One or a pair of small, globular galls bursting out of splits on the lower side of leaf midribs on Quercus rubra in Boston, Massachusetts. When the galls first appear in August-September, they are light colored, but darken to red and nearly black over time. They are almost perfectly spherical in shape and tethered to the midrib by a pedicel-like structure. Their texture is slightly bumpy but hairless. The splits they emerge from are small and subtle compared to the bulges formed by species like Callirhytis piperoides or Dryocosmus deciduus on similar hosts in the fall.

This may be a Zopheroteras, possibly Z hubbardi.

The "type" observation
The same gall a week later

Other observations made nearby:
1
2
3

Similar galls on Quercus rubra have also been reported from Newton, Massachusetts, Michigan 2, Ontario, Pennsylvania, Connecticut, Illinois, and Ohio 2 3 4 5 6 7 8