. M o g g r i d g e was able to distinguish four types of nest a m o n g the s p e c i e s h e s t u d i e d . T h e first w a s a s i m p l e c y l i n d r i c a l t u b e w i t h a thick 'cork door', the second h a d a thin 'wafer door', the third a thin outer door with a second door part of the way down, while the fourth was the most complicated: a tube capped on the outside by a thin door and having an oblique side tunnel at the entrance to w h i c h was a n o t h e r t r a p - d o o r . Since t h e n several other types of

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nest have b e e n discovered in different p a r t s of t h e world, s o m e of t h e m of even m o r e complicated design. T h e m a j o r i t y o f h u n t i n g s p i d e r s live i n s i l k e n cells u n d e r s t o n e s , b a r k o r fallen l o g s . S o m e o f t h e s m a l l e r s p e c i e s s e e m t o b e a b s o l u t e w a n d e r e r s a n d h a v e n o h o m e a t all, s p e n d i n g t h e n i g h t u n d e r a n y suitable rock or stone that they c o m e across, whilst t h e larger k i n d s live p e r m a n e n t l y i n b u r r o w s f r o m w h i c h t h e y n e v e r g o far.

F I G . 3 4 . T r a p d o o r spider and b u r r o w . (After Moggridge, 1 8 7 3 . ) H a b i t s vary considerably. O n e h a n d s o m e l y m a r k e d wolf spider, Arctosa perita, m a k e s its silk l i n e d b u r r o w s i n d u n e s o f f i r m s a n d and on heathland where the vegetation has been b u r n e d away. W h e n a l a r m e d i t will s e i z e w i t h its c h e l i c e r a e t h e r i m o f t h e silk t h a t l i n e s its b u r r o w , a n d p u l l i t a c r o s s t h e e n t r a n c e like a c u r t a i n . T h e n r a p i d l y t u r n i n g r o u n d i t c l o s e s t h e last c h i n k w i t h a f e w

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s w e e p i n g s t r o k e s o f its s p i n n e r e t s ( B r i s t o w e , 1 9 5 4 ) . S o m e t i m e s s e v e r a l o f t h e s e s p i d e r s live q u i t e c l o s e t o g e t h e r i n a c o l o n y . W e b - b u i l d i n g spiders usually construct a retreat amongst the vegetation from w h i c h their snare is s u s p e n d e d . Vibrations of a signal-thread connecting their shelter with the web enable t h e m instantly to detect the struggles of any insect that has been caught. S o m e species are peculiar in that they show a t e n d e n c y towards social h a b i t s . T h i s i s a p p a r e n t a m o n g a n u m b e r o f c r i b e l l a t e f a m i l i e s a n d a n A u s t r a l i a n s p e c i e s Amaurobius socialis f r o m t h e Jenolan Caves constructs e n o r m o u s c o m m u n a l and densely fabric a t e d w e b s m e a s u r i n g a s m u c h a s 1 2 feet i n l e n g t h a n d 4 feet i n width, which are inhabited by a large n u m b e r of individuals. In a s i m i l a r w a y c o m m u n a l w e b s c o n s t r u c t e d b y Theridion socialis a n d Uloborus republicanus h a v e b e e n d e s c r i b e d . T h e spider's web is u n i q u e a m o n g animal productions in that, (save o n e c o n s t r u c t e d by a caddis larva) it is t h e only t r a p built by a n a n i m a l . T h e w e b i s s o efficient for o b t a i n i n g f o o d t h a t its o w n e r seldom makes use of any sense save that which the action of the w e b d e m a n d s , a n d t h e lives o f w e b - b u i l d i n g s p e c i e s a r e a l m o s t entirely governed by responses to tactile a n d vibratory stimuli supplemented by the development of the muscular sense. T h e m e t h o d s of construction of the various types of web have attracted a great deal of attention, in particular from M a c C o o k (1889-94), P e t e r s ( 1 9 3 3 , e t c . ) , T i l q u i n ( 1 9 4 2 ) a n d W i e h l e . T o r e v i e w all t h i s work would be beyond the scope of the present volume, but fortunately m u c h of it has been summarised recently by Savory (1952), from w h o s e book further details can be obtained. Bristowe ( 1 9 3 0 ) h a s s u g g e s t e d t h a t t h e o r i g i n o f w e b s lies i n t h e u s e o f silk a s a c o v e r i n g for s p i d e r s ' e g g s w h i c h w e r e t h e n g u a r d e d b y t h e mother and from which r a n d o m threads radiated but Savory thinks t h a t t h e y h a v e r e s u l t e d f r o m a n a c c u m u l a t i o n o f d r a g l i n e s , laid d o w n by ancestral h u n t i n g spiders w h e n their prey was captured a n d w h i c h later gave t h e spiders w a r n i n g of o t h e r insects passing by. T h e typical p r o c e d u r e in the construction of an orb w e b is the c o n s t r u c t i o n of a frame followed by t h a t of t h e radii. A few spirals a r o u n d t h e centre hold the radii in place while t h e spider travels outwards spinning a widely spaced t e m p o r a r y spiral. Finally the s p i n n i n g of viscid spirals starts at t h e outside a n d works inwards L

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with the simultaneous destruction of the t e m p o r a r y spiral as it is reached. M a n y orb weavers renew their webs, other than the framework, daily, b u t renewal m a y be p o s t p o n e d if t h e s p i d e r s are well fed o r t h e w e a t h e r u n s u i t a b l e . T h e c h i e f e c o n o m i c u s e o f s p i d e r s ' silk lies i n t h e c o n s t r u c t i o n o f fine g r a t i c u l e s for o p t i c a l i n s t r u m e n t s . C o b w e b s w e r e u s e d y e a r s a g o a s d r e s s i n g s for w o u n d s t o s t a u n c h t h e flow o f b l o o d , for w h i c h t h e y w e r e e x t r e m e l y effective. M o u l d s s u c h a s Penicillium w e r e sometimes added, perhaps foreshadowing the present-day use of penicillin a n d other antibiotics. W h e n several sheet-webs are s u p e r i m p o s e d t h e y f o r m a fine t r a n s p a r e n t silk f a b r i c o n w h i c h delicate and beautiful pictures w e r e p a i n t e d early in t h e n i n e t e e n t h century b y a n I n n s b r u c k family n a m e d B u r g m a n . T h e y are 'exquisite examples of an art that n o w ranks as scarcely m o r e t h a n a curiosity'.

F o o d and f e e d i n g habits T h e food of spiders includes a variety of insects, woodlice, myriapods, false-scorpions, harvest-spiders a n d other Arachnida. Bristowe (1941),* w h o has discussed t h e subject at s o m e length, has s h o w n that t h e potential food s u p p l y of different species varies w i t h i n w i d e limits. A h u n g r y s p i d e r is liable to accept an insect w h i c h i t will r e j e c t w h e n fully fed, t h e r e b y i n d i c a t i n g t h a t its d i s t a s t e i s r e l a t i v e a n d n o t a b s o l u t e . B y t h e i r m o d e o f life, t h e i r h u n t i n g m e t h o d s a n d t h e n a t u r e of t h e i r snares, different species of spiders b e c o m e adapted within wide limits to the capture of particular insects a n d m a y refuse t y p e s t o w h i c h t h e y are u n a c c u s t o m e d . T h u s a l t h o u g h Amaurobius s p p . m a y i n v e s t i g a t e w i t h t h e i r legs a w o o d l o u s e t h r o w n i n t o t h e i r w e b s , t h e y n e a r l y a l w a y s r e t r e a t w i t h o u t h a r m i n g it. U n l i k e Segestria senoculata, w h i c h will a t t a c k a b l a d e o f g r a s s d r a w n a c r o s s its w e b , a n d n o r m a l l y e a t s w o o d l i c e , A. ferox a n d A. similis will r e s p o n d o n l y to t h e v i b r a t i o n s of a t u n i n g fork, a n d will a t t a c k a w o o d l o u s e if a v i b r a t i n g t u n i n g fork i s p l a c e d o n t h e w e b j u s t b e s i d e i t ( C l o u d s l e y - T h o m p s o n , 1956). Atypus affinis, t h e sole B r i t i s h r e p r e s e n t a t i v e of t h e s u b - o r d e r M y g a l o m o r p h a , b u r r o w s i n t h e soil, b u t i n s t e a d o f m a k i n g a t r a p d o o r , i t c o n t i n u e s t h e silk l i n i n g o f its b u r r o w a b o v e t h e g r o u n d a s a

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closed t u b e . W h e n insects crawl o n this, t h e s p i d e r seizes t h e m f r o m w i t h i n a n d p u l l s t h e m t h r o u g h t h e silk. T h e c l o s e d p u r s e w e b o f t h i s s p e c i e s c l e a r l y r e s t r i c t s its d i e t t o c r a w l i n g i n s e c t s , worms and woodlice, whereas the orb webs of the Argiopidae a r e a d a p t e d t o t h e c a p t u r e o f i n s e c t s i n flight. A p a r a l l e l a m o n g s t h u n t i n g s p i d e r s is a f f o r d e d by Dysdera erythrina or Drassodes lapidosus, w h i c h h u n t m a i n l y u n d e r s t o n e s o r a t t h e r o o t s o f h e r b a g e a t n i g h t , w h i l s t t h e f l o w e r - l i v i n g h a b i t o f Misumena vatia a n d Thomisius onustus b r i n g t h e m i n t o c o n t a c t w i t h w i n g e d i n s e c t s . Protective flavours have b e e n evolved by m a n y invertebrates w h i c h t e n d t o r e n d e r t h e m d i s t a s t e f u l t o s p i d e r s . A t least s o m e species avoid earwigs, stoneflies, c a d d i s flies, m o t h s , beetles, b u g s , ants and other Hymenoptera, harvest-spiders, mites, woodlice and millipedes, and m a n y of these have developed warning m o v e m e n t s s i n c e n e i t h e r a p o s e m a t i c n o r p r o t e c t i v e c o l o r a t i o n a r e o f a n y avail against spiders t h a t r e s p o n d to tactile r a t h e r t h a n visual stimuli. Although invertebrate animals, particularly Arthropoda, form the bulk of t h e diet of spiders, there are a n u m b e r of records of vertebrates being eaten. As already mentioned some semi-aquatic L y c o s i d a e a n d P i s a u r i d a e m a y c a t c h fishes, w h i l e a m p h i b i a , l i z a r d s , y o u n g snakes, birds and small m a m m a l s not infrequently form the prey of larger spiders, especially the T h e r a p h o s i d a e . T h e subject has been reviewed by Millot (1943), to w h o m the reader is referred for f u r t h e r d e t a i l s . Spiders are a d a p t e d to various habitats within w h i c h s o m e attack large insects, others capture smaller kinds: s o m e spiders attack d i u r n a l insects, others h u n t by night; s o m e specialise in crawling insects, others in those that fly. Bristowe (1941)* discusses t h e m e a n s e m p l o y e d for t h e c a p t u r e o f p r e y a n d o n this basis divides t h e various families into h u n t i n g spiders, t u b e builders, s h e e t - w e b b u i l d e r s , b u i l d e r s o f scaffolding w e b s , m e s h e d w e b s a n d orb webs. S o m e h u n t i n g spiders seek their p r e y by day, t r u s t i n g to their good sight, while others are active at night a n d d e p e n d mainly on t h e sense of touch. J u m p i n g spiders (Salticidae) have t h e keenest s i g h t o f all a n d s t a l k t h e i r p r e y f r o m afar. O u r c o m m o n e s t s p e c i e s , Salticus scenicus, p r o v i d e s a c o n v e n i e n t e x a m p l e of t h e g r o u p . Equally at h o m e on a p e r p e n d i c u l a r surface or on t h e u n d e r s i d e of a

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h o r i z o n t a l b e a m , i t i s a b l e t o m a i n t a i n its p o s i t i o n b y m e a n s o f a n a d h e s i v e t u f t o f h a i r s , t h e ' s c o p u l a ' , o n e a c h o f its feet. A s i t m o v e s , t h e z e b r a s p i d e r t r a i l s b e h i n d i t a n e x c e e d i n g l y fine t h r e a d o f silk w h i c h i s a t t a c h e d a t f r e q u e n t i n t e r v a l s like a c l i m b i n g r o p e , s o t h a t i n t h e e v e n t o f a slip t h e s p i d e r d o e s n o t fall t o t h e g r o u n d . T h e species has a curious w a y of exploring t h e surface over w h i c h it is working by successive short r u n s alternating with periods of a b s o l u t e s t i l l n e s s . I t will o f t e n p a t i e n t l y s e a r c h a l a r g e a r e a b e f o r e i t c a t c h e s s i g h t o f a n i n s e c t , w h e n i t c a n b e s e e n t o t u r n its h e a d s o a s t o b r i n g its f o u r l a r g e a n t e r i o r e y e s t o b e a r u p o n t h e q u a r r y . T h e f o u r p o s t e r i o r e y e s a r e s m a l l e r a n d less i m p o r t a n t . F o r a t i m e i t remains motionless, t h e n begins to edge stealthily nearer until it is c l o s e e n o u g h for a s u d d e n s p r i n g . T h e f r o n t p a i r o f legs i s u s e d for s e i z i n g t h e p r e y a n d t h e r e m a i n i n g p a i r s for j u m p i n g . H o w e v e r , t h e j u m p i s n o t a l w a y s s u c c e s s f u l : o f t e n t h e i n s e c t s e e s its p e r i l a t t h e last m o m e n t a n d flies a w a y , a n d t h e s p i d e r h a s t o b e g i n all o v e r again. In contrast, t h e wolf spiders (Lycosidae) capture their prey by sheer strength and speed. T h e typical crab spiders (Thomisidae) are seldom seen by the o r d i n a r y o b s e r v e r , for t h e i r h a b i t s a r e r e t i r i n g a n d m a n y o f t h e m a r e r a t h e r s m a l l . T h e y w a i t m o t i o n l e s s for p a s s i n g i n s e c t s w h i c h a r e s e i z e d b y t h e p o w e r f u l o u t s t r e t c h e d legs, a n d h a v i n g b u r i e d their jaws in the head or thorax of the prey, they draw their limbs backwards out of danger of t h e victim's bite or sting. S o m e species however are true rovers h u n t i n g by day a n d passing the night w h e r e v e r t h e y h a p p e n t o f i n d t h e m s e l v e s . T h o s e t h a t lie i n w a i t often s h o w a r e m a r k a b l e degree of r e s e m b l a n c e to t h e colour of their background. O n e East I n d i a n species spins a white patch of silk o n t h e u p p e r s u r f a c e o f a leaf. L y i n g o n t h i s , i t l o o k s e x a c t l y like t h e d r o p p i n g o f s o m e b i r d , a n d s u c h d r o p p i n g s s e e m t o b e particularly attractive to butterflies! No doubt, however, predation by birds has b e e n an even m o r e i m p o r t a n t factor in natural selection. T h e O x y o p i d a e , s o m e t i m e s called lynx spiders, are h a n d s o m e h u n t i n g s p i d e r s t h a t h a v e b e c o m e s p e c i a l i s e d for life o n p l a n t s . T h e y can r u n o v e r v e g e t a t i o n w i t h great agility a n d leap from stem to stem with a precision surpassed only by that of true j u m p i n g spiders. T h e only British e x a m p l e of this family is the rare Oxyopes heterophthalmus.

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T h e r e m a i n i n g families s u c h a s t h e T h e r a p h o s i d a e , D y s d e r i d a e , Oonopidae, Gnaphosidae and Clubionidae contain mostly shortsighted nocturnal hunters that depend u p o n the sense of touch and grapple with any suitable insect they c o m e across in their w a n d e r i n g s . Harpactea hombergi, a s m a l l g r e y s p e c i e s c o m m o n u n d e r b a r k , h o l d s its v i c t i m s w i t h its t a r s a l c l a w s , w h i l e t h e l a r g e a n d f o r m i d a b l e Dysdera crocota a n d D. erythrina, easily r e c o g n i s e d by t h e i r r e d c e p h a l o t h o r a x a n d y e l l o w a b d o m e n , feed m o s t l y u p o n w o o d l i c e a n d l u n g e f o r w a r d s o q u i c k l y t h a t few e s c a p e . T h e i r c h e l i c e r a e a r e e s p e c i a l l y a d a p t e d for d e a l i n g w i t h t h i s p r e y ; t h e y a r e e x c e p t i o n a l l y large a n d powerful, a n d by tilting the p r o s o m a sideways one fang

F I G . 3 5 . Dysdera sp. eating a woodlouse. (After Bristowe, 1 9 5 4 . ) i s i n t r u d e d b e n e a t h t h e w o o d l o u s e a n d t h e o t h e r a b o v e it. Scotophaeus blackwalli is a m o u s e - c o l o u r e d h o u s e s p i d e r t h a t o f t e n falls into baths a n d sinks a n d t h e n cannot climb out. Like many other G n a p h o s i d a e a n d C l u b i o n i d a e , i t r e l i e s u p o n its s p e e d for t h e c a p t u r e of its p r e y , w h i l e t h e f e r o c i o u s Drassodes lapidosus, f r e q u e n t l y f o u n d u n d e r b a r k a n d s t o n e s , i m m o b i l i s e s its p r e y b y s w a t h i n g i t i n b a n d s o f silk. Perhaps the most interesting m e t h o d employed in the capture of i n s e c t s is t h a t of t h e r a r e Scytodes thoracica. T h i s s l o w - m o v i n g y e l l o w c o l o u r e d s p e c i e s s q u i r t s p o i s o n o u s g u m f r o m its j a w s w h i l s t o n t h e m o v e after t h e m a n n e r o f a c r u i s e r t a n k s p r a y i n g

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infantry with m a c h i n e - g u n fire. T h e prey is stuck firmly to the g r o u n d while t h e spider advances a n d eats it at leisure. T h e v a r i o u s u s e s o f silk e m p l o y e d b y s p i d e r s i n t h e c a p t u r e o f prey have already been mentioned. T h e Ctenizidae dart from their tubes and capture insects passing near the trap-door while the Atypidae strike t h r o u g h their purse-webs at any small animal

F I G . 36. Scytodes thoracica binding its prey with g u m which it squirts from the fangs. ( F r o m C l o u d s l e y - T h o m p s o n , 1953.)

c r a w l i n g o v e r t h e e x p o s e d p a r t . Segestria senoculata a n d o t h e r m e m b e r s of t h e g e n u s m a k e their t u b e s in crevices of walls a n d r o c k faces. T h e r i m o f t h e o p e n e n t r a n c e i s s t r e t c h e d o u t w a r d s by half a d o z e n or m o r e long s t o u t straight t h r e a d s . W h e n an insect or woodlouse touches one of these the spider darts forth to s e i z e a n d r e t i r e w i t h it. A s i m i l a r m e t h o d i s e m p l o y e d b y t h e F i l i s t a t i d a e , s u c h a s t h e w e l l - k n o w n M e d i t e r r a n e a n s p e c i e s Filistata insidiatrix. S h e e t - w e b s are built by several families, a n d in Britain by s o m e of t h e A g e l e n i d a e , L i n y p h i i d a e a n d Pholcus phalangioides ( P h o l cidae). In t h e first family t h e spiders r u n in an erect position on t h e u p p e r surface of the sheet, b u t in the other two they are s u s p e n d e d in an inverted position from t h e lower surface. Scaffolding w e b s a r e c h a r a c t e r i s t i c of t h e T h e r i d i i d a e . In Stearodea bipunctata, for example, a sheet of wide meshes is kept taut from above a n d below by a n u m b e r of threads extending vertically to t h e g r o u n d . T h e s e h a v e v i s c i d d r o p l e t s for p a r t o f t h e i r l e n g t h a n d b r e a k off easily

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at their point of attachment. As they are drawn very taut, an insect w h i c h b l u n d e r s into one not only breaks the a t t a c h m e n t b u t m a y b e lifted i n t o t h e a i r w h e r e its s t r u g g l e s b r i n g i t i n t o c o n t a c t w i t h other viscid threads. T h e m e s h e d w e b s o f t h e D i c t y n i d a e a n d some Uloboridae with their typical calamistrated threads have a l r e a d y b e e n m e n t i o n e d . T h e s e t h r e a d s e n t a n g l e t h e legs o f i n sects very securely a n d e n a b l e t h e spiders to c a p t u r e p r e y often m u c h larger t h a n themselves.

F I G . 37. Diagrammatic stages in the spinning of an orb-web. (After Savory, 1952.) Finally, typical orb webs are m a d e by the T e t r a g n a t h i d a e and A r g i o p i d a e . D u r i n g t h e d a y t i m e t h e g a r d e n s p i d e r Araneus diadematus g e n e r a l l y a b a n d o n s t h e h u b o f its w e b a n d r e s t s i n its retreat nearby, but towards evening it usually comes to the centre and remains there until early m o r n i n g w h e n it constructs a n e w w e b . Peters (1933) has s h o w n that t h e prey is dealt with by m e a n s o f a s e r i e s o f c h a i n reflexes. T h e s t r u g g l e s o f a v i c t i m i n t h e w e b a r e t h e s t i m u l u s for a l o n g b i t e a n d t h e t a s t e e x p e r i e n c e d s t i m u lates t h e e n s h r o u d i n g o f t h e p r e y . T h e silk b a n d s p r o v i d e a t a c t i l e s t i m u l u s f o r t h e reflex o f t h e s h o r t b i t e , w h i c h i n t u r n p r o d u c e s a s t i m u l u s for t h e c a r r y i n g reflex: s m a l l i n s e c t s a r e c a r r i e d t o t h e h u b

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of the w e b in the chelicerae, while heavier prey are carried on a t h r e a d f r o m t h e s p i n n e r e t s a n d s u p p o r t e d b y a h i n d leg. W h e n a lifeless i n e d i b l e o b j e c t t o u c h e s t h e w e b i t i s u s u a l l y c u t o u t a n d a l l o w e d t o fall t o t h e g r o u n d , a s a r e f o r m i d a b l e a n d d a n g e r o u s insects such as wasps and bees, whereas suitable prey is bitten and t h e n w r a p p e d u p . T h e b e h a v i o u r w h i c h follows t h e b i t i n g of a d i s t a s t e f u l i n s e c t i s s u r p r i s i n g : t h e s p i d e r m a k e s its w a y , s o m e t i m e s c l u m s i l y a s i f i n d i s t r e s s , t o t h e e d g e o f its w e b w h e r e i t g e t s r i d o f t h e d i s t a s t e f u l l i q u i d b y p r e s s i n g its m o u t h t o t h e g r o u n d o r w i p i n g it on a leaf. T h e s e brief descriptions of t h e m e t h o d s e m p l o y e d by spiders for t h e c a p t u r e o f p r e y b y n o m e a n s e x h a u s t t h e list o f i n g e n i o u s m e t h o d s that have arisen in the course of evolution. T h e water s p i d e r Argyroneta aquatica n o l o n g e r u s e s its w e b t o e n t r a p its p r e y , b u t h u n t s for s m a l l a q u a t i c c r e a t u r e s w h i c h a r e e a t e n o n d r y l a n d o r i n its b e l l , w h i l e a S o u t h A f r i c a n s p i d e r b u i l d s a s m a l l s n a r e r e s e m b l i n g a p o s t a g e s t a m p in size a n d s h a p e . T h e c o r n e r s are held b y t h e s p i d e r ' s long legs. W h e n a n insect a p p r o a c h e s , t h e w e b i s s t r e t c h e d t o n e a r l y five t i m e s its n o r m a l size a n d h u r l e d o v e r t h e prey. T h e r e can b e few d e v e l o p m e n t s m o r e r e m a r k a b l e h o w e v e r t h a n t h a t of certain A r g i o p i d a e in Australia a n d S o u t h Africa (Dicrostichus magnificus a n d Cladomelea akermani) w h i c h emerge at nightfall a n d whirl a t h r e a d weighted with a g u m m y globule until this strikes s o m e passing insect w h i c h is t h e n h a u l e d in.

