Giant Flatworms Invade France, Science Finally Notices

Paper's authors 'amazed' how nobody in power reacted to the arrival of brightly colored hammerhead flatworms, until 'citizen scientists' took photos of them

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Diversibipalium multilineatum: One of the species of Hammerhead flatworm that invaded France
Diversibipalium multilineatum: One of the species of Hammerhead flatworm that invaded FranceCredit: Pierre Gros / CCBY 4.0
Ruth Schuster
Ruth Schuster
Ruth Schuster
Ruth Schuster

There are invasive species and there are invasive species. France finds itself the reluctant host of giant flatworms that can reach the length of your arm.

In an article wonderfully titled "Giant worms chez moi!" Jean-Lou Justine of the National History Museum in Paris and the team share their feelings: "The authors were amazed to discover that conspicuous 40-cm long worms could invade a developed European country for more than two decades without any response from scientific authorities."

Hammerhead flatworms originated in Asia, and the fact that they're being found around the world is generally ascribed to the international trade in plants. They get transported with the earth, for instance. They are distinguished from other flatworms by the hammer-ish shape of their head, if one squints. Let's just say they have big heads at the end of slim wormy bodies.

Bipalium vagum, a hammerhead flatworm invading French GuyanaCredit: Sebastien Sant / CCBY 4.0

They also tend to be brightly colored, again begging the question of how the authorities failed to notice their arrival and proliferation. Maybe it's because they live, to be fair, underground.

Bipalium kewense (right) killing an earthworm.Credit: Pierre Gros / CCBY 4.0

Anyway, the report on people finding Asian hammerhead worms up to 40 centimeters long in metropolitan France, and somewhat smaller ones in French-speaking territories in the Caribbean, South America, Africa and Oceania, appeared Monday in the open-access journal PeerJ.

"Several invasive flatworms, including the New Guinea flatworm, Platydemus manokwari, have already been reported from France," write Justine and the team, following work by citizen scientists, which is probably a euphemism for absolutely horrified people.

More than 100 photographs arrived from people noticing the planarians, some dating as back to 1999, the paper says.

So far people sending experts photographs of worms has unveiled five species of hammerheads in France and its territories. Two of the species seem to be unknown to science, including a turquoise type found on Mayotte, off the African East Coast.

Happily, most of the invasive planarians infesting France are smaller than your pinkie.

This is a blue Diversibipalium hammerhead flatworm in Mayotte.Credit: Laurent Charles / CCBY 4.0

But first of all, the two giant species noticed so far (Bipalium kewense and Diversibipalium multilineatum) were in "metropolitan France," not some remote island. Secondly, hammerheads can grow to be over a meter in length, though none of that size have been reported from France. Yet.

Hammerhead flatworms are predators that eat other soil-dwelling animals, such as other worms. What effect the invaders are having on the ecology of the host soil has yet to be elucidated, though a good place to study that might be metropolitan south–west France, which proved to be a hot-bed of flatworm invasion, probably because of the clement climate, the researchers suggest.

One final note. Molecular studies on three flatworm species – found in more than one place – detected zero genetic variation. None. Meaning, they may look like giant penii but these animals do not have sex, the scientists postulate: they reproduce by cloning.


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