Summary
Invasive species are a serious threat to biodiversity worldwide. The relatively simple ecological systems of the subantarctic have the potential to be signiWcantly damaged by predatory species that invade. Two species of exotic, predatory, terrestrial Xatworms were Wrst collected in 1997 from two localities only 2 km apart, in the southeast of subantarctic Macquarie Island. The species were later identiWed as Kontikia andersoni and Arthurdendyus vegrandis. We report here the results of Weldwork in 2004 that established that both species now occupy about a seventh of the southeast of the island which has a total area of only 170 km2 and that there seem to be no barriers to further expansion. The island was Wrst discovered in 1810 and so it is likely the species were introduced by means of human intervention within the last 200 years. We provide evidence to show that both species originated in New Zealand and have probably been on the island for »100 years giving an average rate of spread of about 10 m per year. Other species of Arthurdendyus have been introduced from New Zealand to the United Kingdom where they prey on earthworms. The quarantine signiWcance of A. vegrandis for Australia is discussed and recommendations made to reduce the probability of it entering Tasmania where it has the potential to become an agricultural pest.