Walnut caterpillar are the larval stage of this pest that feeds exclusively on foliage of woody shrubs and deciduous trees of the walnut family, Juglandaceae. Hosts include black and English walnuts, butternut, pecan, and various species of hickory. The walnut caterpillar is a native to North America and is found from the eastern US spreading westward to Kansas, Minnesota, Oklahoma, and Texas.
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.
The larvae can defoliate a mature tree and cause economic damage to this crop. In warm climates, like Texas, there can be 2 – 3 generations of this caterpillar each year. To prevent extensive damage, Texas A&M recommends careful observation for the following signs of infestation:
- Clustered areas where leaves are skeletonized.
- Clusters of reddish-brown larvae.
- Frass on the ground surrounding the tree or shrub.
- Molted skins in clusters on the plant trunk or scaffold limbs.
- Tangle-Trap or Stiky Stuff are safe adhesives that can be applied to trunks and branches to trap larvae as they migrate to main branches or the tree trunk to molt. Apply when there are early signs of larval feeding on the ends of the branches.
Control products are shown below. For more information please see our Caterpillars and Moths Control page.Photo courtesy of Forrest L. Oliveria, USDA Forest Service, www.forestryimages.org