Overwintering Oak Galls

Last October I spotted a couple of tiny, pearl-like cynipid wasp galls on the underside of a fallen white oak (Quercus alba) leaf.

Gall (2 mm) on a white oak leaf, sporting a tiny springtail (Hypogastruridae).

I stuck the leaf in a plastic bag to see if anything would emerge in the spring.  Meanwhile, I checked Lewis H. Weld’s 1959 Cynipid Galls of the Eastern United States, and the only mention I saw of a gall remotely resembling these had the simple note, “never reared.”

Going through all my bags in April, I discovered that a wasp had emerged from the gall pictured above.

Cynipid wasp from the same gall (0.8 mm).

Unfortunately, I’m pretty sure this wasp is an inquiline, i.e., not the wasp responsible for the gall, so the identity of the latter remains a mystery.  What I thought was interesting, though, was the appearance of the dry, empty gall on the moldering leaf.  The outer layer had exfoliated to reveal an even tinier cell within, and I don’t think I would have recognized this as the fleshy white gall I had seen in the fall if I hadn’t collected it.