Why are oak trees suddenly covered in fuzzy balls?

A graphic of wooly oak galls.
A graphic of wooly oak galls. Special to the Sun Herald

The reason this week’s column is so short is simple.

The subject is harmless and there is nothing you can do about it even if you wanted to try. Every few years we have a bumper crop of wooly oak leaf galls. A gall is is an abnormal growth on plant tissue.

Judging by the calls and letters I’ve received, this is one of those years. I suppose it can be a tad unnerving if you happen to be under an oak tree when these galls start to shower down.

As their name implies, these galls form on oak leaves and look like tan cotton balls. They are formed by a tiny (less than 1 mm) wasp in the family Cynipidae that has the scientific name of Andricus fullawayi. Because they are harmless, very little research has been done regarding their life cycle.

This time of year, when oak leaves start to get brown, the galls detach themselves and fall to the ground where they remain over the winter while the wasp passes through its pupal stage. In the spring when the oaks are putting out new growth, the wasps chew their way out of the galls.

They mate and the females lay their eggs on the newly formed leaves. Upon hatching, the larvae bore into the leaf and begin to form a protective gall along the mid vein of the leaf. Occasionally, if more than one larva tries to form a gall on the same mid vein, they will align themselves along lateral veins. The galls themselves range in size from three to 25 millimeters in diameter.

If you see these little fuzz balls spread out on the ground under your oak tree, don’t panic. Just stop and take the time to admire another one of Mama Nature’s little marvels.

Tim Lockley, a specialist in entomology, is retired from a 30-year career as a research scientist for the U.S. Department of Agriculture. For answers to individual questions, please send a stamped, self-addressed envelope to Tim Lockley, c/o Sun Herald, P.O. Box 4567, Biloxi MS 39535.