22 CONNECTICUT GEOL. AND NAT. HIST. SURVEY. [Bull. 



Howard, in an address before the Washington Biological Society, 

 pointed out those families of insects which could be called dis- 

 tinctly injurious or distinctly beneficial, and found that they 

 were about equally divided, as follows : 



Injurious, . . 116 families. 



Beneficial, . . 113 



Both, or undetermined, 71 



300 



It will be seen at a glance, therefore, that there are about as 

 many insects which are distinctly beneficial to man as there 

 are which cause him injury. The great majority of insects are 

 neither friends nor foes to man in any important degree, but 

 each species fills a place perhaps no less important in relation 

 to other organisms. 



How Insects are Injurious. 



Insects are regarded as injurious if they destroy crops, like 

 the potato beetle, and if, like the elm-leaf beetle, they attack 

 highly prized shade trees, or, in fact, any other plant life which 

 seems desirable to man. This is perhaps the most important 

 injury caused by insects, and it has been estimated that fully 

 one-tenth of all the agricultural crops of the United States, 

 or a value of more than $700,000,000, is annually destroyed by 

 insects. Methods of spraying and other forms of remedial treat- 

 ment have been devised to prevent or check such destruction, and 

 this phase of the subject has reached a higher development in 

 the United States than elsewhere. 



Certain kinds of insects also cause injury to stored foods, 

 books, and clothes, and to dwelling houses. Other kinds attack 

 live stock and other useful animals, and a few species annoy 

 man. Recently it has been discovered that insects are more 

 important as carriers of disease than was formerly supposed. 

 Certain mosquitoes are the essential hosts of the malarial para- 

 site, and it is only through their bites that these parasites are 

 naturally transferred to man. Another kind likewise transmits 

 yellow fever through its bites, and the disease called elephan- 

 tiasis is transmitted to man by mosquito infection. 



