182 THE COLOURS OF ANIMALS 



numbers are kept down by special liability to the 

 attacks of insect parasites, in one or more stages. 

 Thus the larva of the Large Garden White {Pieris 

 hrassiccE) is known to be nauseous, but the im- 

 munity from attack which it enjoys by no means 

 extends to its insect foes. In the autumn of 1888 I 

 collected some hundreds of these larvae in order to 

 experiment upon the colours of their pupae. I ob- 

 tained 109 pupae, while 424 mature larvae died from 

 the presence of the parasitic grubs of Ichneumon flies 



The likes and dislikes of Insect-eating animals are 

 purely relative 



It may be taken as proved that the continued 

 spread of some distasteful form and the correspond- 

 ing diminution of edible species would lead to the 

 former becoming the prey of insect- eating animals ; 

 for a point would ultimately be reached, as it was 

 reached in many of my experiments, when hunger 

 would become a stronger stimulus than those lesser 

 prejudices in which a species can very well afford to 

 indulge while palatable food is abundant. These pre- 

 judices having been overcome in confinement, there is 

 nothing in the conditions of natural life which could 

 prevent the same result from being reached, as doubt- 

 less it has been reached again and again. The com- 

 parison of all experiments of this kind ever made with 

 insects will show that the likes and dislikes of insect- 



