Source : Webster's Revised Unabridged Dictionary (1913)

Palmerworm \Palm"er*worm`\, n. (Zo["o]l.)
      (a) Any hairy caterpillar which appears in great numbers,
          devouring herbage, and wandering about like a palmer.
          The name is applied also to other voracious insects.
          --Joel. i. 4.
      (b) In America, the larva of any one of several moths,
          which destroys the foliage of fruit and forest trees,
          esp. the larva of {Ypsolophus pometellus}, which
          sometimes appears in vast numbers.