oak leaf gall midge

Common

Autumn

This is a long-legged, 1 ⁄16″ to ⅛″ long, mosquito-like fly (midge). The abdomen has ten segments, each covered with upper (dorsal) and lower (ventral) exoskeletal plates. On the female the seventh lower plate (sternite) is much longer than the sixth; and the eighth upper plate (tergite) is wide, strongly hardened, and laterally notched. The wings are clear, are covered with hairs, and have reduced venation. Only four veins reach the wing margin. The basal segment of the foot (tarsus) is much shorter than the second segment. The mouth parts are reduced. The large compound eyes meet at the top of the head. There are no simple eyes (ocelli). The antennae are long and have 12 segments. On the female these segments are cylindrical.

Adults are impossible to identify by appearance in the field. However, the species can easily be identified by the gall it produces. Galls appear always on the upper surface of northern pin oak, northern red oak, and possibly black oak leaves. They are hard, 1 ⁄16″ to 3 ⁄16″ in diameter, and irregular in shape. They are green when they first appear in the spring, soon turning red or magenta. As they age they become brown and crusty. They can be easily detached from the leaf surface.

The larva is bright orange.

Oak leaf gall midge (Polystepha globosa) forms similar spherical galls on the undersurface of the leaves of black oak and possibly other oaks in the red oak group.

Northern pin oak (Quercus ellipsoidalis), northern red oak (Quercus rubra), and possibly black oak (Quercus velutina)

Larvae break out of the gall in the fall and reproduce before reaching maturity.

Sources: 7, 24, 29, 30.

Galls

Bright color (not captured in photo) to these formations on oak leaves.

Leaf upperside

Leaf underside

Lateral veiw

Galls