Caterpillars are normally present from late July or early August until mid-October. There is only one generation per year. The walnut caterpillar is closely related to the yellownecked caterpillar. Its favorite food trees are pecan, hickory, walnut, and butternut. Walnut caterpillars, like the yellownecked, feed in colonies, moving from branch to branch.
Young larvae are yellowish cream with black heads and faint greenish stripes along the body.
The head is cherry red, and the body is yellow-green with dark green longitudinal stripes. There are two distinctive long, black spines behind the head and rows of shorter black spines along the body. Oaks, as the name implies, are the primary food trees. Larvae feed in a group until about half grown, then tend to separate to feed. Like the preceding caterpillars, their color changes as larvae develop.