Source : Webster's Revised Unabridged Dictionary (1913)

Cankerworm \Can"ker*worm`\, n. (Zo["o]l.)
   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.

   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 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.