The Two- winged Flies 



3 2 5 



feed on the decomposing substance in which the eggs are .aid, sometimes 

 spinning silken webs for protection. They pupate in the food-substance or 

 crawl away to some more sheltered spot, often forming a thick cocoon in 



FIG. 452. A fungus-gnat of the family Mycetophilida; larva, pupa, and adult. 



(Much enlarged.) 



which to transform. Perhaps the most singular habits noted in the family 

 are those connected with the strong gregarious instinct which leads the 

 larvae of many species to live closely together. Some of the species of Sciara, 

 known as " army- worms, " have "the singular propensity of sticking to- 

 gether in dense patches, and will 

 form processions sometimes twelve 

 or fourteen feet in length and two 

 or three inches broad. This phe- 

 nomenon has been observed fre- 

 quently both in Europe and Amer- 

 ica, but the reason therefor is not 



11 j j .1 i .1 FlG. 4<?v Diagram of wing of fungus-gnat, 



yet well understood, though the Mycetophill sp., showing venation, 



object of the migration seems to be 



the search for better feeding-grounds." Various species of this genus live 

 in potatoes and other vegetables, while the serious injury to potatoes called 

 "scab' ? is caused by a fungus-gnat known as Epidapus scabies. 



With larger and more robust bodies and relatively shorter and thicker an- 

 tennae, the March-flies, Bibionidae, serve as a sort of transition family between 

 the long-legged, slender -bodied midge type of fly with its thread-like hairy 

 antennae, and the compact, heavy-bodied, short-legged type of fly with short 

 and club-like three-segmented antennae, characteristic of the many families 

 grouped in the section Brachycera. The March-flies (Fig. 454) are from 

 one-eighth to one-half inch long, with fairly robust, often hairy, body, black- 