Enemies S o far o n l y o n e s i d e o f t h e p i c t u r e h a s b e e n c o n s i d e r e d . I n a d d i t i o n to t h e vast n u m b e r s killed as a result of u n f a v o u r a b l e climatic conditions, spiders are beset with enemies t h r o u g h o u t t h e i r lives. T h e i n f a n t m o r t a l i t y r a t e i n p a r t i c u l a r i s i m m e n s e . B a b y s p i d e r s d o n o t feed u n t i l t h e y h a v e d i g e s t e d all t h e y o l k w i t h w h i c h t h e eggs from w h i c h t h e y h a t c h e d w e r e supplied, b u t after t h e i r first m o u l t t h e little s p i d e r l i n g s d e v e l o p t h e i r t y p i c a l c a n n i balistic tendencies a n d m a n y are eaten by their o w n kin. As W a r b u r t o n ( 1 9 1 2 ) w r o t e : ' T h e c a s e o f t h e s u r v i v o r o f t h e Nancy Bell i n t h e B a b B a l l a d s w o u l d b e e x c e e d i n g l y c o m m o n p l a c e i n t h e araneid world.' In addition to the n u m b e r s devoured by other spiders, b o t h of their o w n as well as of other species, spiders a n d

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their eggs are e a t e n by hosts of different k i n d s of animals. In this c o u n t r y t h e m o s t i m p o r t a n t o f t h e s e are p r o b a b l y t o a d s a n d frogs, starlings a n d other insectivorous birds, shrews, wasps a n d centipedes. Invertebrate enemies are very m u c h m o r e n u m e r o u s and probably destroy larger n u m b e r s of spiders than do vertebrates, b u t s p i d e r s e n t e r l a r g e l y i n t o t h e d i e t o f s m a l l e r b i r d s , b e i n g fed especially to t h e nestlings. M o r e o v e r , m a n y species of b i r d s use s p i d e r s ' e g g c o c o o n s t o line t h e i r n e s t s . S o c i a l w a s p s o f t e n kill s p i d e r s t o feed t h e i r l a r v a e , a n d t h e r e a r e t w o British families of solitary digger wasps, t h e P o m p i l i d a e a n d Trypoxylinidae, which h u n t spiders. T h e spiders are paralysed by stings, often in t h e principal nerve ganglia and are t h e n dragged to p r e v i o u s l y p r e p a r e d cells o r b u r r o w s . A f t e r t h i s t h e w a s p lays a n egg on each carcass a n d other paralysed spiders are a d d e d before che b u r r o w i s s e a l e d u p . T h e s e m u s t p r o v i d e e n o u g h f o o d for t h e w a s p g r u b , w h e n i t h a t c h e s , t o last t h r o u g h o u t t h e w h o l e o f its l a r v a l d e v e l o p m e n t , for t h e m o t h e r w a s p n e v e r s e e s h e r o f f s p r i n g . Fabre, Hingston and other naturalists have written graphic acc o u n t s of t h e habits of s p i d e r - h u n t i n g w a s p s . All k i n d s of spiders are attacked, a l t h o u g h wolf spiders are p e r h a p s t h e m o s t frequent victims of the Pompilidae, a n d in t h e tropics even large T h e r a p h o s i d a e fall p r e y t o t h e s e t e r r i b l e foes. T h e first a c t i o n o f o n e o f t h e s e w a s p s w h e n i t a t t a c k s a s p i d e r i s t o r e m o v e t h e l a t t e r f r o m its e n v i r o n m e n t , for a g a r d e n s p i d e r i s m u c h m o r e v u l n e r a b l e w h e n t o r n a w a y f r o m its w e b a n d a b u r r o w i n g s p i d e r d r a g g e d i n t o t h e open is nearly defenceless. It has been observed, however, that spiders appear completely 'panic-stricken' w h e n confronted by a fossorial w a s p . T h e i r i m m e d i a t e r e a c t i o n s e e m s t o b e t o flee, a n d they do not try to defend themselves even w h e n cornered. T h e parasites of spiders include Protozoa and N e m a t o d a , but there are few r e c o r d s in t h e literature. Infinitely m o r e i m p o r t a n t , especially in tropical climates, are 'parasitoids' or lethal parasites, particularly of the family I c h n e u m o n i d a e . T h e s e insects probably p a r a l y s e a s p i d e r b y m e a n s o f t h e i r s t i n g b e f o r e l a y i n g a n e g g o n its back. A l t h o u g h the most frequent victims of spider parasites are w e b - s p i n n e r s , s e v e r a l d i f f e r e n t k i n d s o f h u n t i n g s p i d e r h a v e also been found with eggs or larvae on their backs. T h e s e larvae eventually cause t h e death of their victim by feeding on the contents of

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t h e a b d o m e n . B y s o m e e x t r a o r d i n a r y instinct t h e vital o r g a n s are n o t e a t e n u n t i l last s o t h a t t h e s p i d e r d o e s n o t d i e u n t i l t h e i n s e c t i s r e a d y t o e m e r g e f r o m t h e n o w e m p t y s k i n o f its h o s t . T h e A c r o c e r i d a e ( D i p t e r a ) a r e a f a m i l y o f flies w h i c h h a v e e v o l v e d s i m i l a r p a r a s i t i c h a b i t s a n d m e m b e r s o f s e v e r a l o t h e r fly f a m i l i e s a s w e l l a s the Pimplinae and Cryptinae ( H y m e n o p t e r a ) are parasitic on the eggs of spiders. A p p a r e n t l y cryptic coloration a n d other protective d e v i c e s a r e o f little avail a g a i n s t t h e s e c r e a t u r e s , b u t e v e n s o , I c h n e u m o n s a n d o t h e r p a r a s i t o i d s a r e p r o b a b l y a far less i m p o r t a n t factor in controlling t h e n u m b e r s of spiders t h a n t h e y are in c o n trolling insect population. W i t h s o m a n y t e r r i b l e foes i t i s n o t s u r p r i s i n g t o find t h a t s p i d e r s h a v e e v o l v e d all k i n d s o f p r o t e c t i v e d e v i c e s , i n c l u d i n g p r i c k l y s p i n e s , u n p l e a s a n t f l a v o u r a n d s c e n t : s o m e e v e n eject u n p l e a s a n t fluids t h a t d e t e r p r e d a t o r s . Scytodes thoracica s q u i r t s g u m f r o m its f a n g s for d e f e n s i v e p u r p o s e s a s w e l l a s w h e n i t i s h u n t i n g . M a n y h u n t i n g s p i d e r s b u i l d s i l k e n p r o t e c t i v e cells i n w h i c h t h e y r e s t w h e n n o t i n s e a r c h o f p r e y . Scotophaeus blackwalli h a s e v o l v e d t h e habit of retreating with a b d o m e n raised, trailing b e h i n d it a r i b b o n o f silk t h a t s e r v e s a s a p r o t e c t i o n a g a i n s t a t t a c k f r o m t h e r e a r . M a n y spiders achieve concealment by m e a n s of cryptic coloration, closely r e s e m b l i n g t h e i r n a t u r a l b a c k g r o u n d , w h e t h e r t h i s i s a c o l o u r e d flower, a leaf, l i c h e n , s a n d o r b a r k . T h e c r a b s p i d e r s p r o v i d e n u m e r o u s fine e x a m p l e s o f s u c h c a m o u f l a g e . S o m e t i m e s t h e outline of t h e spider is camouflaged by m e a n s of a 'dazzlep a t t e r n ' , as in t h e c a s e of Salticus scenicus w h o s e i r r e g u l a r p a t c h e s of contrasted colours tend to draw the attention of the observer from t h e s h a p e t h a t bears t h e m . E g g cases too are frequently c o n c e a l e d w i t h t w i g s a n d p i e c e s o f leaf. P o i s o n o u s a n d p o w e r f u l s p e c i e s m a y s h o w c o n s p i c u o u s c o l o r a t i o n s , w h i l e all k i n d s o f poisonous a n d distasteful insects s u c h as ants, wasps, b u g s , beetles a n d e v e n s c o r p i o n s a r e effectively m i m i c k e d b y v a r i o u s s p i d e r s (Bristowe, 1941).* F o r example, amongst the Argiopidae s o m e species of the genus Cyclosa r e s e m b l e s m a l l s n a i l s w h i c h , o n a c c o u n t o f t h e h a r d n e s s o f their shells, w o u l d b e eaten b y few b i r d s a n d w o u l d certainly be neglected both by Pompilidae and Ichneumonidae, the principal enemies of spiders. O n e such species has been recorded from

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Ceylon, a n o t h e r from N o r t h A m e r i c a . T h e latter, w h e n clinging t o t h e u n d e r s i d e o f a leaf w i t h its legs d r a w n u p , i s a l m o s t a n e x a c t copy in colour a n d s h a p e of a small snail w h i c h is a b u n d a n t in similar situations in t h e s a m e locality d u r i n g t h e w a r m m o n t h s of the year. T h e resemblance is enhanced by the complete i m m o b i l i t y t h e s p i d e r m a i n t a i n s w h e n t o r n f r o m its h o l d o r w h e n t h e plant is rudely shaken. A p a r t from beetles, the insects m o s t frequently m i m i c k e d by spiders are ants and so n u m e r o u s and perfect are the instances that all o t h e r e x a m p l e s o f m i m i c r y a m o n g s t s p i d e r s fall i n t o i n s i g n i ficance b e s i d e t h e m . A c o n s t r i c t i o n o n e a c h s i d e o f t h e s p i d e r ' s carapace divides it into an anterior part resembling the head, a narrow intermediate part representing the neck and a posterior p a r t r e p r e s e n t i n g t h e t h o r a x of t h e insect. In m a n y cases t h e appearance of slenderness a b o u t the neck is a u g m e n t e d by a strip of white hairs on each side of t h e constriction, w h i c h has the o p t i c a l effect o f c u t t i n g o u t a n e x t r a p i e c e o f t h e i n t e g u m e n t . T h e waist of the ant is r e p r o d u c e d by the conversion of the e n d of t h e carapace a n d often of t h e anterior e n d of t h e a b d o m e n into a n a r r o w s t a l k . I n s o m e c a s e s t h e a b d o m e n i s itself s h a l l o w l y c o n stricted and even the abdominal segments of the insect m a y be r e p r e s e n t e d b y t r a n s v e r s e b a n d s o f h a i r s . T h e legs a r e a l w a y s s l e n d e r , like t h o s e o f a n a n t , a n d o n e o f t h e a n t e r i o r p a i r s i s h e l d u p i n f r o n t o f t h e h e a d a s a s u b s t i t u t e for a n t e n n a e . F i n a l l y , i t h a s been found that the spiders carry deception to the extent of copying t h e m a n n e r s a n d gait of t h e insects (Pocock, 1909). As m i g h t be expected, ant-mimicry is of m u c h c o m m o n e r occurrence amongst ground-living species of spiders t h a n it is a m o n g s t t h e sedentary w e b spinners, b u t instances are not u n k n o w n amongst the latter. S u c h m i m i c r y represents a wonderful e x a m p l e of convergent evolution a m o n g s t spiders b e l o n g i n g to t h e families Salticidae, G n a p h o s i d a e , Clubionidae, T h o m i s i d a e , T h e r i d i i d a e , A r g i o p i d a e e t c . A s i n all c a s e s o f B a t e s i a n m i m i c r y , t h e m i m i c s exist i n s m a l l n u m b e r s c o m p a r e d w i t h t h e i r m o d e l s . L i k e scorpions a n d Solifugae, m a n y of t h e larger spiders can stridulate, p r o b a b l y as a w a r n i n g to e n e m i e s . In t h e case of smaller species in w h i c h s o u n d - p r o d u c i n g organs are confined to the males, their function is probably that of courtship. C h r y s a n t h u s

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(1953) h a s reviewed t h e subject of h e a r i n g a n d stridulation in spiders. He c o n c l u d e s t h a t v i b r a t i o n s of t h e air are perceived, so s p i d e r s m u s t p o s s e s s a real f a c u l t y o f h e a r i n g . In conclusion, it should be r e m e m b e r e d that of the enemies of spiders, m a n is in the first rank not only on account of the n u m b e r s d e s t r o y e d b y i n s e c t i c i d e s a n d i n a g r i c u l t u r e , b u t also for t h e n u m b e r s e a t e n b y p r i m i t i v e p e o p l e s i n all p a r t s o f t h e w o r l d . I n S i a m for e x a m p l e t h e L a o s e a t t w o d i f f e r e n t t y p e s , t h e g i a n t o r b w e b b e d Nephila s p p . a n d t h e l a r g e h a i r y M y g a l o m o r p h a . T h e f o r m e r a r e known by a Siamese n a m e that means 'the golden one'. W h e n r o a s t e d a n d d i p p e d i n salt t h e a b d o m e n , w h i c h i s t h e o n l y p a r t eaten, has a flavour of r a w p o t a t o a n d lettuce m i x e d . M y g a l o m o r p h a are even m o r e highly prized: their chelicerae are pulled out a n d t h e spiders are roasted on sticks w h i c h r e m o v e s t h e hair, a n d t h e n e a t e n w i t h salt. I n c i d e n t a l l y t h e h a i r s o f t h e s e M y g a l o m o r p h s p i d e r s c a n c a u s e v e r y g r e a t d i s c o m f o r t , a n d i f t h e face i s t o u c h e d after s t r o k i n g o n e o f t h e s e c r e a t u r e s , s i g h t m a y e v e n b e endangered. On the other h a n d the bites of giant bird-eating M y g a l o m o r p h a are usually not serious. F a r m o r e dangerous are s o m e o f t h e C t e n i z i d a e , a n d t h e s p i d e r s o f t h e g e n u s Latrodectus s u c h a s L . mactans, t h e n o t o r i o u s ' b l a c k w i d o w ' o f N o r t h A m e r i c a , whose bite causes agonising pain that develops and spreads within a q u a r t e r of an h o u r . T h i s is often a c c o m p a n i e d by profuse sweating, difficulty i n b r e a t h i n g , v o m i t i n g , p r o s t r a t i o n , c o n v u l s i o n s a n d n u m e r o u s o t h e r effects. D r o p for d r o p t h e p o i s o n i s s a i d t o b e m o r e virulent t h a n that of the rattlesnake, b u t the a m o u n t injected by the spider is small a n d variable: d e a t h has o c c u r r e d in a b o u t 5 % of k n o w n cases of bites, b u t this figure is p r o b a b l y m i s l e a d i n g as m a n y cases are n e v e r r e c o r d e d o r d i a g n o s e d ( T h o r p a n d W o o d s o n , 1945). T h e food o f t h e ' b l a c k w i d o w ' i n c l u d e s v e r y t o u g h a n d r e s i s t a n t b e e t l e s and it has b e e n suggested t h a t t h e virulent toxicity of its v e n o m m a y b e c o r r e l a t e d w i t h t h e t o u g h n a t u r e o f its p r e y .

Mating habits S p i d e r s a r e n e a r l y a l w a y s o n t h e offensive a n d a r e r e a d y t o kill a n d e a t m o s t a n i m a l s o f s u i t a b l e size t h a t c o m e w i t h i n r a n g e . T h e y are inveterate cannibals, so it is obvious that m a t i n g m u s t be a h a z a r d o u s u n d e r t a k i n g f r a u g h t w i t h real d a n g e r , p a r t i c u l a r l y t o t h e

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male w h o is usually smaller and weaker t h a n his intended mate. I n d e e d , h e will a l m o s t c e r t a i n l y b e d e v o u r e d u n l e s s h e s u c c e e d s i n allaying temporarily t h e carnivorous instincts of the female, and this he m u s t do before he ventures within reach of her rapacious jaws. Bristowe ( 1 9 4 1 , * etc.) has e m p h a s i s e d t h a t it is of t h e u t m o s t i m p o r t a n c e to the male to establish his identity so that he is not t r e a t e d like a n i n s e c t v i c t i m , a n d t h e r e a f t e r c o u r t s h i p m u s t p r o ceed until the female has b e e n stimulated to a state in w h i c h her s e x u a l i n s t i n c t s h a v e b e e n a r o u s e d s o t h a t s h e will p e r m i t m a t i n g t o take place. C o n s e q u e n t l y , w h i c h e v e r of t h e senses is t h e one on w h i c h t h e s p e c i e s chiefly r e l i e s for t h e c a p t u r e o f its p r e y , i s t h e sense m o s t employed in courtship. M a l e j u m p i n g spiders and wolf s p i d e r s m a k e use of visual signs, s h o r t - s i g h t e d a n d n o c t u r n a l species of contact stimuli, w e b spinners use distinctive tweaks and vibrations of the threads of the snare, and so on. T h e m a t i n g p r o c e d u r e o f s p i d e r s i s q u i t e u n i q u e , for w h e n t h e m a l e r e a c h e s m a t u r i t y h e w e a v e s a s m a l l p a d o f silk o n w h i c h a d r o p of s p e r m is deposited a n d this is sucked up by t h e specially modified 'pedipalps' or h a n d s w h i c h in d u e course are inserted i n t o t h e v a g i n a o f t h e f e m a l e . E a c h s p e c i e s h a s a p a l p w i t h its o w n d i s t i n c t i v e s h a p e , a d i a g n o s t i c c h a r a c t e r e s s e n t i a l for a c c u r a t e identification. C o u r t s h i p is a subject of great interest a n d i m p o r t a n c e a n d the literature on the subject is immense. I n T h e r a p h o s i d s p i d e r s s u c h a s Dugesiella hentzi, w h e n a r e s t lessly w a n d e r i n g m a l e h a p p e n s t o t o u c h w i t h h i s legs s o m e p a r t o f t h e b o d y o r leg o f a f e m a l e , h e a t o n c e s t o p s s h o r t a n d b e g i n s t o strike it simultaneously a n d violently with his anterior a n d s o m e t i m e s w i t h all f o u r f r o n t feet. T h i s c o n t i n u o u s b e a t i n g w i t h t h e f r o n t legs u p o n t h e b o d y o r legs o f t h e f e m a l e c o n s t i t u t e s t h e f i r s t step in courtship. At first the female assumes an attitude of defence, b u t after a w h i l e s h e r i s e s h i g h o n h e r h i n d l e g s w h i l e still h o l d i n g up h e r front legs. Finally she o p e n s h e r fangs a n d t h e m a l e catches t h e m w i t h t h e hooks o n his front legs. H e n o w forcibly p u s h e s back the cephalothorax of the female, at the same time d r u m m i n g on h e r s t e r n u m w i t h t h e patellas of his p e d i p a l p s . M a t i n g lasts only a m i n u t e o r t w o , after w h i c h t h e t w o s e x e s p a r t , t h e f e m a l e m a k i n g no a t t e m p t to attack ( P e t r u n k e v i t c h , 1911).

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W h e n t h e m a l e Atypus affinis f i n d s t h e t u b e of a f e m a l e , he d r u m s u p o n it with his palps and p r e s u m a b l y is able to ascertain by the reactions of t h e i n m a t e w h e t h e r he is welcome. After a while he cuts open the tube and enters; the rent is afterwards repaired by the female. M a t i n g occurs deep in the t u b e and the m a l e i s b e l i e v e d t o live i n t h e b u r r o w f o r m a n y m o n t h s b e f o r e h i s m a t e eventually eats h i m . Amongst short-sighted hunting spiders the male's chemotactic sense often w a r n s h i m of the presence of a female in the vicinity. H e m o v e s w i t h c a u t i o n a n d i n s o m e species vibrates his legs. Drassodes s p p . t a k e p o s s e s s i o n o f t h e i r f e m a l e s b e f o r e t h e s e h a v e a t t a i n e d m a t u r i t y o r full s t r e n g t h . S o m e , s u c h a s Pachygnatha s p p . avoid injury by seizing t h e chelicerae of t h e females a n d holding these w i t h t h e aid of special a d a p t a t i o n s , while o t h e r s s p a r w i t h t h e i r m a t e s a n d r e l y o n t h e i r o u t s t r e t c h e d legs a n d t h e i r a g i l i t y t o a v o i d i n j u r y f r o m a n y i n i t i a l a t t a c k r e s u l t i n g f r o m t h e first c o n t a c t . T h e n o c t u r n a l Dysdera crocota h a s a p l a c i d t a c t i l e c o u r t s h i p w h i c h a p p a r e n t l y can b e initiated b y e i t h e r sex. O n e s p i d e r a p p r o a c h e s t h e o t h e r , q u i v e r i n g a n d g e s t i c u l a t i n g w i t h f r o n t legs h e l d aloft. D u r i n g copulation t h e palps are inserted simultaneously a n d t h e t w o spiders stroke a n d caress each o t h e r w i t h their forelegs. S o m e of t h e s e d e n t a r y s p i d e r s w i t h inferior eyesight s h o w few of t h e p r e l i m i n a r y activities identifiable as t r u e c o u r t s h i p . E v e n t h o u g h t h e e y e s o f s o m e o f t h e T h o m i s i d a e a r e fairly l a r g e , t h e s p i d e r s m a k e little u s e o f s i g h t i n c o u r t i n g . W h e n a m a l e d i s c o v e r s a female of his species he immediately climbs u p o n her back or seizes a n a p p e n d a g e w i t h h i s c h e l i c e r a e . H e i s m o r e agile a n d c a n tickle a n d caress h e r b o d y until he is able to accomplish his p u r p o s e . T h e m a l e Xysticus s p . p r o t e c t s h i m s e l f i n m a t i n g b y f a s t e n i n g h i s m a t e t o t h e g r o u n d w i t h a few s i l k e n t h r e a d s ( B r i s t o w e , 1 9 2 2 , e t c . ) , w h i l e i n Pisaura mirabilis ( P i s a u r i d a e ) h e c a t c h e s a n d w r a p s a n i n s e c t i n silk b e f o r e a p p r o a c h i n g t h e f e m a l e a n d h a n d s i t to her as a preliminary to mating. T h i s behaviour is u n i q u e in s p i d e r s b u t h a s a p a r a l l e l a m o n g s t E m p i d flies. T h e visual displays of the Lycosidae a n d Salticidae have been studied especially by Bristowe a n d L o c k e t (Bristowe, 1929, 1941,* etc.), a n d m o r e recently C r a n e (1948, 1949, etc.) has m a d e detailed analyses of t h e behaviour of various tropical Salticidae such as

