black fly vs buffalo gnat

black fly and buffalo gnat both are nouns.

Word	Noun	Adjective	Verb	Adverb
black fly	Yes	No	No	No
buffalo gnat	Yes	No	No	No

As nouns, black fly and buffalo gnat are synonyms defined as:

black fly and buffalo gnat: small blackish stout-bodied biting fly having aquatic larvae; sucks the blood of birds as well as humans and other mammals

Other synonyms of black fly include blackfly.

black fly (noun)	buffalo gnat (noun)
small blackish stout-bodied biting fly having aquatic larvae; sucks the blood of birds as well as humans and other mammals	small blackish stout-bodied biting fly having aquatic larvae; sucks the blood of birds as well as humans and other mammals