CHAPTER XLIX 



INSECTS IN RELATION TO HUMAN WEALTH 



Questions. 1. Why have insects caused more damage in this country 

 than in others ? 2. Why does the number of insects of a particular spe- 

 cies seem to increase suddenly in some years or in some regions ? 

 3. How can we tell whether a particular kind of insect is injurious or 

 harmless ? 4. Why cannot all injurious insects be combated in the same 

 way ? 5. Are all the injurious insects being killed off ? 6. Can an insect 

 be injurious in some ways and useful in other ways ? 



405. Destructive insects. All kinds of organic matter will 

 serve as food— if not for one organism, then for another. The 

 insects, taking the class as a whole, are fitted to make use of 

 almost anything organic. In this country alone insects of vari- 

 ous kinds destroy each 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. 229). 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. To kill 

 the eggs of clothes moths, furniture cleaners and upholsterers 

 sometimes fumigate with carbon disulfid. 



The cockroaches, of which there are several species, will eat 

 almost any organic matter, but are seldom destructive to valu- 

 able materials. Their presence in a house is an indication 

 that there are crumbs and other scraps of food about, and it is 

 perhaps as well for the cockroaches to eat these as for some 

 more objectionable animals to do so. On the other hand, they 



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