Hessian Fly , a small gnat or midge, of the order diptera, family cecidomyiadoe or gall gnats, and genus cecidomyia (Latr.). It was called Hessian fly from the supposition that it was brought to this country in some straw by the Hessian troops during the revolutionary war; it was scientifically described in 1817 by Mr. Say as cecidomyia destructor. The body is about one tenth of an inch long, and the expanse of wings one quarter of an inch or more; the head, antennas, thorax, and feet are black; the hind body is tawny, marked with black on each ring, and with fine grayish hairs; the wings are blackish, tawny at the narrow base, fringed with short hairs, and rounded at the tip; the legs pale red or brownish; the egg tube rose-colored. The antenna) are long, with bead-like swellings most distinct in the male, surrounded by whorls of short hairs, with 15 to 18 joints, globular in the male, oblong oval in the female; the proboscis is short, without piercing bristles; eyes kidney-shaped; legs long and slender, with the first joint of the feet short; and the wings with few veins.
This insect, so destructive in some seasons in the fields of wheat, barley, and rye, generally matures two broods in the course of a year, appearing in spring and autumn, earliest in the southern states; the transformations of some are retarded in various ways, so that their life from the egg to the perfect insect may be a year or more, rendering the continuance of the species in after years more sure. The eggs, about 1/50 of an inch long, translucent, and pale red, are placed in the longitudinal creases of the leaves of both winter and spring wheat very soon after the plants are above the ground, to the number of 20, 30, or more on a leaf; if the weather be warm, they are hatched in four or five days, and the larva), small footless maggots, tapering at each end, and of a pale red, crawl down the leaf and fix themselves between it and the main stalk, just below the surface of the ground, there remaining head downward till their transformations are completed, nourished by the juices of the plant, which they obtain by suction. Two or three larvae thus placed will cause the plant to wither and die.
In about six weeks they attain their full size, 3/20 of an inch long, when the skin gradually hardens and becomes of a bright chestnut color, about the 1st of December in the autumn brood, and in June or July in the spring brood. In the beginning of this, the pupa state, they look like flax seed; in two or three weeks the insect within becomes detached from the leathery skin, and lies loosely in it, a motionless grub; within this it gradually advances toward the winged state about the end of April or beginning of May, according to the warmth of the weather. When mature, it breaks through this case, enveloped in a delicate skin, which soon splits on the back, setting the perfect insect at liberty. Many of those laid by the spring brood are left in the stubble, and remain unchanged until the following spring; some, however, do not get so low on the stalk as to be out of the way of the sickle, and thus with the straw may be transported long distances, and might have been brought in the flax-seed state across the Atlantic from Europe. The perfect insects, though small, are active and fly considerable distances in search of fields of grain.
The insect supposed to be the Hessian fly, which Miss Morris found laying its eggs in the seeds of wheat instead of on the leaves, she afterward ascertained to be another species, which she called G. culmicola. This destructive insect was first observed in 1776 on Staten island, near the place of debarkation of the Hessian troops under the command of Sir William Howe; thence it spread to Long Island, southern New York, and Connecticut, proceeding inland at the rate of about 20 miles a year; it was seen at Saratoga, 170 miles from Staten island, in 1789, and west of the Alleghanies in 1797; so great was the destruction, that the cultivation of wheat was abandoned in many places. Burning the stubble in wheat, rye, and barley fields, afterward ploughing and harrowing the land, appears to be the best method of getting rid of this insect; steeping the grain, rolling it in plaster or lime, or other methods of securing a rapid and vigorous growth, sowing the fields with wood ashes and feeding off the crop by cattle in the autumn, are useful accessory means. Various minute parasitic insects, of the hymenopterous order, similar in their habits to the ichneumon flies, destroy a very large proportion of every generation of the Hessian fly, preying upon their eggs, larvae, and pupae.
The insect which commits such depredations on the wheat crops of Great Britain, C. tritici (Kirby), will be described under Wheat Fly. For details on the history, habits, and transformations of the Hessian fly, the reader is referred to "Insects Injurious to Vegetation," by Dr. T. M. Harris.
Hessian Fly (Cecidomyia destructor), enlarged.