Alien balls

One of the boys that plays here found these strange green balls in the oak tree while he was climbing it this weekend. About the size of a golf ball, he thought it was some kind of fruit.
I did some research and found out they were caused by a bug called the gall wasp. Apparently it lays it's egg in the main vein of a newly developing leaf and the leaf becomes this strange ball with the larvae growing safely inside. I passed all this on to the kids that were here and we looked at some pictures, it was all very interesting.
Today, the little boy who found them was up in the tree again and talking to me about them so we decided, in the interest of science, to look inside one of for ourselves. We had quite a little crowd, 8 kids altogether, so my little buddy pulled one off the tree and one of the older boys sliced it carefully in two, then we passed it around so everyone could take a look. Pretty cool.

I snapped a few pics which really didn't come out as well as I had hoped, but by now (11pm), it's a bit shriveled up so this is the best I have :0)