Oak marble gall

Okay, picture this - you know how sometimes an insect might bite you and it leaves a little bump or swelling on your skin? Well, something similar can happen to oak trees.

When a certain type of wasp lays its eggs on the bark of an oak tree, it causes the tree to react in a funny way. The bark gets all bumpy and lumpy and starts to form a little ball around the eggs. This is called a gall.

The wasp eggs then hatch and the baby wasps start to feed on the tree tissue inside the gall. The tree, still trying to protect itself, starts to form layers around the gall to try and keep the babies in and the outside world out.

Over time, this process creates something called an oak marble gall. It looks like a little ball made out of wood, usually about the size of a marble or golf ball. It's really interesting to look at and study, but it doesn't hurt the tree - it's just kind of like a little bump that the tree has to deal with.