of certain lepidopterous larvce and ptipce. 39 



an acute angle with it. Accordingly the larvae in nearly 

 all cases tend to assume this position when at rest, and 

 the resemblance is often carried further by the presence 

 of roughnesses and tubercles on the larvae exactly like 

 those on a twig. The usual brown colour of the cater- 

 pillar may even have a slight green dusting in places 

 {R. cratagata) indistinguishable in appearance from the 

 lichenous growth with which bark is generally covered 

 in damp situations. A practised entomologist has often 

 to touch a larva before he is sure that he is not looking 

 at a twig ; and he may often at the first glance mistake 

 the one for the other, when the larva is shaken from its 

 hold and falls, still perfectly rigid, into the beating-tray 

 or umbrella. And the protection is far more complete 

 when the larva clings to a branch of its food-jjlant. 

 These facts are well known to every collector of insects : 

 it is their limitation which I believe has been less 

 noticed. This characteristic protective attitude is espe- 

 cially applicable to larvae feeding on the leaves of trees, 

 and would not be nearly so effective for those feeding on 

 low-growing plants of which only a tuft of leaves is 

 apparent above the ground. It may be safely assumed 

 that the usual attitude would even be dangerously con- 

 spicuous for any fair-sized Geometer larva (unless green) 

 which rested by day on the leaves of its food-jjlant. 

 Thus the larvae of Aspilates citraria and A. gilvariahsiYe 

 the habit of coiling up the anterior part of the body verti- 

 cally into a fiat spiral, with the head in the centre. If 

 shaken from the food-plant the attitude is maintained. 

 In this case the resemblance to a small bleached snail- 

 shell is very striking, both in shape and colour. The 

 situation which the larva frequents is exactly that where 

 small empty shells are found in abundance, and all the 

 localities I know of in which these moths are common are 

 upon limestone, which is also favourable to the presence 

 of these mollusca. 



Two points about this protective attitude are of great 

 interest, firstly, that the position when assumed upon 

 the food-plant is just as dependent upon the normal 

 structure of a Geometer larva as the more usual attitude 

 of resemblance to twigs, &c. Secondly, that the object 

 resembled is a dead and bleached shell ; for it is very 

 likely that many enemies of the larva (birds, &c.), would 

 not object to a living snail, and the resemblance might 

 thus be no protection if the pale colour did not coexist 

 with the spiral posture. 



