Biology of the Fall Cankerworm
The fall cankerworm has four life stages: egg, larva (caterpillar), pupa (cocoon), and adult (moths). The first hard freezes in late fall to early winter cause the adult moths to emerge from their cocoons in the ground. The female adult moth is gray and wingless. The male is a small, brown moth with wings.
The adult females crawl up any nearby vertical object to lay their eggs after mating. They climb all species of trees as well as utility poles and houses. The females attempt to climb to the highest branches to lay their eggs. The eggs over-winter in the trees, hatching in the spring as small green inchworms or caterpillars. The caterpillars emerge as soon as the leaf buds begin to open in early to mid March.
Once hatched, the cankerworm caterpillars begin to feed on the unfolding buds. In response, the trees set out new buds and leaves. The cankerworms will consume repeated refoliation attempts by the tree over several weeks. The cankerworm caterpillars feed from early March to late April. When the cankerworms have finished feeding, they descend to the ground, burrow into the soil, and form a cocoon.
The cankerworm caterpillar spins a silken thread that serves several purposes. The caterpillar attaches the free end of the thread to a leaf or twig, and uses the thread as a safety line to crawl back up if dislodged from the tree. Cankerworms can use their threads to “balloon” from tree to tree on the wind. They also use their threads to lower themselves to the ground when they are ready to pupate.
Don McSween, longtime Charlotte City Arborist, relates in TCI (Tree Care Industry) Magazine, that “Literature put out by the U.S. Forest Service in the 1960s stated that finding more than 90 females over the course of a season can be regarded as a heavy infestation. We’ve had traps capture 9,000 to 10,000 females on a single tree. I think that clearly qualifies as heavy.” Since each female moth will lay between 100 and 200 eggs, a heavily infested tree may have as many as 1,000,000 cankerworms eating its foliage in the spring!
The adult females crawl up any nearby vertical object to lay their eggs after mating. They climb all species of trees as well as utility poles and houses. The females attempt to climb to the highest branches to lay their eggs. The eggs over-winter in the trees, hatching in the spring as small green inchworms or caterpillars. The caterpillars emerge as soon as the leaf buds begin to open in early to mid March.
Once hatched, the cankerworm caterpillars begin to feed on the unfolding buds. In response, the trees set out new buds and leaves. The cankerworms will consume repeated refoliation attempts by the tree over several weeks. The cankerworm caterpillars feed from early March to late April. When the cankerworms have finished feeding, they descend to the ground, burrow into the soil, and form a cocoon.
The cankerworm caterpillar spins a silken thread that serves several purposes. The caterpillar attaches the free end of the thread to a leaf or twig, and uses the thread as a safety line to crawl back up if dislodged from the tree. Cankerworms can use their threads to “balloon” from tree to tree on the wind. They also use their threads to lower themselves to the ground when they are ready to pupate.
Don McSween, longtime Charlotte City Arborist, relates in TCI (Tree Care Industry) Magazine, that “Literature put out by the U.S. Forest Service in the 1960s stated that finding more than 90 females over the course of a season can be regarded as a heavy infestation. We’ve had traps capture 9,000 to 10,000 females on a single tree. I think that clearly qualifies as heavy.” Since each female moth will lay between 100 and 200 eggs, a heavily infested tree may have as many as 1,000,000 cankerworms eating its foliage in the spring!
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