Arthurdendyus triangulatus



Conservation status

Not Assessed

Legal status

Regulated invasive  species of Union concern under the European Regulation on the prevention and management of the introduction and spread of invasive alien species [1143/2014].

First reported in the wild



Invasive species - risk of High Impact

Irish status


Introduction pathways - 1

Transport Contaminant

Introduction pathways subclass - 1

Contaminant nursery material

Invasive score


NAPRA Ireland risk assessed


Species Biology


Flatworm with a very flat body, non-segmented and pointed at both ends; brown upper body (often dark brown to purplish) with pale speckled edges and with a pale buff coloured underside with grey-brown specks (Booy et al., 2015). Entire body covered in a fouling smelling sticky mucus. Up to 15cm in length and can weigh more than 2g (Blackshaw, 1990). Produces shiny, black oval eggs (capsules), 1-2mm in width (Booy et al., 2015).


New Zealand flatworms have been shown to significantly reduce the biomass of earthworms (Lumbricus terrestris and, to a lesser extent, Aporrectodea longa) in field plot experiments (Murchie & Gordon, 2013). The impact on earthworm biomass was particularly acute in the case of anecic species (worms that make permanent burrows in the soil) such as L. terrestris but not on epigecic species (worms that live on the surface or in leaf litter), (Murchie & Gordon, 2013).


Mires, bogs & fens; Grasslands and landscapes dominated by forbs, mosses or lichens; Regularly or recently cultivated agricultural, horticultural or domestic habitat; Constructed, industrial or other artificial habitats


Hermaphrodite, producing ~6 capsules per adult, laid from March to October with a peak in early summer (Blackshaw, 1997). Capsules take approximately 2 months to hatch (Blackshaw, 1997).

Pathway and vector description

Initially introduced into Ireland in the 1960s, the majority of initial samples were found in gardens, garden centres and greenhouses (Willis & Edwards, 1977) indicating the most likely source of introduction as contaminants of ornamental plants. It may have spread locally by natural means since introduction but genetic analysis suggests that there were a number of introduction events (Dynes et al., 2001) which may have aided spread.

Mechanism of impact


Broad environment


Habitat description

Found mainly in lawns and gardens, agricultural land and in containers with potted plants. Food availability appears to be a limiting factor so likely to be found anywhere earthworms are available (Jones et al., 2001; Murchie et al., 2003)

Species group


Native region



World distribution(GBIF)

Irish distribution

Established - Widespread. More common in Northern Ireland than elsewhere, this may be an artefact of recording effort and it may be under recorded in the Republic. However, based on distribution in the UK, Scotland and northern England, and its absence from continental Europe (Murchie et al, 2003) it may be limited in its abundance in the south of Ireland due to climatic conditions.

Native distribution

New Zealand

Temporal change

Date of first record category


Fifty year date category


Records submitted to Data Centre in 2023

The following map is interactive. If you would prefer to view it full screen then click here.

How can you help

Report any sightings to the National Biodiversity Data Centre.

Further information

You may wish to undertake surveillance and control of the New Zealand flatworms. Regularly checking for and removing of the flatworms from under pots, stones, logs etc. in your garden is the best way to try and control their numbers.

Trapping them by laying out black plastic on the ground with weights on edge to keep down and checking periodically under that is often recommended. Many websites advise on different ways to kill the flatworms however, Jones (2005) simply recommends killing them by putting them into hot water.

Alternatively, the flatworms can be killed by placing in a sealed container and put in the freezer.

Import and horticulture guidance for New Zealand flatworms have been published by the European Plant Protection Organisation (EPPO):

EPPO (2001a) Guidelines on Arthurdendyus triangulatus. EPPO Bulletin 31:1-3.

EPPO (2001b) Import requirements concerning Arthurdendyus triangulatus. EPPO Bulletin 31:5-6.

EPPO (2001c) Nursery inspection, exclusion and treatment for Arthurdendyus triangulatus. EPPO Bulletin 31:7-10. 



Blackshaw, R. P. (1990). Studies on Artioposthia triangulata (Dendy)(Tricladida: Terricola), a predator of earthworms. Annals of applied biology, 116(1), 169-176.

Blackshaw, R.P. (1997) Life cycle of the earthworm predator Artioposthia triangulata (Dendy) in Northern Ireland. Soil Biology and Biochemistry, 29(3/4):245-249.

Booy, O., Wade, M., & Roy, H. (2015). Field guide to Invasive Plants & Animals in Britain. Bloomsbury.

Dynes C, Fleming CC, & Murchie AK (2001) Genetic variation in native and introduced populations of the ‘New Zealand flatworm’, Arthurdendyus triangulatus. Annals of Applied Biology 139(2):165–174.

Jones, H. D., Santoro, G., Boag, B., & Neilson, R. O. Y. (2001). The diversity of earthworms in 200 Scottish fields and the possible effect of New Zealand land flatworms (Arthurdendyus triangulatus) on earthworm populations. Annals of Applied Biology, 139(1), 75-92.

Jones, H.D. (2005). British Land Flatworms. British Wildlife. February, 2005. pp. 189-194. Willis, R. J., & Edwards, A. R. (1977). The occurrence of the land planarian, Artioposthia triangulata (Dendy) in Northern Ireland. The Irish Naturalists' Journal, 112-116.

Murchie, A.K., Moore, J.P., Walters, K.F.A. & Blackshaw, R.P. (2003) Invasion of agricultural land by the earthworm predator, Arthurdendyus triangulatus (Dendy). Pedobiologia 47:920–923.

Murchie, A.K. & Gordon, A.W. (2013) The impact of the ‘New Zealand flatworm’, Arthurdendyus triangulatus, on earthworm populations in the field. Biological Invasions 15:569–586.

CABI Datasheet

Identification guide

Report your sighting - please include a photograph to aid in verifying the record

Additional comments