Walnut caterpillars, Datana integerrima Grote and Robinson (Lepidoptera: Notodontidae), early stage (instar) caterpillars. Photo by H. A. Turney.
Common Name: Walnut caterpillar
Scientific Name: Datana integerrima Grote and Robinson
Order: Lepidoptera
Description: The adult moth has a 2-inch wing span, is brown and tan with a dark region on the body behind the head and has wavy, dark lines across the front wings. Caterpillars are reddish brown to black with white markings and long white hairs. Large larvae are conspicuously fuzzy and may grow up to 2 inches (50 mm) long. Larvae characteristically arch their heads and tails in a defensive posture when disturbed.
Another common species of Notodontidae is the yellownecked caterpillar, Datana ministra (Drury). Caterpillars grow to 2 inches long, have yellow stripes along their orange to black body, and have a yellow “neck” just behind their black head capsule. They feed in groups (aggregates) on leaves of cherry, crabapple, elm, maple, peaches, oak and walnut and display a defensive posture, raising the head and tip of the abdomen, when disturbed. The unicorn caterpillar, Schizura unicornis (J. E. Smith) occurs on apple, cherry, rose and other woody ornamental plants. Caterpillars grow to 1-1/3 inches long and are variegated brown. They have a prominent projection on the first abdominal segment and feed together.
Yellownecked caterpillar, Datana ministra (Drury) (Lepidoptera: Notodontidae), on oak. Photo by Drees.
Life Cycle: Adults emerge from pupae which overwinter in the soil at the base of a host tree. The female moth deposits about 300 eggs on the underside of a leaf. Caterpillars (larvae) hatch from the eggs in about 9 days, living together in a group. The caterpillars often move in a group to the tree trunk to molt from one stage (instar) to the next, leaving a patch of fur-like hair and cast skins. When they finish feeding, they drop to the ground and pupate in the soil. They do not spin a cocoon but form a naked pupal case. Populations of this species are variable from year to year and there may be several years between outbreak levels. In Texas, at least two generations of the insect develop each year. The second generation is usually larger in number and causes more damage.
Habitat, Food Source(s), Damage: Caterpillars have chewing mouthparts. Adults have siphoning mouths. Host plants include hickory, walnut, oak, willow, honey locust and certain woody shrubs. Young larvae feed only on soft tissue, leaving a skeletonized leaf behind, while older larvae feed on the entire leaf, including the petiole. The last few stages, or instars, do the majority of the feeding damage. Damage may be localized to just a branch to two because they feed together. Isolated trees are more subject to attack than forest or orchard trees. They can rapidly defoliate ornamental and orchard trees if not controlled. In some past years, almost all of the native pecan trees in certain areas of the state were defoliated by walnut caterpillars.
Unicorn caterpillar, Schizura unicornis (J. E. Smith) (Notodontidae), on swamp rose. Photo by Drees.
Pest Status: A serious but occasional threat to pecan, hickory, walnut and other trees and shrubs. It also feeds on oak, willow, honey locust and certain woody shrubs.
For additional information, contact your local Texas A&M AgriLife Extension Service agent or search for other state Extension offices.
Literature: Jackman 1981.