CHAPTER XII 



PLANT-EATING INSECTS 



A little reflection will convince the reader that all 

 insects — indeed, all animals of every kind — are entirely 

 dependent for food upon the vegetable kingdom, the 

 reason being that of all living things green plants alone 

 are empowered to build up food material from the simple 

 chemical substances of the earth and air. To this rule 

 there are no exceptions. Many predaceous insects feed 

 directly upon vegetarian species ; but even when they 

 prey upon flesh -eaters, and these again upon other car- 

 nivorous kinds through several successive stages, we are 

 sure to get back to plants in the end. 



The number of insects which one kind of plant 

 supports is often astonishing. It has been computed that 

 the oak tree provides food and shelter for at least 1500 

 kinds, while some 500 more are attached to these as 

 parasites. Probably the oak has an insect population 

 greater than that of any other tree; but birches, elms, 

 willows, poplars, and firs are all subject to the attacks 

 of very many species. The same may be said of almost 

 all cultivated plants. The apple has some 400 insect 

 pensioners, not a few of which are harmful to the interests 

 of mankind. Corn is attacked by about 200 species, fifty 

 or more being notably injurious, while some twenty are 

 devastating pests. Quite as many depend upon the clover 

 if we include predaceous insects, parasites, and flower 

 visitors. Nor are the poisonous plants exempt. The 

 beautiful moth known as P/usia moneta feeds as a cater- 



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