That Slimy Thing on Your Pet Could Be an Invasive Flatworm Spreading Between Homes
If your dog or cat spends time outdoors, here’s something that might make your skin crawl — but shouldn’t make you panic. Researchers have confirmed that invasive flatworms can hitch rides on your pet’s fur, clinging to their coat after time in the yard or garden. The good news? These worms are not parasites. They do not feed on or live within your animal.
Still, finding a slimy worm tangled in your pet’s fur is understandably alarming. Here’s what the research says and what you should do if it happens.
What Researchers Found
A study published in PeerJ documented 15 pet-related incidents in France involving flatworms found on animals’ fur — 13 cats and two dogs. Parasitologist Jean-Lou Justine at the French National Museum of Natural History identified a recurring pattern while reviewing reports collected across the country. Owners described finding worms on their pets after the animals had been outdoors.
Among roughly ten introduced flatworm species recorded in France, only the Australian species Caenoplana variegata was consistently found on pets. Its mucus — a sticky coating the worm uses for movement and adhesion — appears to help it cling to surfaces, including animal fur.
One owner in southwestern France reported, “They cling to the hair of my Persian cats,” while another stated, “It was very slimy, stuck in the fur,” describing removal of the worm with tweezers.
These Are Not Parasites
This is the most important detail for pet owners: the flatworm does not infect your pet. Researchers categorize the interaction as phoresy, meaning the worm simply uses the animal for transportation. It does not burrow into skin, lay eggs on your pet or cause disease.
Researchers emphasize that while the worms do not infect pets, they may still cause irritation and concern for owners who encounter them unexpectedly. Veterinary response focuses on removal rather than treatment for infection.
How to Spot and Remove Them
Owners frequently noticed the worms only after their pets returned indoors. If you find one on your dog or cat, the worm can be removed with tweezers, as described by owners in the study. Because the flatworm produces a sticky mucus coating, it may cling to fur rather than fall off easily.
This isn’t limited to one country. Similar cases of flatworms found on pets have also been reported in countries including Australia, the United States, New Zealand and Brazil, suggesting that pet-assisted transport may not be limited to France.
Between 2020 and 2024, 10 of 137 recorded sightings of this species in France involved pets, representing 7.3% of cases. Over a broader dataset of 447 sightings, the species was found distributed across the country rather than concentrated in a single region.
In July 2025, the European Union listed three land flatworm species as invasive species of Union concern, reflecting growing awareness of their ecological impact.
Should You Change Your Pet’s Routine?
The research does not suggest that owners need to keep pets indoors or alter their routines because of these flatworms. The worms are not a health threat to your animals or your family.
That said, the species does prey on small soil-dwelling organisms such as woodlice, insects and spiders that play a role in maintaining garden ecosystems. Its ability to reproduce asexually allows a single individual to establish a new population if transported to a suitable environment. So if you do find one, removing and disposing of it helps protect your local garden ecosystem.
Flatworms are often introduced to new regions through potted plants. Dogs and outdoor cats then provide mobility by carrying worms across yards, sidewalks and fences. Because many instances likely go unnoticed when worms fall off outdoors or remain undetected, researchers note that current records likely underestimate the true frequency of pet-assisted spread.
Citizen-submitted observations have played a key role in identifying these patterns. If you spot a flatworm on your pet, documenting it with a photograph could contribute to ongoing research.
This article was created by content specialists using various tools, including AI.
