AVAENING COLOEATION". 151 



of colour thus produced must obviously stand out in greater 

 contrast to tlie surroundings. This suggestion is particularly 

 applicable to the larvaj of many of the Vanessidas; several 

 species of these butterflies lay their eggs upon nettles, and the 

 larva3 remain associated together in herds, sometimes entirely 

 defoliating the plants. Now, the caterpillars of the Tortoise- 

 shell and others are greenish-black ; seen singly, their appear- 

 ance is not very striking : indeed, it is almost a case of pro- 

 tective resemblance : the caterpillar, with its hairy or rather 

 spiny coat and greenish-black colour, is not unlike a half- 



Fig. 15.— Butt'-tip Motli and Caterxiillar. 



withered and rolled-up leaf of nettle. But a. whole battalion 

 of these caterpillars could hardly be passed over by any insect- 

 eating bird; and, like the other instances mentioned, they have 

 been proved to be usually unacceptable to birds, lizards, andfrogs. 

 Some of the experiments made may be fairly criticised, 

 notably those upon the larva of the Elephant Hawk moth. 

 This insect when disturbed retracts the head and distends the 

 anterior end of the body. Two pairs of large eye-like markings 

 are thus brought into great prominence, and suggest the head 

 of a serpent. Dr. Weismann found that a tame jay ate the 

 larva at once, but that wild sparrows and chaffinches were 

 frightened by it, and would not even approach the trough in 



