A hammerhead flatworm (Bipalium vagum) in French Guyana Photo : Sébastien Sant

France is known for many of its cultural items, including exceptional cuisine, wine, and the Louvre. Soon, it may also be known for its arm-length, shovel-headed, carnivorous worms.


New research suggests that several species of these discomfiting creatures—known as hammerhead flatworms—have slithered into the country as invasive species. Perhaps even stranger is the fact that they’ve been establishing themselves in France almost undetected for decades.



Hammerhead flatworms don’t look like they belong on Earth. The ribbon-shaped critters that sport a bizarre fan-shaped “headplate” that makes them look unnervingly like that alien “Hammerpede” thing that killed a bunch of scientists in Prometheus. Most of them are about the size and shape of a fragment of cooked fettuccine noodle, but some giants can reach intimidating lengths of a meter or more.


They are also ravenous predators of soil invertebrates like earthworms and slugs, which they immobilize with powerful muscles and, in some species, tetrodotoxin—the same paralytic poison in pufferfish. Once prey is captured, the flatworm everts its “stomach” out of its mouth, secretes digestive enzymes, and slurps the victim’s liquified tissues up into its gut.

All of this is perfectly fine and normal and not terrifying in the least.

Bipalium kewense killing an eathworm Photo : Pierre Gros

Their predatory nature is cause for concern, though, because several species of hammerhead flatworms—originating in places like Madagascar, India, and Southeast Asia—have colonized vast portions of the globe, and it’s not well-understood how these invasive predators are impacting local species. The new study, published today in the journal PeerJ, highlights just how far the worms have spread under our noses.

The presence of hammerhead flatworms in France first came to the attention of Jean-Lou Justine—lead author and parasitologist at the French National Museum of Natural History—in 2013.


“A colleague sent me a photograph of an unknown land flatworm, taken in France,” Justine told Earther. “That was unusual and unexpected. After a few other emails, I realized that several species were involved and that nobody was working in this field.”

What followed was a national flatworm survey driven by citizen science. Justine and his colleagues advertised that they were looking for these strange worms, and over the next four years, hundreds of reports poured in from across the country and overseas French territories. Some people just sent in photos of weird, unfamiliar worms in their gardens. But other accounts are jarring, like a record from 2013 where a kindergarten class was terrified of hundreds of “small snakes” wriggling in the grass.


Others sent in live worms by post, which Justine says was critical for using genetics to ID the worms to species.

Diversibipalium multilineatum recreating a scene out of Life (2017) Photo : Pierre Gros


In the end, Justine and his team found that five species of hammerhead flatworm are present in France and its overseas territories, all of which appear to be non-native and likely also invasive.



Perhaps most shocking was that two invasive species likely originating from Asia—Bipalium kewense and Diversibipalium multilineatum—were consistently turning up in gardens in metropolitan regions of France. These two species theoretically would be hard to miss, being brightly-colored and capable of growing as long as your shin, yet they went relatively unnoticed by scientists or governmental authorities for twenty years. Incredibly, some of the accounts sent in to the research team dated back to 1999.


Justine isn’t sure how such conspicuous animals could evade official acknowledgement for so long in such a densely populated area, but he thinks widespread unfamiliarity with terrestrial flatworms—even among scientists—may be partly responsible.

“We have reports by some citizens that they went to universities with their flatworms in a small box and that they were not taken seriously,” Justine said, “probably the person who received them simply did not know what the animals were.”




Diversibipalium ‘blue’ in Mayotte, showing off its mesmerizing, glittery coloration Photo : Laurent Charles

That such a high diversity of invasive predatory animals has slipped by undetected is a bit of a wake up call. It isn’t known exactly how introduced flatworms will impact local soil ecology, but their diet of earthworms makes their spread legitimately worrying.




“Earthworms are a major component of the soil biomass and a very important element in the ecology of soils,” Justine said. “Any predator which can diminish the populations of earthworms is thus a threat to soil ecology.”

Jake Buehler is a science writer living on Washington’s Olympic Peninsula with an adoration for the Tree of Life’s weird, wild, and unsung—follow him on Twitteror at his blog.