Although several invertebrates have been introduced by Man into the Antarctic, no holometabolous insects have survived to colonize terrestrial habitats successfully. Data are presented on the survival of populations of a chironomid midge, together with an enchytraeid worm, for 17 years in a maritime Antarctic site at Signy Island, South Orkney Islands. Both species are thought to have been introduced on plant material transplanted from either South Georgia or the Falkland Islands or both in 1967. Population densities average 25718m-2 for the dipteran larvae and 3243 m-2 for the worms. Successful completion of the midge's life cycle was indicated by emergence of brachypterous adults and oviposition (the population is parthenogenetic with only females present). Although both taxa are capable of supercooling to between -13 and -26°C, this capacity may not be sufficient in a severe winter to avoid lethal freezing. Four potential cryoprotectants were found in insect extracts, but in concentrations (< 1 % fresh weight) unlikely to influence cold hardiness. Both invertebrates appear to be pre-adapted for survival in much harsher conditions than they normally experience, by the extension of existing physiological mechanisms. It is concluded that the main limitations to invertebrate colonization of suitable Antarctic land areas by soil-dwelling species are geographical.