414 



ELEMENTARY BIOLOGY 



also some of the ants. In this way they may be looked upon 

 as scavengers. And a few insects, in the course of their 

 predacious activities, devour forms that happen to be injuri- 

 ous to us. This is illustrated by some of the beetles like the 

 ladybug, which eat plant lice and thus keep them in check. 



We make direct use of very 

 few insects. Many species are 

 nevertheless of indirect value 

 to us as important links in that 

 chain of life extending from 

 decomposing organic matter at 

 one end to the larger useful 

 animals at the other. It is cer- 

 tain also that very many species 

 of insects are essential to the 

 propagation of various species 

 of plants, since they are the 

 sole agents in the distribution 

 of pollen (see pp. 309 ff.). 



447. Destructive insects. In 

 this country alone insects of va- 

 rious kinds destroy every year 

 materials and goods estimated 

 to be worth more than two 



hundred million dollars. This includes stored food, clothing, 

 furniture, carpets and hangings, and furs. 



The clothes moth is one of the most familiar of these destruc- 

 tive insects, for it is found nearly everywhere that human beings 

 are (Fig. 213). Thorough airing and exposure to sunlight for 

 a few hours will be likely to kill any of the eggs. Naphthalin 

 moth balls do not kill the animals, but repel them and thus 

 prevent destruction. Infested material should be treated with 

 gasoline and then thoroughly aired before being used. 



The cockroaches, of which there are several species, will 

 eat almost any organic matter, but are seldom destructive to 



FIG. 215. Meal-worm 



Adult and larva of the miller beetle 

 (Tenebrio molitor) 



