Notes from Papaw: Jumping What?

Here in the central Valley of California, we have many strange and unusual things. Every year at about this time, for only a few weeks, we see a fascinating event that I want to share with you, jumping galls. Galls are strange formations that form on the leaves of trees when an insect damages the leaf tissue. Think of it as a “forest pearl”. Pearls form when something like a grain of sand or other debris irritates an oyster and it forms a hard shell around the object. In the same way, when the insect lays an egg in the leaf, the tree starts to grow a protective area around it. They can come in many shapes, sizes, and colors. Some can be as big as a baseball; others look like tiny little seeds. Here is a picture of the many kinds we can see.

My favorite one is very small. The gall is about the size of the letter “o”. The wasp is about ½ the size of a mosquito. It contains the wasp larva of the jumping oak gall wasp. They look like a little white worm. When it’s ready, it starts to wiggle, and the gall falls to the ground. Then the larva starts to make it bounce! It can jump over a centimeter high, and twice as long. Sometimes, if there are enough of them, it can sound almost like it is raining! Scientists believe that they are trying to get under the leaf litter to get out of the summer heat and so that birds or ants don’t eat them. As fall begins, they form a pupa and rest through the winter. They stay there until early spring, and then they break out and fly away. Here are a couple videos of them jumping.