INTRODUCTION 



Some one has remarked in a rather facetious vein 

 that, from a zoological standpoint, the present age may 

 be called the age of insects. On second thought, the 

 remark holds more reason than might appear at first 

 sight. We are especially impressed with the impor- 

 tance of the relation to man of these tiny, but multitu- 

 dinous, forms of life when we recall that the species of 

 insects outnumber the species of all other animals com- 

 bined ; that the insect pests in this country alone cause 

 a loss of over a billion dollars annually ; that several 

 hundred trained men in the United States are giving 

 their entire time to a study of these pests ; and that 

 thousands of letters are sent each year to our govern- 

 ment agencies, requesting information regarding insects 

 and means of fighting them. Until within the last few 

 years the economic importance of insects has been at- 

 tributed to their indirect injuries to man through attacks 

 on the things that he produces. Suddenly, almost 

 within the last decade, insects have assumed an entirely 

 new and exceedingly important significance through 

 knowledge of their direct injuries to man himself. 



Since the epoch-making discoveries were made that 

 mosquitoes carry malaria and yellow fever, insects, es- 

 pecially those frequenting the household, have assumed 

 a most unexpected importance. The hum of the mos- 

 quito and the buzz of the house-fly have become fraught 

 with an entirely new significance. Even the dog and 



