Wool sower galls
Callirhytis seminator, the wool sower, is a species of gall wasp in the family Cynipidae. The adult wasps are about 1/8" in length and dark brown in color. The larvae are white and fat and have no legs. The wasps only lay eggs on white oak trees and only in the spring. They lay the egg in a gall, a round, white structure resembling a cotton ball. It starts out white and later changes color.