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 
cross-veins III-V and V-VII are oblique, and near the 
base of the wing (Fig. 572). Vein VII a is very short, and 
extends towards the base of the wing. In the females vein 
