Non-native flatworms

There are approximately 21 species of land flatworms in Britain, only four are native. The non-native Australian and New Zealand flatworms, are perhaps best known and have become widespread. These animals are predatory and some feed on earthworms.

New Zealand and Australian flatworms
New Zealand and Australian flatworms

Quick facts

Common name  Non-native flatworms
Scientific name Platyhelminthes
Damaged caused Predatory on earthworms and other soil organisms 
Main symptoms Small, flattened, smooth worms. Found underneath pots and other sheltered areas on soil surface
Most active All year

What are flatworms?

Land flatworms (Platyhelminthes) are a group (class of animal) of free-living worms. They are small, flattened, animals often with a ribbon like appearance and unsegmented body. They are covered with mucus and usually leave a trail. They are found throughout the world, in Britain and Ireland there are about four species considered native and probably 17 non-native species that have become established, originating from the southern hemisphere.

The majority of the non-native flatworm species prey on earthworms, slugs, snails and other soil organisms. Australian and New Zealand flatworms are two species that have become established and widespread in Britain and Ireland. Both species specialise on earthworms and they can severely reduce the populations of some earthworm species and consequently affect the soil ecosystem. However, several other species had been accidentally introduced including two Kontikia species and there is evidence that non-native flatworms continue to be introduced including the Obama flatworm

The Australian flatworm (Australplana sanguinea) is salmon-pink, pointed at both ends and reaches 2-8cm in length. It was first recorded on the Isles of Scilly in 1980’s and since has become widespread in southern England and Wales.

The New Zealand flatworm (Arthurdendyus triangulates) reaches 20cm (8in) in length and is dark brown with a paler margin. It arrived in Britain, probably with imported plants, during the 1960s and it has since become widely distributed. It feeds exclusively on earthworms and is capable of reducing earthworm populations. 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 originates from New Zealand and is now thriving in Scotland, Northern England and Northern Ireland. 

The Obama flatworm (Obama nungara), was first reported in 2014, it is native to South America, and is spreading across Europe. Its name means ‘leaf animal’. It is up to 7cm long with a light brown to black coloured body with a pale middle line and small black marks across its body.  It preys on earthworm and snails. This species is considered extremely invasive, and it has been characterised as the most threatening flatworm species to the soil ecosystem and native soil organisms presently in Europe.

The black and brown Kontikia flatworms (Kontikia ventrolineta and Kontikia andersoni) are small (1-2.5cm long and 1-2mm wide), native to Australia and New Zealand. Kontikia ventrolineata is black coloured with two narrow grey lines, the first report in Brtain was from Liverpool in 1994. It is known to feed on small snails and possibly slugs. Kontikia andersoni is pale brown with three lines of darker spots along its body.

Because of their potential impact to populations of earthworms and other soil animals, the introduction of non-native flatworms poses a great risk to agriculture and horticulture. As such all non-native flatworms are included under schedule 9 of the Wildlife and Countryside Act 1981, which states that it is an offence to introduce or release them into the wild. Additionally, the New Zealand flatworm is included in the Invasive Alien Species of European Union Concern list.

If you find non-native flatworms they can be reported to the Non-Native Secretariat

What is the problem?

Flatworms are usually found in shady and wet places on the soil surface e.g. under pots, containers, tarpaulins, and leaf litter. The lack of earthworms they can cause often goes unnoticed.

Why flatworms pose a risk?

They are not plant pests, but the majority of non-native flatworms eat native earthworms, slugs, snails and other soil organisms.
They pose a threat to soil biodiversity and natural ecosystems. Australian and New Zealand flatworms that feed on earthworms, can have an impact on wildlife species dependent on earthworms (e.g. birds and small mammals) and could have a long-term harmful effect on soil structure locally.

Non-native flatworms are considered invasive and are included in Part I of Schedule 9 of the the Wildlife and Countryside Act 1981, which states that is an offence to release or allow to escape into the wild.



Introduction into gardens and surveillance
  • Flatworms are hitchhikers and are usually introduced into our gardens via plants bought from plants sales, plant swaps, garden centres, and nurseries
  • If you are buying plants for your garden, you can inspect your pots and new plants carefully to help prevent the introduction of flatworms into your garden
  • Flatworms like damp places and they often hide at the base of plant pots, between the root ball and the inside of the pots
  • In the garden, you can also find them under loose turf, plastic or other sheeting, rocks, flat stones and plant containers. Egg capsules can also be found in such areas
  • Due to the mucus, flatworms can also attach themselves onto gardening tools, plastic sheets and machinery, which can potentially be another entry pathway, ensure you follow the procedures and principles for reducing plant disease transmission.  
  • Where containers stand on black polythene, mypex or capillary matting. Where possible frequently check the underside of the polythene or matting for the presence of flatworms
If you find flatworms in your garden avoid spreading them to other areas:
  • Avoid the exchange of plants between gardens; re-use of top soil or compost can be responsible for the spread of flatworms. So be careful about giving 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

How to check for flatworms

  • Check whether flatworms have hidden under pots; they may still be on the ground surface or they may be adhered to the underside of the pot
  • They particularly like to hide in the grooves at the base of the pot
  • When planting new plants, carefully pull out the root ball and check the sides and the base of the root ball for worms and eggs. Note that flatworms can curl up into a small ball, which makes them harder to see


Flatworms belong to the class of animals called Platyhelminthes, they are unsegmented worms (as opposed to segmented earthworms) and can be found in a variety of habitats throughout the world. Many species are aquatic although a few can be found on land. Land (terrestrial) flatworms are generally smooth, slimy and have variable colours.

In Britain there are about four native species, these are generally smaller than the non-native species.

The biology and feeding preferences of most flatworms are not well known. It seems to vary with the species and available food sources. Many flatworms are thought to be generalist predators of soil organisms, capable of feeding on animals much larger than themselves, whilst some species are detrivores (feeding on dead material).

All flatworms are hermaphrodite; they have a complex system of both male and female genitalia and they produce hard-shelled egg cocoons (egg capsules). These are laid in the soil, are small (<5mm), shiny and black, resembling blackcurrants. Some species are also capable of reproducing by fission, whereas the flatworm divides and the separated segment regenerates and produces a new individual. Like slugs and snails they produce mucus, which not only help them to move and attack their prey but also protects them from dehydration.

Join the RHS

Become an RHS Member today and save 25% on your first year

Join now

Gardeners' calendar

Find out what to do this month with our gardeners' calendar

Advice from the RHS

Get involved

The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.