For the past 20 years, towns in southwestern France have been invaded by giant cloned flatworms, and no one noticed.
A paper published in the journal PeerJ reports the widespread existence of five species of long, hammer-headed worms. Two of them are unknown to science, and some grow up to 40 centimetres, eat earthworms and should be considered, say the authors, “as active predators [that] constitute a danger to native fauna wherever they are introduced”.
Using reports by citizen scientists compiled between 1999 and 2017, a team headed by Jean-Lou Justine from the National Museum of Natural History in Paris identifies the invading creatures as land planarians – flatworms that belong to two genera, Bipalium and Diversibipalium. The worms stemmed originally from warm regions in Asia, but international trade has spread them to many countries around the world.
Indeed, Justine and his colleagues also report the presence of the flatworms in most French overseas territories, stretching from Polynesia in the Pacific, Monserrat near Central America, and La Reunion Island, off the south-east coast of Africa.
In France itself, planarian colonisation was widespread, but tended to find its most dense expression in a small region in the Pyrenees-Atlantiques department, at the southwest extremity of the country, in the Basque lands.
The number and diversity of the worms in the region, the scientists suggest, is because of the mild local weather.
The researchers tested the samples they acquired for variation in a portion of mitochondrial DNA known as “cytochrome c oxidase subunit 1” – commonly used to “barcode” genomes.
They found no differences at all, implying that the worms in each species were all clones of each other and that sexual reproduction had not been occurring.
Justine and colleagues urge authorities to treat the giant worms as invasive and dangerous to local fauna and farmland, calling for control strategies to be developed.
They also could not resist adding a note of incredulity regarding the fact that presence of planarians was unrecognised until they decided to collate isolated citizen science reports.
“We were amazed,” they write, “that these long and brightly coloured worms could escape the attention of scientists and authorities in a European developed country for such a long time.”
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