1. 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.

Origin of webworm

An Americanism dating back to 1790–1800; web + worm
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for webworm

Historical Examples of webworm