THE POTENTIAL IMPACT OF THE NEW ZEALAND FLATWORM, A PREDATOR OF EARTHWORMS, IN WESTERN EUROPE

Abstract

The New Zealand flatworm Arthurdendyus triangulatus (=Artioposthia triangulata) is an example of an invasive organism that, by reducing lumbricid earthworm populations, could have a major impact on soil ecosystems in Britain and the Faroe Islands. How it was introduced into the British Isles is not known, but like many invasive species, it is suspected that it was introduced by humans and was associated with the trade between New Zealand and Britain. Once established in Britain it found in the large, readily available earthworm population a niche that it could exploit. The microclimate of the forests in the center and south of the South Island of New Zealand from whence the flatworm came is similar to that in parts of the British Isles and consequently conducive to its survival. Although when compared with many other invertebrate introductions (e.g., insects) the flatworm's rate of increase has been slow, a retrospective study strongly suggested that, in Scotland, they spread from botanic gardens to horticultural wholesalers, then to domestic gardens, and only latterly did they invade agricultural land. As with other invasive species, the application of the CLIMEX computer model and geographic-information-system techniques have been used to try to ascertain its potential distribution within both the British Isles and Europe. The data suggest that A. triangulatus could become established in northwest continental Europe, and Denmark, Iceland, and Sweden have added it to their quarantine pest lists. The fact that A. triangulatus is the only one of 12 alien terrestrial planarians in Britain to be considered a pest suggests that this group of invertebrates is behaving in a fashion similar to other invasive organisms and obeys the “tens rule” suggested by M. Williamson. Since within the period 1995–1997 another three species of predatory terrestrial planarians have been recorded in Scotland it is evident that the existing phytosanitary regulations must be more strongly enforced or new ones introduced if the spread of terrestrial planarians is to be halted. For reprints of this Invited Feature, see footnote 1, p. 1259.