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.
Common names: Cabbage Looper, Looper, Inch Worm
Scientific name: Order Lepidoptera, family Noctuidae, Trichoplusia ni
Size: Adult wing span--1 1/2" to 2", larva--1" to 1 1/2"
Identification: Adults are brownish gray moths with silvery spots in the center of each wing. Active at night. Eggs are greenish white, round and laid singly on the upper sides of leaves. Larvae are green with pale stripes down the back. They form a loop when walking--thus the name.
Biology and life cycle: Loopers overwinter as greenish to brownish pupae wrapped with delicate cocoons of white thread. The cocoons are so thin that the pupae outlines can be seen. Adult moths emerge in the spring to lay eggs on the surface of leaves. Larvae emerge and feed from two to four weeks and then spin cocoons similar to the ones used to pass the winter. Three to four generations per year or more. The number of worms increases with each generation. Complete metamorphosis.
Habitat: Vegetable gardens, especially those with brassicas. Enjoy cabbage, broccoli, celery, kale, parsley, peas, potatoes, cauliflower, brussels sprouts, lettuce, beans, radishes, tomatoes, and other garden crops.
Feeding habits: Larvae eat lots of holes in green leaves.
Economic importance: Destruction of food crop foliage.
Natural control: Trichogramma wasps, birds, paper wasps, and yellow jackets. Loopers are usually controlled by natural diseases and parasites; these function effectively only in an organic program.
Organic control: Bt (Bacillus thuringiensis) products.
Insight: Even the organiphobes recommend Bt because the chemical poisons don't work on this animal. Here is a quote from a 1962 college text: "The looper caterpillars are often almost completely destroyed, usually late in the season, by a wilt disease which causes their bodies to rot." Bacillus thuringiensis was the wilt pathogen, but not yet discovered, named, and made available to gardeners.