Present situation of the New Zealand flatworm (Arthurdendyus triangulatus) in UK
The New Zealand flatworm, Arthurdendyus triangulatus (Artioposthia triangulata), is a predatory planarian species feeding on earthworms which has been introduced 40 years ago into some north European countries. It originates in New Zealand, where it appears to be confined to woodlands and gardens in South Island. It was introduced into Northern Ireland in 1963, England and Scotland in 1965 and the Faroe Islands (Denmark) in 1982 (see EPPO RS 96/042), and is reported in Iceland and Ireland. A general review (Cannon et al., 1999) presents the current knowledge on A. triangulatus geographical distribution in UK, biology and ecology, and environmental impact.
- In Northern Ireland: A. triangulatus occurs in all six counties but is concentrated in the more populated areas, in particular around Belfast, in gardens and vegetable plots. However, it is found in grassland in some places, but its impact is difficult to appreciate. In grassland, studies have showed that after an increase of A. triangulatus populations from 1984 to 1988, they decreased from 1989 to 1992.
- In Scotland, it was first found in 1965 in the Royal Botanical Gardens of Edinburgh. It occurs throughout mainland Scotland (in particular central Scotland) and on the isles of Gigha, Islay, Bute and Orkney. It is found essentially in botanical and private gardens, and is not considered as a problem in agricultural land (e.g. in potato-producing areas).
- In England and Wales: it was first found in 1965 near Carlisle and not seen again for 27 years until it was found in a garden centre near Manchester in 1992. A gradual increase of populations has been observed but A. triangulatus is much less common in England and Wales than in Northern Ireland and Scotland.
The authors concluded that the distribution of A. triangulatus in UK is limited and discontinuous and that despite its rather long presence in UK, knowledge on its biology and ecology remains limited. Therefore, it is quite difficult to appreciate its potential distribution in Europe and its impact on the environment.
There are also published records of A. triangulatus in Ireland.
Note: A. triangulatus is not considered by EPPO to be a quarantine pest. However, work has been done on possible practical measures to prevent any further spread in Europe and two draft EPPO Standards are in preparation (Import requirements and Nursery inspection, exclusion and treatment). Under the Convention on Biodiversity, A. triangulata is probably to be considered as an "alien invasive species".
Sources
Cannon, R.J.; Baker, R.H.A.; Taylor, M.C. Moore, J.P. (1999) A review of the status of the New Zealand flatworm in the UK.
Annals of Applied Biology, 135(3), 597-614.