They occur worldwide except for the extreme northern parts of the temperate zone, and are the most common form of mosquito encountered in some major U.S. cities, such as Los Angeles.

In naming this genus, Carl Linnaeus used the nonspecific Latin term for a midge or gnat: culex.

As in all Diptera capable of flight, the second pair of wings is reduced and modified into tiny, inconspicuous halteres.

Anopheline mosquitoes tend to sit with their heads low and their rear ends raised high, especially when feeding, while culicine females keep their bodies horizontal.

The metamorphosis is typical of holometabolism in an insect: the female lays eggs in rafts of as many as 300 on the water's surface.

The tiny, cigar-shaped, dark brown eggs adhere to each other through adhesion forces, not any kind of cement, and are easily separated.