Invasive Flatworms Discovered in Sweden Threaten Local Ecosystems

Two invasive flatworm species have been discovered in Sweden, raising ecological concerns. The Asian hammerhead worm (Bipalium kewense), originating from Southeast Asia, can grow up to 40 centimeters and emits chemicals that may cause skin irritation in humans and even vomiting in cats. It was first found in Sweden in late 2022 in a Karlstad store among imported Mediterranean plants. Another species, Caenoplana variegata from Australia, has been detected in Swedish nurseries. This worm produces a sticky mucus that can cling to pets but is not harmful to them.

Researcher Chahinez Bouguerche from the Swedish Museum of Natural History highlighted that these flatworms are spread primarily through international trade in ornamental plants. They often hide under pots, in moist soil, or among garden waste, silently preying on earthworms, spiders, and insects—a situation complicated by the lack of natural predators in Sweden.

While the Asian hammerhead is not expected to survive harsh Swedish winters, other invasive species like the South American leaf flatworm have already established themselves locally. Authorities urge the public and plant stores to carefully inspect plants and report any sightings to the Swedish University of Agricultural Sciences' species database to monitor and manage these invasive populations effectively.