1 2 INSECTS : THEIR STRtlCTUHE AND POOD. 



eat the roots ; tliey suck out the sap and live as parasites upon all parts of 

 the plant. Perhaps one-third of the total number of insects live on plant 

 life directly, thus constituting one big" division called the Herbivores. 



There are others which live on the dead or decaying- plant, on dead 

 leaves, on rotting fruits, on dry timber. Any vegetable tissue that is no 

 longer alive and growing furnishes food to this division. We may 

 include with them the feeders on decaying animal tissue, such as the dung 

 feeders, the carrion beetles, the corpse buriers. We may term them all 

 Scavengers, since they, with the bacteria and fungi, cleanse the earth 

 of its rubbish and convert it into good plant-food again. They also 

 form a large division, not less important but far less visible to us, work- 

 ing in the dark and in hidden places. 



As the plant world furnishes food for so many insects, so also these 

 insects in turn are fed on by others, and we find a very large division 

 which get their food from the herbivorous and scaveng'ing insects or from 

 each other. These work in two ways, by preying upon insects and eating 

 them bodily, as a tiger eats a cow, or by living within their bodies 

 parasitically, as a tapeworm lives in a horse. The former, the Predators, 

 we see daily at work and we may compare them with the many insec- 

 tivorous birds. The latter, the Parasites (Ichneumons and flies), are not 

 less numerous and abundant ; their larvae live in the insect, absorbing the 

 food laid up by the host and gradually killing it. The two groups 

 together check the immense increase of insect life and form the third 

 great division. 



There are also a small number of insects that live parasitically in or 

 on warm-blooded animals. They feed on the blood of man, cattle, wild 

 beasts, birds and other animals, or live parasitically within their bodies. 

 They form a small division. 



There are lastly the insects which have found that man offers many 

 comfortable homes in his houses and buildings ; they live upon grain, 

 flour, drugs, all manner of produce and household stores ; they inhabit our 

 houses, deriving a precarious existence from what they can pick up. 

 These are the household pests ; they have been carried in ships to all parts 

 of the world and established themselves wherever man is. This division 

 is not large or very important but an aberrant and distinct oli'shoot from 

 the great scavenger class mentioned above. 



We have now included practically every insect in our divisions, and 

 if we subdivide them, almost every species whose habits are known would 

 flt in. We see the part each plays in the great cycle of life. The herbivores 

 feed on the plants, which build up organic matter from the soil and air 

 under the influence of the sun. These herbivores build up the plant tissue 



