Most recently reviewed by: Molly Keck & Wizzie Brown (2021)
Common Name(s): Walnut caterpillar
The walnut caterpillar has a wide host range of woody plants and trees such as pecan, walnut, hickory (Ree and Jungman 2015). The larvae range in color from reddish brown as young larvae to black with grayish lines and hairs as mature larvae, and can reach lengths of up to two inches when fully grown. Damage caused by young larvae is typically localized to a few branches because the larvae feed in colonies. Later instar larvae can cause more damage as they spread throughout the canopy as they venture away from each other. Larvae damage the plant by feeding on leaves, eventually consuming the entire leaf surface and leaving only the main leaf vein and petiole.
Origin and Distribution
The walnut caterpillar is native to North America and is common throughout most of the eastern United States. The walnut caterpillar can be found as far west as Kansas, Minnesota, Oklahoma, and Texas. In Texas, the walnut caterpillar is found throughout areas east of the Pecos River (Knutson and Ree 2016).
Habitat & Hosts
The walnut caterpillar has a wide host range of both shrubs and trees. The primary host for walnut caterpillar include trees in the Juglandaceae family such as butternut, hickory, pecan, and walnut including black, English, Japanese and Persian (Ree and Jungman 2015).
The walnut caterpillar is in the insect order Lepidoptera, and has a complete life cycle passing through egg, larval, and pupal stages before becoming an adult. In mid to late spring, overwintering pupae emerge as adult moths. After mating, adult females lay eggs once in a mass of around 600 eggs. Egg masses are laid in a single layer on the underside of leaves. Larvae hatch from eggs in roughly 9 days and pass through five larval stages (instars) over the course of about three weeks (Ree and Jungman 2015). During the first four larval stages, larvae are a reddish-brown color and can be found feeding in clusters. When molting from the fourth instar to the fifth instar, the caterpillars move to the trunk or a main branch and molt together. Larvae in the 5th instar are black with grayish markings and long hairs. Fifth instar larvae venture out to feed on their own. In Texas, the walnut caterpillar can complete 2 to 3 generations per year depending on the number of frost-free days (Knutson and Ree 2016).
ManagementIf you live in the State of Texas, contact your local county agent or entomologist for management information. If you live outside of Texas, contact your local extension for management options.
In Texas, the walnut caterpillar rarely reaches levels that cause economic damage, but there have been occasional outbreaks that have caused economic loss (Knutson and Ree 2016). Typically parasitic insects, predatory insects, and arthropods like lady beetles and spiders keep populations from causing economic damage. Management of walnut caterpillars on small trees and in residential yards can be done by removing egg masses from leaves. Using insecticides to prevent economical damage on large trees and in orchards is more practical than physically removing egg masses. If you live in the state of Texas, contact your local County Agent or Entomologist for more management information. If you live outside of Texas, contact your local extension service for management options.
Walnut Caterpillar Factsheet https://citybugs.tamu.edu/files/2018/09/ENTO-041-Walnut-Caterpillar.pdf
Managing Insect and Mite Pests of Commercial Pecans in Texas. https://cdn-ext.agnet.tamu.edu/wp-content/uploads/2019/03/ENTO-048_-Managing-Insect-and-Mite-Pests-of-Commercial-Pecans-in-Texas.pdf
Knutson, A., and Ree, B. 2016. Managing Insect and Mite Pests of Commercial Pecans in Texas. Texas A&M AgriLife Ext. ENTO-048:1–28.
Ree, B., and Jungman, M. 2015. Walnut Caterpillar. Texas A&M AgriLife Ext. ENTO-041.