CHAPTER X. 



The Colouration of Insects. 



IN the decoration of insects and birds, nature has exerted all her 

 power ; and amongst the wealth of beauty here displayed we 

 ought to find crucial tests of the views herein advocated. It will 

 be necessary, therefore, to enter somewhat into detail, and we shall 

 take butterflies as our chief illustration, because in them we find the 

 richest display of colouring. The decoration of caterpillars will 

 also be treated at some length, partly because of their beauty, and 

 partly because amongst them sexual selection cannot possibly 

 have had any influence. 



Butterflies are so delicate in structure, so fragile in constitution, 

 so directly affected by changes of environment, that upon their 

 wings we have a record of the changes they have experienced, 

 which gives to them a value of the highest character in the study of 

 biology. In them we can study every variation that geographical 

 distribution can effect; for some species, like the Swallow-tail 

 (Papilio machaori) and the Painted Lady (Cynthia cardui), are almost 

 universal, and others, like our now extinct Large Copper (Lycarna 

 dispar), are excessively local, being confined to a very few square 

 miles. From the arctic regions to the tropics, from the mountain 

 tops to the plains, on the arid deserts and amidst luxuriant vege- 

 tation, butterflies are everywhere to be found. 



Before entering into details, it will be as well to sketch some of 

 the broad features of butterfly decoration. In the first place they 

 are all day-fliers, and light having so strong an influence upon 

 colour, there is a marked difference in beauty between them and the 

 night-flying moths. A collection of butterflies viewed side by side 

 with a collection of moths brings out this fact more strongly than 