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Corythalia s p p . I n m o s t w o l f s p i d e r s t h e p e d i p a l p s a n d f r o n t legs are provided with an ornamentation of hair that contrasts sharply with the rest of the body. T h e male stands before the female waving these simultaneously or alternately in a kind of s e m a p h o r e courtship. O n e species found on Staten Island, Argentina, makes a c u r i o u s p u r r i n g n o i s e a t m a t i n g t i m e b y d r u m m i n g o n d e a d leaves w i t h its p a l p s . I t i s p r o b a b l e t h a t i n t h i s c a s e t h e f e m a l e a p p r e c i a t e s the vibrations at some distance. E v e n m o r e dramatic are the courti n g d a n c e s o f m a l e j u m p i n g s p i d e r s . I n t h e t r o p i c a l s p e c i e s Hasarius adansoni f o u n d i n m a n y h o t h o u s e s i n B r i t a i n , t h e m a l e i s a h a n d s o m e , squat, glossy black a n d b r o w n spider w i t h c o n s p i c u o u s w h i t e m a r k i n g s o n t h e p e d i p a l p s , a b d o m e n a n d distal l i m b segm e n t s . D u r i n g courtship he advances slowly in zig-zag fashion, waving his palps up a n d d o w n . W h e n the female, w h o is a s o m b r e

F I G . 38. Hasarius adansoni) the male in courting attitude. ( F r o m C l o u d s l e y - T h o m p s o n , 1953.) b r o w n colour, t u r n s towards h i m he stops and remains motionless w i t h his large forelegs held horizontally above t h e g r o u n d . T h e n h e m o v e s forward again. As he nears the female he m a y j u m p rapidly sideways or backwards. Again and again this display continues u n t i l a t l a s t h e i s p e r m i t t e d t o i n s e r t first o n e a n d t h e n t h e o t h e r o f his p e d i p a l p s , a n d copulation takes place, t h e palps b e i n g inserted alternately ( C l o u d s l e y - T h o m p s o n , 1949). M o c k , bloodless battles n o t infrequently o c c u r b e t w e e n rival male j u m p i n g spiders. Bristowe (1929) believes these to result from

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mistaken identity, one male being stimulated sexually by another of t h e s a m e species, b u t C r a n e (1948) regards t h e m as threat disp l a y s a n d s h e h a s s h o w n t h a t i n Corythalia s p p . s u c h b e h a v i o u r i s d i s t i n c t f r o m c o u r t s h i p . T h e f r i n g e d , i r i d e s c e n t legs a r e a l w a y s u s e d in threat displays, b u t are never employed in courtship. A m o n g web-builders courtship usually consists of the male telegraphing to the female occupant of a web by tweaking the t h r e a d s as he a p p r o a c h e s , b u t in later stages a tactile stroking of t h e b o d y precedes coition. T h i s r o u t i n e m a y constitute a tactile display almost equal in interest to the visual displays of t h e longsighted hunting spiders. In ethological terminology, the function of courtship is to p r o v i d e r e l e a s e r s t i m u l i for t h e m a t i n g i n s t i n c t w h i c h a t t h e s a m e t i m e b l o c k h u n g e r d r i v e s . T h e c o n c e p t o f r e c o g n i t i o n m a y n o t i n fact b e necessary. P o l y g a m y i s t h e c u s t o m a m o n g s p i d e r s a n d i t i s i n d e e d w i s e for the m a l e to retreat hastily immediately copulation is finished. It is p r o b a b l e t h a t t h e m a l e Atypus affinis i s n o t g i v e n a n y o p p o r t u n i t y t o e s c a p e f r o m t h e f e m a l e ' s lair, b u t t h e r e i s n o e v i d e n c e t h a t t h e w i d o w will refuse a d m i t t a n c e to a succession of h u s b a n d s . In c o n t r a s t i t s e e m s p r o b a b l e t h a t Amaurobius ferox f e m a l e s m a t e o n l y o n c e . O c c a s i o n a l l y t h e s e x e s a p p e a r t o live t o g e t h e r p e a c e f u l l y , b u t e x p e r i m e n t h a s s h o w n t h a t i n t h e c a s e o f Meta segmentata t h i s a p p a r e n t f a i t h f u l n e s s i s f i c t i o n a l a n d m a l e s m a y visit t h e w e b o f m o r e t h a n o n e f e m a l e . I n t h i s s p e c i e s t h e m a l e s o f t e n kill o n e another. Since courtship is deferred until the female is engaged in t r u s s i n g a v i c t i m o r e a t i n g a m e a l , i t i s n o t u n c o m m o n t o see i t taking place over t h e d e a d b o d y of a v a n q u i s h e d rival (Bristowe, 1941).*

Life history S p i d e r s lay t h e i r e g g s i n r e t r e a t s a n d c o c o o n s w h i c h t h e y c o n s t r u c t o f silk a n d o f t e n m o u n t g u a r d o v e r t h e m u n t i l t h e y o u n g have h a t c h e d . T h e r a p h o s i d a e p r e p a r e great flabby egg p u r s e s in their b u r r o w s a n d g u a r d t h e m assiduously, while the delicate silken sacs of t h e t r a p - d o o r spiders often h a n g from t h e side of t h e tube. Wolf spiders (Lycosidae) carry their globular cocoons a t t a c h e d t o t h e i r s p i n n e r e t s w h e r e v e r t h e y g o , a n d after h a t c h i n g

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t h e y o u n g c l i m b o n t h e i r m o t h e r ' s b a c k w h e r e t h e y r e m a i n for several days. I n t h e Pisauridae t h e m o t h e r spider carries h e r cocoon u n d e r h e r s t e r n u m : w h e n t h e y o u n g a r e r e a d y t o e m e r g e s h e fixes i t t o t h e e n d o f a b r a n c h a n d m o u n t s g u a r d o v e r it, w h i l e t h e f e m a l e Pholcus phalangioides g l u e s h e r f e w e g g s t o g e t h e r l i g h t l y a n d c a r r i e s the mass in her chelicerae. S o m e of the most elaborate cocoons are s p u n b y w e b - b u i l d i n g spiders: t h e sac m a y h a n g from t h e w e b o r m a y b e fixed t o t h e v e g e t a t i o n n e a r b y . T h e u s e o f silk t o p r o t e c t t h e e g g s w a s p r o b a b l y e v o l v e d e a r l y i n the history of spiders and m a n y refinements have since been added. T h e covering is often t o u g h e n e d a n d t h i c k e n e d w i t h several layers o f silk a n d m a y b e p l a s t e r e d w i t h l a y e r s o f m u d o r e m b e l l i s h e d w i t h bits of w o o d , leaves a n d o t h e r d e b r i s w h i c h r e n d e r it inc o n s p i c u o u s . S o m e s p i d e r s s p i n a s e r i e s o f e g g - s a c s w h i c h a r e left singly h e r e a n d t h e r e , t h u s m i n i m i s i n g t h e risk o f t h e w h o l e b r o o d being parasitised. T h e n u m b e r o f eggs laid b y different species varies e n o r m o u s l y . Theraphosa blondi, t h e l a r g e s t of all s p i d e r s , is s a i d to lay as m a n y as 3,000 a n d t h e larger orb-weavers a n d Pisauridae m a y p r o d u c e m o r e t h a n 2 , 0 0 0 . W h i l e t h e t i n y Oonops pulcher lays o n l y t w o , t h e m a j o r i t y o f s p i d e r s p r o b a b l y lay a b o u t 100 e g g s , a n d t h o s e p r o d u c i n g m o r e t h a n o n e c o c o o n u s u a l l y lay f e w e r e g g s i n e a c h . T h e l a r g e r s p e c i e s t e n d t o lay m o r e e g g s t h a n t h e s m a l l e r s p e c i e s . N o t only is there an obvious physical relationship, b u t there m a y be an e c o l o g i c a l c o n n e c t i o n b e t w e e n size a n d e g g n u m b e r , for b i g s p i d e r s usually take longer to reach m a t u r i t y t h a n the smaller kinds. T h e n u m b e r o f e g g s l a i d i s c l e a r l y r e l a t e d t o t h e size o f t h e m o t h e r s p i d e r w h e r e different species of t h e s a m e family are c o n cerned. P e t e r s e n (1950), in a discussion of t h e significance of this r e l a t i o n s h i p i n t h e e v o l u t i o n o f s i z e i n v a r i o u s s p e c i e s o f Lycosa, c o n c l u d e s t h a t s i n c e l a r g e r s p i d e r s lay m o r e e g g s a n d t h e size o f t h e m o t h e r is to a certain extent inherited, there m u s t be a selection t o w a r d s l a r g e r size w h i c h i n n a t u r e i s p r o b a b l y b a l a n c e d b y efficient c o u n t e r s e l e c t i o n . A s i m i l a r r e l a t i o n s h i p h a s also b e e n s h o w n to e x i s t in Amaurobius ferox a n d A. similis by C l o u d s l e y T h o m p s o n ( 1 9 5 6 ) . I n A . ferox, a b o u t t h r e e w e e k s e l a p s e i n t h e s u m m e r after egg laying before t h e y o u n g b e g i n t o leave t h e i r cocoon and the m o t h e r remains in the breeding nest until they M

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have dispersed. S o m e t i m e s she dies a n d t h e n t h e spiderlings a p p e a r t o feed o n h e r b o d y b e f o r e t h e y l e a v e t h e n e s t . I n t h i s s p e c i e s t h e life c y c l e o c c u p i e s t w o o r m o r e y e a r s . S p i d e r l i n g s hatching in the s u m m e r reach maturity in the a u t u m n of the f o l l o w i n g y e a r a n d lay t h e i r e g g s w h e n t h e y a r e t w o y e a r s o l d . T h e y m a y live for a n o t h e r s e a s o n o r e v e n l o n g e r . A f t e r h a t c h i n g , a period of s o m e days m a y elapse before the spiderlings scatter, d u r i n g w h i c h , a s w e h a v e s e e n , t h e y e a t little o r n o t h i n g . B r i s t o w e ( 1 9 4 7 ) s t a t e s t h a t t h e m o t h e r Theridion sisyphium f e e d s h e r y o u n g from her m o u t h . Whilst she hangs downwards, the babies jostle o n e a n o t h e r t o r e a c h t h e d r o p s o f fluid s h e r e g u r g i t a t e s for t h e i r b e n e f i t , b u t t h i s m u s t b e a f t e r t h e first e c d y s i s . F o r s e v e r a l d a y s t h e p r o c e d u r e c o n t i n u e s a n d t h e n for s o m e w e e k s a f t e r w a r d s m o t h e r a n d y o u n g feed s i m u l t a n e o u s l y o n t h e i n s e c t s s h e c a t c h e s . T h e n u m b e r of moults necessary to attain maturity varies widely i n s p i d e r s . I t h a s b e e n s h o w n t h a t i n m o s t s p e c i e s , size i s t h e d e t e r m i n i n g factor: small spiders m o u l t four or five t i m e s , t h o s e of m e d i u m size seven o r eight t i m e s while s o m e o f t h e T h e r a p h i s o d a e m a y m o u l t m o r e t h a n t w e n t y times. E v e n within t h e same species there is variation in the n u m b e r of ecdyses. F o r example, in Dolomedes plantarius t h e f e m a l e m a y m o u l t a s f e w a s n i n e o r a s m a n y a s t h i r t e e n t i m e s , t h e n u m b e r b e i n g correlated w i t h size a n d nourishment. M o s t s p i d e r s t h a t i n h a b i t t h e t e m p e r a t e z o n e s live o n l y o n e y e a r , b u t t h e m o r e p r i m i t i v e s p e c i e s t e n d t o live l o n g e r . I n t h e m a j o r i t y o f s p e c i e s t h e life c y c l e v a r i e s f r o m e i g h t m o n t h s t o f o u r y e a r s , a n d t h e r e c o r d f o r l o n g e v i t y i s h e l d b y a T h e r a p h o s i d , Eurypelma s p . , w h i c h lived for t w e n t y years. T h e m a l e s m a t u r e i n eight o r n i n e years, a n d usually die a few m o n t h s later. T h e dispersal of y o u n g spiders of m a n y species is achieved by 'ballooning', already mentioned. T h o s e that survive the rigours of these perilous j o u r n e y s a n d land in a suitable e n v i r o n m e n t begin a life o f t o i l a n d s l a u g h t e r , o f sacrifice a n d p a r e n t a l c a r e w h i c h , for a small proportion of fortunate individuals, m a y culminate in the production of yet another batch of baby spiderlings.

SPIDERS BIBLIOGRAPHY Identification BLACKWALL, J. (1861) A History of the Spiders of Great Britain and Ireland 1. London. (1864) Ibid., 2. BOSENBERG, W. (1901-3) Die S p i n n e n D e u t s c h l a n d s . Zoologica Stuttgart, 14,1-465. BRISTOWE, W. S. (1938) T h e classification of spiders. Proc. Zool. Soc. Lond., B 1 0 8 , 285-322. BRYANT, E. B. (1940) C u b a n spiders in the M u s e u m of Comparative Zoology. Bull. Mus. Comp. Zool, 8 6 , 249-532. CHECKERING, A. M. (1946) T h e Salticidae (spiders) of P a n a m a . Ibid.,97, 1-248. D A H L , M . (1926) Spinnentiere oder Arachnoidea, 1 : Springspinnen (Salticidae). Tierw. Deuts, 3 , 1 - 5 5 . (Various other families have been treated subsequently by different authors u n d e r the general editorship of F. D A H L ) . H O L M , A. (1947) Svensk Spendelfauna Araneae F a m . 8-10. Stockholm. KASTON, B. J. (1948) Spiders of Connecticut. State Geol. Nat. Hist. Surv. Hartford, 7 0 , 1 - 8 7 4 . LOCKET, G. H. and M I L L I D G E , A. F. (1951) British Spiders, 1. L o n d o n . (1953) Idem., 2. LOHMANDER, H. (1942) Sudschwedische S p i n n e n , 1. G n a p h o s i d a e . Medd. Goteborgs Mus. Zool, 9 8 , 1-163. PETRUNKEVITCH, A. (1933) An inquiry into the natural classification of spiders, based on a s t u d y of their internal anatomy. Trans. Conn. Acad. Arts Sci., 3 1 , 2 9 9 - 3 8 9 . et al. (1939) Catalogue of American spiders, P a r t 1. Ibid., 3 3 , 133-338. PICKARD-CAMBRIDGE, O. (1879) The Spiders of Dorset, Part I. S h e r b o u r n e . (1881) Ibid., P a r t 2. S I M O N , E. (1892-1903) Histoire naturelle des Araignees, 2 ed. Paris. (1914-1937) Arachnides de France, 6 , 1 - 1 2 9 8 . TULLGREN, A. (1944) Svensk Spindelfauna Araneae, F a m . 1-4. Stockholm. (1946) Ibid., F a m . 5-7. W I E H L E , H. (1953) Spinnentiere oder Arachnoidea (Araneae) I X . Tierw. Deuts., 4 2 , 1 - 1 5 0 . me

Biology BISHOP, S. C. (1945) O u r L a d y ' s t h r e a d s . Trans. Conn. Acad. Arts Sci., 3 6 , 91-7. BRAENDEGAARD, J. (1938) Aeronautic spiders in the Arctic. Medd. om Gronland, 1 1 9 , (5), 1-9. (1946) T h e spiders (Araneina) of East G r e e n l a n d . Ibid., 121, (15), 1-128.

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BRISTOWE, W. S. (1922) Spiders found in the n e i g h b o u r h o o d of Oxshott Proc. S. Lond. Ent. Soc, 1 9 2 2 , 1 - 1 1 . —— (1923) A British semi-marine spider. Ann. Mag. Nat. Hist., (9), 1 2 , 154-6. (1928) Facts and fallacies about spiders. Proc. S. Lond. Ent. Nat. Hist. .Soc, 1 9 2 8 - 9 , 1 2 - 2 3 . (1929) T h e mating habits of spiders with special reference to the problems s u r r o u n d i n g sex d i m o r p h i s m . Proc. Zool. Soc. Lond., 1 9 2 9 , 309-58. (1930a) N o t e s on the biology of spiders. 1. T h e evolution of spiders' snares. Ann. Mag. Nat. Hist. (10), 6, 334-42. (1930b) N o t e s on the biology of spiders, 11.—Aquatic spiders. Ibid., (10), 6, 3 4 3 - 7 . (1932) Insects and other invertebrates for h u m a n c o n s u m p t i o n in Siam. Trans. Ent. Soc. Lond., 8 0 , 387-404. (1945) Spider superstitions and folklore. Trans. Conn. Acad. Arts Sci., 3 6 , 5 3 - 9 0 . (1947) A Book of Spiders. L o n d o n . (1954) T h e chelicerae of spiders. Endeavour, 1 3 , 4 2 - 9 . CLOUDSLEY-THOMPSON, J. L. (1949) N o t e s on Arachnida, 11. M a t i n g habits of Hasarius adansoni Sav. Ent. Mon. Mag., 8 5 , 2 6 1 - 2 . (1953) T h e biology of h u n t i n g spiders. Discovery, 1 4 , 2 8 6 - 9 . (1956) T h e life histories of the British cribellate spiders of the genus Ciniflo Bl. (Dictynidae). Ann. Mag. Nat. Hist., (12), 8, 7 8 7 - 9 4 . (1957) Studies in diurnal r h y t h m s , V. N o c t u r n a l ecology and water relations of the British cribellate spiders of the genus Ciniflo B\.J. Linn. Soc. (Zool), 4 3 , 1 3 4 - 5 2 . CRANE, J. (1948) Comparative biology of Salticid spiders at R a n c h o G r a n d e , Venezuela. Part 1. Systematics and life histories in Corythalia. Zoologica, 3 3 , 1-38. (1949) Idem. P a r t I V . An analysis of display. Ibid., 3 4 , 1 5 9 - 2 1 4 . CHRYSANTHUS, F. (1953) Hearing and stridulation in spiders. Tijdscr. Ent., 9 6 , 57-83. DUFFEY, E. (1956) Aerial dispersal in a k n o w n spider population. J. Anim Ecol, 2 5 , 85-114. M A C C O O K , H. C. (1889-94) American Spiders and their Spinningwork, 1 - 3 , Philadelphia. M I L L O T , J. (1943) Les araign6es mangeuses de vertebres. Bull. Soc. zool. Fr., 6 8 , 1 0 - 1 6 . MOGGRIDGE, J. T. (1873) Harvesting Ants and Trap-door Spiders. L o n d o n . (1874) Ibid. S u p p l e m e n t . NEMENZ, H. (1954) O b e r den Wasserhoushalt einiger Spinnen, mit besonderer Beriicksichtigung der T r a n s p i r a t i o n . Ost. Zool. Zeits., 5, 123-58. NIELSEN, E. (1932) The Biology of Spiders, 1, 2. Copenhagen.

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PECKHAM, G. W. and PECKHAM, E. G. (1889) Observations on sexual selection in spiders of the family Attidae. Occ. Pap. Nat. Hist. Soc. Wisc, 1 , 1 - 6 0 . PETERS, H. (1933) Weitere U n t e r s u c h u n g e n u b e r die F a n g h a n d l u n g der K r e u z s p i n n e . Z. vergl. Physiol., 1 9 , 4 7 - 6 7 . PETERSEN, N. (1950) T h e relation between size of m o t h e r and n u m b e r of y o u n g in some spiders and its significance for the evolution of size. Experientia, 6, 9 6 - 8 . PETRUNKEVITCH, A. (1911) Sense of sight, courtship and m a t i n g in Dugesiella hentzi ( G e r a r d ) , a T h e r a p h o s i d spider from T e x a s . Zool. Jahrb. (Syst.), 3 1 , 3 5 5 - 7 6 . POCOCK, R. I. (1909) M i m i c r y in spiders. J. Linn. Soc. (Zool), 3 0 , 256-70. SAVORY, T. H. (1952) The Spider's Web. L o n d o n . T H O M A S , M. (1953) Vie et Moeurs des Araignees. Paris. T H O R P , R. W. and W O O D S O N , W. D. (1945) Black Widow: America's most Poisonous Spider. Chapel Hill. T I L Q U I N , A. (1942) La Toile geometrique des Araignees. Paris. WARBURTON, C. (1912) Spiders. C a m b r i d g e . [Note: A complete list of spider literature up to 1939, systematically classified by subject, will be found in t h e first volume of: P. B O N N E T (1945) Bibliographia Araneorum. T o u l o u s e . ]

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O N ACCOUNT o f t h e i r e c o n o m i c a n d m e d i c a l i m p o r t a n c e t h e o r d e r Acari w h i c h comprises t h e mites a n d ticks has attracted m o r e a t t e n t i o n t h a n all t h e o t h e r A r a c h n i d a p u t t o g e t h e r . B e c a u s e o f t h e i r v a s t n u m b e r s , s m a l l s i z e a n d t h e e n o r m o u s t a x o n o m i c diffic u l t i e s i n v o l v e d , t h e i r s t u d y i s v e r y m u c h a m a t t e r for t h e s p e c i a l -

F I G . 3 9 . Examples of various kinds of mites: 1. Notostigmata, 2 . Dermanyssidae, 3 . Halarachnidae, 4 . Ixodid tick, 5 . Argasid tick, 6 . Demodicidae, 7 . Bdellidae, 8 . Halacaridae, 9 . H y d r a c h nidae, 1 0 T h r o m b i d i i d a e , 1 1 . T y r o g l y p h i d a e , 1 2 . Sarcoptidae, 1 3 . Oribatei, 1 4 . Eriophyidae. ( F r o m various sources.) 182

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ist, a n d i n t h i s c h a p t e r o n l y t h e b r i e f e s t o u t l i n e o f t h e b i o l o g y o f t h e g r o u p will b e a t t e m p t e d .

