Knopper gall

A knopper gall is a little ball that grows on a tree, like an acorn tree! When a special kind of wasp called the knopper gall wasp lays an egg on a leaf bud or acorn of the tree, it releases a special substance that tricks the tree into growing a big, round ball around the egg.

The ball protects the egg so it can grow big and strong, kind of like a castle protects a king or queen. Once the egg hatches, the baby wasp eats its way out of the ball and flies away.

Even though knopper galls may look strange and a little bit scary at first, they actually help the tree by helping to control the population of other pests that can harm it. So next time you see a knopper gall on an acorn tree, you can remember that it's actually a helpful little castle protecting a baby wasp!