Walnut Caterpillars

Walnut caterpillars feed only on the foliage of trees in the Juglandaceae family including walnuts, pecans and hickory trees. In large numbers these caterpillars can defoliate large trees and severely affect tree vigor. The larvae tend to feed in groups or clusters, consuming all the leaves on a single branch before moving to another branch. There can be one to two lifecycles per year depending on the weather. The second lifecyle caterpillars overwinters as pupa to hatch in the spring and lay eggs as adults.

The round eggs are white and loosely laid in groups on the underside of the host plant leaves. Young larvae are yellowish-green and ¼-inch long. As they mature the larvae turns a dark red and eventually almost black with white hairs. At the final larval stages, they can be two-inches long. A larval shed can be seen on the trunks which resembles a hairball. The caterpillars feed for approximately one month before reaching maturity. When disturbed the caterpillars will arch their head and end of the abdomen to ward off predators.

Adult walnut caterpillars’ moths have approximately a 1 ¾” wingspan and the wings light brown with four narrow brown bands on each front wing. The primary effective means of dealing with infestations of walnut caterpillars are to hand-pick caterpillars and place in a container of soapy water, use a forceful water spray to quickly dislodge caterpillars, or apply insecticides with one of the following active ingredients: acephate, spinosad, malathion, cyfluthrin, permethrin, or bifenthrin.

Have questions? Contact our office where our Horticulture Extension Agent will assist you with questions.

Phone: (316) 321-9660

Email: callae@ksu.edu