cankerworm

noun2

1. •
   Either of two caterpillars, the larvae of geometrid moths, that are destructive to fruit, buds and leaves.
2. •
   (figurative) A corrupting or destructive force.

   • O cursed Eld the cankerworme of writs, / How may these rimes, so rude as doth appeare, / Hope to endure, sith workes of heauenly wits / Are quite deuourd, and brought to nought by little bits? — 1596