How-To Features Tree Registry Register your trees for customized advice. It is also called the oak slug sawfly because of the fact that the larvae are covered with a coat of slime that helps them adhere to foliage. Larvae feed on the lower surface of the leaves, leaving only a fine network of veins which gives the leaf a transparent appearance.
Defoliation starts in the upper crown in early summer and progresses downward.
By late summer, heavily infested trees may be completely skeletonized. Larvae overwinter in cocoons in the litter layer, and adults emerge in the spring. Females lay eggs in rows in the lower leaf surface along the sides of the midribs and larger veins. Eggs hatch within 1-2 weeks, depending on the temperature. Several larvae feed on the same leaf.