Orange-Striped Oakworm
Anisota senatoria (J.E. Smith)

Submitted by Dr. James Robinson, Professor and Extension Entomologist,
Extension Center at Overton, Texas

IDENTIFICATION: Larvae of the orange-striped oakworm are charcoal black with orange-yellow stripes. The head is jet black and the segment just behind the head is bright orange-yellow. The second thoracic segment (right behind the head) have long, black spines. These spines or “horns” are used to scare predators away and do not have the capacity to sting. The abdominal spines are relatively small. The larvae, when mature, are about 1-½ " long. They may be found in East Texas forests from August to October. There is one generation per season.
The larvae are gregarious when they are small. When they reach maturity, they become solitary. These older larvae are often seen crawling around on lawns or the sides of houses, or feeding singly on foliage. After maturity, the larvae burrows three to four inches into the soil to pupate and overwinter.

This insect may be found in large numbers on the various species of oak. Infestations are usually localized, but defoliation may be severe.
The moths emerge from June to August and lay their eggs in clusters on the undersides of leaves. The adult moth is 1-1/4” long with wings closed. They are reddish brown, translucent with a submarginal dark stripe and a white spot on each forewing. Over a period of a month the female will deposit up to 500 eggs in a single cluster on the underside of an oak leaf, usually on the lower branches.

DAMAGE: Young caterpillars feed by skeletonizing the leaf surface. Older caterpillars are defoliators and may consume all but the leaf midrib. Defoliation usually occurs one branch at a time when populations are small. Occasionally the insect reaches outbreak densities.
Tree health is rarely affected by oakworm defoliation. Because the caterpillars feed in late summer, most photosynthesis is complete and foliage loss has little impact on the tree. Native predators and parasites usually help keep the insect from being a problem every year.

CONTROL: Manually destroy aggregations of young larvae when detected on small trees. An application of Bacillus thuringiensis (Thuricide) or horticultural oil will control young larvae. Damage is seldom widespread and chemical control is rarely needed.

QUOTE: Joe Pase, an entomologist with the Texas Forest Service at Lufkin has the quote of the day, “The larvae are really doing homeowners a favor by converting leaves to pelletized fertilizer for free.”