Preface 



occur in North America north of Mexico, the effort was made to 

 select those species which would adequately represent the various 

 families and the commoner and more important genera, thus pro- 

 viding a work which might serve as an introduction to the study. 

 This process of selection had to be made with much patience and 

 care. Another cause of delay arose from the fact that it is some- 

 times difficult to obtain perfect specimens" for purposes of photo- 

 graphic reproduction. Even where species are well known and 

 common, and are abundantly represented in the collections to 

 which I have access, it has not infrequently happened that it was 

 almost impossible to discover specimens so perfect as to allow 

 of their being reproduced by color-photography in a satisfactory 

 manner. Minor defects, which signify little to a working natural- 

 ist, and which can easily be eliminated from sight by a draughts- 

 man, become very serious blemishes when resort is had to methods 

 of photographic illustration. Much time had, therefore, to be spent 

 in searching through various collections for the kind of material 

 which was required, and often in remounting specimens which, 

 while good enough for the cabinet, were not so set as to permit 

 them to be employed in the photographic laboratory. Patience 

 and perseverance, however, always bring in due time their re- 

 ward, and I have been able to assemble enough properly prepared 

 material to enable me in the main to accomplish my purpose. 



"Brevity is the soul of wit," and this fact has not been 

 forgotten by the writer in preparing the pages of this book. The 

 limitations necessarily imposed by the space available precluded 

 the preparation of lengthy descriptions. This brevity in descrip- 

 tion is, however, as the writer believes, abundantly compensated 

 for by the illustrations in the Plates. One good recognizable 

 figure of a species is worth reams of mere verbal description. 

 Those who desire to go deeply into the subject, and who wish 

 to famiharize themselves with all its technicalities, will find in 

 the list of works named in that part of the introduction devoted 

 to the bibliography of the subject much that they desire. 



I am indebted to many scientific friends for assistance, but to 

 no one am I more indebted than to Dr. L. O. Howard, the Ento- 

 mologist of the United States Department of Agriculture and the 

 Honorary Curator of Entomology in the United States National 

 Museum, and to his amiable associates, Dr. William H. Ashmead 



viii 



