The ground around the cabin was littered with these galls on our last trip. There were dozens of them. These are just a little bit smaller than golf balls.
I don’t pretend to understand the “life” cycle of a gall, but I know that it grows around the larva of a certain type of wasp. The egg is laid in the leaf or stem of a tree, generally an oak. Now, whether these larvae overwinter in the gall or hatch out in time to frolic in the Ozark winter, I can’t say. (I suspect they overwinter, but I welcome your information to the contrary.) I do find more gall “husks” in the spring. They’re hollow but round, with a small exit hole in them.
I can say that I’ve seen them often, and apparently throughout the warmer months, given the June date of this old post of mine. It may be that whatever species of wasp this is, the galls “ripen” in the late summer. And I say that based on this interesting post at the Naturespeak blog that is also dated in September (of last year). If you go there you can read about dik-dik livers too. That’s a kind of bonus.