DIPTERA. 



469 



other soft-bodied insects. They are usually found in damp 

 places, covered with rank vegetation. Some species occur 

 chiefly on the leaves of aquatic plants, and about dams and 

 waterfalls ; and some are able to run over the surface of 

 water. Others occur in dry places. 



The larvae live in earth or decomposing vegetable matter. 

 They are long, slender, and cylindrical, and have two pairs 

 of spiracles, one at each end of the body. In most cases the 

 pupae are free ; but some form cocoons. The thorax of the 

 pupa bears a pair of long breathing-tubes. 



The family is a large one ; more than two hundred North 

 American species have been described already. 



Family LONCHOPTERID.E (Lon-chop-ter'i-dae). 

 The Spear-winged Flies. 



These are minute flies, which measure from one twelfth 

 to one sixth of an inch in length, and are usually brownish 

 or yellowish. When at rest the wings are folded flat, one 

 over the other, on the abdomen. The apex of the wing is 

 pointed ; and the wing as a whole is shaped somewhat like 

 the head of a spear. This suggested the family name. 



The venation of the wings is very characteristic, and is 

 sufficient to distinguish these flies from all others. The 



Vila 



Vj VII i 

 FIG. 572. Wing of Lonchoptera. 



cross-veins III-V and V-VII are oblique, and near the 

 base of the wing (Fig. 57 2 )- Vein VII, is very short, and 

 extends towards the base of the wing. In the females vein 



