Only in Matthew 23:24, a small two-winged stinging fly of the genus Culex, which includes mosquitoes. Our Lord alludes here to the gnat in a proverbial expression probably in common use, "who strain out the gnat;" the words in the Authorized Version, "strain at a gnat," being a mere typographical error, which has been corrected in the Revised Version. The custom of filtering wine for this purpose was common among the Jews. It was founded on Leviticus 11:23. It is supposed that the "lice," Exodus 8:16 (marg. R.V., "sand-flies"), were a species of gnat.

Noah Webster's New International Dictionary of the English Language

1. (n.) A blood-sucking dipterous fly, of the genus Culex, undergoing a metamorphosis in water. The females have a proboscis armed with needlelike organs for penetrating the skin of animals. These are wanting in the males. In America they are generally called mosquitoes. See Mosquito.

2. (n.) Any fly resembling a Culex in form or habits; esp., in America, a small biting fly of the genus Simulium and allies, as the buffalo gnat, the black fly, etc.