3i8 



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 i)robably take flower-nectar for food. Both males and females of several 

 genera have the compound eyes divided 

 into a large-facetted and a small-facetted 

 part (Figs. 435 and 437). The egg-laying 

 has not )-et been obser\ed, although the 

 eggs must almost certainly be deposited 

 on rocks in the stream or on its edge. 



Wi;h the mosquito wrigglers and the 

 blood-worms (larvae of the Chironomidx) 

 may ])erhaps be found a third kind of lly 

 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 imder side of the 



Fig. 43Q. Fig. 440. 



Fig. 430. — Diagram of horizontal section through head of old larva of net-winged midge, 

 Bibiocephala doanci, showing formation of adult head-parts inside. I.md., larval 

 mandible; /.m.i;., larval ma.xilla; /.c, larval cuticle; (.»i</., adult mandible; i.mx.p., 

 adult ma.xillary palpus; id., hvpoderm (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 comer. (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 