Classification and distribution T h e Acari do not represent a natural group, but comprise several h e t e r o g e n e o u s a n d distinct phylogenetic lines. T h e y are m o s t l y o f s m a l l size a n d p o s s e s s f o u r , six o r e i g h t l e g s : u s u a l l y t h e larval stages have t h r e e pairs, t h e n y m p h a l a n d adult four pairs of limbs. T h e shape of the b o d y varies considerably a n d m a y be elongated a n d w o r m - l i k e , short, r o u n d e d , elliptical or spherical. T h e more primitive forms show traces of segmentation which disappear completely in the m o r e advanced groups. Six sub-orders a r e r e c o g n i s e d b y A n d r e (in G r a s s e , 1 9 4 9 ) * a n d t h e s e a r e s e p a r a t e d largely according to t h e position of t h e spiracles. T h e N o t o s t i g mata is a small g r o u p of primitive mites in which the segmentation of the b o d y is manifest. T h e m e t a p o d o s o m a consists of two somites, the opisthosoma of nine. T h e s e animals resemble harvestspiders in general form b u t are brightly coloured and exhibit a c o m b i n a t i o n of gold, blue a n d violet h u e s u n k n o w n elsewhere in t h e o r d e r . T h e y a r e all r e f e r r e d t o a s i n g l e g e n u s Opilioacarus, t h e species of w h i c h are found free-living u n d e r stones a n d are widely d i s t r i b u t e d i n E u r o p e , N o r t h Africa a n d S o u t h A m e r i c a . T h e s u b - o r d e r Holothyroidea again contains b u t a single genus of wide distribution found in the Seychelles, Mauritius, Australia, N e w G u i n e a a n d C e y l o n . A f e w s p e c i e s o f Holothyrus f o u n d i n P a p u a are o f interest b e c a u s e t h e i r size, w h i c h m a y r e a c h 7 m m m a k e s t h e m t h e l a r g e s t o f all t h e m i t e s , o t h e r t h a n t i c k s . T h e i r segmentation is h i d d e n by a strongly chitinised plate which covers the u p p e r surface of t h e body. T h e Notostigmata and H o l o t h y roidea are b o t h included in the sub-order Onychopalpida by Baker and W h a r t o n (1952). T h e t h i r d s u b - o r d e r , t h e Parasitiformes, contains a vast assemblage of genera a n d species b o t h free-living a n d parasitic on other a n i m a l s a n d p l a n t s . T h e y fall i n t o t w o d i s t i n c t g r o u p s , t h e M e s o stigmata containing the super-families Gamasides and U r o p o d i n a a n d t h e Ixodoidea or ticks, w h i c h in t u r n are s u b d i v i d e d into three super-families, the Ixodei, the Nuttalliellei and the Argasides. F r o m the point of view of the biologist the M e s o s t i g m a t a are t h e

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m o r e i n t e r e s t i n g , s i n c e t h e r a n g e o f h a b i t a t a n d m o d e o f life i s m o r e varied. T h e g r o u p s e e m s t o h a v e b e c o m e a d a p t e d t o different h a b i t a t s w i t h little r e s u l t i n g c h a n g e i n f u n d a m e n t a l s t r u c t u r e . T h e ticks are the m o s t familiar of the mites, not only on account o f t h e i r l a r g e size, b u t b e c a u s e t h e y a r e o f m e d i c a l a n d v e t e r i n a r y i m p o r t a n c e . T h e majority of species are i n c l u d e d in t h e family I x o d i d a e in w h i c h a s c u t u m or shield is always present. T h e sexes a r e d i s t i n c t : t h e m a l e s f e e d little o r n o t a t all, b u t t h e f e m a l e s a n d i m m a t u r e stages i m b i b e large quantities of blood so that t h e s c u t u m becomes a m e r e patch on the anterior portion of their greatly dist e n d e d bodies. T h e y take several days to gorge themselves, a n d each stage feeds only once. T h e Argasidae, o n t h e o t h e r h a n d , are ticks w i t h leathery integ u m e n t , no portion being specially chitinised to form a s c u t u m . W h e n g o r g e d t h e r e is no e x t r a v a g a n t increase in size as in female Ixodidae. T h e fourth sub-order is the Thrombidiformes or Trombidiformes which includes a very diverse g r o u p of mites probably derived from m o r e than one ancestral type. A considerable degree of segmentation is retained in m a n y species of t h e super-family T a r s o n e m i n i w h i c h contains a n u m b e r of insect parasites. T h e super-family Prostigmata comprises a group k n o w n as the Eleut h e r e n g o n a in w h i c h are f o u n d a n u m b e r of p l a n t - f e e d i n g families, of which the most important economically are the 'red-spider' m i t e s o r T e t r a n y c h i d a e , t h e u n i v e r s a l f o l l i c l e - m i t e s Demodex s p p . , t h e familiar Bdellidae o r ' s n o u t - m i t e s ' a n d t h e salt w a t e r H a l a caridae. T h e Parasitengona is the group of the Thrombidiformes which contains t h e fresh w a t e r mites, s o m e t i m e s k n o w n as H y d r a c a r i n a . T h e s e b e l o n g to a large n u m b e r of families s u c h as t h e H y d r a chnidae, Limnocharidae, Eylaidae, Limnesiidae and Arrenuridae, etc. T h e y are related to t h e irritating harvest-mites, chiggers or T h r o m b i d i i d a e which are becoming increasingly important m e d i cally a s t h e y h a v e b e e n s h o w n t o t r a n s m i t m a n y f o r m s o f s c r u b t y p h u s ( A u d y a n d H a r r i s o n , 1951). T h e fifth s u b - o r d e r , t h e S a r c o p t i f o r m e s , i s p r o b a b l y t h e m o s t specialised and external s e g m e n t a t i o n is r e d u c e d to a m i n i m u m . It contains two large a n d successful g r o u p s : t h e Acaridiae w h i c h in-

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eludes t h e cheese-mites a n d other T y r o g l y p h i d a e w h i c h are often p e s t s of s t o r e d p r o d u c t s , as w e l l as t h e i t c h - m i t e Sarcoptes scabei. and the Oribatei or beetle-mites. Generally speaking, the Acaridiae a r e soft a n d t h e O r i b a t e i m o r e o r less a r m o u r e d , b u t e x c e p t i o n s occur in both groups. Finally, t he Tetrapodili or E r i o p h y i d mites are an aberrant s u b o r d e r of t h e A c a r i as t h e y possess only t h e front t w o p a i r s of legs: t h e t w o p o s t e r i o r p a i r s a r e l a c k i n g o r r e d u c e d t o fine h a i r s . T h e s e i n c l u d e t h e g a l l - m i t e s a n d o t h e r p l a n t p a r a s i t e s , all o f w h i c h h a v e elongated, worm-like bodies in which the original segmentation is i n d i s t i n g u i s h a b l e , for t h e r i n g - l i k e a p p e a r a n c e o f t h e p o s t e r i o r p a r t of t h e b o d y is only an e p i d e r m a l feature. A general characteristic is t h e possession of t w o long sinuous setae arising from t h e posterior part of the body. T h e A c a r i a r e w i d e l y d i s t r i b u t e d all o v e r t h e w o r l d f r o m t h e north of Greenland to the antarctic. Terrestrial forms occur from s e a level t o t h e m o u n t a i n t o p s , w h i l e m a r i n e a n d f r e s h w a t e r s p e c i e s are not u n c o m m o n . T h e distribution of parasites a n d commensals is intimately related w i t h that of their hosts, b u t even free-living m i t e s s h o w m a r k e d d e g r e e s o f a d a p t a t i o n t o e n v i r o n m e n t s far removed from their original biotope.

General behaviour M i t e s a r e f o u n d e v e r y w h e r e : m a n y a r e p r e s e n t i n d a m p soil a n d m o s s i n s h a d y p l a c e s , w h e r e t h e y live o n s m a l l f u n g i , o t h e r s live o n plants, sucking t h e sap a n d s o m e t i m e s causing gall-like t u m o u r s , w h i l e still m o r e a r e t h e p r e d a t o r s o r p a r a s i t e s o f i n s e c t s , v e r t e brates and other animals. W h e r e a s insects are numerically the l e a d i n g g r o u p o f a n i m a l s i n h a b i t i n g a r a b l e soils, i n f o r e s t s t h e i r p l a c e i s t a k e n b y t h e A c a r i w h i c h , i n h u m u s a r e easily t h e m o s t abundant invertebrates. It has been shown that they constitute 2 - 3 % of the total weight of the invertebrate fauna in D a n i s h beech w o o d s a n d 5 - 7 % i n s p r u c e w o o d s . T h i s difference, d u e t o vast n u m b e r s of Oribatid mites w h i c h are practically limited to h u m u s , appears to be a constant one. M a n y mites are cavernicolous, others are myrmecophilous: of t h e s e s o m e a r e s c a v e n g e r s , o t h e r s e a t t h e a n t s ' f o o d a n d still m o r e feed o n t h e a n t s t h e m s e l v e s .

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T h e N o t o s t i g m a t a a r e s e c r e t i v e a n d live u n d e r s t o n e s a n d o t h e r debris. Chitinous remains of arthropods have been found in their guts a n d it is p r o b a b l e t h a t t h e y are predatory, b u t so few specim e n s h a v e b e e n c o l l e c t e d t h a t little i s y e t k n o w n o f t h e i r b i o l o g y . T h e h a b i t s a n d life h i s t o r i e s o f t h e H o l o t h y r o i d e a t o o a r e v i r t u a l l y u n k n o w n . M a n y o f t h e M e s o s t i g m a t a live o n p l a n t s a n d p r e y o n small insects a n d other mites. A great m a n y of the genera of Gamasides a n d U r o p o d i n a are found in d a m p places, in m a n u r e heaps a n d a m o n g s t m o s s a n d d a m p leaves, t h e G a m a s i d e s p r e y i n g on smaller creatures. T h e U r o p o d i n a , w h i c h are slow m o v i n g and s l u g g i s h , feed o n f u n g i a n d v e g e t a b l e m a t t e r . T h e m e m b e r s o f t h e P a r a s i t i d a e , for e x a m p l e , a r e f o u n d t y p i c a l l y i n a c c u m u l a t i o n s o f organic material s u c h as r o t t i n g logs a n d litter. O t h e r families however, such as the Laelaptidae, are usually parasitic on vertebrates a n d to a lesser extent on invertebrates. I n d e e d , this family includes the most c o m m o n ectoparasites of m a m m a l s , while the H a l a r a c h n i d a e live i n t h e a i r p a s s a g e s o f m a m m a l s , o n e g e n u s o c c u r r i n g e x c l u s i v e l y i n t h e r e s p i r a t o r y p a s s a g e s o f seals o f t h e family P h o c i d a e , a n o t h e r parasitising t h e o t h e r Pinnipedia. T i c k s a r e c o m p a r a t i v e l y l a r g e , l e a t h e r y a n i m a l s w h i c h a r e all parasitic on v e r t e b r a t e s . E v e n t h e larval forms or 'seed ticks' are v i s i b l e t o t h e n a k e d e y e a n d a fully g o r g e d f e m a l e m a y a t t a i n a length of half an inch. T h e I x o d i d a e are of great e c o n o m i c a n d m e d i cal i m p o r t a n c e . H e a v y i n f e s t a t i o n b y t h e s e c r e a t u r e s c a n c a u s e anaemia in domestic animals, a n d t h e y carry several noxious diseases t o m a n a n d o t h e r v e r t e b r a t e s . T h u s R o c k y M o u n t a i n s p o t t e d fever a n d T e x a s fever of cattle in A m e r i c a are t r a n s m i t t e d by Dermacentor andersoni a n d Boophilus annulatus r e s p e c t i v e l y , w h i l e m a n i s i n f e c t e d w i t h R o c k y M o u n t a i n fever, K e n y a t y p h u s , Q fever a n d T u l a r e m i a b y t h e b i t e s o f v a r i o u s t i c k s . T i c k p a r a l y s i s o f m a n and animals is believed to be due to toxins secreted in the saliva o f t h e t i c k s . T h o u g h m o r e f r e q u e n t l y o b s e r v e d i n t i c k infested animals, a n u m b e r of h u m a n cases have b e e n r e p o r t e d in the U n i t e d States, C a n a d a and Australia. T h e ascending paralysis is caused by a rapidly engorging female tick attached to t h e base of t h e h e a d w h e r e t h e h a i r m a y h i d e its p r e s e n c e for a l o n g p e r i o d . C o m p l e t e r e c o v e r y follows w i t h i n a d a y o r t w o o f r e m o v a l o f t h e offending parasite, b u t d e a t h m a y occur if t h e paralysis has reached

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the respiratory centres of t h e h u m a n or animal victim before the tick h a s d r o p p e d off o r b e e n r e m o v e d . T h e ill effects o f t i c k s o n t h e i r h o s t s h a v e b e e n r e c o g n i s e d s i n c e 2 0 0 B.C. w h e n M . P o r c i u s C a t o r e f e r r e d t o t r e a t m e n t s w h e r e b y ' t h e r e will b e n o sores a n d t h e wool will b e m o r e plentiful a n d i n b e t t e r c o n d i t i o n a n d t h e t i c k s ( r i c i n i ) will n o t b e t r o u b l e s o m e ' . E a r l i e r , A r i s t o t l e i n h i s f a m o u s Historia Animalium m a d e s o m e observations on the ecology of these ectoparasites and stated that t h e ' t i c k i s g e n e r a t e d f r o m c o u c h g r a s s ' . H e w a s also a w a r e o f t h e h a r m t h a t t h e y c a u s e d . D e s p i t e t h e e a r l y r e a l i s a t i o n o f t h e fact t h a t ticks are ectoparasitic on m a m m a l s , it was n o t until t h e late n i n e t e e n t h c e n t u r y that their role in t h e transmission of disease was first s u s p e c t e d . T h e c o m m o n s h e e p t i c k i s Ixodes reduvius, f o u n d a l s o o n c a t t l e and horses. Its distribution in Britain has been shown to be inf l u e n c e d b y s u p e r f i c i a l soil d e p o s i t s . W h e r e g o o d p a s t u r e o c c u r s alongside 'islands' of d a m p ground, discrepancies in the distribution of t h e ticks are n o t e d . S u c h 'islands' m a y h a r b o u r ticks while t h e r e s t o f t h e p a s t u r e i s free, a n d w h e n c a t t l e m o v e i n t o t h e s e 'islands' t h e y are infested ( A r t h u r , 1952). M i l n e (1945) has s h o w n t h a t t h e d u r a t i o n o f t h e h u m i d i t y level d u r i n g d a y l i g h t i n c o n j u n c tion with the temperature may decide the a m o u n t and extent of activity of these animals in s u m m e r . D u r i n g recent years considerable attention has been devoted to the physiology a n d b e h a v i o u r of ticks. F o r example, L e e s (1947) has shown that they owe their resistance to desiccation primarily to a superficial layer of w a x in t h e i n t e g u m e n t : after e x p o s u r e to increasing t e m p e r a t u r e s , water-loss increases a b r u p t l y at a certain 'critical t e m p e r a t u r e ' as in insects. Species h a v i n g h i g h e r critical temperatures are m o r e resistant to desiccation at temperatures within t h e biological range. A b r o a d correlation is possible b e t w e e n these powers of resistance and the natural choice of habitat: Argasidae infest dry, d u s t y situations, w h e r e a s I x o d i d a e o c c u p y a w i d e r variety of ecological niches. U n f e d ticks are able to take up water rapidly through the wax-layer w h e n exposed to high humidity. T h i s w a t e r u p t a k e is d e p e n d e n t on t h e secretory activities of t h e e p i d e r m a l cells a n d i s c o m p l e t e l y i n h i b i t e d b y a b r a s i o n o f o n l y a p a r t o f t h e t o t a l c u t i c l e s u r f a c e w h i c h s u g g e s t s t h a t t h e cells a r e

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functionally interconnected. Resistance to desiccation at low humidities is achieved by a dual m e c h a n i s m : active secretion and the physical retention of water by the wax-layer. T h e unfed sheep tick w h e n at rest a d o p t s either a questing attit u d e w i t h t h e fore legs e x t e n d e d , or an a t t i t u d e of repose w i t h t h e legs f o l d e d . T h e t i c k s r e s p o n d t o g r a v i t y , h u m i d i t y , t e m p e r a t u r e , smell, light a n d tactile stimuli. T h e y climb u p w a r d s towards the t i p s o f t h e l e a v e s o f t h e g r a s s i n w h i c h t h e y live u n t i l t h e y b e c o m e desiccated w h e n they b e c o m e active a n d m o v e d o w n w a r d s again to t h e m o i s t air near t h e g r o u n d w h e r e t h e y recover their water balance by active secretion t h r o u g h the cuticle: t h e n they climb u p w a r d s again. If a suitable host h a p p e n s to pass they are attracted b y t h e m o i s t u r e a n d s c e n t o f its b o d y , a n d t h e v i b r a t i o n s c a u s e d b y its m o v e m e n t s , a n d r e s p o n d b y a c t i v e q u e s t i n g . A f t e r f e e d i n g , t h e engorged ticks d r o p to t h e g r o u n d a n d are t h e n strongly p h o t o n e g a t i v e (Lees, 1948). T h e main stimulus governing the ascent of grass blades by l a r v a e of t h e A u s t r a l i a n c a t t l e t i c k , Boophilus microplus, is p o s i t i v e phototaxis to m o d e r a t e light intensities: t h e ticks shelter from direct sunlight. In the field they are found to be m o r e exposed in t h e early m o r n i n g w h e n they are often at t h e tops of grass stalks. T h e strongest questing behaviour occurs in response to odours, b u t v i b r a t i o n , air c u r r e n t s , i n t e r r u p t e d i l l u m i n a t i o n , w a r m t h a n d m o i s t u r e all p l a y a p a r t i n t h e r e a c t i o n s t o t h e h o s t ( W i l k i n s o n , 1953). A r g a s i d t i c k s a r e also o f c o n s i d e r a b l e e c o n o m i c a n d m e d i c a l importance. T h e y occur on a wide variety of hosts including r e p tiles, b i r d s a n d m a m m a l s a n d i n h a b i t s s o m e w h a t r e s e m b l e b e d b u g s . As a rule they are nocturnal, feeding moderately a n d at freq u e n t i n t e r v a l s . W h e n f a s t i n g t h e y a r e flat a n d r e a d i l y c r e e p i n t o n a r r o w c r e v i c e s . Argas persicus is n o t o n l y a t r o u b l e s o m e d o m e s t i c p e s t i n s o m e p l a c e s b u t i t a l s o i n f e s t s p o u l t r y all o v e r t h e w o r l d , c a u s i n g m u c h d a m a g e b y its b i t e s a n d s o m e t i m e s t r a n s m i t t i n g a spirochaete disease. Cattle are susceptible to t h e spinose ear tick a n d r e l a p s i n g f e v e r i s c o n v e y e d t o h u m a n s b y t h e n o t o r i o u s Ornithodorus moubata. T h e T h r o m b i d i f o r m e s s h o w a g r e a t d i v e r s i t y o f f o r m , life h i s t o r y a n d b e h a v i o u r a n d b u t a few s e l e c t e d e x a m p l e s c a n b e

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mentioned. M a n y of the T a r s o n e m i n i are parasitic on other A r t h r o p o d a a l t h o u g h t h e s u p e r - f a m i l y also c o n t a i n s s o m e wellk n o w n plant pests. T h e family Scutacaridae are m i n u t e , bizarre c r e a t u r e s f o u n d i n m o s s a n d soil t h r o u g h o u t t h e w o r l d , a s w e l l a s o n a n t s a n d o t h e r i n s e c t s . O n e s p e c i e s , Acarapis woodi, i n f e s t s t h e t r a c h e a l t u b e s o f b e e s c a u s i n g t h e fatal ' I s l e o f W i g h t d i s e a s e ' found t h r o u g h o u t E u r o p e . T h e mites cause injury by imbibing the hosts' body fluids, and by mechanically blocking their tracheae. T h e b e h a v i o u r o f t h e r e d - l e g g e d e a r t h m i t e Halotydeus destructor (family E u p o d i d a e ) has b e e n investigated e x p e r i m e n t a l l y by Solom o n (1937) in Australia. T h e dry season is b r i d g e d over by resting eggs p r o d u c e d i n O c t o b e r . T h e s e eggs are laid i n great n u m b e r s o n t h e s u r f a c e soil, u n d e r c l o d s o f e a r t h o r s t i c k s a n d a r e h i g h l y resistant to heat, d r o u g h t or desiccating winds: moisture and suns h i n e a r e n e c e s s a r y for t h e m t o h a t c h . T h e a d u l t i s a s o f t - b o d i e d m i t e w h o s e f r o n t legs a c t a s s e n s o r y o r g a n s . I t lives f r o m 2 5 t o 5 0 d a y s , p r e f e r s l i g h t , w e l l - d r a i n e d soils a n d i s k i l l e d b y h e a t a n d drought. T h e Tetranychidae include the well-known red-spider mites, s u c h a s Metatetranychus ulmi, w h i c h a r e p r o b a b l y t h e m o s t i m p o r t a n t e c o n o m i c a l l y o f all t h e p l a n t f e e d i n g m i t e s . P o p u l a t i o n s m a y build up to such fantastic n u m b e r s if uncontrolled that trees m a y be completely defoliated a n d killed. T h e s e m i t e s are often brightly c o l o u r e d a n d d o d a m a g e n o t o n l y b y s u c k i n g p l a n t j u i c e s b u t also by spreading virus infections. T h e follicle m i t e s , Demodex s p p . , a r e r e s p o n s i b l e f o r v a r i o u s skin diseases in m a n a n d animals. Usually t h e general health of the h o s t i s n o t affected, b u t n o d u l e s o r p u s t u l e s a r e c a u s e d o n t h e s k i n w h i c h , in t h e case of cattle parasites, m a y v a r y in size f r o m t h e head of a pin to that of a h e n ' s egg. O n e species causes red m a n g e in dogs, w h i c h is a c c o m p a n i e d by a foul a n d d i s g u s t i n g o d o u r . T h e C h e y l e t i d a e , s u c h a s Syringophilus s p p . , a r e o f t e n f o u n d w i t h i n the quills of birds a n d are correspondingly elongated, while others have s t o u t claws w i t h w h i c h t h e y cling to t h e fur of m a m m a l s . It is p r o b a b l e t h a t t h e y feed on t h e d e t r i t u s inside t h e quills a n d on t h e skin. T h e majority of t h e family h o w e v e r are free-living p r e dators and have a world-wide distribution. B d e l l i d m i t e s a r e u s u a l l y t o b e f o u n d i n m o s s , l i c h e n , leaf m o u l d

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and debris, wherever there is an a b u n d a n c e of small insects and other mites. T h e y are predaceous in habit and s o m e species are s a i d t o c a p t u r e t h e i r p r e y b y s q u i r t i n g o n t o t h e m a l i q u i d silk which enmeshes their appendages while the mite sucks their body contents. A few m i t e s are littoral a n d r u n a b o u t t h e s a n d b e t w e e n tides, w h i l e o t h e r s , t h e H a l a c a r i d a e , a r e d r e d g e d f r o m t h e sea. N e w e l l (1947) records a total of 41 species, sub-species a n d varieties from N o r t h America and G r e e n l a n d a n d has studied their ecology. He found that the fauna of the sub-tidal zone is m o r e uniform than that of t h e inter-tidal zone, especially from a qualitative standpoint. T h e r e is a well-developed sand fauna, a fauna based u p o n molluscs and various algicolous faunas, while habitats characterised by low salinity have their o w n peculiar m i t e fauna containing b u t a small n u m b e r of species. N u m e r o u s species are f o u n d s w i m m i n g in fresh water. T h e s e w a t e r m i t e s c o n s t i t u t e a far f r o m n e g l i g i b l e p r o p o r t i o n o f t h e f a u n a o f all n o r m a l a n d p e r m a n e n t w a t e r s . B i o l o g i c a l l y a n d e c o l o g i c a l l y t w o g r o u p s c a n b e d i s t i n g u i s h e d : t h e e u r y t h e r m i c f o r m s w h i c h live mostly in standing waters naturally subject to wide variation of t e m p e r a t u r e , a n d t h e s t e n o t h e r m i c forms w h i c h dwell in cold waters and are able to e n d u r e only slight variations of t e m p e r a t u r e . T h e latter are largely restricted to s p r i n g waters, s t r e a m s a n d overflowings, b u t i n a d d i t i o n t o t h e t e m p e r a t u r e factor g o v e r n i n g t h e c h o i c e o f h a b i t a t , t h e r e i s also a n e c e s s i t y for f a s t - f l o w i n g , r i c h l y oxygenated water. Viets (1940, etc.) has s t u d i e d t h e distribution of some 219 species in E u r o p e a n d has d r a w n some extremely interesting conclusions regarding the probable pre-glacial fauna and the p o s s i b l e r o u t e s a n d t i m e s o f m i g r a t i o n t h a t t o o k p l a c e a f t e r t h e ice age. A b o u t 220 species are r e p r e s e n t e d in t h e British fauna, a n d their distribution is often peculiar. T h e dispersal of m a n y of t h e m d e p e n d s u p o n t h e larvae attaching themselves to the bodies of v a r i o u s a q u a t i c i n s e c t s for t r a n s p o r t . T h e T h r o m b i d i i d a e are extremely n u m e r o u s i n b o t h n u m b e r s and kinds. T h e y are of world-wide distribution and have been found o n e v e r y l a n d m a s s e x c e p t t h o s e p e r m a n e n t l y c o v e r e d b y ice a n d snow. T h e y are more a b u n d a n t in the tropics than in temperate climates and constitute a conspicuous portion of the m i t e faunas

