33 6 



The Two-winged Flies 



Dolichopus (Fig. 473) is the largest genus of the family, nearly 100 species 

 occurring in this country. The males are curiously ornamented by special 

 outgrowths or expansions on the feet. These make the feet at the end of 

 the long legs very conspicuous and are believed to serve the male to help 

 attract the female in his courtship of her. These ornaments are not con- 

 fined to the males of this genus, other genera of the family showing similar 



FIG. 474. Diagram of wing of a Dolichopodid, Psilopus ciliatus, showing venation. 



characters. Other ornaments, too, are found in various species, some occur- 

 ring on the face, others on the antennae and elsewhere. Aldrich says that 

 the males of the flies of this family show more pronounced and various special 

 ornamentation than the males of any other single family of animals. He 

 has seen the males dangle their tufted feet in the faces of the females during 

 courtship. 



Occasionally the general collector or nature observer will find an insect 

 that he has taken at first glance for a wasp, but which on examination, after 

 capture, is found to have but a single pair of wings, and short, clubbed anten- 

 nae like a fly. The puzzle is readily solved with 

 these clues: the insect is a fly, not a wasp; it simply 

 looks so much like a wasp that it undoubtedly is 

 frequently mistaken for a wasp by certain enemies 

 which are afraid to attack the well-defended hornet, 

 but would make short work of a defenceless fly. 

 The wasp-flies, Conopidae, thus save their lives by 

 an innocent deception; they are protected by their 

 curiously close mimicry of wasps. All of them are 

 narrow- waisted, and most have the abdomen spindle- 

 shaped and tapering like a wasp's, and often banded 

 and colored so as to increase the similitude. All 

 of them, too, have robust heads and have been sometimes called "thick- 

 head-flies." They are all flower-flies, feeding on nectar and pollen, and 

 hovering on heavy wing about blossoming shrubs. The oval or pear-shaped 

 larvae are parasitic, living in the bodies of other insects, especially wasps, 



FIG. 475. A wasp-like 

 fiy,Physocephala affinis. 

 (One and one-half times 

 natural size.) 



