Woollybear Caterpillar Complex in Soybean

The term “woollybear” refers to several species of hairy caterpillars. Three common species found throughout much of the United States and southern Canada are the saltmarsh caterpillar (Estigmene acrea), the yellow woollybear (Spilosoma virginica), and the banded woollybear (Pyrrharctia isabella).

Crop Damage

Saltmarsh caterpillars: In soybean, early instars feed on the underside of leaves between veins, resulting in a skeletonized appearance. As larvae mature, they consume larger portions of leaf tissue, creating holes and potentially causing severe defoliation.

Yellow woollybears: Larvae typically feed in the upper third of the soybean canopy. Early instars feed in groups, scraping leaf surfaces and producing a “windowpane” appearance. As they mature, larvae disperse and consume entire leaves.

Banded woollybears: Caterpillars are rarely observed feeding on soybean, preferring instead to feed on weeds like dandelion, goldenrod, and certain grasses.

Pest Description

Saltmarsh caterpillars: Full-grown larvae reach approximately 2¼ inches in length and range from yellow to dark brown. They are covered with long hairs of varying length and color (cream to dark brown), with indistinct longitudinal striping and dark spots. Adults (saltmarsh moths) have white forewings with irregular black spots and 4 to 6 black spots along the margins. Female hindwings are white; male hindwings are yellow.

Yellow woollybears: Full-grown larvae are about 2 inches long, pale yellow to brown, and covered with dense, uniform white to cream-colored hairs. Adults (Virginia tiger moths) are white with two small dark spots on each forewing.

Banded woollybears: Larvae are approximately 1 inch long, with stiff hairs and a distinctive orange-brown band across the middle segments, flanked by black bands at both ends. Adults (Isabella tiger moths) are light brown to orange with variable banding and spotting on the forewings and pink hindwings.

Scouting

Established sampling protocols and economic thresholds are limited. However, saltmarsh caterpillars and yellow woollybears can cause significant defoliation, even late in the growing season. Randomly sample plants across the field and estimate whole-plant defoliation. The Crop Protection Network’s Insect Defoliation Tool can assist in accurate assessment.

Management

Saltmarsh caterpillars and yellow woollybears are defoliators. When multiple defoliators are present, consider their combined impact when making management decisions. Standard soybean treatment thresholds are 30% defoliation during vegetative stages and 20% during reproductive stages. If insecticide applications are necessary, ensure compliance with pre-harvest intervals, particularly for late-season treatments. For current management recommendations, consult your local extension specialist.

Developed and reviewed by Carol Pilcher, Iowa State University and Robert Wright, University of Nebraska-Lincoln, with support from the United Soybean Board.