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.
or cankerworm or inchworm

Larva of any member of a large, widespread group (mostly in the family Geometridae, with some in the family Noctuidae) of moths. Loopers move in a characteristic “inching” or “looping” gait by extending the front part of the body and bringing the rear up to meet it. Resembling twigs or leaf stems, they feed on foliage, and can seriously damage or destroy trees.

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Distinctive green, white-lined larva, or caterpillar (Trichoplusia ni), of the owlet moth family (Noctuidae). Like other loopers, it moves in an “inching” motion. It is an economic pest of cabbages and associated crops, particularly in the U.S. and Europe. The adults, known as Ni moths, migrate considerable distances. They are mottled brown with a pale Y-shaped mark on each forewing. The typical adult wingspan is about 1 in. (25 mm).

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