The galls can grow to more than 2 inches in diameter. Horned oak galls can be found on pin, scrub, black, blackjack, and water oaks while gouty oak galls occur on scarlet, red, pin or black oak. These galls have a long and complex development that takes two or more years to develop. The first stage is a blister-like leaf gall that occurs along larger leaf veins. The second stage is a knotty twig gall that is started in mid-summer and becomes fully mature in 1 to 2 years.
Adults emerge in the spring.
One female wasp can emerge from each horn. Generally, insecticidal control is not satisfactory because the wasps are physically protected within the galls. Correctly timing applications to provide effective preventive control is difficult. Where practical, pruning of infested twigs may help to reduce the problem on lightly-infested trees. However, pruning is impractical if large trees are heavily infested.