478 Mr. H. Eltringham on Lepidopteroiis Larvae. 



appearance of the previously discarded ivy-fed example 

 whilst an apple-fed specimen was in no case rejected and 

 again seized, but always swallowed uninterruptedly and 

 without any of the characteristic nose-rubbing and other 

 contortions which accompanied the dealings with those 

 fed on ivy. From these facts it seems quite reasonable to 

 conclude that when feeding on apple this highly cryptic 

 larva remains as edible as are most other insects which are 

 well protected by their colour, shape, and habits. The 

 caterpillar is even better protected on ivy owing to the 

 density of the foliage and the irregularity of the twigs, 

 and yet when on that plant it becomes extremely dis- 

 tasteful, and furnishes an exactly similar case to that of 

 Mania typica, discovered and described by Prof. Poulton. 

 We thus have further evidence that the distasteful qualities 

 of larvae may have arisen in similar accidental ways, and 

 the difficulty of those "first steps" in evolutionary changes 

 are still further decreased. We can see how a cryptic 

 larva which occurs on a certain food-plant might be sought 

 out and discovered by its enemies, and if the latter were 

 sufficiently numerous and persistent, the insect might be 

 exterminated. If, hoAvever, the larva can adapt itself to 

 a change of food, it may gain some respite until again dis- 

 covered. This may bring about a great change in the 

 creature's method of defence. Its new food-plant endows 

 it with inedible properties, and thus the insect has a further 

 opportunity of developing a new mode of protection along 

 different lines. To extend such reasoning, it seems not 

 impossible that a purely Batesian mimic might become 

 a Miillerian mimic by the same method. Batesian mimics 

 are much associated with their models during life, and the 

 instinct which guides a butterfly to lay its eggs on the 

 right food-plant is not invariably infallible. Thus ova of 

 an inedible species deposited on a new food-plant might 

 conceivably give rise to larvae which survived and produced 

 distasteful butterflies ; and whilst the fact of such an 

 occurrence may remain unproved, its evident possibility 

 should serve to remind us once more of the complicated 

 conditions under which butterflies in common with other 

 creatures maintain their existence in the struggle for life. 



(Note. — I am indebted to my friend, Conmiander J. J. 

 Walker, for kindly identifying the Geometrid larvae above 

 described.) 



