PREFACE. 



The present manual attempts to bring together a brief yet com- 

 plete key to the families of American insects, unhampered by more 

 than the explanations needed to make such a tabulation available 

 to the general student. It has been prepared to meet the require- 

 ments, not alone of college courses in systematic entomology, but 

 also of agricultural high schools and of physicians, fruit inspectors, 

 the modern farmer, the nature-lover, or any one who is concerned 

 with the practical identification of insects. 



More than fifty thousand different species of insects are now 

 known from North America. Their descriptions fill libraries and 

 their final identification requires the knowledge of specialists. 

 Obviously no single volume can provide for their determination. 

 But this host of species is divided into groups of related forms, the 

 families of insects, and it is with their recognition that the present 

 work deals. 



Identification of the families has been effected by means of 

 analytical keys, which have been arranged as dichotomies. In 

 the first couplet, for example, two contrasting descriptions are 

 given, one of which should agree with the insect to be determined. 

 The number at the end of this description indicates the couplet 

 which should then be studied, and so on until the final name is 

 secured. All of the keys have been arranged in this way, as the 

 writers' experience in the classroom shows that specimens can be 

 most easily and rapidly classified with a key of this type, which 

 also requires much less space for printing. While the dichotomies 

 frequently represent the natural relationships or the lines of 

 phyletic development, no attempt has been made to preserve 

 natural divisions wherever the convenience and practical opera- 

 tion of the keys would have been sacrificed. 



As the tabulation is designed mainly for identification, charac- 

 ters not readily seen on the usual pinned laboratory specimens 

 have been minimized. The nomenclature of the body-parts and 

 of the wings has been adapted from that used in the bulk of the 

 systematic literature upon the separate orders. Such terms un- 

 fortunately do not always agree with undoubted homologies of 

 these parts but are those which are encountered in the literature 

 to which reference must be made for more extended taxonomic 



