This Year Probably A Good One For Cankerworms

Hatch to south called 'epic'; Kansas may see worms hatching well into May, K-State horticulturist says

Published on: May 3, 2012

"Two and two are four. Four and four. …"

The Inchworm Song remains popular on Sesame Street. So, even youngsters know how to recognize cankerworms – which children and adults alike may have a good chance of seeing this spring.

"Some Charlotte, North Carolina residents have already described this year's hatch as epic," said Ward Upham, K-State Research and Extension horticulturist. "Kansas' hatch may extend into May. We're in wait-and-see mode."

Cankerworms are moth larvae. Their mothers are wingless females that crawl up a deciduous tree's trunk to lay eggs in spring -- or fall, depending on species. Their favorite nurseries include apple, ash, elm, linden and oak trees.

This Year Probably A Good One For Cankerworms
This Year Probably A Good One For Cankerworms

The resulting larvae's color, striping and number of tiny pencil-point legs will also vary by species, Upham said.

But, all cankerworms hatch in spring, ready to eat and get around by "looping." They bend in half -- arching their back to bring their rear "prolegs" up next to their front "real legs." Then they stretch out again, moving their front legs forward.

Cankerworms are easiest to control before they reach a half-inch long.

"At that stage, you usually have to be scouting to notice inchworms or their damage," Upham said. "You can try rapping on branches, though. If disturbed, cankerworms will often drop down on a silken thread."

Unless the pests stage three straight years of heavy, tree-weakening infestations, however, controls generally aren't necessary.  

Tree leaves may look skeletonized by the time cankerworms mature at about an inch long. But, that's when the larvae start spinning their way to the ground, to pupate into adults. Their damage is done.

"For about a week, you may find yourself walking into worms and webby strings. Worms may drop onto everything outdoor and crawl around," Upham said. "But then a healthy tree will put out new leaves and be just fine."