sandfly vs gnat

sandfly and gnat both are nouns.

Word	Noun	Adjective	Verb	Adverb
sandfly	Yes	No	No	No
gnat	Yes	No	No	No

As nouns, gnat is a hypernym of sandfly; that is, gnat is a word with a broader meaning than sandfly:

sandfly: any of various small dipterous flies; bloodsucking females can transmit sandfly fever and leishmaniasis
gnat: any of various small biting flies: midges; biting midges; black flies; sand flies

sandfly (noun)	gnat (noun)
any of various small dipterous flies; bloodsucking females can transmit sandfly fever and leishmaniasis	any of various small biting flies: midges; biting midges; black flies; sand flies
	(British usage) mosquito