The scientific name for the common gnat is Culex pipiens. However, the term "gnat" can apply to a wide variety of insects that resemble flies and belong to a number of families in the Diptera order.
The common gnat is a vector, or transmitter, of several diseases, including meningitis, some types of encephalitis and the West Nile virus. Gnats are usually 3 to 7 millimeters long and resemble flies. Male gnats only feed on nectar, but female gnats feed on human blood. The fungus gnat, whose scientific name is Lycoriella spp., is a member of the same order but a different family.