Land dwelling flatworms (Platyhelminthes) are invasive organisms that usually expand their range through the movement of plants. This process is largely tied to human activity, such as gardening and plant trade. Still, that explanation did not fully solve the puzzle. These worms move very slowly, raising the question of how they manage to show up in nearby gardens that have not received new plants.

Citizen science reveals pets as carriers

To explore this mystery, researchers reviewed more than twelve years of observations gathered through citizen science programs across France. The long term data revealed a previously overlooked pathway of spread. In several cases, flatworms were discovered clinging to the fur of dogs and cats, indicating that domestic animals can carry them between locations.

One invasive species stands out

Out of the roughly ten flatworm species that have invaded France, only one was linked to this type of transport: Caenoplana variegata. This species produces especially sticky mucus, which is related to its diet as a predator of arthropods. It can also reproduce without a partner, a trait that increases its ability to establish new populations after being transported.

Because pets travel substantial distances each year, researchers suggest that this form of movement could meaningfully contribute to the worldwide spread of certain invasive flatworm species.