SPIDERS 171 



Ceylon, another from North America. The latter, when clinging 

 to the underside of a leaf with its legs drawn up, is almost an exact 

 copy in colour and shape of a small snail which is abundant in 

 similar situations in the same locality during the warm months of 

 the year. The resemblance is enhanced by the complete immo- 

 bility the spider maintains when torn from its hold or when the 

 plant is rudely shaken. 



Apart from beetles, the insects most frequently mimicked by 

 spiders are ants and so numerous and perfect are the instances that 

 all other examples of mimicry amongst spiders fall into insigni- 

 ficance beside them. A constriction on each side of the spider's 

 carapace divides it into an anterior part resembling the head, a 

 narrow intermediate part representing the neck and a posterior 

 part representing the thorax of the insect. In many cases the 

 appearance of slenderness about the neck is augmented by a strip 

 of white hairs on each side of the constriction, which has the 

 optical effect of cutting out an extra piece of the integument. The 

 waist of the ant is reproduced by the conversion of the end of the 

 carapace and often of the anterior end of the abdomen into a 

 narrow stalk. In some cases the abdomen is itself shallowly con- 

 stricted and even the abdominal segments of the insect may be 

 represented by transverse bands of hairs. The legs are always 

 slender, like those of an ant, and one of the anterior pairs is held 

 up in front of the head as a substitute for antennae. Finally, it has 

 been found that the spiders carry deception to the extent of copy- 

 ing the manners and gait of the insects (Pocock, 1909). As might 

 be expected, ant-mimicry is of much commoner occurrence 

 amongst ground-living species of spiders than it is amongst the 

 sedentary web spinners, but instances are not unknown amongst 

 the latter. Such mimicry represents a wonderful example of con- 

 vergent evolution amongst spiders belonging to the families 

 Salticidae, Gnaphosidae, Clubionidae, Thomisidae, Theridiidae, 

 Argiopidae etc. As in all cases of Batesian mimicry, the mimics 

 exist in small numbers compared with their models. 



Like scorpions and Solifugae, many of the larger spiders can 

 stridulate, probably as a warning to enemies. In the case of smaller 

 species in which sound-producing organs are confined to the 

 males, their function is probably that of courtship. Chrysanthus 



