Luciano Sampietro lifted a three-foot aluminum pipe to his lips and blew, sending a blow dart laced with sedatives, muscle relaxers and painkillers toward the world’s largest rodent, lounging near an artificial pond.
The veterinarian’s target, a roughly 110-pound alpha male capybara, was hit in the hind leg. Mr. Sampietro fired again and struck a female. Within 15 minutes, workers dressed in the tan outfits of safari guides scooped up the sleeping patients.
But they were too late: The female was already pregnant. So they injected the male with a drug designed to stop him from impregnating any more.
Yes, in the wealthy suburbs of Buenos Aires, they are sterilizing the capybaras.
The rotund, laid-back, dog-sized rodents native to South America have recently become a darling of the modern internet. They have catapulted to the top of the unofficial adorable animal rankings via countless videos showing them mellow, plump and perfectly happy to let monkeys and ducks ride on their backs. Their image adorns backpacks and stuffed animals, and in Tokyo, tourists pay premiums to feed them carrots at capybara cafes.
But to some people in one corner of their native land, the cuddly capybara has become a menace.
Since the pandemic, “carpinchos,” as they are known in Argentina, have proliferated in Nordelta, a ritzy, picturesque gated community of 45,000 people north of Buenos Aires. When residents retreated indoors in 2020, the capybaras began to colonize the manicured neighborhoods, finding green grass, fresh water and no predators, according to biologists hired by the community.
Over the past two years, the biologists estimate Nordelta’s capybara population has tripled to nearly 1,000, posing a tricky test case for the urban coexistence of humans and wildlife.
On a visit last month, capybara families grazed near the tennis courts, dozed on the volleyball courts and waded in the artificial lagoons. Just past a sign warning of crossing capybaras, a family crossed the street in a single-file line, illuminated by waiting headlights.
Sure, most residents admitted, the capybaras are cute. But they also cause traffic accidents, chomp their way through gardens and, on occasion, have attacked some of the community’s smallest dogs.
“It’s a wild animal versus a domesticated dog. I mean, it’s totally different,” said Mr. Sampietro, the veterinarian hired to help manage the capybara population. “I’ve had to do necropsies on capybaras and it’s difficult to cut the hide with a knife.”
Pablo Pefaure, one of Nordelta’s 26 neighborhood representatives, said his neighbors frequently complain to him about the amphibious rodents. “They see them as dangerous, they see them as invasive, they fear for their young children,” he said.
He said that capybaras have sometimes followed his miniature schnauzer, Grumete. “I don’t leave him alone in the garden because I don’t know what might happen,” he said.
His neighbor sitting nearby, Veronica Esposito, did not agree. “No capybara has ever approached my dogs,” she said. “Everyone says they eat the plants. Yes, they do. But the plants grow back,” she added. “I don’t see the problem.”
Ms. Esposito is one of a small group of neighbors leading a rebellion against the capybara controls. They have protested in the streets, taken legal action against developers and gathered 25,000 signatures for an online petition to protect the animals. They’ve also attracted 34,000 followers to an Instagram page where they sometimes shame their neighbors, including one who had used a whip to scare capybaras off her dock.
“I believe their adorableness is a strategy of the species itself to survive,” said Silvia Soto, the most vocal neighbor. “Their lovability have conquered us, and we’re fighting for them.”
So far, the fight has not worked. Last year, Argentina’s national government began an experiment to perform vasectomies on three capybaras in Nordelta, hoping to track how it affected the males’ standing in their packs. If successful, the practice could be expanded.
In February, the Nordelta organization told residents in an email that it was moving ahead with a different plan: a “contraceptive vaccination program,” approved by the local government, to sterilize 250 adult capybaras.
Costanza Falguera, the organization’s lead biologist, said her team is using a “vaccine” that halts the production of sperm and inhibits ovulation. It requires two injections several months apart, but then might last only for several months, meaning they might have to keep tranquilizing the capybaras repeatedly.
They aren’t sure how long the sterilization lasts because the drug — Improvac, made by a New Jersey drug maker, Zoetis — has not been used on capybaras. It is designed to alter pigs’ hormones before slaughter so the meat tastes better. “Only for use in male pigs,” Zoetis says on its disclaimer for the drug.
In 2019, Nordelta sprayed its grass with the scent of a carnivore, scaring off many capybara. But Ms. Falguera said the efficacy dropped over time as the capybara in Nordelta became long removed from having regular predators.
So, she said, the community settled on the injections, which she said are better than castration or vasectomies because they are less likely to alter the rodents’ behavior and group dynamics.
In other words, they still mate, she said, “but they don’t fertilize.”
The decision to sterilize the capybaras ultimately rested with one of Argentina’s richest men, Eduardo Constantini, an entrepreneur and real estate developer whose company controls the Nordelta organization. His spokeswoman did not respond to requests for comment.
To the capybara advocates, intervening in the animals’ reproduction is an escalation of Nordelta’s attack on the species.
Thirty years ago, Nordelta was largely untouched wetlands where capybaras roamed freely, hunted by pumas, jaguars, caiman and sport hunters. In the late 1990s, Mr. Constantini began transforming the area with roads, ponds, mansions, condo towers, a shopping center and a golf course designed by the American golfer Jack Nicklaus. Construction has been nearly nonstop — with 17 more buildings underway now — and it is now home to some of Argentina’s richest people.
Ms. Soto argued that the capybara population is only increasing because developers destroyed the animals’ wild habitat, forcing them out of the forest and into the suburbs.
“In a matter of hours they knock down a forest,” Ms. Soto said. “What happened to the wildlife? Have they died? Have they been displaced?”
Her group is pushing for the capybara to be given their own nature reserve, but there appears to be little interest from Nordelta’s developers. “I don’t understand how they can only think of vasectomy and sterilization,” she said.
On a recent weekday, as capybara grazed on a playground, Lidia Schmidt and Felipo Contigiani walked past, hardly noticing. The married couple agreed the capybara population had to be checked somehow, but they did not see eye to eye on the causes of the problem.
Mr. Contigiani, who said that he used to hunt capybara as a child, had less sympathy for the animals. “It’s a wild animal that came to live in the city,” he said.
His wife corrected him. “No, the city came to settle where the wild animal was,” she said. “It’s the other way around.”
Jack Nicas is the Brazil bureau chief for The Times, leading coverage of much of South America.
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