MAN'S CHIEF COMPETITORS, THE INSECTS 



In the preceding pages frequent mention has been made of 

 insects, those omnipresent httle creatures that force them- 

 selves on your attention everywhere. The insects number 

 about three-quarters of all known kinds of animals, and on 

 the land and in fresh water are the most important of the 

 living creatures; for not only are there half a million known, 

 and many more unknown, but each of these half million kinds 

 exists in countless numbers. To explain the conditions under 

 which we live it is first necessary to present a brief account 

 of the food relationships and some of the activities of insects. 



We are accustomed to think of insects as feeding on vege- 

 tation or on each other, but in reality their feeding range is 

 far beyond this; and if we include substances which insects 

 chew, whether for food or for some purpose still unknown to 

 us, there are few things which are free from their attacks. 



In the first place, an enormous number live as larvae, and 

 often also as adults, on green leaves, mostly by consuming 

 them entire, but some by mining through the tissues. Such 

 insects are nearly all the moths and butterflies, most grass- 

 hoppers, crickets and their allies, most saw-flies, many beetles, 

 many flies, and many millepeds. While some of these will 

 eat a large variety of plants, most are more or less restricted 

 in their diet, and very many will eat only a single kind. All 

 plants, no matter how poisonous they may be to us, have their 

 insect depredators. Some of these are not at all affected by 

 the poison, like many that feed upon Euphorbias; others 

 cleverly avoid the portions where the poison lies. 



The juices of plants sucked out through a tube from the 

 leaves or stems or roots support aphids, scale insects, leaf- 

 hoppers, cicadas, and many bugs. 



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