Giant predatory worms from Asia are invading France

Entomologists missed this giant worm invading France for 20 years.
Entomologists missed this giant worm invading France for 20 years.
Image: CC/Pierre Gros
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It’s not every day that an amateur gardener’s observations become the subject of scientific study. But one keen-eyed French naturalist named Pierre Gros has managed to alert professional entomologists to a long-ignored giant predatory worm invasion.

In a Peer J study published on May 22, “Giant worms chez moi!” zoologist Jean-Lou Justine of the Muséum National d’Histoire Naturelle in Paris, entomologist colleagues, and Gros, outline a discovery that “highlights an unexpected blind spot of scientists and authorities facing an invasion by conspicuous large invasive animals.” About 100 citizen scientists ultimately contributed to the assessment of this alien invasion, identifying five (!) giant predatory worm species in France that grow up to 10 inches long.

It all began back in 2013, when Gros photographed a large, never-before-seen worm in his garden. The photograph of the worm species, which is believed to have traveled from Asia via plants, eventually reached Justine’s email inbox. The zoologist told the Independent, ““I looked at it and said ‘Well, this is not possible–we don’t have this kind of animal in France.’”

Justine dismissed the image as a prank. But Gros offered further proof that the worms were real, and real weird, taking two more photos of giant exotic hammerheads—so called because of the distinctive flat, arrow shape of their heads, which resemble hammerhead sharks. This convinced Justine to verify the existence of these strange species.

Indeed, the worms were real. He and Gros soon embarked on a five-year assessment of the worms. “What we know now is that there are invasive flatworms almost everywhere in metropolitan France,” Justine says.

Map of giant hammerhead worms all over France and Corsica.
Hammerhead worms all over France and Corsica.
Image: CC/Justine et al.

The study relied on contributors’  worm sightings, reported “mainly by email, sometimes by telephone.” Researchers requested photographs and details about locality. In 2013, the Washington Post reports, “a group of terrorized kindergartners claimed they saw a mass of writhing snakes in their play field.” These were giant flatworms!

The study concludes that the alien creatures appear to reproduce asexually. They prey on other, smaller earthworms, stunning them with toxins. “The planarian also produces secretions from its headplate and body that adhere it to the prey, despite often sudden violent movements of the latter during this stage of capture,” researcher note. In other words, the hammerheads produce a substance that allows them to stick to victims while killing them.

Hammerhead "capping" an earthworm.
Hammerhead “capping” an earthworm.
Image: CC/Pierre Gros

France is not alone in facing alien worm invasions, the paper points out. In recent years, European scientists have reported invasive alien flatworms from New Zealand, Papua New Guinea, Brazil, and Australia—all “conspicuous animals, several centimeters in length.” But the five species of  hammerhead flatworms invading France are giants, growing up to 27 centimeters.

The giant hammerhead flatworms have also been observed in Guadeloupe, Martinique, Saint Barthélemy, French Guiana, Réunion, and Mayotte. Three of these species are attributed to known binomial taxa, including Bipalium kewense, B. vagum, and Diversibipalium multilineatum. Two are utterly alien to the stunned scientists and are as yet unnamed.

Justine now believes that the hammerheads been living in France for about 20 years. “I am still amazed,” he admits to the Independent. “I don’t understand how this is possible.”