The round, ball-like growths on the valley oak trees are called galls. These structures form when tiny wasps lay their eggs in the tree’s bark. In response, the oak produces a protective tissue around the eggs, creating the gall. This serves a dual purpose: it helps the tree prevent infection and also shields the wasp eggs from predators. Once the eggs hatch, the larvae feed on the inner gall tissue. Interestingly, this natural process does not appear to harm the tree.
