Wasps in the family Cynipidae form galls on oak trees. The wasp larva establishes a feeding site on a leaf or bud. Through substances injected into the plant, the gall wasp hijacks the plant normal plant development and induces the plant to instead grow a protected feeding site for the wasp. The galls can be quite hard and loaded with tannins that afford some protection against predators.One type of oak gall, Neuroterus saltatorius, as the name “saltatorious” implies, can jump. When the larvae fully develop, the hard, round gall detaches from the leaf and falls to the ground. Movements of the larva inside the gall will cause it to “jump” into the air. Jumping helps the gall to roll into a crack where it is better protected from potential enemies and the elements.
Neuroterus saltatorius is common in California and is known as the “California jumping gall”. In some years, (such as 2012) large populations develop in the Midwest including Ohio, Kentucky and Indiana. “singtolearn” has the YouTube video: