Invasive New Guinea Flatworm Has Made Its Way to Florida

A New Guinea flatworm in Coral Gables, Florida. It has no known American predators and is likely to spread widely. Makiri Sei

Looking like a cross between a slimy slug and a flattened snake, the New Guinea flatworm has a renowned hunger for snails and the ability to live in just about any environment. In the past few decades, it has spread out of its native New Guinea to islands throughout the Pacific and as far away as France. It has now been discovered in mainland United States, in several gardens in Miami.

A study published Tuesday in the journal PeerJ shows that the odious worm has also made its way to Puerto Rico, Singapore, several New Caledonian islands and the Solomon Islands.

That's a major concern, as it is considered one of the world's worst invasive species, says study author Jean-Lou Justine, a researcher at the National Museum of Natural History in Paris. (In fact, the Invasive Species Specialist Group, a global network of scientific and policy experts, has placed the worm on their 100 worst invasive species list.)

The New Guinea flatworm in New Caledonia. Scale is in centimeters. Claire Goiran

Researchers from around the world reported findings of flatworms in the new areas, after which they sent photographs and DNA samples to Justine in Paris for his confirmation.

The flatworm (Platydemus manokwari) has few natural predators outside of New Guinea, and it likely will have no predators in the United States, Justine says. It gobbles up soil-dwelling invertebrates like snails, which could have a big impact on the environment.

"It will not make differences between abundant common species and rare endemic snails," Justine says. "In that, it is a significant potential threat to all [native] snail species." This could ripple up the food chain to affect creatures that eat snails, like birds. It could have impacts in the other direction of the food chain as well: The plants that snails eat, like certain weeds, might spread and become overgrown.

In New Guinea, the worm is found in high-elevation areas where temperatures occasionally dip below freezing, but not in colder areas. That means it isn't likely to spread into the extreme northern U.S. or Canada. It also isn't likely to end up in the deserts or in rockier mountain areas, since it prefers areas with soil and plants. However, it could probably find itself at home just about anywhere else in the Americas.

Previously, the flatworm was mostly found on islands, where its spread is limited by factors including "customs and quarantines, and simply by the fact that merchandises are transported only by boats or planes," Justine says. The flatworms in Florida face no such limitations.

A New Guinea flatworm eating a Mediterranean snail. You can see the white pharynx, or feeding tube, of the worm, which is ingesting the snail's tissues. Pierre Gros

In fact, it has probably already spread to many gardens in Miami, since these "are often attended by professionals with many clients. Movements of the flatworm from garden to garden together with soil, compost, rooted plants, potted plants and garden waste will certainly disseminate the invasive species," Justine adds.

Once they are in an area, it is very difficult to halt their spread, since they are small—2 inches long—and live in the soil.

Justine recommends not touching them. "Land planarians," a family of flatworms that includes the New Guinea variety, "produce dangerous chemicals and release them with their mucus, which is a protection against possible predators," he says. "These chemical substances can be toxic and could induce allergic reactions."