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The Book of Bugs. 



the way the " balance of nature " operates in this particu- 

 lar instance: The tussock-moth caterpillars destroy the 

 leaves on the trees. Then the Pimpla gets very plentiful 

 and the majority of the caterpillars a-re stung by it and 

 never come to maturity, because the young Pimpla eats 

 the insides out of them. But Pimpla has a parasite that 

 eats its insides out. When Pimpla is about exterminated 



Fig. 35. Tussock-moth caterpillar, third and fourth stages 



there is nothing for this parasite to eat, and nearly all 

 of them starve to death. By this time the trees have 

 got their strength back, and an era of great business 

 prosperity sets in for the tussock moth remaining. Then 

 the few Pimplas find plenty to do and multiply enorm- 

 ously. So do their parasites, and thus the wheel goes 

 around, with us and our preferences entirely outside it. 



To this membrane-winged order belong the insects 

 most useful to man, prime among them being the bee, to 

 which a later chapter will be devoted. They deserve a 

 book, but unless a man knows more and can write better 



