WARNING COLORATION. 100 



and exhibited warning colours, or exhibited warning colours 

 without becoming distasteful, birds and other insect-eating 

 animals would be compelled to feed upon them ; and it has 

 been proved by Mr. Poulton and by others that if pressed by 

 hunger animals will eat such distasteful insects. 



It appears to me, however (as I have already said on p. 133), 

 that the same objection might be applied to other characters : 

 protectively-coloured caterpillars are suffered to escape their 

 enemies by their powers of concealment ; but if all, or the 

 majority of insects became thus difficult to find, some improve- 

 ment in their foes additional keenness of sight or smell 

 would tend to render these disguises easier to detect. 



Objections to the Current Theory of Warning Coloration. 



The larva of the Swallow-tail (Papilio Machaon) is coloured! 

 with green, black, and orange ; it possesses, in Prof. Weismann's 

 opinion, "a striking appearance," and when offered by this 

 naturalist to Lacerta r/r/V//x, was untouched by the lizard. 

 This caterpillar becomes specially conspicuous when touched 

 or interfered with in any way ; it then everts from the neck a 

 glandular apparatus of a red colour. 



When at rest upon its food plant the colours are by no 

 means conspicuous. These invisible glands referred to have 

 been termed "osmateria" or "stench throwers" ; they secrete 

 an offensive-smelling substance ; the caterpillars are no doubt 

 to some extent protected by them. 



Mr. Wallace thinks that their function is chiefly to ward off 

 the attacks of ichneumons ; but they may also, he considers, 

 frighten small birds. 



We may consider, perhaps, that this larva is inconspicuous, 

 but when found it possesses a means of defence in the osma- 



