[Reprinted from Psyche, Vol. XVIII, No. 3, 1911.] 



A REVISION OF THE NORTH AMERICAN SPECIES OF 

 THE DIPTEROUS GENUS HYDROPHORUS. 



By J. M. Aldrich. 

 The University of Idaho, Moscow, Idaho. 



The genus Hydrophorus, established by Fallen in 1823, as lim- 

 ited by Loew in 1857, as generally used since and as herein un- 

 derstood, comprises those flies of the family Dolichopodidae which 

 have the posterior crossvein located near the hind margin of the 

 wing (distant about its own length, measured on the fifth vein); 

 fourth vein ending in or behind the apex (this excludes Scellus, in 

 which it ends before the apex); front femora thickened (this ex- 

 cludes Liancalus), more or less spinose beneath; dorsum of thorax 

 not with a concave or flattened space before the scutellum (ex- 

 cludes Medeterus); and with the usual single row of postorbital 

 small bristles replaced below with a loose tuft of pale hairs cover- 

 ing all the posterior surface of the head below the neck. 



The species are rather small, from 2.5 to about 6 mm. in length. 

 The adults are always found close to the edge of water on wet 

 earth, or else running on the surface of the water. They are 

 carnivorous, seizing smaller flies, etc., and holding them with 

 their raptorial front legs while they suck out the juices. The 

 larvae have not been reported to my knowledge, but it is almost 

 certain that they live in mud at the edge of water. 



The adults have a wide range of season, as will be indicated 

 by the dates cited in connection with the descriptions. Con- 

 sidering the fact that several species can easily be found in any 

 locality, the genus has been little collected. This is partly due 

 to the lack of those conspicuous male characters which render 

 some other Dolichopodidae so interesting, and partly to a general 

 similarity of appearance which has made the taxonomy of the 

 genus comparatively unattractive. However, in the following 



