6 - Oak Galls

The ball-like structures that grow on the valley oak trees here are galls. Galls are formed when wasps lay their eggs in the bark of the oak tree. The tree forms tissue around the eggs, protecting itself from infection and at the same time protecting the wasp eggs from predators. After the eggs hatch, the larvae of the wasp eat some of the gall tissue. The formation of galls does not seem to harm the tree itself.