PREFACE. 



In tlie early summer of 1889 a circular letter was is- 

 sued to " The Workiug Eutomologists of the Country," 

 offering prizes for essays containing original investigations 

 regarding methods of destroying the mosquito and the 

 house fly. 



The object of this effort was to bring about an intelli- 

 gent discussion of the question, what natural enemies of 

 these irritating insects may be easily and efficiently ar- 

 rayed against them. 



The voracious and harmless dragon fly, of which our 

 country supplies so many beautiful varieties, was especially 

 designated as possessing qualities that made it a promising 

 subject for careful investigation. 



The plan of destruction thus sought for is that so com- 

 monly observed in operation upon a grand scale in Nature, 

 where individual species and whole families are swept out 

 of existence through its operation. 



The questions formulated in the circular letter were 

 widely discussed. Newspapers and other periodicals treat- 

 ed them from a hundred standjioints — the grave — the gay 

 — the lively — the serene — a volume could be filled with 

 articles relating to the subject published in this country 

 and in Europe. 



The most valuable results were, as expected, those sub- 

 mitted by the scientific experts especially appealed to. The 

 essays that they presented are the outgrowth of long years 



