CANKERWORM
cankerworm
(noun) green caterpillar of a geometrid moth; pest of various fruit and shade trees
Source: WordNet® 3.1
Etymology
Noun
cankerworm (plural cankerworms)
Either of two caterpillars, the larvae of geometrid moths, that are destructive to fruit, buds and leaves.
(figurative) A corrupting or destructive force.
Source: Wiktionary
Can"ker*worm`, n. (Zoöl.)
Definition: The larva of two species of geometrid moths which are very
injurious to fruit and shade trees by eating, and often entirely
destroying, the foliage. Other similar larvæ are also called
cankerworms.
Note: The autumnal species (Anisopteryx pometaria) becomes adult late
in autumn (after frosts) and in winter. The spring species (A.
vernata) remains in the ground through the winter, and matures in
early spring. Both have winged males and wingless females. The larvæ
are similar in appearance and habits, and beling to the family of
measuring worms or spanworms. These larvæ hatch from the eggs when
the leaves being to expand in spring.
Source: Webster’s Unabridged Dictionary 1913 Edition