Small gnats with large broad wings, much narrowed at the root, rounded at the tip, and generally rough with hairs. Feelers made up of a large number of spherical or cylindrical joints, covered with spreading hairs. Proboscis short, legs long. The female has an ovipositor, with which she inserts eggs in any part of a plant. At this particular spot a luxuriant growth of vegetable tissue takes place later on, of varying extent, and even forming a regular gall. The species of gall gnat are usually brightly coloured, often red or yellow; these colours are lost, however, in dried specimens. The larvæ are spindle-shaped, yellowish white, yellow, or red; they become pupæ either in the soil or within the part of the plant which they inhabit. Several species are destructive to fruit-tree culture or forestry; I mention here only the most destructive kinds which attack cultivated plants. The =Hessian Fly= (_Cecidomyia destructor_). [Illustration: FIG. 111.—Plant of Barley, attacked by Hessian Fly. The pupæ at _a_. ] Female about one-eighth of an inch long, male somewhat smaller. The former velvety black, with black hairs, red belly, and red markings; wings greyish; antennæ one-third the length of the body. Male black, with reddish-yellow hairs, dirty red belly, and red markings. The name “Hessian flies” was given in North America, during last century, because it was believed they were introduced from Germany, in 1778, by Hessian soldiers, in their straw. It is still very destructive in North America, also in Germany, Russia, England, and Scotland. _Habits_: During April or May, on warm still evenings, the female lays her eighty or ninety eggs, singly or in pairs, on the lowest leaves of the still very short haulms of rye, wheat, and barley. Eight days, on an average, after this the maggots, which are at first oblong and spotted with reddish yellow, are hatched, and glide down into the leaf-sheath, where they begin to suck the haulm. They gradually alter their shape, becoming ovoid, and transparent with the exception of the large yellowish white, quite opaque fat body. They soon become pupæ (Fig. 111), which look like grains of linseed, and are found in summer on the haulms of the ripe grain. The presence of the constantly sucking larvæ causes great and injurious distortions of the plant, especially obvious during the flowering time, and for a short time afterwards. The haulm withers, and shrivels at the point where the larvæ are present, _i.e._ above the lowest node, or the lowest but one. At the time when the haulm begins to turn yellow—that is, when the grain begins to ripen,—the larvæ become pupæ; the haulm now easily breaks off at the infected spot; a strong wind or heavy rain throws it to the ground. A badly infested field looks, on this account, as if a herd of cattle had got loose and trodden it all down, or as if the grain had been devastated by hail. Only a few haulms bear ears containing normally developed grains.