oak leaf gall midge

Oak leaf gall midge 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.

Gall: 1 ⁄16″ to 3 ⁄16″

Blackjack 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, northern red oak

Autumn

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

Northern pin oak, northern red oak, and possibly black oak

Sources

7, 24, 27, 29, 30, 82.

Common

Galls

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

Leaf upperside

Lateral veiw

Leaf underside

Galls

Karen Frances
Yates
8/7/2024

Location:1730 East Elm St, Jefferson City, MO

This is the second year for these critters on this same tree.

Sheila Muise
7/1/2024

Location: Boston, Ontario

Evie Knapp
9/14/2022

Location:  Orono, MN 55359

I have seen this on a few leaves on our oak tree and am wondering if it will do damage to the tree!

John Valo
9/14/2022

Not according to University of Missouri Extension:

Those unsightly round, brown growths seen on oaks this time of year won’t harm the tree, says a University of Missouri Extension fruit specialist.