webworm vs caterpillar

webworm and caterpillar both are nouns.

Word	Noun	Adjective	Verb	Adverb
webworm	Yes	No	No	No
caterpillar	Yes	No	No	No

As nouns, caterpillar is a hypernym of webworm; that is, caterpillar is a word with a broader meaning than webworm:

webworm: several gregarious moth larvae that spin webs over foliage on which they feed
caterpillar: a wormlike and often brightly colored and hairy or spiny larva of a butterfly or moth

webworm (noun)	caterpillar (noun)
several gregarious moth larvae that spin webs over foliage on which they feed	a wormlike and often brightly colored and hairy or spiny larva of a butterfly or moth