OPAL New Zealand Flatworm Survey

Data entry for the OPAL New Zealand Flatworm Survey is now closed.  However, survey resources and identification guides can still be downloaded for free below. 

Thank you to all those who took part in the survey!

Survey data will soon be available for download from the OPAL website.

In addition, all verified New Zealand Flatworm sightings will be uploaded the NBN Atlas, the principal national repository for biological recording data, thus ensuring that collected data is available for scientists and policy makers.

Family find a flatworm under log

The New Zealand Flatworm was introduced into the UK in the 1960s and feeds on earthworms.

The New Zealand Flatworm Survey was created to find out how far this flatworm has spread and what influence it is having on the environment.

How to identify flatworms

The New Zealand Flatworm is a flat, ribbon-like organism, and has a dark purple-brown upper surface with pale margins and a creamy pale underside.

They are usually about 0.3-1cm wide and 5-15 cm long and are pointed at both ends and covered in sticky mucus.

New Zealand Flatworm and eggTheir egg capsules look like blackcurrants, though smaller, and contain about 7 young flatworms, so it’s important to spot these and not move them to new locations.

Where to find them

New Zealand Flatworms are usually found under pieces of wood, stone or polythene or lying on bare earth often curled up like a Swiss roll. They leave slime circles where they’ve been resting. 

Flatworm facts

New Zealand Flatworm coiledNew Zealand Flatworms attack earthworms by wrapping their bodies around them and secreting digestive mucus to dissolve them before consuming them.

Amazingly, New Zealand Flatworms can survive for over a year by shrinking in size to as little as 10% of their full-grown body mass until they find another earthworm. 

More info

For more information about the ecology, invasion history, distribution and impact of New Zealand Flatworms, download the following resources:

How to take part

While it is hard to control New Zealand Flatworm once present, learning more about their distribution can help target initiatives to prevent further introductions via gardens, soil movement etc.

This is where you come in…

  • Step 1 – Download and print the survey postcard.
    New Zealand Flatworm Survey Card
  • Step 2 – Explore your local outdoor space and look for New Zealand Flatworms.
  • Step 3 – Although data entry for the OPAL New Zealand Flatworm Survey is now closed, you can submit a sighting via iRecord.


Explore results from the OPAL New Zealand Flatworm Survey on an interactive map:

By downloading this survey you agree to the terms and conditions for the OPAL New Zealand Flatworm Survey