Heavily damaged leaflets turn entirely brown and drop, often resulting in premature tree defoliation. Piercing-sucking mouthparts arise on the front of the head. Infested nuts are usually held together at their base by silken webbing containing conspicuous, dark, grass eliminated by the larvae. One larvae can destroy all the nuts in a cluster. Second generation larvae also attack the nuts but damage is usually less severe.
Later generations feed on foliage or in green shucks, causing little damage.
Stem infesting forms frequently cause weakened shoots which finally die. Leaf infesting forms are not normally a serious pest of mature trees but may contribute to premature defoliation of individual trees when infestations are heavy. Heavy spring infestations can keep trees partially defoliated for several weeks. Later generations feed on the undersides of leaflets and cause little damage. They are commonly found in the spring and again in mid-summer.