The earthworm-eater planarian, Artioposthia triangulata

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The earthworm-eater planarian, Artioposthia triangulata

War of the worms

Artioposthia triangulata (Dendy, 1895), an unremarkable flatworm first described from the Southern Hemisphere city of Christchurch, New Zealand, has since won induction into the alien-pests hall of infamy by hitch-hiking to Ireland a year or two prior to 1963, then reaching Scotland by 1965, and now some other parts of the United Kingdom, in those places threatening to be an economic problem and certainly a newsworthy one. It eats the earthworms which normally help aerate and drain soils and cycle nutrients. Artioposthia may considerably reduce worm populations and adversely affect agricultural production. In Northern Ireland experiments demonstrate it can severely and quickly reduce numbers of at least four earthworm species: Apporectodea caliginosa, Eisenia foetida, Lumbricus rubellus, and L. terrestris. Fortunately conditions to its liking do not occur everywhere and indications at the moment are that only Northern Ireland farmland has been significantly affected, with elsewhere most occurrences in home gardens and nurseries. Several other earth-worm eating introduced planarians besides Artioposthia are now also arousing interest in the UK. It is not yet certain that Artioposthia triangulata itself will live up to its advance publicity.

Ironic footnote: The "New Zealand flatworm" or "Canterbury flatworm" as it is now known is one of the few NZ land species to become an invasive in the Northern Hemisphere. Most of the traffic has been in the other direction. New Zealand is a land overrun by adventive weeds and colonised by all manner of creeping, crawling, walking, jumping, and flying vermin from Europe.

What is Artioposthia triangulata?

Platyhelminthes: Turbellaria (free-living flatworms): Tricladida (planarians): Geoplanidae (pointed head, eyespots on body margins): Artioposthia.

Artioposthia triangulata is pointed at both ends, dark brown with a pale margin and pale underside, about 50 mm long, 10 mm wide at rest, but up to 200 mm long when moving. It produces shiny black egg oval capsules each with several young inside. In its native land, New Zealand, it probably evolved in beech forests of the Canterbury Plains. The first extensive account of the appearance and habitat of the species is by Marion Fyfe (1930: citation) from NZ urban gardens :

Habitat: "While this planarian undoubtedly lives in the soil, it is more readily found under boxes, sacks, tins, or any large object which has been lying undisturbed on the soil for some time. Here the soil must be moist and the worm is usually found in association with slaters, slugs, and centipedes. In moist soil of a clayey nature the worm was found several inches below the surface. In one garden in which this worm was known to occur, none was found after extensive digging in the more dry loamy parts.

Behaviour: "On turning over the boxes, etc., I found the planarian on the surface of the soil in a very characteristic coiled position, with the ventral surface pressed firmly against the soil so as to form a flat spiral outlined by the pale lateral bands of the dorsal surface. In captivity the planarian still assumed that position, lying on the surface of the soil with the anterior and posterior ends buried."

Appearance: "The dorsal surface can be distinguished from the ventral by its strong convexity, [it is] a dark purplish-brown colour ... with marginal bands of pale yellowish dotted with minute specks of [purplish-brown]. The anterior tip is orange-pink ... Throughout the length of the dorsal surface there is a narrow mid-dorsal line of a dark purple colour. [...] The ventral surface is pale yellowish in colour, thickly peppered with purplish specks ... There are two apertures on the ventral surface ..."

Artioposthia on the Net

Current Research Activity

The International Workshop on Terrestrial Planarians, held at the Department of Zoology, University of Canterbury, New Zealand, 16-20 February, 1998, included several presentations related to Artioposthia and invasive planarians. Papers were published in a special edition of Pedobiologia Volume 42(5-6) in 1999, and a short REPORT on the events and recommendations is on the OECD web pages.

Press quotes

Further reading

Compiled by GBR.
Original 1 February 1998. Last (minor) update 6 March 2000 by Geoff Read

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