INTnoDTOTION. 
74 
tliem do not hesitate to devour each other whenever 
they have an opportunity. 
hlost 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 he 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 he seen in a species of 
pretty large size, common in autumn on ehciTy-trees 
throughout the south of Scotland and many parts 
of England, which so closely resembles the hark, 
that it is detected with the utmost difficulty. The 
same circumstance accounts for a fact sometimes 
mentioned with smprise, 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 imdue extent, and occasion considerable injury. 
