Galls may occur on leaves, bark, flowers, buds, acorns, or roots. Leaf and twig galls are most noticeable. The inhabitant gains its nutrients from the inner gall tissue.
Galls also provide some protection from natural enemies and insecticide sprays.
Important details of the life cycles of many gall-makers are not known so specific recommendations to time control measures most effectively are not available. Gall makers must attack at a particular time in the year to be successful. Otherwise, they may not be able to stimulate the plant to produce the tissue which forms the gall. Once the symptom or gall appears, the causative arthropod is protected within the structure. This means that remedial actions, other than pruning in some cases, are not effective.