Cankerworms belong to a group of insects known as inchworms and loopers. There is a species that feeds in late spring (Paleacrata vernata) and another that does its damage in fall of the year (Alsophila pometaria).

These insects are members of the Family Lepodoptera along with all the butterflies and moths. They have legs at the front and back of their bodies but none in the middle. So, they creep along by grabbing hold with the front legs and the allowing the back legs to move forward. This forms the "loop" that is characteristic of this group of insect larvae.

As with the gypsy moth, the male adult cankerworm can fly but the female cannot. In fact, she is wingless and must stay near where she emerges from her pupal case. In late spring, the male is attracted to her by a strong pheromone, they mate and then she lays eggs on the bark and twigs.

The fall cankerworm goes through the same cycle except that they lay their eggs in October or later.

Since these are chewing insects, you will find holes in the leaves and missing tissue on the edge. Also, the cankerworm itself will be evident if they are in numbers large enough to do any damage.

Only occasionally do either the spring or fall cankerworm population rise to a level where serious tree defoliation will occur. Large numbers of cankerworms may warrant a treatment but this is the exception rather than the rule. The fall cankerworm does its feeding late in the fall when the trees have already completed much of their photosynthesis for the year anyway.

Most infestations of cankerworm do not rise to level that would cause severe damage. Also, since these insects often attack very large trees, it would be difficult and expensive to treat much area.

For smaller ornamental trees in the landscape that might be inundated by canker worms, the biological control, Bacillus thuringiensis (Bt) is effective in reducing populations. Several commercially available insecticides are also labeled for cankerworm.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

Types of Insects

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