Oak Tree Leaf Disease

OK, so I have these trees, which I think are Shumard (or Red) Oak. And back in mid-April I noticed these lime-looking growths on the leaves. Some leaves had full grown “limes” and others were just starting to show signs of “lime” growth.

The best I can determine is that the tree has blisters. But, since no one can confirm my “diagnosis” I’m turning to you for assistance. If you or someone you know is a leaf expert or botanist or just some leaf enthusiast I’d love a little help identifying this leaf disease.

Here’s a photo of several “limes.”

A close up of a “lime.”

Here’s a dead one cut in half. Each “lime” is about the size of a golf ball, less than an ounce in weight, and each has what appears to be some kind of spore inside (though that’s really just a guess).

Seriously, I’m stumped. Anyone have an idea what is ailing my neighborhood oak trees?

Update: Thanks to some knowledgeable Redditors the above leaf disease has been identified as Oak Galls and are caused by small wasps that infest the oak tree. Unfortunately there’s almost nothing that can be done to prevent the wasps from wreaking havoc on my neighborhood oaks.