Common Name:  Oak Gall  (also known as oak apples)

Causation:  Gall Wasps (Family Cynopidae)

Oak trees support about 800 different species of  gall making insects. Almost all of these species are members of the Cynipids, a family of gall-making wasps of the order Hymenoptera, which includes bees and ants

Potpourri:    Gall formation is caused by the larval insect secreting a fluid as it feeds on the plant that induces the plant to form a swelling tumor-like growth. Insects evolved to use the growth as a means to protect the developing larvae.

The process starts when the eggs which are laid on the oak twigs hatch and the larvae tunnel into the plant, causing the formation of a gall. The gall is initially green and then red and finally brown, growing to about 2 inches in diameter.

Each gall can house a number of larvae. The oak apple galls are frequently  invaded by other insects that prey on the cynipid wasp larvae.

Other gall forming insects include flies  (682  species known as gall gnats) that form galls on wheat and legumes, especially clover;  beetles that form galls on maples, poplar and virginia creeper; and moths of the genus Gnorimoschema  that form galls on goldenrods and asters.