The Collaborative International Dictionary of English v.0.48:

Dropworm \Drop"worm`\ (dr[o^]p"w[^u]rm`), n. (Zool.)
   The larva of any geometrid moth, which drops from trees by
   means of a thread of silk, as the cankerworm or inchworm.
   See inchworm and geometrid.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Cankerworm \Can"ker*worm`\, n. (Zool.)
   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 larv[ae] are
   also called cankerworms.
   [1913 Webster]

   Note: The autumnal species (Anisopteryx pometaria) becomes
         adult late in autumn (after frosts) and in winter. The
         spring species (Anisopteryx vernata) remains in the
         ground through the winter, and matures in early spring.
         Both have winged males and wingless females. The
         larv[ae] are similar in appearance and habits, and
         belong to the family of measuring worms or spanworms.
         These larv[ae] hatch from the eggs when the leaves
         begin to expand in spring.
         [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Caterpillar \Cat"er*pil`lar\, n. [OE. catyrpel, corrupted fr.
   OF. chatepelouse, or cate pelue, fr. chate, F. chatte,
   she-cat, fem. of chat, L. catus + L. pilosus hairy, or F.
   pelu hairy, fr. L. pilus hair. See Cat, and Pile hair.]
   1. (Zool.) The larval state of a butterfly or any
      lepidopterous insect; sometimes, but less commonly, the
      larval state of other insects, as the sawflies, which are
      also called false caterpillars. The true caterpillars have
      three pairs of true legs, and several pairs of abdominal
      fleshy legs (prolegs) armed with hooks. Some are hairy,
      others naked. They usually feed on leaves, fruit, and
      succulent vegetables, being often very destructive, Many
      of them are popularly called worms, as the cutworm,
      cankerworm, army worm, cotton worm, silkworm.
      [1913 Webster]

   2. (Bot.) A plant of the genus Scorpiurus, with pods
      resembling caterpillars.
      [1913 Webster]

   Caterpillar catcher, or Caterpillar eater (Zool.), a bird
      belonging to the family of Shrikes, which feeds on
      caterpillars. The name is also given to several other
      birds.

   Caterpillar hunter (Zool.), any species of beetles of the
      genus Callosoma and other allied genera of the family
      Carabid[ae] which feed habitually upon caterpillars.
      [1913 Webster]

WordNet (r) 3.0 (2006):

cankerworm
    n 1: green caterpillar of a geometrid moth; pest of various
         fruit and shade trees

Easton's 1897 Bible Dictionary:

Cankerworm
   (Heb. yelek), "the licking locust," which licks up the grass of
   the field; probably the locust at a certain stage of its growth,
   just as it emerges from the caterpillar state (Joel 1:4; 2:25).
   The word is rendered "caterpillar" in Ps. 105:34; Jer. 51:14, 17
   (but R.V. "canker-worm"). "It spoileth and fleeth away" (Nah.
   3:16), or as some read the passage, "The cankerworm putteth off
   [i.e., the envelope of its wings], and fleeth away."