ROBBERFLIES OF THE GENERA PROMACHUS AND 

 PROCTACANTHUS. 



James S. Hike. 



The species of these two genera from America north of 

 Mexico, have been considered by Williston in Volume XII, of 

 the Transactions of the American Entomological Society, and 

 the Mexican species of Promachus have been tabulated by 

 Osten Sacken in Biologia, Diptera I, 192. The fact that it has 

 been possible to get together an extensive collection of spec- 

 imens of various species from different parts of North America 

 has led me to make an attempt to identify many of the Nearctic 

 forms, and as some success at least has been attained the fol- 

 lowing results are offered for the consideration of those, who 

 for any reasons, have interest in the various species included. 



One can not study these flies in the field without noting 

 their highly predaceous habits. These habits have attracted 

 the attention of observers in the past with the result that a few 

 of the species have been mentioned as injurious from the stand- 

 point of killing honey-bees and other useful insects, but in most 

 cases the feeding habits are variable to the extent that each 

 species accepts a large variety of insect life as food, so that 

 after all it seldom happens that their attacks are concentrated in 

 a particular direction sufficiently to establish a marked habit 

 which shall be considered either injurious or beneficial. They 

 are among the largest species of their subfamily, some speci- 

 mens measuring nearly forty-five millimeters in length and the 

 smallest over twenty millimeters, so if their predaceous habits 

 could be controlled the results, very likely, would be of extraor- 

 dinary importance. 



The material used in the preparation of this paper has been 

 procured from various sources and I am under many obligations 

 for favors. The United States National Museum and the 

 museums of Cornell University and the University of Kansas 

 each have loaned specimens for study. Professor J. R. Watson, 

 of Albuquerque, New Mexico, has sent me several specimens 

 from that interesting region; Professor J. H. Schaffner has 

 donated the material he collected during two summers in cen- 

 tral Kansas; Professor C. F. Baker has sent me much material 

 that D. L. Crawford collected in Mexico during the season of 

 1910; while Charles Dury of Cincinnati, and H. S. Harbeck, of 

 Philadelphia, and others have forwarded various species from 



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