New Zealand Flatworms

What are they? Why are they are threat? And where are they?

New Zealand flatworms are distinctively large and flat. And they are a threat to our native earthworm.

NZ Flatworm

They first arrived in the UK in the 60s – probably from imported plant soil. Easily recognisable as different from the earthworm, the NZ flatworm is flat, with dark purple-brown markings on top of a creamy pale underneath and sides. They are usually 5-15 cm long, pointed at both ends, and covered in sticky mucus. Their eggs are like flattened, hard, black currants.

They are found in cool, damp places, such as under pieces of wood, stone or polythene. Often curled up like a Swiss roll, they leave slime circles where they’ve been resting.

Why are they a threat?

They eat earthworms. This could be potentially disastrous, not just for the native earthworm population, but also because it will deprive us of the benefits that earthworms bring, such as aerating the soil, breaking down nutrients for plants, and being a source of food for birds and mammals.

The flatworm wraps its body around the earthworm, and secretes a digestive mucus to dissolve and consume it.

Where are they?

At the moment, we know flat worms are predominantly in Scotland and the north of England where the conditions are ideal for them – cool and damp. They travel in pot plant soil and other soil transfers. However, exact numbers are still unknown. They can survive for over a year by shrinking in size to as little as 10% of their full-grown body mass until they find a suitable habitat or worms to eat.

Can you help?

Sightings of the flat worm, and its eggs, should be reported. This will help give an indication of how far the worm has travelled. You can sign up to the Open Air Laboratories (OPAL) survey:

Advice for Gardeners

lf the New Zealand flatworm is already established in your garden it is very hard to eradicate. They will travel from neighbouring areas. You can set about catching them, by creating refuges ie stones, logs, weighted down polythene sheets in cool shady areas. Once the worms have gathered, destroy them – either by putting in hot water (>30c), sprinkling with salt, or squashing them. This has to be done regularly, as part of a sustained campaign. It is recommend that you do not touch them, the mucus can cause skin irritation. Wear gloves. And be sure to log your site onto the OPAL survey web page.

Further advice from OPAL scientists here

If you are in doubt as to whether you have found a flatworm, and you need help with identification, check here