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New Zealand Flatworm in Europe Facts

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New Zealand Flatworm

New Zealand Flatworm

The New Zealand Flatworm, Arthurdendyus triangulatus , is posing a serious threat to wildlife in Europe, by consuming the indigenous and garden-friendly earthworm, Lumbricus terrestris.

This affects not only soil conditions, which quickly become impacted and unfertile without the earthworms, but also the wildlife that depends on earthworms for food.

First discovered in Belfast, Northern Ireland in 1963, the New Zealand flatworm has rapidly spread to other parts of the British Isles and mainland Europe, especially places with higher than average rainfall, like Scotland.

It is widely believed that the first flatworm came from New Zealand, where they are indigenous, via the rootball of a potted plant.

The European Community now rigorously enforce their Directive 2000/29/EC which prevents the movements between member states of plant and plant material without first obtaining special licences which are only granted after their health inspectors have thoroughly inspected said material and the premises in which they are housed, and granted certificates to state they are a completely free of viruses and insects which could be harmful to another community state.

It's a pity they weren't in existence in 1963.


So, how do we recognise the flatworm?

Its body is flattened but with very similar colouring to the normal earthworm from above, but it's underside is a paler colour, unlike the earthworm which is the same colour all over. It has no segments on its body, unlike the earthworm. It is also covered with a thick mucous membrane, giving it a slimey appearance.

They are pointed at both ends and have numerous eyes on the lateral margins at the head end. Native (harmless) flatworms have 2 eyes at the head end.

Less problematic (so far) but another introduced species is the Australian Flatworm and it differs by having multiple eyes along its length, and a more rounded read end.

The New Zealand Flatworms average about 1cm across and 6cm long, extending to about 12cm when they move. Some adults are as long as 17cm (6.7"). Sadly even when all the earthworms in their area are gone, they can survive without food for up to 2 years during which time they shrink and get even flatter.

They have been likened to a mini Swiss roll when lying on the soil all curled up, and are frequently to be found on the surface of the earth underneath solid objects such as rubble, old tiles, plastic bin bags etc., in damp areas.





Flatworm Reproduction

They lay egg cocoons that are a bright red colour at first, deepening after a few days to black.

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These eggs are about 5 to 8mm wide, each containing up to 10 baby flatworms, which when hatched, are around 30mm long and creamy pink in colour.The incubation period is unknown.

These babies are able to reproduce asexually (meaning they do not need a mate) when they reach 5cm (2") in length.

Finding the brittle remains of these shells are suggestive of a problem in your garden.

Environmental Effects


Pasture farms are suffering more than arable farms, because ploughed land deters any kind of worm anyway, including the flatworms. Earthworms break down decaying matter, and open up the soil in areas of compaction (through animals), as well as improve drainage.This is of considerable importance in areas like Scotland which are subject to high rainfall throughout the year.

The demise of the earthworm populations are resulting in compacted unfertile land on which grass struggles to grow, and so the natural foodstuff of many farm animals - cows, sheep etc - is in decline. The farmer then has to buy animal food which pushes his costs up, which in turn damages the economic viability of his farm, especially when he has to compete against other farms who have not yet suffered the devastation caused by the New Zealand Flatworm.

The latest report suggests 12 farms have been badly affected in Scotland alone, mainly on the Western side of the country which gets more rain than the East.

While the New Zealand Flatworm is rapidly affecting the wetter parts of the British Isles, Ireland, Iceland and the Faeroe Isles, it is also reckoned to be causing problems in Norway, Denmark, Germany, Sweden and Poland.


Many small creatures feed off the earthworm, whose population more or less stayed stable up until the arrival of the New Zealand Flatworm because these small creatures did not follow the earthworm underground and get into all its holes and burrows.

These creatures include rodents, voles, moles, shrews, frogs and other amphibians, a wide range of birds including rooks and songbirds and invertebrates including slugs, leeches, beetles etc.

It has still to be seen if the populations of these creatures will remain the same following the demise of the earthworm (yes the have become extinct in some places), or whether or not Mother Nature will provide sufficient food alternatives.

The big danger to the countryside is that as land becomes less fertile without the native earthworm, different plants will grow in place of the current ones, so changing the natural habitat of many small creatures, which could result in the loss of many species.


At the time of writing this, no chemical solution has been found to eradicate the New Zealand Flatworm, as anything that poisons it, also poisons the indigenous earthworm. The only advice seems to be to crush and kill them as they are found.

They do have natural predators in the form of ground beetles and rove beetles, but studies have shown both to co-exist peacefully with the flatworm, and so therefore not much help in a wholescale eradication plan.

It has been reported that the maggot of a Tasmanian gnat parasitises the flatworm, but this may not be the best biological control means, because this gnat is also an alien species, so no-one knows what other indignenous species it may cause harm to.

Government Intervention

You'll love this, after reading above.

In 1995, they introduced a new Law under the Wildlife and Countryside Act of 1992 making it illegal to release the New Zealand Flatworm into the wild, or to allow it to escape unless all reasonable steps have been taken to prevent its escape.

Oh well, I'm sure that's a big help.

One Final Thought

We should all use vermicomposting to break down our organic kitchen waste into excellent worm compost, and save the earthworm.

My thanks for information go to the following websites.


jen on January 26, 2011:

Hi, I was quite perturbed on finding a mystery freaky orange thing in my garden. I offered it to my ducks but they looked at it suspiciously and wandered off. Turns out it's an australian flatworm. gross little fella! great article, really helped to figure out what it was and what it does. :)

IzzyM (author) from UK on November 05, 2010:

Trouble is...the damage is already done now.

jtrader on November 04, 2010:

More plant lovers should be educated about this. Then people would be less likely to even try to break the rules.

IzzyM (author) from UK on February 21, 2010:

I don't think I have ever seen one either, but they are causing a lot of problems everywhere it seems.

2uesday on February 21, 2010:

Thanks for this hub Izzy it is very helpful as I was not sure what they looked like. I am hoping I never find one. After reading this I now know the difference in appearance between our good old earthworms and these nasties.

IzzyM (author) from UK on February 11, 2010:

Glad you liked it :) Don't know about you, but I'm keeping an eye out for them in my garden - got few enough ordinary earthworms without them having a predator such as this.

blpelton on February 11, 2010:

Very informative! great hub

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