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Common name:  Cankerworms

Scientific name:  Fall Cankerworm (Alsophila pometaria) and Spring Cankerworm (Paleacrita vernata)

Hosts:  There are two species of cankerworms, the fall and spring cankerworms. The names refer to the season during which their eggs are laid. The eggs of both species will hatch about the time buds on trees begin to open in spring. As a result, both species occur together in mixed populations and can often be found on the same tree. Both species feed on a wide range of deciduous trees and shrubs and are found across much of the United States and Canada.

Favored host trees are elm (Ulmus) and apple (Malus), but several other species can be attacked. These include oak (Quercus), cherry (Prunus), hickory (Carya), honey locust (Gleditsia), maple (Acer), beech (Fagus), linden (Tilia), birch (Betula), and hawthorn (Crataegus).

The young larvae of both fall and spring cankerworm feed on the buds and new leaves of host trees in spring. Feeding begins as small holes in the leaves, but can become more extensive. In some cases, the caterpillars will devour all but the veins of the leaf. Heavy populations can defoliate the entire tree. Trees suffering a heavy infestation will usually produce a second crop of leaves after the initial spring defoliation, but overall vitality may be diminished.

Cankerworm larvae can be seen dropping by silken threads from host trees before damage is noticed. Large numbers of caterpillars coming to the ground in this manner can produce an unpleasant environment in backyard living spaces for a few days. Other infestation signs to watch for are their droppings on cars, sidewalks, and driveways.

Fall Cankerworm (Alsophila pometaria)

Fall cankerworm overwinters as eggs. The caterpillars hatch out of the eggs in spring around the time that buds of host trees are opening. Caterpillars can vary in color. The dark version has a dark stripe bordered by lighter stripes on the back. There is also a light version that is green with narrow white stripes on the back. Fall cankerworm caterpillars have three pairs of prolegs.

The caterpillars will feed on the leaves of the host plant for four to six weeks until they reach full size, about one inch. They then spin silken threads and drop to the ground to pupate.The adults emerge from their pupal stage after fall frosts, to mate and lay their eggs. The adult moth of fall cankerworm is brownish-gray and about one inch long. The male moth has wings marked with two whitish bands running diagonally, while the female moth is wingless. The female must crawl up the trunk of host trees to deposit her eggs. The eggs are brownish and barrel-shaped, and laid in neat clusters on twigs.

Spring Cankerworm (Paleacrita vernata)

Unlike the fall cankerworm, which overwinters in the egg stage, the spring cankerworm spends the winter as larvae in cells in the ground. Pupation takes place in late winter, with adults emerging about the time frost leaves the ground in early spring. Like the fall cankerworm, the wingless female must crawl up the trunk of a host tree to lay her eggs, which are white and oval-shaped clusters deposited in bark crevices along the trunk and larger limbs. Eggs will hatch in the spring at the same time as the fall cankerworm, making identification of their larvae difficult.

The caterpillar of the spring cankerworm is smaller than that of  the fall cankerworm.  It is about 3/4 inch long when fully grown and has only two pairs of prolegs. The caterpillars can range in color from light green to brown or black, with whitish lines running down its back. The adult male moth is pale gray to brown. The wings have three diagonal dark lines, but these may be rather indistinct. The female is wingless.

Cultural management: 

It is possible to trap and destroy the wingless female moth before she deposits her eggs by applying a commercially available sticky compound to a band wrapped around the tree trunk. The sticky compound should not be applied directly to the trunk. It is important to remember that the two species are named because of the season in which their eggs are laid, so traps are most effective in the late winter (February) and fall (mid-October).

Biological management:

The cankerworm’s natural enemies include flies, wasps, and birds, but these are not always effective by themselves.

Chemical management:

Cankerworm larvae feed on leaves and buds in early spring, so this is when they are the most vulnerable to chemical control. Any insecticide used will be most effective while the caterpillars are still small.

The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.

For more information, contact The Morton Arboretum Plant Clinic (630-719-2424 or