FAQ - Answer
You are witnessing the “jumping oak galls” that are the nursery “cells” for small predacious wasps. The female wasps lays her eggs on the underside of the leaves, the eggs and the female produce chemicals that cause the tree to grow the “galls” around the egg. As they incubate and mature the larvae begin to move causing the jumping motion that you are witnessing. We once saw a similar thing sold in stores as “Mexican jumping beans” as a worm inside the beans caused them to “jump”. The wasps are predacious on aphids, whiteflies and other small insects that are commonly found on oaks. They cause no harm to the trees are a simply a part of the “living system” found living on oaks.