Walnut Caterpillar

Walnut Caterpillar (Datana integerrima)
The walnut caterpillar is found on hardwood trees from Ontario through most of the eastern United States, west to Minnesota, and south to northern Mexico.

The adult moth is dark tan with four rust-colored lines and has a wingspan of about 4.2 to 4.9 cm. Females can lay eggs in clusters of anywhere from 120 to 880 eggs on the underside of leaves. Newly emerged larvae are light green but they turn reddish brown as they age and are covered by short white hairs. Full grown larvae are about 2 inches long, black, and covered with long white hairs.

Walnut caterpillars will only feed on trees in the family Juglandlaceae, but they will attack trees of all sizes. Their preferred hosts are butternut, walnut, hickory, and pecan. Younger larvae skeletonize leaves while older larvae consume entire leaves. Groups of walnut caterpillars can heavily defoliate host trees, entire limbs on larger trees and even all the leaves on smaller trees. This insect emerges in the spring, but feeding is at its peak in August.

Bacillus thuringiensis is a well know effective treatment. Tanglefoot sticky trap glue could also be used to ensnare larvae as they migrate to main branches or the tree trunk to molt. Look for early signs of feeding on the ends of the branches.

Photo courtesy of Forrest L. Oliveria, USDA Forest Service, www.forestryimages.org

For control products and more information please see our Caterpillars and Moths Control page.