A collection of Tydeus erebits Strandtmann from widespread localities in East Antarctica is reported. The mean body lengths of adult specimens from some of these localities differ significantly from those at other localities and vary with the type of habitat. Geographic variation in size of the magnitude reported here has not been found in other species of Antarctic mites, and possible causes are discussed. Other morphological variation between the specimens is described and brief notes on the behaviour and reproduction of T. erebus at the Vestfold Hills are presented. Three paratypes of Tydeus wilkesi Strandt mannare compared with specimens of T. erebus Strandtmann and are considered to belong to the latter species.