74 INTRODUCTION. 



them do not hesitate to devour each other whenever 

 they have an opportunity. 



Most of these caterpillars feed during the day, 

 but many are as exclusively nocturnal in their 

 habits as the moths that spring from them. The 

 geometers especially may often be observed during 

 the whole day perfectly motionless, either stretched 

 flatly along a branch, or projecting from it like a 

 broken twig ; but the gnawed leaves in their vicinity 

 show that they are not always thus inactive. An 

 example of this kind may be seen in a species of 

 pretty large size, common in autumn on cherry-trees 

 throughout the south of Scotland and many parts 

 of England, which so closely resembles the bark, 

 that it is detected with the utmost difficulty. The 

 same circumstance accounts for a fact sometimes 

 mentioned with surprise, that the extent of the 

 injury done to our culinary vegetables is often quite 

 disproportionate to the number of depredators seen 

 upon them the season of their greatest activity 

 being that in which they are not exposed to observa- 

 tion. Others take their food only in the morning 

 and evening, the middle of the night and of the 

 day being their seasons of repose. 



Although the enemies of caterpillars are numerous 

 and destructive, consisting of birds, parasitical ich- 

 neumons, &c. and although they are occasionally 

 subject to a kind of epidemic disorder which destroys 

 them in great numbers, yet they often increase to 

 an undue extent, and occasion considerable injury. 



