Dogs and cats can spread an invasive flatworm between gardens by picking it up on their fur, according to research. This illustrates how a slow-moving species spreads locally in spite of its restricted capacity for independent migration.
Owners reported seeing worms entangled in fur when their pets returned from the outside, according to accounts from all over France. Parasitologist Jean-Lou Justine of the French National Museum of Natural History (MNHN) began to see the same pattern as she went through those reports. The study included fifteen pet cases, two involving dogs and thirteen involving cats. Because it consistently identified the same species in these instances, that little count was nonetheless significant.
Why the mucus is important
Only the Australian species Caenoplana variegata continued to appear on fur out of the roughly ten invasive flatworm species found in France. The worm uses its mucus, a smooth covering that facilitates movement and adhesion, to seize prey, which makes it appear unusually sticky.
Woodlice, insects, spiders, and other tiny soil creatures that support garden life are examples of this prey. A single dropped worm may create a new local population because European populations reproduce asexually, creating progeny without a mate.
Plants, flatworms, and pets
Potted plants continue to provide an explanation for how invasive flatworms initially cross borders and get to nurseries. After that, problems arise because a worm moving at only a few inches per minute shouldn’t be able to get to the next street with ease.
Dogs and outside cats provide an easy solution by transporting the animal across sidewalks, lawns and fences. As a result, pets become less of a curiosity and more of the final stage of the spread.
Huge mileage, few sightings
Ten out of 137 French records for this species between 2020 and 2024 included dogs or cats. Despite the fact that Obama nungara, the flatworm most frequently reported in France, never appeared on pets, that amounted to 7.3%. Instead than concentrating in one area, the worm was found throughout France in 447 observations over the course of the lengthier record. Rare pickup incidents became to seem insignificant as researchers calculated that pets in France spend 11.2 billion miles outdoors annually.
Pets also sense it.
The worms were typically only discovered by owners when an animal returned inside, frequently with something sticky twisted in its fur. “They cling to the hair of my Persian cats,” commented an owner in southwest France about a persistent issue.
After using tweezers to remove the worm, another owner commented, “It was very slimy, stuck in the fur.” Despite the fact that the flatworm does not reside on pets like a parasite, those remarks imply that the worms may cause problems for pets.
Not a parasite for pets
The animals are carrying a brief example of phoresy, which is the use of one species for transportation by another. When the flatworm is trapped outside the body, it does not consume skin, blood, or tissue. This distinction is important because when a weird worm shows up on a dog’s coat or cat’s paw, owners could become alarmed. Veterinarians can record the animal’s roaming areas while treating the incident as irritation and removal rather than infection.
Danger outside of gardens
Because this species hunts woodlice, insects, spiders, and other small animals in soil and leaf litter, every carried worm is important. It would seem insignificant to remove that type of prey from a single garden, but repeated introductions might put strain on nearby food webs.
Three land flatworms were added to the EU’s list of invasive species of Union concern in July 2025. Controlling these animals becomes more difficult once they are in regular yards, which is another reason to treat pet transport carefully.
Beyond the gardens of France
Similar worms have been discovered on pets in Australia, the US, New Zealand, and Brazil, according to reports from countries other than France. These records suggest that domestic animals, not only this particular striped species, may aid a number of flatworm invaders.
Because people provided images and comments that MNHN researchers could fully read, citizen science made that pattern obvious. A worm on a paw might vanish into a dull record of location and time without the remarks.
Keeping people and pets safe from flatworms
Since the count only begins when owners discover a worm at home, even these figures most likely miss a lot of visits. While some worms probably fall off in a different yard, others might sneak up on a home and then crawl away.
Because of this bias, it is preferable to read the published cases as a floor rather than a complete census. Researchers now require more countries to provide teams like MNHN with the same information regarding worms on pets, as well as easier reporting mechanisms. This realization may alter how people monitor their animals, keep tabs on intrusions, and consider the invisible movement that passes through backyards.
