The gall fly is a small fly that produces on plant leaves and stems an injurious, abnormal growth called a gall. The gall fly belongs to the insect order Diptera, which also includes the true flies, mosquitoes, and gnats.
The gall fly causes the formation of galls by piercing tender leaves and stems and by laying its eggs within their tissues. After hatching from the eggs, the larvae remain within the plant tissues and feed upon them until they have metamorphosed into adult insects. Galls are white, yellow, red, or green growths that are of irregular shape and that vary in width from a fraction of an inch to several inches.
The hessian fly is a gall fly that causes much injury to growing wheat. Another gall fly injures growing chrysanthemums.