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of oceanic islands. On a dry, stony p a t h on a s u n n y day in this c o u n t r y , o n e o f t e n find t h e a d u l t s o f s c a r l e t v e l v e t y m i t e s Thrombidium s p . r u n n i n g a b o u t a n d f e e d i n g o n s m a l l i n s e c t s a n d t h e i r e g g s , w h i l e o t h e r s a r e c o m m o n i n leaf l i t t e r a n d u n d e r b a r k . M u c h attention has recently been directed toward the biology of t h e m i n u t e h e x a p o d m i t e s w h i c h for ages h a v e p l a g u e d m a n i n various parts of the world, and which are k n o w n popularly as 'harvest bugs', 'harvest mites', 'bete rouge', 'rouget', 'chigger m i t e s ' , e t c . G r e a t difficulty i s u s u a l l y e x p e r i e n c e d i n o b t a i n i n g t h e c o m p l e t e life h i s t o r y o f t h e s e m i t e s a s t h e l a r v a e a l o n e a r e p a r a s i t e s . Jones (1950a) has investigated the sensory physiology of the harvest m i t e Thrombicula autumnalis. T h e s e a n i m a l s a r e a t t r a c t e d t o l i g h t a n d t o m o i s t air: t h e y a r e v e r y s e n s i t i v e t o t o u c h b u t n o t t o t e m p e r a t u r e a l t h o u g h a r a n g e e x t e n d i n g f r o m 15° t o 2 6 ° C a p p e a r s t o be preferred. T h e gregarious habit of the mites is primarily a response to t h e t o u c h of each others bodies. T h e food of t h e harvest m i t e , Thrombicula autumnalis, c o n s i s t s of t i s s u e , fluid a n d d i s i n t e g r a t e d cells o f t h e m a l p i g h i a n l a y e r p a r t i a l l y l i q u e f i e d b y t h e a c t i o n o f i n j e c t e d saliva, a c o n d i t i o n t y p i c a l o f e x t r a - i n t e s t i n a l digestion. T h e physical factors of t h e skin have b e e n s h o w n to influence t h e choice of habitat u p o n t h e host. On birds t h e mites a p p e a r to favour t h e anal area a n d t h e lateral surface of t h e b o d y b e t w e e n t h e w i n g a n d t h e thigh; b u t o n m a n the factors w h i c h influence the choice are m o r e varied, regions w h e r e t h e skin is thin and which provide the w a r m t h and humidity favoured by the l a r v a e b e i n g m o s t likely t o b e a t t a c k e d ( J o n e s , 1 9 5 0 b ) . L i k e t h e T h r o m b i d i i d a e , t h e A c a r i d i a e a r e n o t a b l e for t h e e x t e n t o f t h e i r d i s t r i b u t i o n . T h e y a r e f o u n d i n all t y p e s o f h a b i t a t f r o m arctic t u n d r a to tropical rain forest a n d w h e r e v e r m a n in his w a n d e r i n g s has taken m i t e s in his food a n d p r o d u c e . Of t h e species a t t a c k i n g s t o r e d f o o d , Tyroglyphus farinae is by far t h e m o s t i m p o r t a n t . I t i n f e s t s all k i n d s o f f a r i n a c e o u s m a t e r i a l , n o t o n l y eating t h e food b u t giving it a c u r i o u s m u s t y smell a n d taste so that i t b e c o m e s u n f i t for h u m a n c o n s u m p t i o n . N o t o n l y i s t h i s s p e c i e s f o u n d in w a r e h o u s e s , b u t it also o c c u r s in t h e nests a n d fur of small r o d e n t s w h i c h act as a n a t u r a l reservoir of t h e m i t e . G r a i n which has b e c o m e attacked by weevils or d a m a g e d mechanically is m a d e m o r e readily accessible to flour m i t e s w h i c h are t h e n able

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to penetrate the pericarp and consume the embryo. Grain that has b e c o m e d a m a g e d by water seeping into t h e holds of ships is often attacked by another g r o u p of mites related to the forms that attack flower b u l b s , p a r t i c u l a r l y i n b a d l y - d r a i n e d soil, w h i l e i f t h e g r a i n becomes completely saturated it m a y be infested with various o t h e r s p e c i e s w h i c h c a n live c o m p l e t e l y i m m e r s e d i n w a t e r . S c a b i e s o f m a n i s a c o n d i t i o n p r o d u c e d b y t h e i t c h - m i t e Sarcoptes scabei w h i c h b u r r o w s i n t h e s k i n w h e r e i t lays its e g g s , t h e m i t e causing intense itching a n d irritation. In aggravated cases, an extensive crusting and scabbing results, particularly over the hands and arms. O r i b a t i d m i t e s live i n m o s s , i n t h e h u m u s o f t h e f o r e s t floor, i n l i c h e n s g r o w i n g o v e r t r e e s t u m p s a n d t r e e s , free o n t w i g s a n d l e a v e s , i n d e c a y i n g w o o d a n d i n t h e s p h a g n u m o f m a r s h e s . A few a r e s l i g h t l y a q u a t i c a n d still f e w e r a r e k n o w n t o i n h a b i t t h e sea. T h e y a r e f o u n d e v e r y w h e r e t h a t p l a n t s d e c a y w i t h sufficient m o i s t u r e a n d are p e n e t r a t e d by fungal mycelia (Willman, 1931). A n u m b e r of species are i m p o r t a n t as vectors of t a p e - w o r m s of sheep, etc. Apparently there is no taxonomic unit of mites that are vectors; t h e d e t e r m i n i n g factor is w h i c h species is d o m i n a n t on pasture a n d large e n o u g h to be able to swallow t h e eggs of t h e w o r m s . O n t h e w h o l e v e r y little i s k n o w n o f t h e h a b i t s o f t h e O r i b a t e i a n d t h e r e i s m u c h s c o p e for f u r t h e r w o r k . T h e curious excrescences and abnormal growths which occur on t h e leaves a n d b u d s of p l a n t s are familiar to everyone. V a r i o u s c r e a t u r e s a r e r e s p o n s i b l e for t h e s e d e f o r m i t i e s , m a n y b e i n g t h e work of insects, b u t others are d u e to mites of t h e s u b - o r d e r T e t r a p o d i l i . T h o u g h t h e galls c a u s e d b y t h e s e m i t e s a r e o f t e n outwardly similar to those of insect origin, they can at once be d i s t i n g u i s h e d on close e x a m i n a t i o n . M i t e - g a l l s c o n t a i n a single c h a m b e r communicating with the exterior by a pore which is u s u a l l y g u a r d e d b y h a i r s . T h e m i t e s live g r e g a r i o u s l y w i t h i n , a p p a r e n t l y f e e d i n g u p o n t h e h a i r s w h i c h g r o w a b u n d a n t l y o n its i n n e r s u r f a c e , w h e r e a s i n i n s e c t - g a l l s e a c h i n s e c t l a r v a lives i n a separate closed c h a m b e r .

Food and feeding habits M i t e s live p r i n c i p a l l y u p o n f l u i d n u t r i m e n t , a l t h o u g h t h i s m a y

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be obtained from living animals a n d plants or from decaying organic matter. S o m e are entirely parasitic u p o n plants or other animals, o t h e r s attach themselves to animals in their larval stage b u t a r e free w h e n a d u l t , w h i l e a g a i n o t h e r s live a n e n t i r e l y i n d e p e n d e n t a n d p r e d a c e o u s life. I n t h e p r e d a t o r y f o r m s t h e m a n d i b l e s are chelate a n d masticatory, b u t in the parasitic forms t h e m o u t h p a r t s a r e m o d i f i e d for s u c k i n g t h e b l o o d o r j u i c e s o f t h e h o s t . T h e largest a n d smallest examples of t h e o r d e r are found a m o n g s t the parasitic species. T h e food a n d feeding habits of m i t e s are closely related to their general b e h a v i o u r a n d have already b e e n discussed in s o m e detail. S o m e s p e c i e s o f m i t e s r a r e l y o c c u r free l i v i n g b u t a r e f o u n d i n association w i t h m a m m a l s : h e r e t h e y feed, n o t o n t h e host, b u t o n o t h e r m i t e s a n d i n s e c t s l i v i n g o n it. I t c a n r e a d i l y b e i m a g i n e d t h a t after a t i m e , i n s t e a d of l i v i n g a b l a m e l e s s e x i s t e n c e , s o m e of t h e s e f o u n d an easy w a y to o b t a i n food by s u c k i n g t h e b l o o d of t h e a n i m a l o n w h i c h t h e y h a p p e n e d t o find t h e m s e l v e s , a n d t h u s developed t h e parasitic habit. In this way m a n y families have become ecto-parasitic on birds and m a m m a l s . T h e majority of t h e m i t e - b o r n e diseases of m a n were originally diseases of animals closely associated w i t h h u m a n s , s u c h as domestic rats a n d mice. At p r e s e n t s o m e of these diseases, w h i c h include dermatitis, rickettsiosis, plague, various t y p h u s a n d other fevers, phthiriasis, scabies a n d gastro-enteritis, t e n d to be e n c o u n t e r e d only in certain localities, b u t t h e r e is always a risk t h a t they m a y be spread either by their original animal hosts, or by m a n , s o t h a t n e w foci o f t h e d i s e a s e a r e c r e a t e d . T h i s i m p o r t a n t subject, s o m e w h a t b e y o n d the scope of the present volume, has recently b e e n reviewed by Z u m p t a n d Graf (1950) to whose publication the reader is referred. Halacaridae are either predaceous, lichen feeders or are parasitic ( N e w e l l , 1 9 4 7 ) . T h e b a s i s o f t h e b e h a v i o u r o f f r e s h w a t e r m i t e s is a r a n d o m l o c o m o t o r y activity in search of food s u c h as Crustacea and aquatic insects w h i c h are detected by touch. A simple action system based on t h e principle of trial a n d error seems t o b e c o r r e l a t e d w i t h a s i m p l e m o d e o f life. T h e p r e d a t o r y h a b i t is o f t e n of e c o n o m i c i m p o r t a n c e a n d Cheyletus eruditus is t h e commonest predator of Tyroglyphid mites in stored products. N o t N

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infrequently mites are of ecological i m p o r t a n c e in controlling t h e n u m b e r s of insects, spiders a n d other mites by eating their eggs.

Enemies T h e predators of mites include a large n u m b e r of arthropods, including other mites, insects, spiders and so on, some of w h i c h appear to specialise in an acarine diet. T h u s species of C o n i o p terygidae (Neuroptera) appear to prey on the fruit-tree red-spider m i t e Metatetranychus ulmi b o t h i n t h e l a r v a l a n d a d u l t s t a g e s . T h e larvae pierce t h e mites w i t h their j a w s a n d suck out t h e contents, l e a v i n g d r y e m p t y s k i n s . T h e m i t e e g g s a r e also s u c k e d d r y , t h e i r completely e m p t y shells alone r e m a i n i n g . T h e adult insects pick u p m i t e s a n d d e v o u r t h e m , b i t e off t h e t o p h a l v e s o f t h e e g g s a n d r e m o v e t h e c o n t e n t s . W h e n h u n t i n g for f o o d t h e y m o v e q u i c k l y a n d a t r a n d o m o v e r a leaf, f e e l i n g t h e s u r f a c e w i t h t h e i r p a l p s . On the whole, despite this, mites tend to be avoided by m a n y predators and their brilliant colours m a y well be a form of w a r n i n g c o l o r a t i o n . I t i s r a r e for s p i d e r s t o kill o r e a t m i t e s . A c c o r d i n g t o Bristowe (1941)* this is in part due to their strong chitinous exoskeletons, b u t in the m a i n to distastefulness. T h e Oribatei come into the former category. T h e y m o v e very slowly a n d d r a w in their legs a t t h e first a l a r m . I n t h i s w a y t h e y e s c a p e t h e a t t e n t i o n o f m a n y s p i d e r s a n d m o s t o f t h o s e t h a t d o a t t a c k t h e m find i t i m p o s s i b l e t o pierce their strong a r m o u r . Of t h e r e m a i n d e r t h e majority are distasteful. O f t e n t h e y are rejected after o n e t o u c h a n d a s p i d e r w h i c h b i t e s a m i t e w i l l n o t i n f r e q u e n t l y r e t i r e t o w i p e its m o u t h o n t h e g r o u n d . S o m e s p e c i e s o f Holothyrus p r o d u c e a s e c r e t i o n w h i c h i s poisonous to poultry. T h e edibility of water mites has been investigated by Elton (1922) a n d C l o u d s l e y - T h o m p s o n (1947) w h o have c o n c l u d e d t h a t the bright colours of so m a n y species m a y have a sematic function and be correlated with unpalatability if not distastefulness to pred a t o r s . I t i s q u i t e p r o b a b l e t h a t t h e fact t h a t s o m a n y s p e c i e s a r e bright red in colour and conspicuous against green vegetation, as t h e berries on holly, m a y be t h e result of M u l l e r i a n m i m i c r y — t h e species t e n d i n g t o r e s e m b l e o n e a n o t h e r s o t h a t n u m e r i c a l losses involved in teaching w o u l d - b e p r e d a t o r s to avoid t h e m are red u c e d . T h e c o m m o n colour facilitates t h e i m m e d i a t e recognition

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of undesirable prey. T h e predators investigated included various a q u a t i c i n s e c t s a n d fishes, m o s t o f w h i c h r e j e c t e d t h e w a t e r m i t e s , b u t sticklebacks a n d newts ate t h e m w i t h alacrity. A survey of the l i t e r a t u r e r e g a r d i n g t h e s t o m a c h c o n t e n t s o f fishes a n d i n v e r t e brate predators has s h o w n that water mites are seldom eaten in n a t u r e ( C l o u d s l e y - T h o m p s o n , 1947) a n d m o r e recently it has b e e n s h o w n b y e x p e r i m e n t t h a t n y m p h s o f Aeschna grandis l e a r n t o a v o i d Hydrachna s p p . T h e integument of m a n y Acari is provided with glands which m a y p r o d u c e distasteful a n d poisonous secretions a n d these are particularly evident a m o n g the water mites. In addition, most mites are covered with hairs a n d setae. M a n y of these are no d o u b t sensory, b u t others serve to protect their owners from attack by predators in t h e same m a n n e r that the quills of a porcupine p r o t e c t it. T h e s h a p e a n d f o r m o f t h e s e s e t a e a r e l e g i o n . In contrast to m a n y of t h e Acari, s o m e of t h e ticks do not appear to be distasteful a n d m a y even be coloured so that they blend inconspicuously with the body of their host. In this way they may n o t o n l y e s c a p e t h e a t t e n t i o n s o f t h e h o s t itself, b u t also o f t i c k birds and other potential predators. T h e e g g s o f t h e t i c k Dermacentor andersoni c o n t a i n a t o x i c p r i n ciple and, w h e n inoculated in q u a n t i t y into e x p e r i m e n t a l animals, may cause death. It is not impossible that this m a y have been evolved as a deterrent to possible predators. No d o u b t further work would produce evidence to show that the bright colours of so m a n y m i t e e g g s a r e a f o r m o f w a r n i n g a d v e r t i s e m e n t , like t h e colours of t h e i m m a t u r e a n d adult stages.

Reproduction and life cycle N e a r l y all m i t e s lay e g g s , a l t h o u g h a f e w o f t h e O r i b a t e i a r e ovoviviparous. Occasionally t h e m o t h e r m a y die at a time w h e n her a b d o m e n contains a few ripe eggs, a n d these are able to c o m p l e t e their d e v e l o p m e n t internally so that fully-formed larvae emerge from the dead b o d y of their parent. T h e y o u n g u n d e r g o metam o r p h o s i s v a r y i n g in c o m p l e t e n e s s in t h e different g r o u p s . A l t o g e t h e r five o r six s t a g e s c a n b e r e c o g n i s e d , b u t t h e y a r e s e l d o m , i f e v e r , all e x h i b i t e d i n t h e d e v e l o p m e n t o f a s i n g l e s p e c i e s . T h e life h i s t o r y n o r m a l l y c o n s i s t s o f t h e e g g w h i c h , i s s o m e c a s e s i s

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p a r t h e n o g e n e t i c , a n d h a t c h e s into a six-legged larva. T h i s passes through from one to three n y m p h a l forms before becoming adult, e a c h s t a g e i n t h e life c y c l e b e i n g p r e c e d e d b y a r e s t i n g p e r i o d . I n m o s t m i t e s t h e l a r v a e , e x c e p t for t h e a b s e n c e o f g e n i t a l o p e n i n g s a n d t h e p o s t e r i o r pair o f legs, s o m e w h a t r e s e m b l e a d u l t s . I n s o m e P r o s t i g m a t a , h o w e v e r , t h e y are q u i t e different a n d m e t a m o r p h o s e i n t o a n y m p h w h i c h i s m o r e like t h e a d u l t i n f o r m . I n t h e a c c o u n t g i v e n b e l o w a f e w t y p i c a l e x a m p l e s o f life h i s t o r i e s will b e g i v e n .

F I G . 4 0 . Stages in the development of an Oribatid mite (Pelops sp.): 1 . egg, 2 . larva, 3 . n y m p h , 4 . adult. (After Michael, 1 8 8 4 . ) T h e life h i s t o r y a n d s e n s o r y b e h a v i o u r o f t h e M e s o s t i g m a t i d s n a k e m i t e Ophionyssns natricis h a s r e c e n t l y b e e n i n v e s t i g a t e d b y C a m i n (1953) w h o found that d e v e l o p m e n t of t h e eggs takes from 28 to 98 hours; larvae 18 to 47 h o u r s , p r o t o n y m p h s 3 to 14 days, d e u t o n y m p h s 13 to 26 hours and adults 10 to 32 days within the r a n g e of t e m p e r a t u r e s 20° to 30° C, c o m m o n l y o c c u r r i n g in snake cages i n zoos. T h e a d ul t female m i t e , after c o m p l e t i n g e n g o r g e m e n t , crawls out from u n d e r t h e scale of t h e host, d r o p s f r o m t h e snake's b o d y a n d w a n d e r s a b o u t until it finds s o m e dark moist crevice w h e r e oviposition takes place. T h e e m e r g i n g larvae remain i n t h e m o i s t r e g i o n w h e r e t h e r e i s little r i s k o f d e s i c c a t i o n a n d t h e p r o t o n y m p h s stay there too until their i n t e g u m e n t becomes sclerotised and the danger of death from water-loss is lessened. T h e n they w a n d e r at r a n d o m until they c o m e u p o n a suitable host, b e c o m e c o n c e a l e d u n d e r a s c a l e a n d c o m m e n c e f e e d i n g . If, o n t h e

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o t h e r h a n d , a m i t e fails t o m e e t w i t h a s u i t a b l e h o s t i t c l i m b s t o t h e top of s o m e object s u c h as a rock or t h e tip of a b r a n c h w h e r e it comes to rest with other n y m p h s . If a snake h a p p e n s to crawl over a c l u m p of these resting mites, they b e c o m e active a n d climb on to t h e s n a k e a n d c o n c e a l t h e m s e l v e s b e n e a t h its s c a l e s . A f t e r f e e d i n g t o e n g o r g e m e n t , t h e p r o t o n y m p h s d r o p off a n d c r a w l a b o u t u n t i l t h e y find a d a r k , m o i s t c r e v i c e . H e r e m a l e s a n d f e m a l e s s o m e t i m e s p a i r off a n d r e m a i n p a i r e d u n t i l t h e y r e a c h m a t u r i t y . E c d y s i s follows s o o n after r e p l e t i o n a n d t h e n e w l y m o u l t e d d e u t o n y m p h s , although active, usually r e m a i n in t h e h u m i d area until t h e next ecdysis. T h e d e u t o n y m p h males and females usually pair if this has not occurred in the previous stage. After moulting to the adult stage, t h e mites r e m a i n in t h e moist crevices until their integument has hardened and then begin to wander about until they come in contact with a suitable host, to which they respond by t h e i r r e a c t i o n s t o g r a v i t y , t e m p e r a t u r e a n d o d o u r . M a l e m i t e s will c o p u l a t e after feeding b u t are n o t a t t r a c t e d b y r e p l e t e females. T h e s e u n f e c u n d e d f e m a l e s lay e g g s w h i c h d e v e l o p p a r t h e n o g e n e t i c a l l y i n t o m a l e s . F e m a l e s n o r m a l l y lay f r o m 6 0 t o 8 0 e g g s , feeding two or three times at intervals of one or two weeks. T h e b l o o d - s u c k i n g m i t e s o f t h e g e n u s Haemolaelaps a r e m a m m a l a n d b i r d p a r a s i t e s a n d s e e m t o s h o w a p r e f e r e n c e for r o d e n t s . T h e y a r e p r o b a b l y o v o v i v i p a r o u s a n d g i v e b i r t h t o t h e first n y m p h a l f o r m . A s i n m o s t p a r a s i t i c m i t e s t h e m a l e s p r o b a b l y d o n o t feed o n the blood of the host, b u t haemoglobin has been demonstrated in b o t h p r o t o - a n d d e u t o n y m p h s w h i c h leave t h e host i m m e d i a t e l y after f e e d i n g a n d m o u l t i n t h e n e s t . T i c k s a r e p a r a s i t i c d u r i n g t h e g r e a t e r p a r t o f t h e i r lives, b u t all l e a v e t h e h o s t i n o r d e r t o d e p o s i t t h e i r e g g s . T h e s e a r e laid o n t h e g r o u n d in e n o r m o u s n u m b e r s a n d hatch into six-legged larvae. T h e y o u n g t i c k s r e m a i n c l u s t e r e d t o g e t h e r for s e v e r a l d a y s b u t then climb the nearest blade of grass and await the coming of their host. M a n y die in t h e attempt, b u t s o m e succeed in attaching t h e m selves to a p a s s i n g a n i m a l a n d p r o c e e d to g o r g e t h e m s e l v e s w i t h b l o o d . A f t e r f e e d i n g for a f e w d a y s t h e l a r v a e d r o p off, s e e k a h i d i n g place a n d m o u l t into n y m p h s w h i c h behave in m u c h the same way. T h e a d u l t stage i s r e a c h e d after o n e m o r e m o u l t . L e e s a n d B e a m e n t ( 1 9 4 8 ) h a v e s h o w n t h a t ' t h e e g g o f t h e s h e e p tick

