SUMMARY 43 



method of preventing mosquitoes from laying their eggs 

 in that locality. When this is not possible, the surface 

 of the water may be covered with kerosene, which kills 

 the larvce by preventing them from getting oxygen from 

 the air. Frequent applications of oil greatly reduce the 

 number of mosquitoes. 



SUMMARY 



The insects include a large number of animals, the 

 smallest of which can be seen only through a microscope, 

 while the largest, certain butterflies, measure nine inches 

 across their wings. S.ome insects are parasitic and lead 

 dependent lives. Insects feeding on plants which we 

 wish to eat are called harmful. Others, like the honey- 

 bees and silkworms, which make products that we use, 

 are beneficial. Insects such as ticks and lice, that injure 

 our domestic animals, are called harmful. Then there 

 are the beautifully colored moths and butterflies whose 

 larvre never become numerous enough to do much damage ; 

 we say that they are beneficial because we get pleasure 

 from their beauty. 



The whole question of what is beneficial or harmful 

 depends on the relation of the insect to man. Insects 

 living on an uninhabited island could not be thus classi- 

 fied. In the earlier stages of our civilization, many insects 

 now regarded as harmful were not so classified, because 

 man had not learned to use the plants upon which they 

 fed. The important relation which insects bear to disease 

 has, in recent years, caused us to classify several insects 

 as harmful which were not so considered earlier. 



Insects, like man, are constantly undergoing a struggle 

 to escape their enemies and to secure food and a place to 

 live. It is interesting in this biological study to try to 

 view ourselves in the same unprejudiced way in which 



