Pests of the home & landscape

June 28, 2000
Oak Defoliaton

A number of leaf-eating caterpillars can occur in oak trees. The following description may help in identifying these caterpillars:

  • Variable Oak leaf Caterpillar-This insect is common in the eastern U.S. where it feeds on all species of oaks, although it seems to prefer those in the white oak group. As the name implies, color is variable, but it is generally yellowish green with a narrow white stripe down the center of the back, bordered dorsally with reddish-brown, and one or two yellowish stripes. Young larvae skeletonize the leaf, while older larvae will eat the entire leaf except for the leaf stalks and main veins. There are two generations per year. One occurs in mid-May to late June, and the other will occur in early August to the middle of September. Pupation occurs in the soil. The adult moth is ashy gray with three dark wavy lines across the forewings.
  • Spiny Oakworm-This insect will feed on oaks of all types and may occur in a variety of sites. The larva is tawny brown, often tinged with rose or pink. The body is covered with tiny white specks that gives the cuticle a granulated look, and there two long, curved spines on the second segment behind the head-remaining segments bear backward-pointing spines. Moth wings are yellowish to rusty brown, sometimes tinged with pink, and heavily speckled in both sexes. The larvae probably feed early in their development as skeletonizers. As the larvae, mature they will consume all but the leaf stalk and the main veins. There appears to be only one generation per year in our area and it will appear in July and August. Pupation occurs in the soil. The orange striped oakworm may appear at the same time as the spiny oakworm.
  • Yellownecked Caterpillar-This insect appears to be more of a problem to ornamental shade threes, either in home lawns or on city streets, than to forest stands. It occurs on birches, oak, maple, elm, honeylocust, etc. The larvae is yellowish and black striped and moderately covered with fine, white hairs. The head is very black; the segment behind the head is bright orange-yellow - hence the name, yellownecked caterpillar. When disturbed, the larvae lift the head and tail in a distinctive "U" shape. Young larvae feed as skeletonizers, while older larvae will devour the entire leaf with the exception of the leaf stalk. Moths are active during June and July, and the larvae can be found feeding in trees during late July and August. Most sources indicate one generation per year.
  • A few oak leaf feeding caterpillars are present every year and some frass may be noticed on patios, driveways or around pool edges, but populations do not reach levels that produce noticeable leaf losses. In other years, the populations are very high and during these years the trees will have noticeable leaf loss. The question most often asked about this condition is "Will it kill the tree?" Hardwood trees such as oaks are hardy trees and one or two years of leaf loss will not hurt the tree. Trees in the northeast part of the country often suffer defoliation from gypsy moth larvae, and they seem to survive quite well.
  • A number of predators (beetles, birds, lizards, spiders, etc.) and parasites (mainly wasps) will help keep these caterpillars in check. In fact, the ground beetle to the left is one of the caterpillar hunter group and it has been reported on trees that are known to have caterpillar infestations. In those years when natural controls do not work and large populations develop, people often want to treat with insecticides. Chemical controls, however, are generally not practical due to the equipment needed to spray large trees, plus it is very difficult to control drift when spraying tall trees. It may be hard to do, but the best policy is to let nature take its course and natural controls will bring the caterpillars under control and the trees will put out new growth.

James H. Jarratt
Extension Entomologist

A black line that separates the body text from footer information