water bug vs Blattella germanica

water bug and Blattella germanica both are nouns.

Word	Noun	Adjective	Verb	Adverb
water bug	Yes	No	No	No
Blattella germanica	Yes	No	No	No

As nouns, water bug and Blattella germanica are synonyms defined as:

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

Other synonyms of water bug include Croton bug, crotonbug, German cockroach.

water bug (noun)	Blattella germanica (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