Question
Dear Jim,
I live in northern California and recently our oak trees have been "buzzing". I can't see any insects but it sounds like a bee hive when you approach these trees. Also, once standing under them, it sounds like rain, and little pin-head-sized balls/seeds/eggs fall to the ground. Once on the ground these balls/seeds/eggs "jump" like Mexican jumping beans. I was wondering what are these balls/seeds/eggs and are they harmful to the trees?
Thank you for your time,
Bridget

Answer
Sounds like minute wasps called Jumping gall wasps. Here is a web link to information about these unusual insects. Like most gall insects they eggs on the leaf and the cells of the leaf expend over the egg forming a gal. They do not really effect the health of the tree.

The galls are actually malformations of plant growth. The tiny gall-forming wasp lays an egg in an oak leaf at a precise moment in the tree抯 growth cycle, causing normal plant cells to multiply at an unusually high rate. As a result, the tiny egg becomes encased in the gall composed of oak leaf tissue.

When the egg hatches, the gall provides both food and a living chamber for the larvae. In summer, the oak gall drops to the ground with the tiny wasp larvae inside. The insect moves in jerks, causing the entire gall to jump around on the ground. It抯 believed that the larvae hop around in an attempt to find a crack in the soil to hide up in. At maturity it transforms into a pupae, and later into an adult which chews its way out of the gall. The wasps themselves are dark colored, so tiny that you抣l probably never see them, and harmless to people.

Jumping oak galls almost never cause tree death. Natural enemies drastically reduce the population of this pest after a year or two, so control measures are unnecessary.

Raking and burning fallen leaves may help reduce infestation the following year


Here is a web link to more information on this insect. http://waynesword.palomar.edu/pldec97.htm