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New Guinea flatworm (Platydemus manokwari) ingesting the soft tissues of a Mediterranean snail

New Guinea flatworm (Platydemus manokwari) ingesting the soft tissues of a Mediterranean snail

Pierre Gros

Snail-killing worm invades U.S. mainland

Nearly 2 years after its debut in Europe, one of the world’s most dangerous invaders has come to the U.S. mainland. And it isn’t pretty. The New Guinea flatworm (Platydemus manokwari)—a squirming, 5-centimeter-long worm with a taste for escargot—has helped decimate some snail populations in certain Pacific Islands, and now it’s rearing its head in Florida, according to researchers.

Pairing molecular gene analysis with specimen observations, a team of experts led by Jean-Lou Justine of France’s National Museum of Natural History in Paris has confirmed that the carnivorous flatworm has taken up residence in Singapore, the Solomon Islands, New Caledonia, Florida, and Puerto Rico, as they report today in PeerJ. Previously, the worm had been found in 15 countries, mainly in the South Pacific.

In the past, the tiny worm has found a valuable traveling companion in humans, who have helped spread the animal around the world—both accidently through the international plant trade and intentionally to control pests like the giant African land snail. The discovery in Florida, however, represents a new, worrying sign to researchers.

“The Florida record matters more than the others because it’s on the mainland,” Justine says. Now, the worm can spread naturally throughout the rest of the state and—potentially—the rest of the country, he says.

David Robinson, a malacologist with the U.S. Department of Agriculture in Philadelphia, Pennsylvania, and one of the study’s co-authors, first spotted what looked like the flatworm in Florida a few years ago, and he feared the worst. “But I wanted to find an expert before sounding the alarm,” he says. After reading Justine’s 2014 study on the worm’s first and only European appearance in a greenhouse in France—an event that led some to predict the demise of the country’s beloved escargot—he sent his photographs and specimens to Justine, who confirmed his suspicions.

Although they also eat earthworms and insects, the olive black creatures—whose mouths are located in the middles of their white bellies—are voracious when it comes to land snails. They are thought to have helped drive several species of these snails to extinction in parts of the Pacific Islands. The aggressive worms are even known to pursue snails into trees.

“This is a pretty big deal for snails and for all of the other animals such as firefly larvae, some songbirds and amphibians, and reptiles that eat snails,” says Marla Coppolino, a land snail scientist and research associate with the Paleontological Research Institution in Ithaca, New York, and the Delaware Museum of Natural History. Most land snails in North America feed on decomposing vegetation and animal matter, absorbing nutrients such as calcium, magnesium, and manganese in the process. These nutrients are in turn essential to the snail’s many predators, especially the egg-laying ones.

And although snails can tuck into their shells for protection, many North American species are still vulnerable to predators like the flatworm, which can wedge its mouth into the gastropods’ protective housing and consume their flesh. While the flatworm feeds on the invasive giant African snails—a major pest in Florida’s Miami-Dade and Broward counties—it could also target endemic snails, which are in particular danger because their limited natural ranges make it even easier for them to be driven to extinction, Coppolino says.

Still, France’s snails haven’t vanished yet, mainly because the flatworm has been contained to the greenhouse where it was originally found. The big unknown for the United States is how sensitive to freezing the tropical and subtropical flatworm will be. “If the flatworm turns out to have the same effect on American land snails as on the ones in the Pacific Islands, and if it can withstand freezing, then it would be a disaster,” says Gustav Paulay, a marine snail expert who is the curator of invertebrates at the Florida Museum of Natural History in Gainesville. “But I’m hoping that it won’t be able to handle freezing, which means its range will be restricted.”

“I think the threat to the continental U.S. is overstated,” says Robert Cowie, a research professor who studies snails at the University of Hawaii, Manoa. “It could perhaps spread in parts of Florida and other parts of the more humid southeast, but I do not see it as a threat further north, although enough global warming could change that.”

Besides, Cowie points out, in some areas where the flatworm is found, such as the Hawaiian Islands, it hasn’t become widespread or a major threat to Hawaii’s endemic snails, although it’s unclear why. For now, the chance of it wiping out an entire U.S. snail species seems limited, he says.