It’s dark, slimy, and one of the world’s worst invasive species. And it might be in your leaf litter.
Originally from Papua New Guinea, the New Guinea flatworm has made its way to North Carolina. On an international scale, it’s been spotted in countries including Australia, Japan, France, and the Philippines.
It’s partial to humid climates and is likely to crop up under rocks or inside plant pots.
“We can predict that it will be everywhere where it is hot enough,” said Jean-Lou Justine, a zoologist at the National Museum of Natural History in Paris, France.
How worried do we need to be that it’s here?
A quickly-spreading flatworm
These worms are very easily moved accidentally. It can be moved by anything from strict commerce to individuals bringing things from state to state.Matt Bertone
The New Guinea flatworm is about two inches long. It has a black body with a pale stripe down its back, looking a bit “like a little cartoon,” according to North Carolina State University entomologist Matt Bertone. Its easily transportable nature makes it likely to crop up in new areas.
“These worms are very easily moved accidentally,” Bertone said. “It can be moved by anything from strict commerce to individuals bringing things from state to state.”
The flatworm was first spotted in the United States in Florida in 2012. Since then, sightings have popped up all over Florida on the citizen science site, iNaturalist.
As of now, there are two iNaturalist reports of the New Guinea flatworm in North Carolina: one near Durham in 2018, and the other near Wilmington in 2021. Both were confirmed by Leigh Winsor, an international expert on flatworm identification and an Adjunct Senior Research Fellow at James Cook University in Australia.
Calculating impact
The New Guinea flatworm is a predator “of almost everything,” said Justine, and feasts on an invertebrate diet including earthworms, slugs and snails. Once in a new environment, the flatworm can dine on native species, reducing their populations. When it traveled to Hawaii, the flatworm slashed the ranks of native Hawaiian tree snails in Oahu.
Snails and slugs can be important food sources for birds and other predators. Most land snails also eat leaf litter, breaking it down to release nutrients in soil that plants can use. The loss of local snails and slugs could leave local predators with less to eat and decrease soil quality.
The flatworm could have a negative impact on native snail populations in North Carolina, but it’s difficult to tell.
“If [North Carolina] was an island, and there were some native snails and slugs, that can be a really big issue, because [the flatworms] can destroy those populations,” Bertone said. “Here in North Carolina, it’s hard to say whether they’re impacting anything. It’s hard to know exactly what’s happening out there.”
To get a clearer picture, Bertone said scientists would need to study environments in North Carolina before and after the New Guinea flatworm’s arrival, keeping an eye on snail and slug populations. The longer the flatworm lingers in North Carolina, the more scientists will know about its impact in the area.
When it comes to risks for humans, the New Guinea flatworm can be a host for rat lungworm parasite, a roundworm that causes a meningitis-like virus. However, the flatworm can’t spread the parasite merely from slithering around: it has to be eaten.
“They’re not deadly unless you were to eat a bunch of the poisonous one,” said Bertone. “I don’t think anybody’s going to be doing that.”
Keeping track of invasive species
New Guinea flatworms have no local predators that we know of. Once they’ve settled into a new environment, eradicating them is “basically impossible,” according to Bertone.
If you spot a New Guinea flatworm in your backyard, you can kill it in a bucket of soapy water or container of alcohol, but it won’t do much to stop the species’ spread.
“You can kill it, but that doesn’t mean that there’s not ten more around your yard that you don’t see,” said Bertone.
Reporting sightings of the New Guinea flatworm and other invasive species to websites like iNaturalist can be useful to track where they’ve been and where they are likely headed. The best thing North Carolinians can do is be aware that the flatworms are around, that they’re not an immediate danger to humans, and that they’re on the move.
“The key is prevention,” said Justine. “The key is not to be invaded by other species in the future.”
Want to learn more about predatory flatworms and other species? CREEP is a new podcast about creatures invading our space, and changing the world around us, presented by WUNC and the North Carolina Museum of Natural Sciences. Listen and subscribe wherever you get your podcasts.
Editor’s Note: An earlier version of this story described an outdated method of killing New Guinea flatworms. Researchers now recommend using soapy water or alcohol instead of boiling water.
