Fall Defoliators

Pinkstriped oakworm

Two-inch long, mature, pinkstriped oakworms, Anisota virginiensis, were observed July 28th lightly defoliating burr oaks near Brainerd on the southeast side of North Long Lake. This pest also feeds on white birch and other hardwoods.

Caterpillars have brownish gray heads, and their bodies are marked with longitudinal dull pink and dark gray bands. Their bodies are also covered with numerous white granulations, and each segment has several short black spines. Two of these spines, just behind the head, are much longer and look like a pair of horns.

It pupates and overwinters in the ground duff, then emerges in the next June as brown moths, sometimes with a purplish cast to the outer portion of their wings. There is a white spot on each of the front wings. Natural enemies control this pest, but none were observed this July, so the caterpillars are predicted to increase in l998 and l999.

Greenstriped maple worms

About 140 acres of scattered red maples in Crow Wing county on the southeast side of North Long Lake near Brainerd were heavily defoliated by the greenstriped mapleworm, Dryocampa rubicunda. By July 29th these caterpillars had grown to one and one-half inches long and one quarter inch wide, and they were dropping to the ground where they form overwintering pupae in the duff.

White moths with a thin, light purple line extending across their front wings will emerge in June, mate. Females will lay about l50 eggs in clusters of forty or more on the underside of maple leaves. About ten days later the larvae hatch, and at maturity each caterpillar will have a pale green body with dark green stripes and a head that may be dark red to near black and bearing two recurved black horns. Short black spines are arranged in rows along its body, and a pink-red band is located on each lower side of its posterior end. Parasitized and diseased caterpillars were only rarely observed in July, and since this was the first year of an outbreak, defoliation by this pest in predicted to be heavy in l998 and perhaps also heavy in l999, but natural enemies will eventually greatly reduce caterpillar numbers.

Orangestriped oakworm

Late July, August, and early September are the months when the orangestriped oakworm, Anisota senatoria, and other fall defoliator insects eat leaves of various hardwoods. When natural enemies are scarce, populations of these pests build up and cause heavy localized defoliation for three or perhaps more years. In late July large numbers of young orangestriped oakworms were observed in Morrison County southeast of Little Falls feeding on bur oak. Their empty egg cases were still nearby on the leaf undersides, and about five to ten percent of the eggs had been parasitized by natural enemies.

Moths that emerge in June from overwintering pupal cases in the soil each deposit as many as 500 eggs in a single cluster on a leaf, usually on the lower branches. Mature larvae (caterpillars) can reach two and one quarter inches long before they drop to the ground and pupate in the soil. Their bodies have black and yellow stripes and two "horns" near their black heads.


Walkingsticks are defoliating basswood trees in Birch Lake State Forest in northern Stearns County. These insects appear in odd-numbered years in Minnesota, and they caused heavy defoliation in this area in l995. Since they remove leaves in late July and August they cause minor stress on trees.