BIG POND, N.Y. — Across their kayaks, the three men passed the green shoot back and forth. Occasionally, one of them would cradle it in one palm and bring a hand lens to it with the other, inspecting the carnivorous plant that was their bounty.
By day’s end, the group — Seth Cunningham and Michael Tessler, biologists at the American Museum of Natural History, and John Thompson, coordinator of the Catskill Regional Invasive Species Partnership — filled eight vials with the plant, Aldrovanda vesiculosa, also known as the waterwheel.
The plant shouldn’t be here, and it presents an ecological conundrum.
Around the world, the waterwheel is going extinct. But from summer through late fall, the carnivorous, rootless, wetland-loving plant is plentiful in this swampy body of water near the Catskill Mountains.
“It’s either site zero for saving a species,” Dr. Tessler said, “or site zero for a really big problem.”
Think of the waterwheel as an underwater Venus flytrap. Its whorled shoots are tiny, typically shorter than eight inches and less than an inch thick. But for a plant, its diet is impressive: seed shrimp, shell-less crustaceans, insect larvae, and occasionally even tadpoles and small fish.
When prey tickles one of the waterwheel’s traps, it snaps shut in less than 10 milliseconds, one-tenth the time it takes for your eyes to blink.
Until recently, the plant floated across fens, ponds and reservoirs in Australia, Asia, Africa and Europe. But today, human-driven habitat destruction has pushed the waterwheel into free fall.
Over the last 150 years, nearly 90 percent of its habitat has vanished worldwide, and the waterwheel’s survival status is extinct or unverified in at least 32 of the 43 countries where it naturally occurs. In 2012, the International Union for Conservation of Nature added Aldrovanda vesiculosa to its “red list” of globally threatened species.
“The species is completely imperiled,” said Adam Cross, an ecologist at Curtin University in Australia who studies the plant.
In 2013, Dr. Cross traveled to the Fort A.P. Hill army base in Northern Virginia to study a newly established population of more than 25 million waterwheels — at the time, more than the rest of the world’s populations combined.
But it’s doing more than just flourishing in the United States: In Virginia, the waterwheel is listed as a highly invasive species and a potential threat to native fish and plants. New Jersey includes the species on its invasive watch list, and it’s also considered invasive in New York.
“It was never native here, it’s exotic,” said Steve Young, chief botanist of the New York Natural Heritage Program, a branch of state government that promotes conservation. “And it’s acting like an invasive.”
It’s concerning when a nonnative plant immediately thrives, he added, even when, as in the waterwheel’s case, there’s no direct evidence yet of it crowding out native species or posing other economic, ecological or health risks.
But some botanists who don’t want the carnivorous plant to disappear see the Northeast’s waterwheels as a glimmer of hope for the species’ global survival — or at least a buffer against its extinction.
Other experts are still grappling with the question of whether an imperiled species can also be a menace. “How do you deal with the blurriness of that?” Dr. Tessler said.
The waterwheel is not alone in its double life as both ecological victim and environmental menace. In Southeast Asia, the Burmese python has been nearly snuffed out. But in Florida, where the pythons were originally imported as pets, officials are scrambling to keep 20-foot, 200-pound snakes from decimating local animal populations.
In the Great Lakes, conservationists battle invasive sea lampreys, overfished in their home region of southwestern Europe. A large garden bumblebee disappearing in Britain has begun to outcompete native pollinators in Argentina.
Is it possible to reconcile a creature’s double billing in both endangered species catalogs and invasive species indexes?
“It’s kind of the perfect paradox,” Dr. Cross said.
‘A quantum leap in growth’
The waterwheel made its American debut in the mid-1970s after trades between Japanese and American carnivorous plant growers. When growers in Virginia struggled to cultivate the Japanese plants in plastic containers, they introduced them to shallow backyard ponds, according to a 2013 account published in the Journal of the Torrey Botanical Society.
By the late 1990s, waterwheel transplants in five counties in Virginia had flourished into established populations. Around that time, Richard Sivertsen, a well known grower of carnivorous plants, decided to bring it to New Jersey and New York.
In 1999, Mr. Sivertsen (who died in 2017) picked a dozen sites, such as abandoned sand and gravel pits, small ditches and artificial koi ponds, which he deemed sufficiently isolated from pristine wetlands and larger water bodies. Then, having harvested some of the Virginia transplants, he drove around for two days, scattering Aldrovanda like a Tristate Johnny Appleseed.
Mr. Sivertsen found no trace of the plant when he returned to the spots — save one. In 2002, in a stinky discharge basin behind a shopping mall prone to green algal blooms and crawling with brown rats and tubifex worms, he spotted a familiar green shoot.
“A visit to the site one week later revealed that the shoots had made a quantum leap in growth,” he wrote in his 2013 account. Over the next decade, botanists documented similar spurts in the Northeast.
In October 2012, Chris Doyle, now director of biology at Solitude Lake Management, an aquatic consulting company, and his colleagues found thousands of waterwheels in Bear Swamp, near Lake Owassa in New Jersey.
