Mystery mites

We're very proud of our silverleaf maple because it's a second-generation tree from one of our friends. He had an old pot of soil on his back porch, into which fell helicopter seeds from his trees, year after year, and he never bothered to pull the seedlings out. So when we moved into this house, we asked if we could have one. It's now a thriving eight-foot-tall tree.

I recently made the amazing discovery that the tree now produces enough shade to cover me, if I position myself just right and the sun cooperates. As I relaxed in the shade, I noticed a bunch of little red lumps, no more than 1/16" in diameter, on the tops of the leaves. I panicked and pulled most of them off (probably around 100) but I saved one so I could take a photo:

It's just above the center of the photo, a tiny red dot on the tip of a green leaf. I was guessing it was some kind of egg, laid there so the little bug would have something to eat when he emerged. But, after a little research, I discovered I was both right and wrong. Actually, it was the leaf reacting to a tiny mite who had laid its eggs there. And although the "galls," as the lumps are called, are not pretty, they are not harmful either. Thanks for the tip, Ohio State University! Isn't the Internet amazing?