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Ixodes reduvius is w a t e r - p r o o f e d by an e x t e r n a l c o v e r i n g of w a x w h i c h i s s e c r e t e d b y t h e f e m a l e after t h e s h e l l l a y e r s a r e c o m p l e t e . T h i s waxy covering is first smeared over t h e egg as it passes d o w n the vagina a n d a further layer of lipoid is applied w h e n t h e egg touches G e n e ' s organ, a glandular structure that is everted shortly b e f o r e o v i p o s i t i o n . I n Ornithodorus moubata t h e w a x is applied s o l e l y b y G e n e ' s o r g a n : t h i s d i f f e r e n c e m a y b e r e l a t e d t o t h e size of t h e egg w h i c h is relatively small in the Ixodoidea. T h e w a x is probably secreted t h r o u g h pore canals distributed over a narrow zone of cuticle b e t w e e n t h e h o r n s of the organ, a n d the cement covering layer of t h e epicuticle does not e x t e n d to this zone. Sexual dimorphism is rare in T h r o m b i d i f o r m mites although it d o e s o c c u r i n s o m e g e n e r a o f w a t e r m i t e s , s o m e t i m e s e v e n affecti n g t h e n y m p h s . I t i s also t o b e f o u n d i n t h e T a r s o n e m i n i a n d i n t h e g e n u s Tenuipalpus o f t h e T e t r a n y c h i d a e a n d s o m e f e w o t h e r s . It is therefore of interest that T u r k a n d Phillips (1946) found r u d i m e n t a r y s e x u a l d i m o r p h i s m i n t h e s l u g m i t e Riccardoella limacum ( f a m i l y E r e y n e t i d a e ) , a s p e c i e s i n w h i c h t h e a d u l t s t a g e i s disappearing. T h e female d e u t o n y m p h produces the eggs which a r e c a p a b l e o f f e r t i l i s a t i o n , b u t w h e t h e r t h e l a r g e r a d u l t f e m a l e also lays e g g s i s u n d e c i d e d . T h e e g g s m a t u r e i n t h e i r o w n o o c y s t s a n d s o m e at least are fertilised in t h e ovary. C o p u l a t i o n takes place on the host and is probably confined to the early s u m m e r , the only t i m e a t w h i c h a d u l t m a l e s a r e f o u n d . T h e e g g s a r e c o m m o n l y laid i n the m a n t l e cavity of t h e host, b u t m a y s o m e t i m e s be found e m b e d d e d in m u c u s on t h e skin. Viviparity a n d oviparity exist side by s i d e a n d s e e m i n g l y n o t all i n d i v i d u a l s r e t a i n a n e g g o f r e t a r d e d d e v e l o p m e n t over t h e winter, while s o m e over-wintering larvae remain in the dry skin of the female. In t h e Bdellidae t h e sexes are very similar. T h e eggs are slightly elliptical a n d are covered w i t h clavate spines a n d projections. T h e y a r e laid o n t h e soil, i n leaf m o u l d o r w h e r e v e r t h e m i t e h a p p e n s t o be a n d h a t c h into a typical six-legged larva w h i c h develops t h r o u g h three n y m p h a l stages to the adult. T h e life c y c l e s o f t h e r e d - s p i d e r m i t e s a r e c o m p a r a t i v e l y w e l l k n o w n . T h e winter is passed as eggs w h i c h are deposited on branches and twigs and are bright red in colour. T h e y hatch in s p r i n g to a larva w h i c h passes t h r o u g h various n y m p h a l stages to

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t h e adult. D u r i n g copulation t h e male crawls u n d e r t h e female f r o m t h e r e a r a n d c l a s p s h i s f r o n t legs a b o u t h e r a b d o m e n a n d h i s s e c o n d p a i r o f legs a b o u t h e r h i n d l e g s . H e t h e n c u r v e s t h e e n d o f his a b d o m e n u p w a r d a n d f o r w a r d u n t i l i t m e e t s t h e e n d o f t h e f e m a l e ' s a b d o m e n . C o p u l a t i o n lasts f r o m t e n t o f i f t e e n m i n u t e s . E g g s a r e laid w i t h i n a d a y o r t w o d a y s o f e m e r g e n c e i n h o t w e a t h e r : these s u m m e r eggs do not s h o w diapause a n d h a t c h in a b o u t eight to ten days. T h e n u m b e r of generations in a year depends on c l i m a t e a n d l a t i t u d e . O v e r - w i n t e r i n g , d i a p a u s i n g e g g s a r e laid towards the autumn, their production being engendered by the d e c r e a s i n g l e n g t h o f d a y l i g h t u n t i l c o l d w e a t h e r kills t h e a d u l t m i t e s o r c a u s e s t h e l e a v e s o n w h i c h t h e y a r e f e e d i n g t o fall ( L e e s , 1955). T h e conditions of the micro-environment under which many p a r a s i t i c m i t e s c a n m u l t i p l y a r e o f t e n l i m i t e d . T h u s 12° t o 14° C r e p r e s e n t s t h e l o w e s t t e m p e r a t u r e a t w h i c h Liponyssus bacoti c a n reproduce and then only with a great lengthening of the cycle and a n i n c r e a s e i n m o r t a l i t y , a n d m a n y o t h e r s p e c i e s t h a t n o r m a l l y feed on t h e b o d y of their host w h e r e they are protected from t h e cold a r e r e s t r i c t e d in a s i m i l a r w a y . M o s t of the Cheyletidae and Demodicidae develop normally from egg, larval a n d n y m p h a l stages to t h e adult, b u t in t h e w a t e r mites only t h r e e stages are n o t e d s u b s e q u e n t l y to t h e egg, viz. t h e larva, n y m p h a n d a d u l t o r p r o s o p o n , b e t w e e n e a c h o f w h i c h m e t a m o r p h o s i s takes place. T h e eggs are usually reddish in colour a n d laid o n a q u a t i c v e g e t a t i o n o r s t o n e s t o w h i c h t h e y a r e f i x e d b y a m u c i l a g i n o u s c o v e r i n g . I n t h e g e n u s Hydrachna, t h e e g g s a r e p l a c e d i n c a v i t i e s p i e r c e d i n t h e s t e m s o f a q u a t i c p l a n t s for t h e i r r e c e p t i o n . T h e larval a n d n y m p h a l stages are usually parasitic o n aquatic insects a n d are separated by resting stages w h e n t h e creatures are c o n c e a l e d i n t h e axils o f l e a v e s o r u n d e r s t o n e s . T h e a d u l t s a r e free living. F o r f u r t h e r details, see S o a r a n d W i l l i a m s o n (1925, 1927, 1929). T h e life c y c l e o f t h e A c a r i d i a e i s s i m i l a r t o t h a t o f o t h e r m i t e s , passing as it does t h r o u g h t h a t of egg, h e x a p o d larva a n d two n y m p h a l stages before b e c o m i n g adult. I n s o m e cases, however, a n a d d i t i o n a l h e t e r o m o r p h i c s t a g e i s i n t r o d u c e d i n t o t h e life history between the two n y m p h a l stages. T h i s is k n o w n as the

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hypopus a n d differs c o m p l e t e l y f r o m all t h e o t h e r s . I n s t e a d o f h a v i n g a flexible c u t i c l e it is w e l l c h i t i n i s e d a n d d e v o i d of a m o u t h : it does not appear to be formed as the result of adverse conditions b u t acts as a m e a n s of dispersal. By m e a n s of a v e n t r a l sucker plate t h r o u g h w h i c h project a series of finger-like suckers, t h e h y p o p u s a t t a c h e s itself t o a p a s s i n g i n s e c t a n d i s c a r r i e d f r o m o n e p l a c e t o another. At the same time it is able to survive drier conditions than the adult. It has b e e n found t h a t a t e m p e r a t u r e of 23° to 25° C is t h e optim u m for r e a r i n g c u l t u r e s o f t h e f u r n i t u r e m i t e , Glycyphagus domesticus a n d t e m p e r a t u r e a n d h u m i d i t y h a v e a m a r k e d effect o n the development of the egg and h y p o p u s stages. T h e life c y c l e o f t h e f e a t h e r m i t e s , f a m i l y D e r m o g l y p h i d a e , i s a s follows: t h e r e are t w o t y p e s of egg, a h a r d shelled a n d a t h i n shelled o n e . T h e l a t t e r c o n t a i n l a r v a e w h i l e still w i t h i n t h e m o t h e r w h o m a y b e either viviparous o r ovoviviparous. T h e six-legged larva hatches from the egg to m o u l t to the eight-legged p r o t o n y m p h which in t u r n forms the d e u t o n y m p h . W h e n mating takes place the male always copulates w i t h t h e female d e u t o n y m p h w h i c h later moults to the adult stage. Detailed knowledge of the d e v e l o p m e n t of t h e larvae a n d n y m p h of the Oribatid mites is virtually non-existent, b u t Sengbusch (1954) has recently succeeded in t i m i n g t h e d e v e l o p m e n t of t h r e e A m e r i c a n s p e c i e s o f Galumna f r o m e g g t o a d u l t . O v i p o s i t i o n m a y occur in nature from spring to a u t u m n and is probably correlated w i t h t e m p e r a t u r e w h i c h also affects t h e t i m e o f d e v e l o p m e n t . T h i s a v e r a g e s 63 d a y s at 2 0 ° C in G. nervosus, b u t o n l y 47 d a y s at 2 5 ° C. Finally, we come to the s u b - o r d e r Tetrapodili. N o t until Keifer's work (1946) on the alternation of generations of the buckeye rust m i t e Oxypleurites aesculifoliae w a s t h e life c y c l e of a n y of t h e E r i o p h y i d a e fully u n d e r s t o o d . T h e d e u t o g y n e s b e c o m e a c t i v e i n late w i n t e r a n d leave their h i b e r n a t i n g q u a r t e r s o n twigs. W h e n t h e b u d s s w e l l i n F e b r u a r y t h e y p e n e t r a t e t h e o u t e r s c a l e s a n d feed o n t h e g r e e n i n n e r tissue b e n e a t h . W i t h t h e d e v e l o p m e n t of leaves, t h e y lay e g g s w h i c h h a t c h i n t o n y m p h s p r o d u c i n g p r i m a r y m i t e s o n t h e leaves. T h e s e soon p r o d u c e additional p r i m a r y mites. I n e a r l y M a y n e w d e u t o g y n e s a p p e a r w h i c h w h e n fully fed t r a v e l d o w n t h e s t e m for six i n c h e s o r m o r e a n d t h e n c r a w l i n t o c r e v i c e s

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of the previous season's wood. T h e p r i m a r y mites are confined to t h e leaves a n d p e r i s h w i t h t h e m b u t t h e d e u t o g y n e s , o n c e t h e y have

attained a

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become

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late

s u m m e r . W i n t e r r a i n s a n d frost t e n d t o b r e a k t h i s d i a p a u s e h o w ever a n d t h e d e u t o g y n e s b e c o m e active again t h e following spring. T h e r e is a high mortality amongst t h e m , principally because of the limited n u m b e r of suitable crevices.

BIBLIOGRAPHY Identification ANASTOS, G. (1950) T h e scutate ticks, or Ixodidae, of Indonesia. Ent. Amer. (N.S.), 3 0 , 1 - 1 4 4 . A U D Y , J. R. (ed.) (1954) Malaysian Parasites, I - X V . Stud. Inst. Med. Res. Malaya, N o . 26, 1-242. BAKER, E. W. and W H A R T O N , G. W. (1952) An Introduction to Acarology. N e w York. BEER, R. E. (1954) A revision of the T a r s o n e m i d a e of the W e s t e r n H e m i sphere ( O r d e r Acarina). Univ. Kansas Sci. Bull., 3 6 , (2), 1091-1387. COOLEY, R. A. and K O H L S , G. M. (1944) T h e Argasidae of N o r t h America, Central America a n d C u b a . Amer. Midi. Nat. Monograph, N o . 1, 1-152. (1945) T h e g e n u s Ixodes in N o r t h America. Bull. Nat. Inst. Health, No. 184,1-246. H A M M E N , L. VAN DER (1952) T h e Oribatei (Acari) of the N e t h e r l a n d s . Zool. Verh. Leiden, N o . 17, 1-139. HOOGSTRAAL, H. (1956) African Ixodoidea 1, Ticks of the Sudan. Cairo. H U G H E S , A. M. (1948) The Mites associated with stored Food Products. L o n d o n : Min. Agric. Fish. KEEGAN, H. L. (1951) T h e mites of the sub-family Haemogamasinae (Acari: Laelaptidae). Proc. U.S. Nat. Mus. Wash., 1 0 1 , 2 0 3 - 6 8 . MICHAEL, A. D. (1883) British Oribatei, 1, L o n d o n . (1887) Ibid., 2. (1901) British Tyroglyphidae, 1. L o n d o n . (1903) Ibid., 2. N U T T A L L , G . and WARBURTON, C , COOPER, W . and R O B I N S O N , L . (1908)

Ticks. A Monograph of the Ixodoidea. Part 1, Argasidae. C a m b r i d g e . (1911) Ibid., Part 2, Ixodidae, the genus Ixodes. (1915) Ibid., Part 3, Ixodidae, the genus Haemaphysalis. ROBINSON, L . E. (1926) Ibid., Part 4, Ixodidae, the genus Amblyomma. PRITCHARD, A. E. and BAKER, E. W. (1955) A Revision of the Spider Mite Family Tetranychidae. San Francisco. SENEVET, G . (1937) Ixodoides Faune de France, N o . 32, 1-100. Paris.

202

MITES

AND

TICKS

SOAR, C. D. and WILLIAMSON, W. (1925) The British Hydracarina. 1. London. (1927) Ibid.,2. (1929) Ibid., 3. TOUMANOFF, C. (1944) Les Tiques (Ixodoidea) de ITndochine. Saigon. VIETS, K. (1955) Die Milben des Sufiwassers und des Meers, 1. Jena. VITZTHUM, G. H. (1940-43) Acarina in H. G. BRONN'S Klass. Ordn. Tierreichs, 5, IV (5), 1-1011. W I L L M A N , C. (1931) M o o s m i l b e n oder Oribatiden (Oribatei). Tierzv. Deutsch., 2 2 , 7 9 - 2 0 0 .

Biology ARTHUR, D. R. (1951) T h e bionomics of Ixodes hexagonus Leach in Britain. Parasitology, 4 1 , 8 2 - 9 0 . (1952) Economic importance of ticks. Discovery, 1 3 , 3 7 9 - 8 3 . A U D Y , J. R. and HARRISON, J. L. (1951) A review of investigations on mite t y p h u s in B u r m a and Malaya, 1945-1950. Trans. R. Soc. Trop. Med. Hyg., 4 4 , 371-404. C A M I N , J. H. (1953) Observations on the life history and sensory behaviour of the snake mite, Ophionyssus natricis (Gervais) (Acarina: M a cronyssidae). Spec. Publ. Chicago. Acad. Sci., N o . 10, 1-75. CLOUDSLEY-THOMPSON, J. L. (1947) T h e edibility of Hydracarina Naturalist, 1 9 4 7 , 1 1 6 - 1 8 . ELTON, C. S. (1922) O n the colours of water mites. Proc. Zool. Soc. Lond., 1922,1231-40. HUGHES, A. M. (1951) A general survey of the Acari (Arachnida). J. Quek. Micr. Club, (4), 3, 2 4 7 - 6 0 . JONES, B. M. (1950a) T h e sensory physiology of the harvest m i t e Trombicula autumnalis Shaw. J. Exp. Biol., 2 7 , 4 6 1 - 9 4 . (1950b) T h e penetration of the host tissue by the harvest mite, Trombicula autumnalis Shaw. Parasitology, 4 0 , 247-60. KEIFER, H. H. (1946) A review of N o r t h American economic Eriophyid mites. J. Econ. Ent., 3 9 , 563-70. LEES, A. D. (1947) T r a n s p i r a t i o n and the structure of the epicuticle in ticks. J. Exp. Biol., 2 3 , 379-410. (1948) T h e sensory physiology of the sheep tick, Ixodes ricinus L. Ibid., 2 5 , 145-207. (1955) The Physiology of Diapause in Arthropods. C a m b r i d g e . LEES, A. D. and BEAMENT, J. W. L. (1948) An egg-waxing organ in ticks. Quart. J. Micr. Sci., 8 9 , 291-332. M I L N E , A. (1945) T h e ecology of the sheep tick, Ixodes ricinus L. T h e seasonal activity in Britain with particular reference to n o r t h e r n England. J. Exp. Biol, 3 6 , 1 4 2 - 5 2 .

MITES

AND

TICKS

203

NEWELL, I. M. ( 1 9 4 7 ) A systematic and ecological study of the Halacaridae of eastern N o r t h America. Bull. Bingham Oceanogr. Coll., 1 0 , (3), 1-232.

SENGBUSCH, H. G. ( 1 9 5 4 ) Studies on the life history of three Oribatoid mites with observations on other species (Acarina, Oribatei). Ann. Ent. Soc. Amer., 4 7 , 6 4 6 - 6 7 .

SOLOMON, M. E. ( 1 9 3 7 ) Behaviour of the red-legged earthmite, Halotydeus destructor, in relation to environmental conditions. J. Anim. Ecol.,6,

340-61.

T U R K , F . A . a n d PHILLIPS, S - M . ( 1 9 4 6 ) A m o n o g r a p h of t h e slug m i t e

Riccardoella limacum (Schrank). Proc. Zool. Soc. Lond., 1 1 5 , 4 4 8 - 7 2 . VIETS, K. ( 1 9 4 0 ) Ausbreitungswege u n d nacheiszeitliche Verbreitung der Kalt wasser u n d S t r o m u n g liebenden Wassermilben in E u r o p a . Arch. Hydrobiol., 3 7 , 2 7 8 - 3 1 9 .

W I L K I N S O N , P . R . ( 1 9 5 3 ) Observations o n the sensory physiology and behaviour of larvae of the cattle tick, Boophilus microplus, (Can.), (Ixodidae). Austr.J. Zool., 1, 3 4 5 - 5 6 . WOODROFFE, G . E . a n d SOUTHGATE, B . J. ( 1 9 5 1 ) B i r d s ' nests as a source of

domestic pests. Proc. Zool. Soc. Lond., 1 2 1 , 5 5 - 6 2 . Z U M P T , F. and G R A F , H. ( 1 9 5 0 ) Medical importance of mites. S. Afr. J. Clin. Sci., 1 , [ 1 9 6 - 2 1 2 .

EPILOGUE I N THE i n t r o d u c t i o n t o t h i s v o l u m e t h e c o m p l e x i t y o f f a c t o r s influencing the ecology a n d distribution of animals was indicated, and the interactions with their e n v i r o n m e n t s of the species m e n tioned have been stressed throughout. Ecology can be studied from the point of view of the species (autecology) or from that of the particular habitat in w h i c h n u m b e r s of species occur (synecology). T h e former is a s i m p l e r a p p r o a c h a n d m o r e suited to t h e activities of t h e individual n a t u r a l historian: t h e latter usually involves t e a m work. W h i c h e v e r is adopted, however, t h e other s h o u l d c o n s t a n t l y b e b o r n e i n m i n d o r else t h e p i c t u r e will b e c o m e unbalanced and distorted. Considerable uniformity is apparent throughout the groups that have been considered here: this is not altogether surprising in m e m b e r s of the same p h y l u m . A r t h r o p o d s have an exoskeleton w h i c h , i n all c l a s s e s , s e e m s t o b e b a s i c a l l y s i m i l a r a l t h o u g h i t m a y vary greatly in complexity. An exceedingly thin outer epicuticular layer of 'cuticulin', a c o n d e n s e d l i p o - p r o t e i n t a n n e d w i t h q u i n ones, is always present b u t only in insects and Arachnids does this s u p p o r t the impervious layer of wax to w h i c h their success on land is l a r g e l y d u e . It would be mistaken however to regard the absence of a discrete cuticular wax layer as a primitive characteristic, a l t h o u g h t h e forms t h a t lack o n e a r e s o r e s t r i c t e d i n t h e i r c h o i c e o f e n v i r o n m e n t t h a t they cannot be regarded as entirely successful land animals. Rather, i t s e e m s t h a t a p a r t i c u l a r m e t h o d h a s b e e n e x p l o i t e d for s u r v i v i n g t h e c o n d i t i o n s o f life o n l a n d . T h e p r i m i t i v e r e s p i r a t o r y o r g a n i s t h e skin, b u t special r e s p i r a t o r y s t r u c t u r e s have b e e n evolved in all but the smallest a n d simplest of the A r t h r o p o d a . In insects a s y s t e m of m i n u t e air t u b e s or ' t r a c h e a e ' lead i n t o e v e n finer 'tracheoles' that carry oxygen directly to the tissues where metabolic processes take place, while t h e A r a c h n i d a possess b o t h t u b u lar t r a c h e a e a n d l u n g - b o o k s . S c o r p i o n s h a v e l u n g - b o o k s , w h i l e 204

EPILOGUE

205

spiders are passing t h r o u g h a primitive lung-book stage from which none has yet emerged. T w o pairs of lung-books without tracheae o c c u r in t h e m o r e p r i m i t i v e families while m o s t others have an anterior pair of lung-books a n d a posterior pair of tracheae. L u n g - b o o k s p r o v i d e a localised respiratory area from w h i c h oxygen is distributed by the respiratory pigment, haemocyanin, in t h e b l o o d . I n s e c t s p o s s e s s n o r e s p i r a t o r y p i g m e n t s b e c a u s e all t h e i r tissues are supplied with oxygen directly by t h e tracheoles. T h e entrance to both lung-books and tracheae is guarded by spiracles closed by m e a n s of special muscles. In this w a y the m i n i m u m q u a n t i t y o f a i r n e c e s s a r y for r e s p i r a t o r y p u r p o s e s i s allowed to circulate and consequently water-loss is m u c h reduced. W h e n an insect or Arachnid is placed in an atmosphere containing an abnormally high p r o p o r t i o n of c a r b o n dioxide t h e spiracles are k e p t o p e n t o t h e i r fullest e x t e n t a n d t h e r a t e o f w a t e r - l o s s i n d r y air is t h e n c o n s i d e r a b l y i n c r e a s e d . I n all o r g a n i s m s g r o w t h t e n d s t o b e a cyclical p r o c e s s , p e r i o d s o f rest alternating with activity. In no animals, however, is it m o r e marked than in the Arthropoda whose development is punctuated by a series of m o u l t s or ecdyses, each of w h i c h is p r e c e d e d by a period of active g r o w t h a n d followed by o n e of a p p a r e n t inactivity. All parts of t h e i n t e g u m e n t are m o u l t e d together, i n d e p e n d e n t l y of n e r v e s u p p l y : t h e s t i m u l u s for this is h o r m o n i c in nature, metamorphosis too being u n d e r h o r m o n e control. D u r i n g m o u l t i n g t h e old endocuticle is digested by e n z y m e s in t h e m o u l t i n g fluid a n d w i t h d r a w n i n s o l u t i o n t h r o u g h t h e ' p o r e canals'. T h e s e are n u m e r o u s fine tubes, sometimes n u m b e r i n g over a million per sq. cm of surface, w h i c h penetrate t h e exo- and endocuticle. A n e w epicuticle is always laid d o w n b e n e a t h t h e old one before m o u l t i n g takes place, so that this process is accompanied b y l i t t l e loss o f w a t e r a n d a h i g h d e g r e e o f e c o n o m y i s a c h i e v e d . Woodlice and millipedes are almost entirely vegetarian, while centipedes and Arachnids, with t h e exception of certain mites, are p r i m a r i l y carnivorous; b u t different species of insects s e e m to be able to thrive on almost any kind of organic m a t t e r capable of supporting metabolism. In most of these animals water conserv a t i o n i s o f p r i m e i m p o r t a n c e ; insufficient w a t e r i s o b t a i n e d w i t h t h e f o o d t o a l l o w for m u c h e x c e s s t o b e lost d u r i n g e x c r e t i o n .

