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. The spring cankerworm 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. The English sparrow was originally introduced in the United States to combat the spring cankerworm. Cankerworms are classified in the phylum Arthropoda, class Insecta, order Lepidoptera, family Geometridae. For control methods see bulletins of the U.S. Dept. of Agriculture.
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