Callirhytis lanata (agamic)

Disholcaspis quercusmamma (agamic)

Contarinia negundinis

Aceria negundi

Callirhytis seminator (sexgen)

Callirhytis clavula

Callirhytis lanata

This gall, which occurs as a woolly mass on the under side of the leaves of several species of the red oak group, is composed of angular galls closely joined. When young the galls are covered with a whitish wool which later turns brown. 

Disholcaspis mamma (Gill.) 

This gall may be confused easily with the preceding [Disholcaspis quercusglobulus]. The distinguishing characters are a velvety surface and pointed apex. It usually occurs in large numbers and in variable sizes on the branches of the burr oak, Quercus macrocarpa. 

Color: green, turning brown. 

Contarinia negundifolia (Felt)

Hosts: Boxelder

This gall is an elongated, succulent, rolled swelling of the leaf on both sides of the midrib.
Color: green

Eriophyes negundi

Hosts: Boxelder

Small warty swellings irregularly scattered over the upper surface of the leaves.
Color: green

WOOL SOWER GALL Callirhytis seminator (Harr.) 

The wool sower is composed of a large number of small hairy galls attached to a common point on twigs of the white oak, Quercus alha, thus forming a compact woolly mass. [Subfigure] A represents a single gall. 

Color: white, often tinged red, turning brown. 

Callirhytis clavula

A hard, woody, club-shaped gall, which occurs on the tips of twigs of the white oak, Quercus alba. Leaves frequently grown from it.

Contains several larval chambers.

Colo: green, often tinged red, turning brown.

50 common plant galls of the Chicago area