After Jim McClarin suggested a gall for this image, I got curious as to what was inside these things. I took four of them off my neighbor's tree and opened them all up.

This photo shows one of these things cut open. Hundreds of what appear to be eggs(?) spilled out. The inside of the thing was hollow, the outer shell was hard, and attached to the outer shell was a layer of squishy wet stuff. The eggs(?) that didn't fall out onto the paper are sticking to the squishy wet stuff.

Galls seem like a possibility, but these black & red things do not in any way seem to be part of the tree. They don't seem like plant growths. So I don't know. I'm baffled.

Of the four "things" I opened up, two were full of eggs (or whatever they are). One had nothing in it except the squishy wet layer around the hollow hole inside. The 4th one turned into a very wet, orangish mess. I won't post the photo of that one.

I hadn't seen these scales/galls since I took their photos on April 1st. Most of them are blacker in color now, but otherwise they look the same, and the ants are still farming them. The ants were upset with me for removing them from the tree.