Walnut Caterpillar
Datana integerrima (Grote and Robinson) (Notodontidae)

L.L. Hyche, Associate Professor
Department of Entomology & Plant Pathology
Auburn University

The walnut caterpillar (Photo 1) occurs throughout much of the U.S. east of the Great Plains. It is reported to feed on foliage by a variety of hardwoods, including oak, birch, ash, apple, and honeylocust, but its primary hosts are trees of the walnut family (Juglandaceae). In Alabama, walnut, pecan, hickories, and butternut are the preferred hosts.

Life Cycle, Description, and Habits

The insect overwinters as a pupa in the soil. Pupae are shiny reddish brown or dark brown and 20-25 mm long. Adults emerge from overwintering pupae in May. The moth (Photo 2) is typical of the Datana adults, front wings are reddish tan with four narrow darker lines across each wing, hind wings are lighter in color. Wingspan is 38-45 mm.

Females lay eggs in masses on the undersurfaces of leaves (Photo 3). Masses usually contain several hundred eggs deposited in a single layer. Eggs hatched in 7-10 days; in Alabama, hatch usually occurs in late May or early June. Newly hatch caterpillars are light in color, but as they grow color changes to brick red, to purplish, then to black (Photo 4) with four white longitudinal lines along each side. The full-grown caterpillar (Photo 1) is black, 45-55 mm long, and densely clothed with long white to grayish hairs. The white longitudinal lines conspicuous on developing larvae may be absent or indistinct on the fully grown caterpillar.

Caterpillars feed in colonies. First-stage larvae are skeletonizers, and feed on the undersurface of the leaf (Photo 3 and Photo 5); later-stage larvae consume whole leaves. Typically, the colony congregates on one branch, strips it of foliage, then moves to another. If disturbed, caterpillars cease feeding and assume what appears to be a defensive posture with head and tail ends raised (Photo 6 ). Periodically, caterpillars leave the foliage and collect in a mass on the bark of the trunk or a large limb (Photo 7 ) and molt. Subsequently, they return to foliage to feed, leaving a hairy mass of shed skins on the bark (Photo 7 ). The larval stage lasts 25-35 days. When fully grown, caterpillars enter the soil and pupate. Two broods of the walnut caterpillar occur each season in Alabama. Moths emerge from first-generation pupae in July and lay eggs to start the second; second-brood larvae are usually found during late July, August, September.

Occurrence, Damage, Importance

The walnut caterpillar is common in Alabama. As noted, infestations occur mainly on walnut, pecan, hickories, and butternut. Trees growing separately and apart in the open, e.g., orchard, shade, and ornamental trees, are the ones most commonly infested. By habit, the caterpillars feed gregariously and defoliate one branch then move to another. On large, full-crowned trees, crown may be only partially defoliated, thus damage is primarily aesthetic. However, walnut caterpillar broods are often large, and brood from eggs of a single female can cause complete defoliation of small and medium-sized trees. Healthy trees generally survive a single defoliation and recover with minimal loss of growth. Consecutive complete defoliations, however, can cause serious dieback of twigs or tree mortality.

For additional information lhyche@acesag.auburn.edu

[ Notodontidae ]  [ Lepidoptera ]   [ Foliage Feeders ]   [ Crown Insects ]   [ Alabama Trees ]

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