“We had no idea what it was,” Mr. Doyle said.
By that year, waterwheels had colonized the edges of Big Pond in New York. Mr. Sivertsen’s son, Kevin, who was a child at the time, recalled his father’s surprise that a finicky species vulnerable to slight environmental changes had taken hold — let alone taken off.
“He was very concerned that the plant would go extinct and be wiped from the face of the earth,” said Kevin Sivertsen. “That was a big part of it for him. He was happy to take the risk of it intruding in a new ecosystem, rather than having it go extinct.”
In 2009, in an online plant forum, Mr. Sivertsen responded to a comment calling his introductions irresponsible: “I consider it as ‘farming.’” He added, “Let’s hope that some of us can find a way to keep it alive.”
“He didn’t realize what he was doing at the time,” Mr. Doyle said. “I think Richard understood later on that people don’t take kindly to inviting invasive species to undocumented habitats.”
Because its arrival is so recent and research so scarce, biologists don’t know how, or how quickly, the waterwheel may spread. They also don’t know what exactly it’s eating in local waters, which could help quantify the threat it poses, if any.
“‘Invasive’ implies that a species is detrimental,” Dr. Cross said. “There hasn’t been a sufficient level of study to say either way.”
In its native range, biologists have extensively studied the waterwheel’s ecological niche. It is highly specific to wetlands, where it is a predator of small invertebrates. Studies have suggested that it can coexist peacefully with other carnivorous plants, Dr. Cross said.
Still, little research has been conducted on the species to see if these findings hold true in North American ecosystems.
In a 2013 study to assess the species’ potential invasiveness, Dr. Cross and other researchers surveyed nine locations at Virginia’s Fort A.P. Hill. They found that, at its most abundant, waterwheels could pack 1,260 strands into each square meter. But the team concluded in a 2015 paper that it was not competing with native aquatic plants.
However, Dr. Cross pointed out, a robust waterwheel population of millions of strands, each studded with dozens of hungry traps, could threaten local invertebrates and other fauna.
Another 2015 study at the Virginia fort cautioned that in a single year, the species had spread from one 27-acre site to 156 acres of wetlands in at least five ponds open to recreational boating and angling — activities which could spread the species further.
Conservation officials are monitoring the plant to see if it’s spreading in New Jersey and Virginia, a task sometimes made difficult because they don’t have access to waters on private lands.
So far, New York’s sole documented site is Big Pond, and environmental DNA sequencing by Dr. Tessler has not turned up the plant’s genetic fingerprint in other Catskills ponds.
Still, officials worry it could spread to nearby waterways and outcompete native carnivorous plant species, Mr. Young said, such as bladderworts.
“It’s something we really need to watch,” said Mr. Thompson.
A survivor imperiled
Carnivorous plants thrive in bogs and other marginal habitats with limited nutrients by surviving on the bodies of small animals. That’s how the waterwheel has survived for about 50 million years.
But as humans have decimated or degraded wetlands for development and agriculture, Aldrovanda, too, has suffered. Warming climates, increasing drought and eutrophication — overly nutrient waters — have only exacerbated unfavorable conditions.
“It’s pretty clear why this species is going extinct,” Dr. Cross said. “It’s experienced an almost perfect storm of what humans can do.”
Now, it’s up to humans to decide what to do with the new, thriving populations in the United States.
It’s not the first time relocated waterwheel has stirred controversy. In 10 European countries, scientists have successfully reintroduced Aldrovanda to locales in which the plant had disappeared, said Lubomír Adamec, a plant ecologist at the Institute of Botany of the Czech Academy of Sciences.
Scientists also transplanted waterwheel to four countries where it never naturally occurred: Switzerland, Germany, Czech Republic and, around 2006, the Netherlands.
There are now tens of thousands of waterwheel strands in a nature reserve near Amsterdam. At first, Dutch authorities attempted to eradicate the plants, but now they have decided to let it be.
Dr. Adamec said he and other European researchers believe rescuing endangered species will increasingly depend on such transplants, “so that the case of Aldrovanda shall not be exceptional, but normal and ordinary in a near future.”
That can still feel like a gamble to wildlife officials in the Northeast, who are already scarred from battles with other invasive aquatic species, such as Eurasian watermilfoil and hydrilla, Mr. Doyle said. From their perspective, early prevention is cheaper than managing an explosion.
“Once it gets out of the barn, you might not be able to do much about it,” he said.
Once waterwheel is entrenched, management options are limited. While it can be hand-collected, just one or two individuals can seed an entire population. The alternative is an herbicide that kills every plant in the area.
With few practical options, Dr. Cross, Mr. Doyle and other experts have suggested the plant should remain monitored, but mostly left alone.
What should not happen again, according to Eric Lamont of the Long Island Botanical Society, are campaigns to introduce plants into environments where they did not evolve — however well intentioned.
“You don’t want to just willy-nilly introduce it to areas,” he said. “This is not the way to try to save a species.”