18 INTRODUCTION 



that there are now known and have been scientifically recog- 

 nized and described something over three hundred thousand 

 species of insects, a number which far surpasses that of all 

 other groups of animals together. Furthermore, the immense 

 numbers of individuals in each species and the great facility 

 which they possess for migration and rapidity of increase 

 make them a very dominant group of animals. 



Not all insects, to be sure, have a direct importance to 

 mankind, but there is so large a number that are very 

 directly related to human interests in the way of destruction 

 of property or menace to health that it is unnecessary to 

 emphasize their importance. Many estimates have been 

 attempted of the extent of loss of crops, livestock, forests, 

 agricultural products, etc., and while none of these can be 

 considered exact, it is increasingly evident that such estimates 

 are conservative and in many cases the loss is greater than 

 is recognized. One of the current estimates is that about 

 10 per cent, of the aggregate of farm crops in the United 

 States is lost by insect attack, and if this be taken as an 

 approximate proportion there is something like one billion 

 dollars to be counted an economic loss from this source 

 each year. 



It must be admitted that the entomologist has not been 

 able as yet to solve all of the problems of insect control. 

 There will doubtless be many cases where a practical control 

 of insects may not be reached for many years, but for a 

 considerable number of the most common and serious pests 

 it has been possible to discover methods by which a very 

 large proportion of the loss can be prevented. One phase 

 of entomological work, therefore, is the demonstration of 

 these possibilities in order to secure a general adoption of 

 control measures that have been proved successful. 



While it is manifestly impossible to include in a small 

 book any full discussion of the many phases of entomology, 

 it is the purpose of this work to present a basis for the under- 

 standing of field observations, and especially for the under- 

 standing of the many articles relating to economic insects 

 which are now appearing in Government and State pub- 



