The adult hessian fly is an eigth of an inch long, dark in color, and resembles a gnat in appearance. Adults become active in fall and lay eggs on the surface of leaves (resembling leaf rust) on wheat seedlings. Hessian fly maggots hatch and move to the base of the plant where they feed between the leaf sheath and stem. Hessian fly overwinters as a pupa, which is termed 'flaxseed' because it is dark red and shaped like a flaxseed. Infested tillers typically die over the winter. Some adults emerge in spring and others emerge in the fall after pupa remain dormant over the summer. Spring damage from larvae causes stem lodging.