Hessian Fly, a two-winged insect pest. It feeds on crop grasses, such as wheat, barley, and oats. It is especially harmful to winter wheat. The adult, about 1/10 of an inch (2.5 mm) long, is a long-legged, brownish insect with dusky-gray wings. The Hessian fly was introduced into America from Europe during the American Revolutionary War.

The Hessian flyThe Hessian fly is a long-legged, brownish insect with dusky-gray wings.

Two generations are produced each year. In September, the female lays several hundred eggs on the upper surfaces of young wheat leaves. The eggs hatch in 3 to 12 days. The small red larvae work their way behind the leaf sheaths and feed on the tender plants. In about four weeks the larvae become brown pupae resembling flaxseed. In late spring the flies emerge from the pupae and lay their eggs on the growing wheat. The feeding larvae cause the wheat plants to lose strength and break or to be snapped off readily by the wind.

An important control measure is the planting of fall wheat at a late date after the flies have died. Some strains of winter wheat have been developed that are resistant to Hessian flies.

The Hessian fly is Mayetiola destructor of the family Cecidomyiidae, order Diptera.