Bitterroot Restoration

Class: Insecta
Order: Lepidoptera
Family: Geometridae

Cankerworm, name for two destructive inchworms, or larvae of geometrid moths. The spring cankerworm (Paleacrita vernata) and the fall cankerworm (Alsophila pometaria) are named for the seasons at which the adults emerge from underground pupation.

The spring cankerworm larva overwinters as a pupa, the fall cankerworm as an egg. The larvae, dark green to brown and about 1 in. (2.5 cm) long, feed on the leaves of orchard and shade trees. It has two pairs of posterior appendages (prolegs).

The fall cankerworm has three. The wingless female lays her eggs on the bark, and one control method is the placing of bands of sticky paper around the tree trunks to trap the females before laying. When alarmed, cankerworms drop and hang suspended in midair at the end of a long silken thread secreted from their mouths; they ascend this thread after the danger has passed.

Both fall and spring cankerworms feed on a wide variety of trees including apple, ash, beech, elm, hickory, linden, maples and oaks. The elm spanworm attacks elms, hickory, ash and oaks as well as a variety of other broadleaf trees.