Midrib or petiole swellings
Oak petiole gall. Somewhat globular, conical above with a depression at apex, hard, green, polythalamous, the larval cells radiating out from the center. On the petiole or basal part of midrib, usually several in close proximity on the tree. In May and June, the adults emerging in late June. On Q. alba, bicolor, and macrocarpa.
- LH Weld: (1928) Cynipid Galls of the Chicago Area©