(1):

(n.) 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.

(2):

(n.) 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.