GALL-GNATS. 565 



food almost entirely by suction, for their jaws are merely 

 two little hooks, that enable them to fasten themselves upon 

 the substances Avhicli 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 which, 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^e, 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 

 punctui'es 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 antenna 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 flat 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. 



