water bug vs Croton bug

water bug and Croton bug both are nouns.

Word	Noun	Adjective	Verb	Adverb
water bug	Yes	No	No	No
Croton bug	Yes	No	No	No

As nouns, water bug and Croton bug are synonyms defined as:

water bug and Croton bug: small light-brown cockroach brought to United States from Europe; a common household pest

Other synonyms of water bug include Blattella germanica, crotonbug, German cockroach.

water bug (noun)	Croton bug (noun)
a true bug: large aquatic bug adapted to living in or on the surface of water	small light-brown cockroach brought to United States from Europe; a common household pest
small light-brown cockroach brought to United States from Europe; a common household pest