Squirrels go after more than acorns on oaks, sometimes to the point where people become alarmed that the trees are diseased.
Nearly every year we get calls about the native oaks dying from the tips back, and the concerned citizens who call are worried the trees have a disease that will result in death of the trees.
It is true, the tips of the oak branches are dying back, but the cause is not lethal. Instead, the damage is due to squirrels trying to get at young oak galls that grow on the leaves and branches (view galls below). The galls are caused by a small wasp (pictured below), and either the immature wasps or the developing galls themselves are tasty, as the squirrels will strip the bark from the branch ends in an attempt to remove the galls. Loss of the bark results in the dieback, which is minor cosmetic damage.
For more information, see Oak Galls: Forest Health Fact Sheet (ODA).
Oak galls on a young oak tree.
A mature spotted oak gall on a leaf.
A young wasp trying to find her way out of the gall in which she matured.