They have webbed feet, sharp orange-stained teeth and can weigh as heavily as hounds. They infest marshlands across the country, chewing up forests, weakening up coastlands for hurricanes and the sea. Giant swamp rodents, called nutrias, are transforming the American South, forcing southerners to adapt to them.

“ Nutria are a bane to the wetlands,” said Michael Massimi, an environmental scientist with the Barataria-Terrebonne National Estuary Program, in Louisiana. “The ecological consequences have been a disaster.”

Nutrias are a case study in how invasive species can worsen the effects of climate change and upend ecosystems humans rely on. In the late 1990s, when the state’s Department of Wildlife and Fisheries began to track the damage, officials found nutrias were destroying over 100,000 acres of marshland a year. “Bulldoze is a good way to put it,” Massimi said. “They denude the area.”

The marshlands are Louisiana’s shield from hurricanes, storm surges, and the rising sea levels of climate change, but nutrias have chewed into them for generations. Unlike their native competitors, like muskrats or marsh deer, nutrias tear up the roots that hold the soil together. Tides eventually carry this loose Louisiana earth away to sea; hurricanes and storm surges can haul packs of dirt away in a single day or night.

Louisiana loses around 25 square miles of land to the sea every year, according to NOAA, and could lose 2,800 square miles over the next 40 years. Losing marshland exposes cities to storms, hastens erosion, and destroys the ecosystems that commercial fishermen rely on to replenish their stocks. “These are critical areas that we can’t afford to lose,” Massimi said.

The slow-motion disaster has many causes, most importantly the unintended consequences of canals, levees, and oil and gas dredging. But in this landscape of manmade infrastructure, warming temperatures, and increased flooding, the versatile nutria thrive. With webbed feet, nutrias are better adapted than native mammals to survive frequent floods; with large claws, they burrow nests in levees and make homes in the sewers. With a reproductive cycle considered strikingly fast even for a rodent, nutrias outnumber predators and natural hazards.

And they’re making their presence known far beyond their native Louisiana. Tens of millions of nutrias have carved tunnels from Washington state through Texas and Florida and back north into Maryland and New Jersey. Like their smaller rodent cousins residing in New York City, they do not fear people. They bite, claw, and carry at least one parasite that can infect humans, called “nutria itch” or “creeping eruption.”

Catherine Normand, a biologist with Louisiana’s Department of Wildlife and Fisheries, said the creatures are intractable. “ Trying to eradicate nutria in Louisiana would not be a feasible goal,” she said. “They’re everywhere.”

Like pythons in Florida or black rats around the Pacific, nutrias have voracious appetites and few predators. Weighing up to 20 pounds, they are too large for coyotes and foxes to prey on; alligators cannot eat enough of them. Like rats, nutrias seem to thrive in the record temperatures of each passing year, suggesting that hardy rodents may flourish in the conditions of climate change, if only temporarily. Female nutrias can have three litters a year, usually with five to a dozen young each time. In warm winters, when the weather only browns foliage but does not kill it, nutrias hide easily among the mud and leaves.

Faced with a plague of rodents, Louisiana has asked humans to join the hunt. In 2002, Louisiana began a bounty campaign–$5 per scalped tail– that a new documentary, Rodents of Unusual Size, presents as a model program. “There’s a lot of controversy about what should be done to rejuvenate the land,” Quinn Costello, one of the film’s directors, told The Daily Beast. “ The nutria control plan is something that people are doing that’s actually having an impact on the culture. When someone can stick around and hunt nutria, they’re not going into the oil and gas industry.”

The film, whose title plays off the “rodents of unusual size” bit in the movie The Princess Bride, concentrates on how Louisiana has adapted to the rodents, turning them into gumbo and dog snacks, fur coats and costumes, and pets. Normand said it was hard to measure how many nutria were killed by the program, but survey results were optimistic. In 2002, the state measured over 82,000 acres destroyed; last year officials measured less than 6,000 acres. On average, Louisiana receives about 330,000 nutria tails every year.

One trapper, Thomas Gonzalez, a 79-year-old resident of Delacroix Island in the marshes southeast of New Orleans, told The Daily Beast that, in a good season, he caught more than 20,000 nutrias. “I bet you I was catching over 200 a day, every day,” he said. “You be out walking, they run out ahead of you, everywhere.”

Yet Gonzalez also suggested that the damage may be already done, saying that over his lifetime, he had seen the animals wipe out forests. Since he was born in the 1930s, Louisiana has lost about 2,000 square miles, according to a 2011 report by the US Geological Survey.

“I grew up with the land,” Gonzalez said. “I know what it was and I know what it is now, and we don't have nothing today. Used to trap muskrats off 160 acres of land. Now, that land, I ride over it with a boat.”

Massimi said Louisiana is working on a similar program to combat feral hogs, an intelligent hybrid of domestic pigs and Russian boars that also tears across the American south. Texas has experimented with poisons for its hog problem, and requires a license to hunt them. Neither Florida and Texas monitor or try to control nutrias in their wetlands, wildlife officials in each state said. But last year Florida sent an expert to learn more about the program, Normand said, in the hopes that it might improve its own python bounty campaign.