206

EPILOGUE

T h e function of excretion, like t h a t of o s m o t i c regulation, is t h e maintenance of a constant internal environment within t h e animal body. An aquatic animal s u r r o u n d e d by a large v o l u m e of water can excrete toxic nitrogenous c o m p o u n d s with impunity, b u t the n e c e s s i t y for w a t e r e c o n o m y i n t e r r e s t r i a l f o r m s g e n e r a l l y r e q u i r e s t h e e x c r e t i o n o f s o m e c o m p o u n d less p o i s o n o u s t h a n a m m o n i a . W o o d l i c e are essentially a m m o n o t e l i c since o v e r half of t h e i r soluble non-protein nitrogen is excreted in the form of ammonia, but the retention of this primitive character has been attended by a general suppression of nitrogenous metabolism. In higher insects, as in m y r i a p o d s , b i r d s a n d reptiles, u r i c acid is t h e chief excretory c o m p o u n d . T h i s s u b s t a n c e h a s i n t h e first p l a c e b e e n e v o l v e d i n r e s p o n s e t o t h e c o n d i t i o n s o f e m b r y o n i c life. U r i c o t e l i c m e t a bolism is correlated w i t h the possession of 'cleidoic' eggs provided w i t h w a t e r a n d enclosed in a comparatively i m p e r m e a b l e shell. A m m o n i a is toxic as we have seen and is only suitable as an e x c r e t o r y c o m p o u n d for e g g s d e v e l o p i n g i n w a t e r : i t c a n n o t b e converted to urea as this w o u l d cause ureamia, a n d in excess upset t h e o s m o t i c relationships of t h e egg. H e n c e u r i c acid, a n o n - t o x i c , highly insoluble substance, has been evolved which can accumulate w i t h i n t h e e g g w i t h o u t c a u s i n g a n y ill effects. T h e chief e x c r e t o r y c o m p o u n d o f t h e A r a c h n i d a i s g u a n i n e w h i c h , like u r i c a c i d , i s v e r y i n s o l u b l e , b u t t h e p h y s i o l o g y o f its excretion has not b e e n studied in t h e s a m e detail. T h r o u g h o u t the A r t h r o p o d a entirely mechanistic patterns of behaviour are found, involving rigid b u t comparatively simple r e s p o n s e s t o t h e s t i m u l i o f t h e e n v i r o n m e n t s i n w h i c h t h e y live. I n d e e d it would seem that the typical arthropodan nervous system i s c a p a b l e o n l y o f s t e r e o t y p e d reflex b e h a v i o u r p a t t e r n s a n d t h a t t h i s p e r h a p s r e s t r i c t s t h e m n o less t h a n t h e i r r i g i d i n t e g u m e n t ! Nevertheless, within the limits i m p o s e d by their basic m o r p h o logy a n d p h y s i o l o g y , e v e r y c o n c e i v a b l e t y p e o f m o d i f i c a t i o n a n d s p e c i a l i s a t i o n o c c u r s w i t h i n t h e A r t h r o p o d a a n d h e r e i n lies t h e great interest of these animals to the serious student of natural history.

GENERAL

BIBLIOGRAPHY

I n a d d i t i o n t o t h e special b i b l i o g r a p h i e s t h a t follow e a c h c h a p t e r , the following m o r e g e n e r a l w o r k s will b e f o u n d t o b e useful. References to t h e m in t h e text have b e e n m a r k e d by an asterisk. BERLAND, L. (1932) Les Arachnides. Paris. B O N N E T , P. (1945) Bibliographia Araneorum, 1. T o u l o u s e . BRISTOWE, W. S. (1939) The Comity of Spiders, 1. L o n d o n . (1941) Ibid. 2. BRUES, C. T . , MELANDER, A. L . a n d CARPENTER, F . M . (1954) Classifica-

tion of Insects. Keys to the living and extinct families of insects, and to the living families of other terrestrial A r t h r o p o d s . Bull. Mus. Comp. Zool,108,1-917. COMSTOCK, J. H. (1940) (edited by W. J. GERTSCH). The Spider Book. (revised ed.). N e w York. DONISTHORPE, H. St. J. K., (1927) The Guests of British Ants. L o n d o n . E D N E Y , E. B. (1957) The Water Relations of Terrestrial Arthropods, Cambridge. GERTSCH, W. (1949) American Spiders. N e w York. GRASSE, P - P . (ed.) (1949) Traite de Zoologie Anatomie, Systematique, Biologie, 6, Paris. HARMER, S. F. and SHIPLEY, A. E. (eds.) (1909) The Cambridge Natural History, 4 , L o n d o n . KAESTNER, A. (1956) Lehrbuch der Speziellen Zoologie, 1 ( 1 3 ) , 4 8 5 - 6 5 8 . Berlin. KEVAN, D . K . M C E . (ed.) Soil Zoology. L o n d o n . K U H N E L T , W. (1950) Bodenbiologie. W i e n . LAWRENCE, R. F. (1953) The Biology of the Cryptic Fauna of Forests. Cape Town. PATTON, W. S. and EVANS, A. M. (1929) Insects, Ticks, Mites and Venomous Animals of Medical and Veterinary Importance, 1. Liverpool. PHISALIX, M. (1922) Animaux venemeux et Venins, 1. Paris. POCOCK, R. I. (1928) Guide to the Arachnida, Millipedes and Centipedes exhibited in the Department of Zoology, British Museum (Natural History). L o n d o n . SAVORY, T. H. (1928) The Biology of Spiders. L o n d o n . (1935) The Arachnida. L o n d o n . SMART, J. and TAYLOR, G. (1953) Bibliography of Key Works for the Identification of the British Fauna and Flora, 2nd ed., L o n d o n . Zoological Record, L o n d o n . (Published annually since 1865). 207

CLASSIFICATORY

INDEX

I N THE f o l l o w i n g s u m m a r y o f classification a r e i n c l u d e d all s p e c i e s , f a m i l i e s , s u b - o r d e r s , o r d e r s a n d classes m e n t i o n e d i n t h e t e x t . T h u s , although it is not absolutely comprehensive, reference has b e e n m a d e i n i t t o m o s t i f n o t all o f t h e m o r e i m p o r t a n t g r o u p s k n o w n . References to text-figs, are given in heavy t y p e . P h y l u m ARTHROPODA [ S u b - p h y l u m CRUSTACEA]

Family Porcellionidae 2, 3 *Cylisticus convexus 3, 13 * Metoponorthus pruinosus 3 *Porcellio scaber XII,

Class Malacostraca ORDER Isopoda (Chapter I) S u b - o r d e r Oniscoidea Family Ligiidae 2 *Ligia s p p . 9 *L. oceanica 3, 6, 9, 12, XIII, 2-4, 10, 11, 13, PL la PI. la,b *P. spinicornis 3 L. baudiniana 6 *P. dilatatus 13 L. exotica 6 *P. rathkei 3 * Ligidium hypnorum 3, P. demivirgo 4 PL la Hemilepistus reaumuri L. longicaudatum 3 7, 8, 9, PL la Family Trichoniscidae 2, Family Armadillidiidae 3,6 * Trichoniscus s p p . 1,12 2,3 _ *T.pusillus XIII, 4, 10 *Armadillidium spp. 12 *A. vulgare XIII, 3, 4, T. commensalis 7 8, 10, 13, PL la * Andr-oniscus dentiger *A. nasatum 3 PL la Family Eubelidae 1 Family Oniscidae 2 Sphaerobathvtropa spp. * Oniscus asellus 1,4,7, 1 8, 10, 11, PL la,b *Halophiloscia s p p . 9 Class Diplopoda (Chapter II) *Philoscia muscorum 4, Sub-class Chilognatha 6 , 1 3 , PL la ORDER Oniscomorpha *Platyarthrus s p p . 1 Family Glomeridae 1 5 , *P. hoffmannseggi 7,10, 17 PL lb * British genera and species. S.S.C.M. 209

210

C L A S S I F I C A T O R Y

*Glomeris marginata 1 6 , 32,33, 35 Family Sphaerotheriidae 17 ORDER

Limacomorpha

Family G l o m e r i d e s midae 17 Family Z e p h r o n i o d e s midae 17 ORDER

Colobognatha

Family Pseudodesmidae 17 Family Platydesmidae 17 Family Siphonophoridae 17 Siphonophora s p p . 17 Family Polyzoniidae 1 5 , 17 *Polyzonium s p p . 29 *P. germanicum 17, 20, 21 ORDER

Ascospermophora

Family C h o r d e u m i d a e 15,18 * Microchordeuma s p p . 18 Family Brachychaeteumidae 18 *Brachychaeteuma spp. 18 Family Craspedosomidae 15,18 *Craspedosoma razvlinsi 18 * Poly micr odon polydesmoides 18,34 Family H e t e r o c h o r deumidae 18 ORDER

Proterospermophora

Family Polydesmidae 15,18, 29,32,33 *Polydesmius s p p . 18, 30, 35 *P.angustus 18,32,33, PI. IVfl P. ricinus 29

I N D E X

Luminodesmus sequoia. 25 Habrodesmus sp. PI. 116 Family Mastigonodesmidae 18 *Eumastigonodesmius bond 18 Family Cryptodesmidae 15,18 Family Strongylosomidae 15,18,36

*Macrosternodesmus palicola 18 * Oxidus gracilis XII, 18, 2 0 - 4 , 27, 28, 32, 34,35 *Ophiodesmus albonanus 18 Fontaria corrugata 21 Family Lysiopetalidae 18 Lysiopetalum s p p . 19, 30 L.foetidissimum 29 ORDER

Opisthospermophora

Family Stemmiulidae 19 Family Iulidae 1 5 , 19, 20, 25 *Iulus s p p . 27,30,31,35 *TachypodoiuIus niger, 27, PI. *Schizophyllum sabidosum 21 * Cylindroiulus spp. 27 Cylindroiulus londinensis 27 *Paraiidus s p p . 30 Pachyiulus spp. 31 Family Blaniulidae 1 5 , 19, 25 *Blaniulus guttidatus 2 0 - 2 6 , PI. I l i a *Proteroiidus fuscus 25 Family Spirostreptidae 19

CLASSIFICATORY Spirostreptus spp. 19, PI. IVb Gymnostreptus parasitarius 31 Ophistreptus sp. 24 Family Spirobolidae 1 5 ,

211

Family Oryidae Orya barbarica O . almohadensis ORDER

Scolopendromorpha

28

Penicillata

Family Polyxenidae

41,

42, 52, 55

hortensis

43

34,35

Rhinocricus lethifer Sub-class Pselaphognatha

42 42

Family Cryptopidae *Cryptops

19

Spirobolus s p p . 31 Arctobolus marginatus

ORDER

INDEX

*C. anomalans 43 *C. p a r i s i 4 3 Newportia s p p . 43 Theatops s p p . 43 Family Scolopendridae

15,

41,42

Scolopendra spp.

19, 2 9

*Polyxenius spp. 19 *P. lagurus 1 9 , 2 5 , 3 5 , PI. lla Lophoproctus spp. 19

43,

56

S . morsitans 4 3 , 5 1 - 5 3 S. angulata 57 S. cingulata

43,51,52,

PI. V i a , 6 S. clavipes 52 S. dalmatica 57 S . gigantea 4 3 , 5 0 57,

Class Chilopoda (Chapter I I I ) ORDER

Geophilomorpha

Family Geophilidae

S.heros

40,

41,50

48,56

*Scolioplanes

maritimus

S . viridis 5 1 , 5 2 Alipes s p p . 43 Cormocephalus spp. 43

Ethmostigmus spp. Rhysida afra 43 ORDER

43

Craterostigmomorpha

Family Craterostigmidae

48,49

*S. crassipes 54 Dignathodon spp. 48 Mixophilus indicus 49 Pectinunguis americanus 48

43

Craterostigmus spp. ORDER

43

Lithobiomorpha

Family Lithobiidae

41,

44

Family Himantariidae *Haplophilus subterraneus 4 2 Family Schendylidae *Hydroschendyla submarina

43, 51,

52

*Geophilus electricus 54 * G . carpophagus 5 4 *Necrophlaeophagus longicornis 54 Pachymerium ferrugineum

51,52,54

S. subspinipes

48-50

* Lithobius spp. 4 4 , 46 * L . forficatus 4 4 , 4 7 , 50, 52, 54, 55, 57, 58,

PI. Vb *L. calcaratus * L . variegatus

48 44 S.S.CM.

CLASSIFICATORY *L.piceus 55 L.fasciatus 44 Bothropolys multidentatus 47 Neolithobius voracior 47, 48 Family Henicopidae 44 *Lamyctesfulvicornis 44 Family Cermatobiidae 44 Cermatobius s p p . 44 ORDER

Scutigeromorpha

Family Scutigeridae 4 1 , 44, 46 Scutigera s p p . 46-8 PL Ya *S. coleoptrata 44, 47, 58 S. chtnifera 44 S. longicornis 44 S. forceps 54

Class P a u r o p o d a ( C h a p t e r IV) Family Pauropodidae *Pauropus s p p . 6 1 , 62, 63 P. amicus 63 P. carolinensis 63 *P. huxleyi 63 P. silvaticus 63 Family E u r y p a u r o p o d i dae Eurypauropus s p p . 62 E. spinosus 63 Class Symphyla Family Scutigerellidae 64 *Scutigerella spp. 61 immaculata 65-7, 68

Hanseniella agilis 67 H. hova 67 Family Scolopendrellidae 64

INDEX *Scolopendrella s p p . notacantha 65

66

[Class Arachnida] ORDER Scorpiones (Chapter V) Family Buthidae 7 0 , 72, 83 Buthus occitanus 70, 7 2 - 4 , 76, 78, 80, 82, 84 Androctonus australis 7 2 - 4 , 76, 78, 80, 85, PI. V i l a , IXa A. aeneas PL IXb Buthotus alticola 82, 84 Parabuthus capensis 74, 77 Isometrus maculatus 72 Centrums s p p . 72 Centruroides vittatus 80 C. scidpturatus 80, 81 C. gertschi 80 Hadrurus s p p . 74, 75 Tityus s p p . 72 P. trinitatis 74 Family Diplocentridae 72 Family Scorpionidae 7 0 , 72,83,84 Scorpio s p p . 74 .S. maurus 7 2 - 4 , 76 Opisthophthalmus latimanus 83 Palamnaeus s p p . 73, 74 P. longimanus 73, 75, 76, 78, 84, 85 P. swammerdami 78 Pandinus s p p . 73 Family Vejovidae 72 Family Chactidae 7 0 , 7 2 - 4 , 77, 83

CLASSIFICATORY Euscorpius s p p . 73 E. carpathicus 84 E. flavicaudis 84 E. germanus 72, 78, 84 E. italicus 73, 76, 80, 84, PI. V i l l a , b Family Bothriuridae 72, 83 ORDER Solifugae (Solpugida) (Chapter V I ) Family Rhagodidae 8 7 , 88,94 Rhagodes s p p . 88, 92,93 Family Karschiidae 89 Gylippus rickmersi 89 Family Ceromidae 88 Family Hexispodidae 8 7 , 88 Chelypus s p p . 88 Family Melanoblossiidae 89 Dinorhax s p p . 88 Family Daesiidae 88 Gluvia dorsalis 89 Family Solpugidae 88 Solpuga caffra 92, 96, 97, PI. Xb S. hostilis 94, 96, 97 S. lineata 90 S. sericea 90 Solpugyla globicornis 90 Family Galeodidae 8 7 , 88 Galeodes arabs 77, 88¬ 93,95 G. araneoides 88, 89, 92 G. caspius 96 Family Eremobatidae 8 7 , 88 Eremobates pallipes 90 E.formicaria 90,97 Family A m m o t r e c h i d a e 8 7 , 88 Mummucia variegata 89

INDEX Pseudocleobis morsicans 89

ORDER

Pseudoscorpiones (Chelonethi) (Chapter V I I ) Sub-order C h t h o n i i n e a Family Chthoniidae 99 *Chthonius s p p . 101, 107, 108 *C. ischnocheles 101, 107,108,111 *C.halberti 101 Sub-order N e o b i s i i n e a Family Neobisiidae 99 * Neobisium s p p . 101, 108 *N. carpenteri 111 *N.maritimum 101, 107,111 *N. muscorum 101,107, 111 N.sylvaticum 101 *Roncus spp. 101,108 *R. lubricus 101 Microbisium femoratum 101 M. dumicola 101 Microcreagris cambridgei 101 Gary pus beauvoisi 101, 102 G. minor 111 Sub-order Cheliferinea Family Cheiridiidae 99 "Cheiridium museorum 101, 111 Family Cheliferidae 108, 110 *Chelifer s p p . 101 *C. cancroides 101, 1 0 2 , 1 0 5 , 1 0 8 , 110-2 *Dactylochelifer latreillei 107-9 * Withius subruber 101

CLASSIFICATORY

214

Ellingsenius

INDEX Mastigoproctus spp. 117 M. giganteus 117-19 Typopeltis spp. 117

hendrickxi

106

Family Chernetidae 99 *Lamprochernes nodosus 103,108 *Pselapho cherries scorpioides 101 *Allochernes zvideri 101 A. italicus 101 *Toxochernes panzeri 101, 111, PI. X I I 6 *Chernes spp. 101 *C. cimicoides 111,112 *Dendrochernes cyrneus 102,108,109,111 Cordylochernes scorpioides 103 Sphenochernes schulzi 105

ORDER Palpigradi (Chapter VIII) Family Koeneniidae 1 1 4 Koenenia spelaea 115 K. draco 115 K. mirabilis 115, 116 K. pyrenaica 115 Prokoenenia wheeleri 116 ORDER

Thelyphonida

Family T h e l y p h o n i d a e 114

Thelyphonus s p p . 117 T. caudatus 119, 1 2 1 , PI. Xlb T. linganus, 119 T.sepiaris 117,119-21 T. skimkewitchii 118— 20 Hypoctonus s p p . 117 H.oatesi 119 Labochirus proboscideus 117,118

ORDER

Schizomida

Family Schizomidae 114,121

Schizomus s p p . 122 S. crassicaudatus 122, 123

*S.latipes 123 S. vittatus 122 Stenochrus s p p . 122 Trithy'reus s p p . 122 T. paradenigensis 122 ORDER Phrynichida (Amblypygi) Family Charontidae 124, 125 Charon grayi 124,127 Charinides bengalensis 125, 127, 128 Charinus milloti 124 Paracharon caecus 126 Family T a r a n t u l i d a e 124,125 Phrynichus ceylonicus 126,127 Damon variegatus 126, 128 Z). medius 126 Masicodamon allanteus 126 ORDER

Ricinulei

Family Ricinoididae 1 2 8 , 129 Ricinoides s p p . 129 sjostedti 129 Cryptocellus s p p . 129 C.dorotheae 129

ORDER

Opiliones (Phalangidea) (Chapter I X )

CLASSIFICATORY Sub-order C y p h o t h a l m i 133

Siro rubens 134 S. duricorius 134 Parasiro corsicus 134 Speleosiro sp. 134 Stylocellus s p p . 134 Ogivea s p p . 134 Paragovia s p p . 134 Purcellia s p p . 134 Sub-order Laniatores Family Phalangodidae 133

Phalangodes s p p . 134 Scotolemon s p p . 134, 140 Family O n c o p o d i d a e 134 Family Assamiidae 135 Family Cosmetidae 135 F a m i l y Triaeonychidae 135,144 Larifugella natalensis 142 Soerensella s p p . 144 Nunciaspp. 137,143 Pristobunus s p p . 137 Algidia s p p . 143 A viridata 137 Muscicola picta 137 Hendea myersi 144 F a m i l y Gonyleptidae 1 3 3 , 135, 142 F a m i l y Synthetonychidae 137 Synthetonychia s p p . 137 Sub-order Palpatores Family T r o g u l i d a e 1 3 3 , 135,140,141,144 *Trogulus tricarinatus 137, 138, 146, PI. ^ XII6 *Anelasmocephalus cambridgei 137,138,146 Family N e m a s t o m i d a e 133

INDEX

215

*Nemastoma lugubre 137,138 *N. chrysomelas 137, 138, P 1 . X I I 6 Family Ischyropsalidae 133,140

Family Phalangiidae 1 3 3 "Homalenotus quadridentatus 138 *Leiobunum rotundum 136,138,139 *L. blackwalli 138, 139, 145 L. calcar 143 *Nelima silvatica 138 *Mitopus morio 13 8,140, 143 * Oligolophus s p p . 146 *0. agrestis 139 *0.meadii 138 *O. tridens 139 *O.hansenii 139 *Odiellus s p p . 146 *0.spinosus 139,145 *Lacinius ephippiatus 139 *Megabunus diadema 139,146 *Platybunus triangularis 139,146 P.pinetorum 145 *Phalangium opilio 136, 139, 144,145 *Opilio parietinus 139, 145 *O. saxatilts 138

ORDER Araneae (Chapter X) Sub-order L i p h i s t i o morpha

Family Liphistiidae 149

148,

216

CLASSIFICATORY Liphistius s p p . 149 L. desultor 149 Sub-order M y g a l o morpha

Family T h e r a p h o s i d a e 1 4 8 , 150, 157, 159, 163, 165, 169, 172, P1.176XIIa Theraphosa sp. 150 T.blondi 177 Lasiodora sp. 150 Dugesiella hen tzi 173 Eurypelma sp. 178 Family Ctenizidae 150, 159,160,166,172 Nemesia caementaria 159 Family Atypidae 150, 166 *Atypus affinis 150, 162,174,176 Sub-order A r a n e o m o r p h a Family Filistatidae 166 Filistata insidiatrix 166 Family Dictynidae 151, 167 *Amaurobius s p p . 162 *A. ferox, 157-8, 162, 1 7 6 , 1 7 7 , P1.XIV6 *A. similis 1 5 7 - 8 , 162, 177 A.socialis 161 Family Uloboridae 151, 167 Uloborus republicanus 161 Family Oonopidae 151, 165 * Oonops pidcher 177 Family Dysderidae 151, 157,165 *Dysdera spp. 165 *D.crocota 10,165,174 *D. erythrina 10, 163, 165

INDEX *Segestria senoculata 162,166 *Harpactea hombergi 165 Family Scytodidae 151, 157 *Scytodes thoracica 165. 1 6 6 , 1 7 0 , PI. X I V 6 Family Pholcidae 157, 166 *Pholcus phalangioides 166,177 Family Gnaphosidae 148,151,157,165,171

*Drassodes s p p . 174 *D.lapidosus 163,165 *Scotophaeus blackwalli 165,170 Family Clubionidae 151, 159,165,171 * Phrurolithus fes tivus 152 Family Anyphaenidae 151 Family Sparassidae 1 4 8 , 152,157 Heteropoda venatoria 152 * Micromtnata virescens 152 Family T h o m i s i d a e 1 4 8 , 152,159,164,171,174 * Thomisius onustus 163 * Misumena va tia 163 * Xysticus s p p . 174 Family Salticidae 148, 152, 157, 159, 163, 171,174 *Salticus scenicus 152, 163,170 *Hasarius adansoni 175 Corythalia spp. 175, 176 Phidippus andax PI. Xllla,b

CLASSIFICATORY Family Oxyopidae

152,

157,164

*Oxyopes mus

Family

heterophthal152,164

Lycosidae

148,

152, 157, 159, 164,

217

*Metamenardi 10 *M. segmentata 176 *Cyclosa spp. 1 7 0 Nephila spp. 172 Dicrostichus magnificus 168

Cladomelea

174, 176

*Lycosa spp. XII, 1 7 7 , PI. XlVa *L. purbeckensis 158 *Arctosaperita 160 *Pirata spp. 158 *P. pisca tortus 1 5 8 Family Pisauridae 1 5 2 , 159,177

*Pisaura mirabilis 174 *Dolomedes fimbriatus 158

D. plantarius 178 Family Agelenidae 148, 152,157,159,166

*Argyroneta

INDEX

aquatica

158,168

* Tegenaria s p p . 149 *T. atrica 10 *T. parietina 150 Desis s p p . 1 5 8 Family T h e r i d i i d a e 148, 153,166,171

*Theridion sisyphium 1 7 8 T. socialis 1 6 1 *Stearodeabipunctata 1 6 6 *Oedothorax fuscus 158 La trodectus spp. 172 L. mactans 172 L. 13-guttatus 136 Family T e t r a g n a t h i d a e 167

*Pachygnatha spp. 1 7 4 Family Argiopidae 148, 167, 170, 171

*Argiope bruennichi PI. XVa * A raneus spp. 1 4 9 *A. diadematus 1 0 , 1 6 7

akermani

168

Family Linyphiidae

148,

153-7, 159,166

ORDER Acari (Chapter X I ) S u b - o r d e r Notostigmata Opiliocarus spp. 182,183,186

S u b - o r d e r Holothyroidea Holothyrus spp. 1 8 3 , 186,194

S u b - o r d e r Parasitiformes

(Mesostigmata) Super-family Gamasides 183,186

Family Parasitidae 183,186

Family Dermanyssidae

182 Ophionyssus

natricis

196

Liponyssus bacoti 1 9 9 Family Laelaptidae 30,186

Haemolaelaps

spp.

