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Spring Cankerworm

Common names: Spring Cankerworm, Inchworm, Measuring Worm

Scientific name: Order Lepidoptera, family Geometridae, Paleacrita vernata

Size: Adult--1/2" to 1", larva 1"

Close up of an adult female cankerworm moth (R. Childs)

Three fall cankerworm larvae. Note the 3 pairs of prolegs.

Identification: Adults are light brown or gray moths with translucent wings. Often called inchworms or measuring worms because of their looping movement. Variable in color, but usually striped longitudinally. Larvae drop from trees on silk threads.

A spring cankerworm caterpillar. Note the 2 pairs of prolegs.

Biology and life cycle:

Female adults are wingless; they climb trees to lay eggs in clusters that hatch in the spring just at bud break. Brownish purple eggs are laid in groups in the bark of trees. One brood per year. Larvae hatch in spring when leaves first open, feed for three or four weeks, crawl into the soil to pupate.

Habitat: Elms, oaks, lindens, sweetgums, apples, and other shade and fruit trees.

Feeding habits: Larvae feed on tree and shrub foliage. They drop down on silk threads to evade predators, then go back and eat some more when danger has passed. Why? Guess they are still hungry.

An adult wingless female spring cankerworm producing
an egg mass on the trunk of a tree. (R. Childs)

Economic importance:

Can defoliate broadleaf trees.

Natural control: Trichogramma wasps, birds, and lizards.

Organic control: Band trunks with sticky material in late winter during egg-laying time. Apply the products to paper bands, not directly to the trunk to avoid girdling the tree. Put the material on a paper band. Spray with Bacillus thuringiensis or plant oil products as a last resort.

Insight: These little guys will do a lot of damage in the spring to plants like dwarf yaupon holly, but the foliage usually grows back without any long-term injury.

A female cankerworm adult. Note that this is a wingless moth.


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