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 antennas 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 
fly ,Physocephala affinis. 
(One and one-half times 
natural size.) 
