31 May 2025

Oak apple galls are shiny and brown so I was surprised to find this fuzzy one on a white oak stem. This not a fuzzy version of the oak apple gall. This is a woolly oak gall made by a completely different species of gall wasp (family Cynipidae).

Woolly oak galls are made by Callirhytis seminator, “the wool sower,” which places its galls only on white oaks and only in the spring.

The wasps are tiny, 1/8″ long, and have many predators including larger parasitic wasps. They do not sting humans.

Gall wasps have a two-generation alternating cycle: One generation produces stem galls, and the wasps that emerge from that stem gall mature and lay their own eggs in leaf galls. The wasps that emerge from the leaf gall mature and produce stem galls. Scientists do not know what the alternate wool sower wasp gall looks like.

— WIkipedia: Callirhytis seminator account

The gall I found and the one pictured below were made by the stem-gall generation.

If you open the gall it has seed-like structures inside that are actually plant material, not the insect. The larvae are white and fat, have no legs.

As the gall matures it turns pink.

If I go back to Raccoon Wildflower Reserve in a few weeks and find the same tree the gall won’t look the same. Will it even be there?