GALL-GNATS. 
565 
food almost entirely by suction, for tlieir jaws are merely 
two little hooks, that enable them to fasten themselves upon 
the substances which serve for their nourishment. They 
increase rapidly in size, and when they are fully grown, they 
change their forms, without casting off their skins at all, 
merely by the gradual shortening of their bodies, which take 
an oblong oval shape, and turn hard and brown on the out¬ 
side. The hardened skin of the larva thus becomes a shell 
or kind of cocoon, within which the insect is afterwards 
changed to a pupa, having its imperfect limbs folded on its 
breast, and from wdiich, in due time, it comes forth in the 
form of a fly, by forcing off one end of the shell.* 
The far-famed Hessian fly, and the 'wheat-fly of Europe 
and of this country, are small gnats or midges, and belong 
to the family called Cecidomyiad^, or gall-gnats. The in¬ 
sects of this family are very numerous, and most of them, 
in the maggot state, live in galls or unnatural enlargements 
of the stems, leaves, and buds of plants, caused by the 
punctures of the winged insects in laying their eggs, or by 
the irritation of the maggots hatched therefrom. The Hes¬ 
sian fly, wheat-fly, and some others, differ from the majority 
in not producing such alterations in plants. The probos¬ 
cis of these insects is very short, and does not contain the 
piercing bristles found in the long proboscis of the biting gnats 
and mosquitos. Their antennm are long, composed of many 
little, bead-like joints, which are more distant in the males 
than in the other sex; and each joint is surrounded with 
short hairs. Their eyes are kidney-shaped. Their legs are 
rather long and very slender. Their wings have only two, 
three, or four veins in them, and are fringed with little hairs 
around the edges; when not in use, they are generally car¬ 
ried fiat on the back. The hind body of the females often 
ends with a retractile, conical tube, wherewith they deposit 
their eggs. Their young are little, footless maggots, tapering 
at each end, and generally of a deep yellow or orange color. 
* See page 5, 
