What Is the Difference Between White Oak Bark and Oak Gall?

White Oak Bark

• The bark of the white oak (Quercus alba) is light gray in color and engraved with shallow furrows that are segmented into small rectangular squares and scales. The bark on the trunk or branches is accentuated by light green or blue-green leaves in the summer that take on a brown, orange or red hue in the fall. When white oak galls begin to form on the tree, they are easy to distinguish from the otherwise smooth bark.

Gall Identification

• Galls are formed by a number of insects, primarily flies, wasps and midges, and may develop on the branches, trunk or leaves of the tree. The difference between white oak bark and oak gall is drastic and easy for even a novice gardener to spot. A typical gall on a white oak has the appearance of several white, toasted marshmallows that are stuck together at a common spot on the bark. A jumping oak gall looks like a small, black seed. It falls off the tree, and the insect inside causes the gall to jump up and down.

Differences

• The shape, color and size of a white oak gall can vary drastically, but the large protrusions -- or bumps -- that show up on the leaf or bark will leave no doubt that it is not a natural part of the white oak. Paradoxically, the gall does become a living part of the tree as chromosomes within the cells of the tree replicate to form the gall. Removing a gall from the white oak becomes the same act as cutting off a branch or twig.

White Oak Galls

• The wool sower gall grows only on white oaks and is produced by the enzymes secreted by the larvae of the gall wasp, Callirhytis seminator. Appearing only in the spring, this white oak gall contains seeds and houses the wasp grubs until they mature. Another gall prevalent on the white oak grows specifically on the stems of the tree and is caused by a wasp of the Cynipid species, Callirhytis clavula