Cankerworms

Pest Description

• adult males: 1 1⁄8 inches long; dull gray brown
• adult females: 5/16 inch long; dull gray brown; wingless
• larvae: ~ 1 inch long; green to light brown to black; inchworms that crawl by arching their backs
• fall cankerworm larvae: three pairs of prolegs and three white stripes on either side of the abdomen
• spring cankerworm larvae: two pairs of prolegs and one larger white stripe down each side of the abdomen
• eggs: barrel shaped, shiny gray with a light brown ring around a dark brown spot; laid in clusters

Host Plants, Diet & Damage

• feed on leaves of apple, ash, red and white oak, maple (including boxelder), elm, cherry, linden and honeylocust
• tattered skeletonizing (leaving veins) or total defoliation
• can stress trees or kill trees over years of defoliation

Biology, Life Cycle & Damaging Life Stage

• overwinter as eggs on host (fall cankerworm) or pupae in soil (spring cankerworm)
• eggs hatch in early spring around budbreak
• fall cankerworm and spring cankerworm larvae feed at the same time
• fall cankerworm adults emerge after a hard freeze in fall; spring cankerworm adults emerge in early spring
• wingless females climb trees to mate with winged males
• larvae can be blown from tree to tree on silken threads
• one generation per year
• larvae are the damaging stage

IPM Recommendations

• Manage trees to maintain overall health.
• Monitor trees in early spring for egg masses and larvae.
• If populations are low, allow minor feeding on trees.
• Apply an insecticide (Bacillus thuringiensis; carbamate; pyrethroid) to target larvae when they are smaller than 1/2 inch (~10 days after egg hatch).

For more information, see our Cankerworms fact sheet.