Walnut Caterpillar
Datana integerrima
A native moth whose caterpillars feed in large groups on walnut, pecan, hickory, and butternut, capable of stripping whole limbs or small trees of their leaves. The colonies have a habit of crawling down to the trunk in a mass to molt, leaving conspicuous clusters on the bark.
🔎 How to spot it
The adult is a tan and cinnamon-brown moth with a wingspan of nearly two inches and wavy dark lines across the forewings. Fully grown caterpillars are black with long whitish hairs and can be two inches long, and they arch their heads and tails in a defensive posture when disturbed. The egg masses are laid in clusters on the undersides of leaves.
🥀 Damage it causes
The caterpillars feed gregariously and, unlike tent caterpillars, do not build webs, but they can eat all the leaves on a small tree or on individual large limbs. A tree defoliated two years in a row may be stunted, and the loss of leaves can weaken trees and leave them more open to wood borers. The damage is most striking when a large colony works through a limb.
🛡️ Prevent it
Watch for the egg masses and young colonies and act while the caterpillars are small and still clustered. Because the larvae gather on the trunk to molt, the clusters can be dislodged with a stick and trampled, or pruned out on small trees. Removing colonies early prevents the heavy late-season defoliation.
🧯 If it is already here
Control is needed only when colonies are numerous, and it works best on small larvae, using Sevin or a labeled pyrethroid, while the organic options Bacillus thuringiensis and spinosad are also effective on young caterpillars. Spraying or physically removing the trunk clusters during a molt is a simple way to wipe out a colony. Large trees usually recover from feeding and may not need treatment.
💡 Good to know
The walnut caterpillar has two generations a year in the South, the first in early summer and the second in late summer, and overwinters as pupae in the soil. It feeds only on walnut, pecan, hickory, and butternut. The mass molting on the trunk and the absence of a web separate it from tent caterpillars and webworms.
🌱 Plants it attacks
13 plants in the library can be attacked by this pest
For educational and informational purposes only. Pest control advice is general guidance drawn from university cooperative extension sources; always identify a pest positively and read and follow the label on any product before use, especially around food crops, children, and pets.