These are made by a Disholcaspis quercusmamma wasp in the Cynipidae family. I collected one of these galls which had a fully formed cocoon inside. Just today I discovered that a wasp had emerged, but I don`t know if it is the species that made the gall or a parasite. It is minuscule and perfectly formed with very long antennae. About the size of the period in this sentence . I was surprised to see it, as I thought these wasps emerged in the fall, and to lay eggs in twig buds, with the wasps eventually emerging the following fall.