120 OUR INSECT FRIENDS AND FOES 



about by a gradual process of evolution that has 

 been going on for millions of years. If we con- 

 sider the extreme variability of insects, the 

 rapidity with which generation succeeds genera- 

 tion, and the intense and constant struggle for 

 existence that has been going on since the 

 earliest chapters in the history of the world, we 

 shall more readily understand how this has come 

 to pass. 



Take, for example, the case of a species of 

 Papilio, an edible butterfly that mimics the dis- 

 tasteful Danaidae. In the early ages of the 

 world, while the Danaidae were gradually ac- 

 quiring the distinctive colouring that was neces- 

 sary for their preservation, some of the Papilio, 

 by an accidental variation, happened to be mis- 

 taken for the obnoxious Danaidae, and were 

 passed over by the birds. This variation of 

 colouring would naturally be transmitted by the 

 Papilio to some of their progeny. Those that 

 were most like the Danaidae would probably 

 escape destruction, while those not so similar 

 would be detected and devoured. The survivors 

 again handed on the protective marking to 

 their descendants, and so through succeeding 

 generations the resemblance became gradually 

 perfected. 



In the same way those insects that by some 

 chance were sufficiently like a leaf, twig, or 

 flower to escape the sharp eyes of their enemies, 

 gradually, through succeeding generations, be- 

 came more and more like the mimicked object, 

 the less adaptable insects being in process of time 

 gradually exterminated until the protective 



