Aedes alternans, commonly known as the Hexham grey, is a species of mosquito in the genus Aedes, subgenus Mucidus. It is primarily found in coastal and freshwater regions of Australia, including the locality of Hexham, New South Wales, after which it is named. While not considered a major disease vector, Ae. alternans has been shown to be capable of transmitting the Ross River virus and Barmah Forest virus under laboratory conditions.
Aedes alternans is distributed across Australia, with specific records indicating its presence in New South Wales, Northern Territory, Queensland, South Australia, Victoria, and Western Australia. It has also been observed in New Caledonia.