197

Family

182,

Halarachnidae 186

Super-family

Uropodina

183, 186,

(Ixodoidea) Super-family Ixodei (Ixodidae) 182, 1 8 3 , 184,186,187

* Ixodes reduvius 1 8 7 , 198

CLASSIFICATORY Amblyomma hebraeum PL XVla Boophilus microplus 188 B.annulatus 186 Dermacentor andersoni 186, 195 Rhipicephalus appendicidatus PL XVb Super-family N u t t a l liellei 183 Super-family Argasides (Argasidae) 182, 183, 184,187 Argas persicus 188 Ornithodorus moubata 188,198 S u b - o r d e r Thrombidi-

formes Super-family T a r s o n e mini 184,189, 198 Family Scutacaridae 189 *Acarapis zvoodi 189 Super-family Prostigm a t a 184, 196 ELEUTHERENGONA

Family Eupodidae 189 Halotydeus destructor 189 Family Ereynetidae 198 *Riccardoella limacum 198 Family Tetranychidac 184, 189,198, 199 *Metatetranychus ulmi 189,194 *Paratetranychas pilosus PL X V I 6 * Tenuipalpus s p p . 198 Family Demodicidae 182,199

INDEX *Demodex s p p . 184, 189 Family Cheyletidae 189,199 * Ch eyle tus eruditus 193 *Syringophilus s p p . 189 Family Bdellidae 182, 184, 189, 198 Family Halacaridae 182,190,193 PARASITENGONA

Family H y d r a c h n i d a e 182,184 *Hydrachna s p p . 195, 199 Family Limnocharidae 184 Family Eylaidae 184 Family Limnesiidae 184 Family Arrenuridae 184 Family T h r o m b i d i i d a e (Trombidiidae) 182, 190 *Erythraeus phalangioides 142 *Belaustium nemorum 142 *Leptus s p p . 142 FamilyThrombiculidae (Trombiculidae) *Thrombidium {Trombidium sp. 191 *Thrombicula (Trombiculd) s p p . 191 *T. autumnalis 191 S u b - o r d e r Sarcoptiformes

(Acaridiae) Family Tyroglyphidae 185 *Tyroglyphus farinae 191

CLASSIFICATORY *Glycyphagus domes ticus 200 Family Sarcoptidae 182 *Sarcoptes scabei 185, 192 Family Dermoglyphidae 200 (Oribatei) 182,185, 192, 194, 195, 200 Family Pelopidae 196 *Pelops sp. 196

INDE

219

Family G a l u m n i d a e 200 *Galumna s p p . 200 *G. nervosus 200 S u b - o r d e r Tetrapodili Family Eriophyidae 182,185,192, 200 *Eriophyes ribis PI. X V I la, b Oxypleurites aesculifoliae 200,201

GLOSSARY AND INDEX OF SCIENTIFIC TERMS I N THE f o l l o w i n g g l o s s a r y , r e f e r e n c e s t o p a g e s o n w h i c h scientific t e r m s h a v e b e e n m o r e fully d e s c r i b e d a r e i n d i c a t e d b y h e a v y t y p e . Page references are not given w h e r e w o r d s are in constant use. W h e n a w o r d is in general use in m o r e senses t h a n one, it is explained below in relation to t h e sense in w h i c h it is used in the text of the present volume, and with reference to the particular groups of animals considered. Aktograph—apparatus for recording locomotory activity 24, 25 Anamorphosis—development involving transformation, characteristic of millipedes, d u r i n g which additional segments appear at each moult or ecdysis. Cf. Epimorphosis (q.v.) 35, 57, 63 Apophysis—projecting outgrowth or process Aposematic coloration or sound—conspicuous warning or advertising coloration or sound, found in or produced by distasteful, poisonous or otherwise formidable animals and their mimics. Cf. Cryptic (q.v.) 79, 80,163,170,194-5 Arolium—median tarsal lobe forming a pad or sucker beneath the claws of the leg of false-scorpions, etc. 103 Asparagine—amino-acid found in plant tissues and known to be strongly attractive to wireworms and other insects 27 Autotomy—reflex separation of part of the body; self-amputation 50, 52, 137, 141 Basiconic sensillae—conical sense-organs found in A r t h r o p o d a 22, 23, 27,66 Batesian mimicry—imitation of the conspicuous appearance of a distasteful, poisonous or otherwise formidable species by a harmless one 171 Berlese funnel—apparatus for extracting small animals from leaf litter and other debris which is placed in a horizontal sieve above a funnel. Heat from an electric light or a water-jacket dries the debris so that the fauna is driven downwards and eventually falls through the sieve and funnel into a bottle of preservative 102 Calamistrum—comb of short spines on the metatarsi of the fourth legs of some spiders 151, 167 220

INDEX

OF

SCIENTIFIC

TERMS

221

Carapace—covering of anterior u p p e r surface in arthropods 71 Carina—lateral keel-like projection from the body segments of some millipedes 18 Cavernicolous—cave-dwelling Cephalothorax—fore part of the b o d y of an Arachnid, corresponding to the head and thorax of an insect; m o r e properly called the prosoma (q.v.) Chelate—pincer-like, as the claw of a lobster. T h e last segment of a limb apposed to that preceding it so that the appendage is adapted for grasping Chelicerae—jaws of an Arachnid; carrying the poison fangs in spiders Chiggers—parasitic larvae of T h r o m b i c u l i d mites 184, 191 Chitin—nitrogenous polysaccharide forming the basic material of the integument or cuticle in the A r t h r o p o d a . Usually hardened by impregnation with calcium or sclerotin (q.v.) Chiton—a mollusc that clings to rocks on the sea-shore 21 Chordotonal organs—integumental sensillae with auditory or p r o preoceptive function 138 Chromatophore—colour p i g m e n t cell 6 Cleidoic egg—one containing e n o u g h water for development and enclosed in a comparatively impermeable m e m b r a n e or shell 206 Clavate—club-shaped Clypeus—narrow strip of prosoma between the eyes and bases of the chelicerae in spiders Collum—first post-cephalic segment of myriapods 64 Commensal—an animal living in a loose association with another and from which only one partner derives benefit 30, 103, 185 Compound eye—eye composed of n u m e r o u s visual elements, found in m a n y of the arthropods 40 Coxa—first segment of the limb attaching it to the body Cribellum—sieve-like plate in front of the spinnerets in some spiders 151,157,161 Cryptic coloration—colour pattern making for inconspicuousness. Cf. Aposematic (q.v.) 133,141, 1 5 2 , 1 6 3 , 1 7 0 Cucullus—mobile hood at front edge of carapace of Ricinulei 129 Cuticle;—hardened integument of arthropods Dermal light sense—appreciation of light stimuli t h r o u g h the integum e n t 22 Deutogyne—secondary female Eriophyid mite differing from the p r i m o gyne or p r i m a r y type and having no male counterpart 200, 201 Deutonymph—second n y m p h a l stage following the larval instar of a mite or false-scorpion 112,197 Diapause—dormant state usually characterised by t e m p o r a r y failure of growth or reproduction, by reduced metabolism and often by enhanced resistance to climatic factors such as cold, heat or drought 199-201

222

INDEX

OF

SCIENTIFIC

TERMS

Digitigrade—walking on the toes or claws. Cf. Plantigrade (q.v.) 46 Distal—part of limb or segment farthest from the centre of the body Ecdysis—moulting, casting of the outer skin in growth Endocuticle—inner layers of the i n t e g u m e n t 205 Endite—endopodite (q.v.) Endopodite—inner r a m u s of a primitively forked arthropodan limb or m o u t h part Endogenous rhythm—rhythm of activity that persists u n d e r constant conditions 24 Epicuticle—thin outermost chitin-free layer of the integument or cuticle xi, 205 Epigyne—external genitalia of the female Arachnid Epimorphosis—development characteristic of centipedes in which slow growth takes place b u t the n u m b e r of segments does not increase 57 Eurythermic—able to tolerate considerable variations in temperature. Cf. Stenothermic (q.v.) 190 Exocuticle—outer layers of chitinous endocuticle beneath epicuticle (q.v.) 205 Femur—third segment of an Arachnid's leg or palp Flagellum—a whip-like extension of the body, a limb or antenna. In false-scorpions, a structure composed of setae on the chelicerae Galea—spinneret on movable finger in false-scorpions 104, 108 Genital operculum—chitinous plate covering reproductive opening Geotaxis—directed m o v e m e n t in response to the stimulus of gravity Gnathobase—projection from the coxa of a limb used to crush food Gnathochilarium—mouth parts of millipedes composed of fused maxillae 1 6 , 1 7 , 2 3 , 2 6 , 2 7 , 6 6 Gonopod—limb modified for sexual reproduction 19, 31, 37 Guanine—insoluble nitrogenous excretory c o m p o u n d characteristic of Arachnids 206 Haemocyanin—respiratory pigment found in Crustacea and Arachnids in which the metallic element is copper and not iron as in haemoglobin 205 Hypopus—resistant, dispersal stage of some mites 199-200 Instar—larval, n y m p h a l or other developmental stage of an arthropod. Instars change at moulting and metamorphosis (q.v.) Ion—electrically charged atom or group of atoms 25 Kinesis—non-directed locomotory response to a stimulus. Cf. Taxis (q.v.) Kinetic reaction—kinesis (q.v.)

INDEX

OF

SCIENTIFIC

TERMS

22

Labium—lower 'lip' or lower surface of m o u t h between the maxillae of an arthropod Labrum—upper 'lip' of an arthropod 75, 107 Lacuna—space among the tissues serving in place of vessels for t h e circulation of the blood 47 Lamella—one of an aggregate of thin plates which compose gills, lungbooks, etc. Lamina—blade-like structure. On fingers of false-scorpion 100 Laterigrade—able to r u n sideways Luciferin—substance oxidised in the presence of luciferase to form oxyluciferin. T h e reaction is accompanied by the production of light 26 Luciferase—enzyme in the presence of which luciferin is oxidised and light produced 26 Lyriform organ—lyre-shaped sensillae of harvest-spiders 138 Malleoli—organs of u n k n o w n function on the legs of the fourth pair in Solifugae, otherwise k n o w n as 'racquet organs' 87 Mandibles—modified anterior limbs of arthropods forming jaws p r i m i tively adapted for chewing. T h e chelicerae of Arachnids Marsupium—brood p o u c h of woodlice 1, 12 Maxilla—one of the anterior appendages of insects and other arthropods so modified as to serve the purpose of mastication Maxillipede—poison claw or toxocognath of centipedes, literally 'jawfoot' 40, 5 0 - 4 Mesopeltidium—central portion of carapace in Schizomida 121 Metapeltidium—posterior portion of carapace in Schizomida 121 Metachronal wave or rhythm—wave of r h y t h m i c m o v e m e n t of similar objects, such as cilia or the legs of a millipede in which each is slightly and equally out of phase w i t h the next 20 Metamorphosis—ecdysis accompanied by a change in form from larva to n y m p h , or n y m p h to adult instar (q.v.) Metapodosoma—posterior part of p r o s o m a of mites, bearing third and fourth pairs of legs 183 Metasoma—hind region of opisthosoma of scorpions, etc., forming a tail region 7 0 , 9 9 Metatarsus—penultimate segment of an A r a c h n i d ' s leg Miillerian mimicry—imitation of the c o n s p i c u o u s or aposematic a p pearance of one distasteful animal by another, resulting in a reduction in the losses required to teach would-be p r e d a t o r s to avoid this particular appearance or colour pattern and t h u s benefiting both species equally 194-5 Myrmecophilous—living in company with ants Ocellus—simple type of eye, sometimes occurring in groups, b u t which, by itself, cannot provide form-vision 40, 44, 47, 138

224

INDEX

OF

SCIENTIFIC

TERMS

Ocular tubercle—prominence bearing the eyes in harvestmen and some spiders, etc. 132-3, 135, 145 Odoriferous glands—repugnatorial glands (q.v.) Ontogeny—origin and development of an individual living being as distinguished from phylogeny (q.v.) Operculum—exoskeletal plate forming a lid or cover. See genital operculum Opisthosoma—posterior region of the body of Arachnids, often known as the abdomen Ovoviviparous—retaining the eggs inside the body of the mother, although within the egg-membrane, until the embryos are fully developed so that living young are produced Osmosis—flow of water from a weaker to a stronger solution through a semi-permeable m e m b r a n e 206 Palp—pedipalp (q.v.). Also tactile head appendage of insects, crustaceans, myriapods, etc. Papilla—a projection Parasitoids—parasitic insects which, like I c h n e u m o n wasps, eventually kill their host 1 1 , 1 6 9 Parthenogenesis—the development of unfertilised eggs Patella—short leg segment between femur and tibia Pectine—comb-like sense-organ on ventral surface of abdomen in scorpions 7 1 , 7 6 - 8 , PI. IXb, Xa Pedicle—the narrow 'waist' of an Arachnid uniting the prosoma and opisthosoma Pedipalp—leg-like tactile organ in front of the legs of an Arachnid forming claw of scorpions, reproductive organ of male spiders, etc. Penolic tanning—sclerotisation (q.v.) Phoresy—utilisation of another animal for transport 30, 101, 103, 142 Phototaxis—directed response in relation to the stimulus of light Phylogeny—evolutionary change in the ancestry of a living organism. Cf. Ontogeny (q.v.) Planidium larva—active larva of parasitic H y m e n o p t e r a developing from an egg laid away from the host. It is a migratory form adapted to seek out the latter 31 Plantigrade—walking on the sole of the foot or on a flat termination of the limb and not on the toes or claws. Cf. Digitigrade (q.v.) 46 Pleopods—plate-like, respiratory endopodites of abdominal limbs of crustaceans 2 , 6 Pleurite—chitinous plate forming the side of a body segment Propeltidium—front portion of carapace in Schizomida 121-2 Proprioceptors—sense organs that detect the positions and movements of different parts of their possessor's body 138

INDEX

OF

SCIENTIFIC

TERMS

225

Prosoma—anterior region of the body of an Arachnid, sometimes called the cephalothorax (q.v.) Prosopon—adult or imago stage in Hydracarina 199 Protonymph—first n y m p h a l stage following the larval instar of a mite or false-scorpion 105, 111, 112, 196, 200 Pseudo-tracheae—respiratory tubules in pleopods of woodlice 2, 6, 7 Pulvilli—lateral tarsal lobes forming suckers beneath the bases of the claws in Phrynichida, etc. 125, 127 Pygidium—posterior part of the body forming a distinct division 117, 122,124,129 Racquet organs—malleoli (q.v.) Ram's-horn organ—extrusible reproductive organ of some male falsescorpions 108,109-10 Reflex—simple, automatic and involuntary response to a stimulus Repugnatorial gland—gland secreting distasteful or unpleasant liquid whose function is to deter aggressors Sclerite—sclerotised or chitinous plate on the body of an arthropod Sclerotin—product of sclerotisation (q.v.) Sclerotisation—chemical process analogous to the tanning of leather by which a protein combines with a phenol or quinone to form sclerotin, a tough, resistant and somewhat impervious component of the arthropodan integument 20 Scopula—brush of hairs or setae at the end of the tarsus 164 Scutum—dorsal plate in ticks and some mites formed by a fusion of tergites 184 Sensilla—arthropodan sense-organ Serrula—row of chitinous teeth as on the maxillae or chelicerae 100, 104,107-8 Seta—hair, bristle or spine, often sensory, on the body of an arthropod Somite—segment of the body Spermathecae—female organs in which are stored the spermatozoa received from the male 110 Spermatophore—envelope or bag containing spermatozoa and secreted by some male arthropods 55, 83, 109-10 Spinneret—spinning organ at rear of body in spiders and on chelicerae of false-scorpions 104-5, 1 4 9 , 1 6 1 , 1 7 6 Spiracle—respiratory aperture, the orifice of a tracheal tube 16, 40, 42, 44,137,183,205 Stabilimentum—narrow ribbon of silk on a spider's web which helps to camouflage the spider PL XVa Stadium—developmental stage Stenothermic—unable to tolerate wide variations in temperature. Cf. Eurythermic (q.v.) 190

226

INDEX

OF

SCIENTIFIC

TERMS

Sternite—chitinous plate on the ventral side of a body segment Sternum—chitinous plate behind the labium, forming the u n d e r s i d e of the prosoma of an Arachnid Stink gland—repugnatorial gland (q.v.) Stridulation—sound production by the mechanical friction of one part of the body against another; usually by means of a n u m b e r of file-like ridges which r u b against another set of ridges or a cluster of chitinous granules or pegs Systole—contraction of the heart or arteries forcing the blood t h r o u g h the system 47 Tarsus—terminal segment of an arthropodan limb which bears the claws Taxis—direct orientation in response to a stimulus. Cf. Kinesis (q.v.) Tergite—chitinous plate on the dorsal side of a b o d y segment Thigmotaxis—directed response to the stimulus of contact 73 Tibia—segment of arthropodan limb between patella and metatarsus (q.v.) Toxocognath—maxillipede (q.v.) Tracheae—fine tubes carrying air from the spiracles and branching into the tracheoles of most terrestrial arthropods 16, 40, 44, 62, 189, 205 Tracheoles—fine tracheal capillaries which conduct air from the tracheae to the tissues in most terrestrial arthropods 205 Trichobothrium—very fine seta or hair usually believed to have an auditory as well as tactile function 75, 112 Tritonymph—third n y m p h a l stage following d e u t o n y m p h (q.v.) 112 Trochanter—the second, ring-like segment of an arthropodan limb Uric acid—insoluble excretory c o m p o u n d characteristic of insects 206 Uropod—terminal abdominal appendage of Crustacea 8 Vulva—external reproductive organ, especially the orifice or opening of that organ 31

INDEX

OF GENERAL

Ballooning of spiders 156 Behaviour centipedes 4 5 - 5 0 false-scorpions 102-5 harvest-spiders 135-9 millipedes 19-26 mites 185-92 Palpigradi 115 Pauropoda 6 2 - 3 Phrynichida 125-7 Ricinulei 129-30 Schizomida 122 scorpions 7 2 - 4 Solifugae 89-90 spiders 154-62 Symphyla 6 5 - 6 Thelyphonida 117-18 woodlice 5-9 Courtship false-scorpions 108-10 harvest-spiders 143 scorpions 8 1 - 3 spiders 172-6 Thelyphonida 120-1

TOPICS

Ricinulei 129 Schizomida 121-2 scorpions 70-2 Solifugae 87-9 spiders 148-54 Symphyla 64-5 Thelyphonida 116-17 woodlice 1-5 Enemies centipedes 52-5 false-scorpions 108 harvest-spiders 140-2 millipedes 27-31 mites 194-5 Palpigradi 116 Pauropoda 63 scorpions 7 6 - 8 0 Solifugae 94-5 spiders 168-72 Symphyla 66-7 woodlice 10-12

Disease transmission by mites 184,189, 193 by ticks 184-8,193

Folklore centipedes 4 9 , 5 3 - 4 harvest-spiders 13 5-6 millipedes 31 spiders 1 5 0 - 1 , 154-5, 158, 162 woodlice 5

Distribution centipedes 4 0 - 4 , 5 6 false-scorpions 99-102 harvest-spiders 132-5 millipedes 15-19 mites 183-92 Palpigradi 115 Pauropoda 61-2 Phrynichida 124-5

Food centipedes 50-2 false-scorpions 105-8 harvest-spiders 139-40 millipedes 26-7 mites 192-4 Palpigradi 115-16 Pauropoda 63 Phrynichida 126-7

22o

INDEX

OF

GENERAL

spiders 172 Thelyphonida

Schizomida 122-3 scorpions 7 4 - 6 Solifugae 90-4 spiders 162-8 Symphyla 66 Thelyphonida 118-20 woodlice 9-10 Gall formation by mites

Pseudoparasitism 26, 4 9 - 5 0

185,192

H u m i d i t y responses centipedes 48 harvest-spiders 136, 138, 140 millipedes 20-5 mites 191,196-7 spiders 157-8 ticks 187-8 Thelyphonida 119 woodlice 5-6, 8 Luminescence centipedes 54 millipedes 25 Migration centipedes 2 3 - 4 , 29 millipedes 2 3 - 4 woodlice 2 3 - 4 M y r m e c o p h i l o u s habits false-scorpions 101, 105-6 millipedes 25 mites 185 Schizomida 123 spiders 152,157,171 woodlice 7 Poison centipedes 52-5 false-scorpions 105-8 scorpions 80-1 Solifugae 91-2

TOPICS 120 by

myriapods

Reproduction and life-cycle centipedes 55-8 false-scorpions 110-12 harvest-spiders 143-6 millipedes 31-7 mites 195-201 Palpigradi 116 Pauropoda 6 3 - 4 Phrynichida 127-8 Ricinulei 130 Schizomida 123-4 scorpions 83-5 Solifugae 96-7 spiders 172-8 Symphyla 67-8 Thelyphonida 120-1 woodlice 12-14 Repugnatorial glands harvest-spiders 132,134,141-2 millipedes 17-19,28-9 Schizomida 123 Thelyphonida 119-20 woodlice 11 Silk production by false-scorpions 104-5 Stridulation centipedes 43, 52 scorpions 78-80 Solifugae 95 spiders 153, 171-2 W e b s of spiders 163,166-8

148-9, 153, 161,