INTRODUCTION 



NSECTS constitute the largest group of the animal kingdom. 

 There are over seven hundred thousand species which 

 have been named and described and still a large number 

 of new species is being added to our knowledge every 

 year. Because of the great diversity of their behavior and 

 habits, their study is filled with interest. From the econo- 

 mic point of view, some insects are considered beneficial 

 and others injurious to human beings. The better we 

 know our insect enemies and insect friends, the better are our chances 

 of anticipating protections or of preparing and conducting our defenses 

 against them. 



Insects are highly different in their young and their adult stages. 

 For example, the butterflies fly in air and feed on nectar of flowers 

 while their caterpillars live on plants and chew these coarse tissues; 

 mosquitoes suck blood while their larvae dwell in water; many moths 

 do not feed at all but their larvae do great damage to our crops. There 

 are thousands of differences in their ways of living and also of the 

 body structures between insect parents and their children. We need 

 to know the adult insects and it is also necessary to know the imma- 

 ture insects. From either the economic standpoint or the evolutionary 

 aspect the more we know of the immature stages the better we un- 

 derstand the adult insects. 



Unfortunately our knowledge of the immature insects is still far 

 away from complete. Much work must still be done in this interesting 

 and very important field. This book is compiled from the available 

 literature and designed to make it as easy as possible to acquire a 

 ready knowledge of the immature insects. It contains a number of 

 illustrated keys for identification of these insects to orders and their 

 principal families. For advanced study, important references are giv- 

 en. In attempting this book the author feels like an explorer entering 

 an uncharted region. At best there will be ommissions and mistakes. 

 I shall be grateful for any corrections or constructive suggestions to 

 put into later printings of the book. 



N The excellent instruction of Dr. W. P. Hayes, Professor of Entomol- 

 v)ogy. University of Illinois on the immature insects during the time 



