612 
DIPTERA. 
% 
bearing a little bristle.^ Their larvae, or young, are fleshy, 
whitish maggots, which never cast their skins, but, when 
the pupa state comes on, shorten, take the oblong-oval 
form of an egg, and become brown, dry, and hard on the 
outside. This immense tribe includes the various kinds of 
flesh-flies, blow-flies, house-flies, dung-flies, flower-flies, fruit- 
flies, two-winged gall-flies, cheese-flies, and many others, 
for which we have no common names, but all composing 
the tribe of Muscans, or Muscad^. Some of these flies 
do not strictly conform to the foregoing characters of the 
tribe, in all respects; but the exceptions are few in number, 
and the most remarkable of them will be noticed in the 
following pages. 
Many flies of this tribe are parasitic in their larva state, 
their young living and undergoing their transformations 
within the bodies of other insects, particularly in caterpillars, 
which they thereby destroy. These flies belong chiefly to 
the family of Tachinad^, a name applied to them on account 
of the swiftness of their flight. In form they somewhat 
resemble house-flies; like them, they have very large wing- 
lets, and their wings spread apart when they are at rest. 
They are easily distinguished, however, by the stiff hairs 
wherewith they are more or less covered, and by the bristles 
on their antennse, which are not usually feathered. A large 
fly of this kind, the Tacliina vivida (Plate VIII. Fig. 1) of 
my Catalogue, is often seen on fences, and on plants, and 
sometimes in houses, towards the end of June and during 
the month of July. Its large, oval hind body is of a clear 
and light red color, with two or three black spots, in a 
row, on the top of it, and a thick row of black bristles across 
each ring. The face is grayish white, like satin, and the 
eyes are copper-colored. The thorax is gray, with brownish, 
lines upon it. The antennas, proboscis, and legs are light 
red. Its body is short and thick, and is about half an inch 
long, and its wings expand rather more than nine tenths 
of an inch. 
