Donald A. Windsor
Oak-Apple Galls are formed by oak tree leaves under the control of the gall wasp Amphibolips confluentus, Family Cynipoidea.
These two specimens were picked up under a Red Oak (Quercus rubra) in front of 51 Sheldon Street in the City of Norwich. I regret that I did not record the date, but it was the late spring or early summer of 2016.
The female wasp lays an egg on a leaf. The egg hatches into a larva that then feeds on the leaf, stimulating the leaf tissue to develop into a gall. The gall acts as a cocoon, protecting the larva as it pupates. When the pupa reaches adult stage, it breaks its way out of the gall.
Note the larval-pupal chamber suspended by fibers in the center of the opened gall.
Oak-Apple Galls have been found in several places in Chenango County.
Craighead, F.C. Leaf galls. In: Insect Enemies of Eastern Forests. Washington DC: US Department of Agriculture. Miscellaneous Publication Number 657. 1950. Pages 597-598.