On the usually wet, sub-Antarctic Marion Island, interspecific competition for refugia during low humidity or dry periods is thought to have been responsible for patterns of body-size and microhabitat distribution of the ectemnorhinine weevils inhabiting the cryptogam-dominated epilithic biotope, whereas this process is thought to be unimportant in the angiosperm-dominated vegetated biotope. Adults of the six weevil species indigenous to the island were tested for their ability to resist desiccation at 10°C and 5% r.h., and to replenish lost water by drinking. Species inhabiting dry, rockface habitats had relatively low rates of water loss, took longer to reach the maximum tolerable water loss, and had a relatively high body water content; species from moist, angiosperm-dominated habitats had a relatively high rate of water loss, reached maximum tolerable water loss faster, and had a relatively low body water content. The very small (1.55 mg), fellfield-inhabiting Antarctonesiotes elongatus differed from the other epilithic species by having rates of water loss similar to species from the moist lowland habitats. Larvae of the supra-littoral Palirhoeus eatoni have a greater tolerance to salt-water than any of the other epilithic species. In at least two of the syntopic species pairs showing body-size differences, these differences are unlikely to have promoted coexistence via the elimination of competition for refugia due to similarities in desiccation resistance.