3 l8 
The Two-winged Flies 
and diagonal veins are the marks of the creases made by the compact folding 
of the wings in the pupal shell. The females are provided with long saw- 
edged mandibles (Fig. 434), and are predatory in habit, catching smaller 
flying insects, especially Chironomid midges, lacerating their bodies with 
the mandibular saws and sucking the blood. The males have no mandibles, 
and probably take flower-nectar for food, 
genera have the compound eyes divided 
into a large-facetted and a small-facetted 
part (Figs. 435 and 437). The egg-laying 
has not yet been observed, although the 
eggs must almost certainly be deposited 
on rocks in the stream or on its edge. 
With the mosquito wrigglers and the 
blood-worms (larvae of the Chironomidae) 
may perhaps be found a third kind of fly 
larva (Fig. 440), a slender, pale-colored, 
cylindrical little “worm,” about one- 
third of an inch long, which can be 
distinguished from the other aquatic 
larvae by its two pairs of short leg-like 
processes borne on the under side of the 
Both males and females of several 
Fig. 439. Fig. 440. 
Fig. 439.—Diagram of horizontal section through head of old larva of net-winged midge, 
Bibiocephala doanei , showing formation of adult head-parts inside, l.md., larval 
mandible; l.mx., larval maxilla; l.c., larval cuticle; i.md., adult mandible; i.mx.p., 
adult maxillary palpus; id., hypoderm (cell-layer of adult skin of head); i.e., adult 
eye. (Much enlarged.) 
Fig. 440.—Larva of Dixa sp., with dorsal aspect of head in upper corner. (From life; 
much enlarged.) 
fourth and fifth body segments. It usually keeps the body bent almost double, 
and when feeding near the surface the head is twisted so that the under or 
