European Hornet Plants Attacked Lilac, boxwood, Viburnum, fruit trees, birch, willow, poplar, Ligustrum, Rhododendron, dogwood and other trees and shrubs. The most conspicuous damage is due to the premature browning of leaves on individual branches in August and September.
European hornets girdle smaller twigs and gnaw holes in the bark of larger branches.
The hornets chew off the bark in order to feed on the sap that flows from the wound. Some of the bark fibers may be used for nest construction. Often the portion of the twig above the girdled area dies. Usually before the twig dies it tries to regrow, causing an abnormal swelling above the wound. Although injury becomes most noticeable in the fall, European hornets may have been removing bark and collecting sap for a month or more.