Australian and New Zealand flatworms

There are several native species and some non-native species of flatworm in the UK. The non-native Australian and New Zealand flatworms are two species that have become established. They feed on earthworms.

New Zealand and Australian flatworms

Quick facts

Common name Australian and New Zealand flatworms
Scientific name Australoplana sanguinea and Arthurdendyus triangulatus
Damaged caused Predatory on earthworms
Main symptoms Low populations of earthworms
Most active All year

What are Australian and New Zealand flatworms?

Flatworms (Platyhelminthes) are a group of unsegmented worm like animals and as the name suggests they are  flattened animals often with a ribbon like appearance. They are found throughout the world, in the UK there are three or four species considered native and ten non-native species that have become established.

All flatworms are predatory with some species feeding on slugs, others feed on earthworms. Australian and New Zealand flatworms are two species that have become established in the UK that feed on earthworms, in some areas earthworm populations have been affected.

The Australian flatworm is orange or pinkish orange and reaches 2-8cm in length. It was first detected in south west England in the 1960s and since then has become more widespread in southern England and Wales. This species does not seem to have had such a big impact as the New Zealand flatworm on earthworm populations. 

The new Zealand flatworm reaches 20cm (8in) in length and is dark brown with a paler margin. It became established in Britain during the 1960s and at first it was thought to be of no consequence. It was only when it had become widely distributed, that it was realised that it was feeding exclusively on earthworms and in some places reducing earthworm populations to a very low level. This has undesirable effects on soil structure and also denies earthworms as a food resource for those native animals that feed on them. This flatworm has come to Britain from New Zealand and is now thriving, particularly in the wetter parts of Britain, it is most common in Scotland, Northern England and Northern Ireland. 

If you find New Zealand flatworms these can be reported to the OPAL New Zealand Flatworm Survey

Symptoms

Flatworms are often found by gardeners under pots or containers. The lack of earthworms they can cause often goes unnoticed.

Control

  • Avoid spreading the flatworm to new areas that are as yet free of flatworms. It is likely to spread to new areas through the movement of growing plants, compost or soil, so be careful about giving growing plants to other gardeners
  • Once in a garden there is nothing effective that can be done to reduce flatworm numbers. Destroying any found underneath pots or stones will remove a few, but this is likely to be only a small proportion of the population in a garden
  • There are no pesticides available that will control flatworms

Biology

Flatworms belong to the class of animals Platyhelminthes, they are unsegmented worms and can be found in a variety of habitats throughout the world. Many species are aquatic although a few are found on land, land flatworms are generally smooth and slimy.

In the UK there are three or four native and about ten non-native species.

There biology and what they feed on is often not well known although they are  predatory. Flatworms are hermaphrodite and they need to mate to produce eggs. Land flatworms lay eggs in the soil in small (<5mm) shiny black egg capsules. Flatworms also have the ability to reproduce by fission where a section of the animal detaches and becomes a new individual.

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