Snail-Eating Invasive Worm Discovered in Florida Gardens

By Joshua Rapp Learn

New Guinea flatworm Scientists recently discovered the New Guinea flatworm for the first time in the mainland U.S.The specimen here is pictured in Coral Gables, Fla.
Image Credit: Courtesy of Makiri Sei. CC- BY 4.0

A killer invasive worm with an indiscriminate appetite for snails and invertebrates has been discovered in Florida gardens — the first time the destructive species has turned up in the mainland United States.

“The climate in Florida is perfectly suited for this species,” said Jean-Lou Justine, a professor at the National Museum of Natural History in Paris and the lead author of a new study published in PeerJ.

A New Guinea flatworm

A New Guinea flatworm collected in a greenhouse at Caen, France. The white pharynx protruding from the underside of this flatworm is ingesting the soft tissues of a Mediterranean snail (Eobania vermiculite).
Image Credit: Courtesy of Pierre Gros.

The New Guinea flatworm (Platydemus manokwari) is around 50 millimeters long and 5 millimeters wide and is colored black with a clear central stripe. The worm feasts on land snails and other invertebrates mostly on the ground, though Justine said it can follow the mucus trails snails leave behind them for up to a meter high in trees.

The invasive worm, originally from the island of its namesake in the South Pacific, first made headlines last year when it was discovered in Caen, France. Newspapers made light of the threat it may cause for escargot — a French appetizer made of the mollusk.

In the case of France, the worm was discovered only in a greenhouse, which was quickly closed and the risk was contained. But the new discovery was made in several gardens in Miami.

“This time there is no joke at all probably because Americans do not eat escargot. It’s sad news for biodiversity,” Justine said, adding that it’s significant that the worm has been discovered on the mainland. The worm’s life cycle will continue unless the temperature drops to 50F, meaning it could spread through the southern U.S. and even down into Mexico and the rest of the Americas.

And that isn’t all. In the prey-predator curve, when predators consume all the prey in their immediate areas, they will often die out themselves for lack of additional food. But Justine worries that the New Guinea flatworm can subsist for weeks without eating, giving prey a chance to recover slightly before finishing them off again. This also allows it to travel around the world in agricultural products or in potted plants. “If you put one Platydemus manokwari in a pot, you can transport the worm to the other side of the planet … it will arrive in perfect health.”

New Guinea flatworm

The distribution of the invasive New Guinea flatworm. The blue represents previous records while the red represents new records reported in recent study published in PeerJ.
Image Credit: Courtesy of Justine et. al.

In fact, researchers found the flatworm in a number of other previously unknown areas, such as New Caledonia (mainland and Loyalty Islands), Tahiti (French Polynesia), Wallis and Futuna, Singapore, and the Solomon Islands. They also found worms in San Juan, Puerto Rico, and Justine worries that this may mean the worm is already found elsewhere in the Caribbean.

“It means that it can go from Puerto Rico to the other islands of the Caribbean, which also have their own endemic species. It would not be good for biodiversity.”

Experiments tracking the snails on some islands in the Pacific have shown that the flatworms increase in numbers and eat endemic snails important for other invertebrates and soil ecosystems. “[Snails] control weeds, they control mushrooms,” he said, but larger effects are still unknown.

“Is it going to destroy them all? I don’t know because we have no detailed scientific work about that,” he said.

Joshua LearnJoshua Rapp Learn is a science writer at The Wildlife Society.

Read more of Joshua's articles.