See under webworm.
Origin of fall webworm
An Americanism dating back to 1860–65
Definition for fall webworm (2 of 2)
[ web-wurm ]
/ ˈwɛbˌwɜrm /
the larva of any of several moths, as Hyphantria cunea (fall webworm) or Loxostege similalis (garden webworm), which spins a web over the foliage on which it feeds.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019