Introduction: The land flatworm Obama nungara is a terrestrial flatworm that was recently (2024) discovered in Sweden. It originally comes from South America and is considered an invasive alien species in Europe. The worm is a predator that feeds on, among other things, earthworms and slugs, which can disrupt the balance of our ecosystems. It has no natural enemies here and can reproduce quickly, so it is important that the public is aware of the species and helps prevent its spread.
Key features – How to identify the species
Size: Fully grown worms are about 5–8 cm long and about 5 mm wide. Juveniles are much smaller (newly hatched only ~1 mm). The land flatworm is therefore significantly larger than any native flatworms, which are very small.
Appearance: The body is flat, thin and slimy with a glossy upper surface. Colour varies from beige to dark brown with blackish longitudinal lines on the back, while the underside is light beige. The worm can resemble a small slug without a shell, but it lacks the slug’s tentacles and lacks the segmentation of an earthworm.
Behaviour: The land flatworm lives on or just below the soil surface. It is most often found hidden under leaves, pieces of wood, stones or pots. The species is most active at night (after dusk). In torchlight it can glisten, which helps when searching for it.
Eggs: The worm lays eggs in small capsules, about 5 mm in size. The egg capsules are bright red when freshly laid and darken to brown-black after a few days. They can be found in the soil, often under pots or in planting boxes. Each capsule can contain many new small worms.
Risks to ecosystems and gardens
The land flatworm poses a risk to biodiversity and soil health. Because it eats important soil-dwelling animals such as earthworms, snails and slugs, it can cause an imbalance in the ecosystem. Earthworms play a crucial role in breaking down organic matter and keeping soil loose and nutrient-rich. If earthworm numbers decrease drastically, soil quality deteriorates – which can affect both gardens and agriculture (for example, reduced plant vigour and yields). Snails and other small animals that the land flatworm eats also normally contribute to the decomposition of plant material, so their loss affects natural nutrient cycles.
An additional risk is that the land flatworm has no natural enemies in Sweden. This means the population can grow quickly and reach high numbers if the species becomes established. In Europe, gardens have been observed with thousands of flatworms once they gain a foothold. Such mass occurrence can severely disrupt local ecosystems. Overall, this is why Obama nungara is classified as a harmful invasive species that needs close monitoring.
Pathways of spread – How does the land flatworm spread?
This flatworm spreads mainly through human activity, as it crawls relatively slowly and can hardly spread far on its own. It often travels with soil or plants that are moved between locations. Trade in potted garden plants is the greatest spread risk – worms or eggs can hide in potting soil. The import of plants from abroad has been identified as the source of how the species arrived in Sweden. Swapping plants between hobby growers, or moving plants/soil from one garden to another within the country, can also spread the worm further if you are unlucky.
Example of spread: when you buy a new potted plant, there may be land flatworms or eggs in the soil without you noticing. The worm can also spread via compost if contaminated plant waste or soil is added and then used in new beds. In short, soil, potted plants, potting compost, compost and other plant materials can act as transport routes for the land flatworm. That is why it is important to be careful when handling soil and plants, especially if they come from areas where the worm has been found.
Handling and reporting sightings
If you suspect you have found a land flatworm in your garden or on a newly purchased plant, you should act quickly and in an environmentally responsible way. Do not use pesticides or chemicals to try to kill the worm – such products can harm other organisms and the environment, and there are no approved pesticides specifically for this species. Instead, follow these steps:
Collect the worm carefully: Put on disposable gloves (the worm’s slimy secretion can irritate the skin). Pick up the worm carefully and place it in a jar or a sealable plastic bag. Avoid splitting or cutting the worm – it can survive if divided.
Kill the worm humanely: The safest methods are heat or cold. Pour boiling water over the worm in the jar or place the jar in the freezer for at least 24 hours. These methods kill both the worm and any eggs. (NOTE: Do not cut the worm in half! Splitting it can result in it surviving and continuing to spread.)
Isolate affected plants: If the worm was found in a potted plant, keep that plant separate from others. Inspect the soil and pot carefully and remove any worms or egg capsules you can find. Continue checking the affected plant daily for at least two days. If you find more worms the next day, remove them and wait a further two days without any findings before considering the plant safe. You can also heat-treat the root ball by placing the entire pot in about 40 °C warm water for at least 15 minutes (make sure the internal soil temperature reaches ~38–40 °C) to kill worms and eggs.
Destroy eggs and contaminated soil: Be careful not to spread any soil from the affected area into your garden. Egg capsules can be very small and hard to see with the naked eye. If you spill soil that may contain eggs or young worms, collect the spill. Place soil and any eggs in a tightly sealed bag. Dispose of it as combustible household waste – absolutely not in compost or garden waste! You should not risk eggs surviving and spreading via compost. Soil can also be sanitised by heating (for example in an oven or using the warm-water method above) if practical.
Report the finding: It is important that authorities are informed about all findings so they can monitor spread. Photograph the worm (preferably before you kill it) and note where you found it. Then report the sighting via the online form for invasive species (for example on invasivaarter.nu or Artportalen). Alternatively, contact your County Administrative Board (Länsstyrelsen) and report by email or phone. Attach the photo and provide the location, and whether the worm arrived with a purchased plant (ideally include which shop or supplier the plant came from). By reporting, you help experts confirm the species and map its spread so the right measures can be taken.
Practical tips to reduce the risk of spread
Inspect new plants carefully: When you buy or bring home new plants, make a habit of inspecting them before planting out. Look under pots, in the bottom of any transport trays, and in the top layer of soil. Carefully lift the plant out of its pot and check the underside and sides of the root ball. Use a torch – even in daylight – as the flatworm’s slimy body can glisten in the light.
Isolate newly purchased plants for a couple of days: Keep new potted plants separate, ideally on a hard surface (for example paving) where any worms cannot escape into garden soil. Keep them away from your other plants for the first 2–3 days and carry out repeated checks during this period. If you discover a worm or eggs on a new plant, keep it in quarantine and check daily until you are sure there are no more before planting it out.
Heat-treat suspected soil: If you suspect soil in a pot may be contaminated (for example if a worm has been found there), you can treat the soil with heat. Submerging the pot or root ball in approximately 40 °C water for at least 15 minutes kills most worms and eggs. Then keep the plant isolated for an extra day as a precaution.
Dispose of infested material safely: Never put plant waste, soil or plants that may contain land flatworms into normal compost or out in nature. Put them in a sealed plastic bag and dispose of them in the bin for combustible waste. This prevents the worm from spreading via waste or compost soil.
Ask questions when buying: Buy from garden centres or nurseries you know are aware of the issue and actively work to prevent the spread of invasive species. Ask staff whether they inspect incoming plant deliveries for the land flatworm or other pests. Choosing responsible retailers reduces the risk of bringing home unwanted “hitchhikers” in the soil.
Share the information: Talk to neighbours and fellow growers about the land flatworm. Greater awareness means more people keep watch and act early. The earlier an infestation is detected, the greater the chance of limiting spread.
With these measures and precautions, we can together reduce the risk that the land flatworm spreads and becomes established. Stay alert when handling plants and soil, and do not hesitate to report suspected findings. In this way we protect our gardens and ecosystems from this new invasive species.
Author: Emma Vogiatzi
Fact-checked by: Erik Hoekstra
Last updated: 2026-01-08