army worm vs caterpillar

army worm and caterpillar both are nouns.

Word	Noun	Adjective	Verb	Adverb
army worm	Yes	No	No	No
caterpillar	Yes	No	No	No

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

army worm: noctuid moth larvae that travel in multitudes destroying especially grass and grain
caterpillar: a wormlike and often brightly colored and hairy or spiny larva of a butterfly or moth

army worm (noun)	caterpillar (noun)
noctuid moth larvae that travel in multitudes destroying especially grass and grain	a wormlike and often brightly colored and hairy or spiny larva of a butterfly or moth