THE DIPTEROUS GENUS DOLICHOPUS LATREILLE IN 



NORTH AMERICA. 



By M. C. Van Duzee, F. R. Cole, and J. M. Aldrich. 



INTRODUCTION. 



By J. M. ALDRICH. 



The dipterous family Dolichopodidae offers such a storehouse of 

 material bearing upon the Darwinian theory of sexual selection that 

 its many beautiful and easily classified species ought to be much more 

 widely known among those who give attention to the larger biological 

 problems. In the present paper a large number of secondary sexual 

 characters are figured, not only as aids to identification, but to give 

 some idea of the wealth of beautiful structures which have been 

 developed in the males of this genus. The species are so abundant 

 and accessible everjrwhere in the United States and Canada, as Avell 

 as Europe, that their peculiar mating habits ought to be recorded for 

 many, instead of the fi.ve which arc given a few paragraphs farther on. 



The family is readily distinguished by a few characters. Its 

 members have antennae with three simple joints and an arista; the 

 tarsi with empodia not pulvilliform; palpi with only one joint; basal 

 cells of wing very small, the second confluent with the discal, anterior 

 cross-vein close to base of wing. The species almost universally 

 have bright metallic green and blue colors. 



Among the genera of this family are two which are strikingly rich 

 in species — Psilojms, with a widely divergent fork on the third vein, 

 which is widespread in the tropics everywhere, and occurs also in 

 temperate zones; and Dolichopus, recognized by having several spines 

 on the upper side of the hind basitarsi, which has a circumpolar 

 distribution in the northern hemisphere, extending southward pretty 

 well across the north temperate zone. 



The presence of the spines just mentioned on the upper side of the 

 hind basitarsi is a sufficient diagnostic character to separate the genus 

 Dolichopus from all others known in North America; it would serve 

 equally well thi'oughout the species of the rest of the world by adding 

 that the arista is never plumose. The Ethiopian and oriental Rluigo- 

 neurus Loew (Lichivardtia Enderlein, 1912) has a plumose arista and 

 a single spine on the hind basitarsus. 



1 



