This Brutal Pesticide Creates a ‘Circle of Death.’ So Why Is It Making a Comeback?

Carbofuran, a century-old chemical, is increasingly being weaponized against birds and other wildlife, decimating entire food webs.

The victim lying on Kevin Hynes’s stainless-steel table on March 11, 2015, showed no obvious cause of death. There were no injuries indicating that she had been hit by a car or electrocuted—the usual killers. Dressed in surgical scrubs and latex gloves, Hynes, a wildlife biologist with the New York Department of Environmental Conservation in Delmar, peered through the magnifying visor affixed to his headband and examined the Bald Eagle more closely.

She was a female, seemingly in good health, and likely a mother incubating eggs, indicated by the bare skin—a brood patch—on her underbelly. Her stomach contents showed that she had been fit enough to find a rabbit earlier that day. Scraps of sheep hair and skin at the back of her mouth provided a clue that a more recent meal had been cut short. Maybe she’d been poisoned, Hynes thought. He ordered a toxicology screening.

A couple of weeks later, the results revealed the culprit: carbofuran­, a neurotoxic chemical that is one of history’s deadliest pesticides. A quarter teaspoon can kill a 400-pound bear in minutes. It’s especially lethal for birds. Whereas the pesticide DDT, banned in the 1970s after driving Bald Eagles, Peregrine Falcons, and Brown Pelicans to near extinction, works its way up the food chain gradually, like a progressive disease, carbofuran’s effect is instantaneous. “It interferes with the enzymes that help nerves talk to each other,” says Ngaio Richards, a Montana-based wildlife biologist with an expertise in forensic science, who wrote a book documenting global animal poisonings from carbofuran. “When an animal is exposed, it goes into convulsions and respiratory failure. It’s an excruciating death.”

Carbofuran was pulled from the U.S. market in 2009, but it didn’t disappear. People here and elsewhere—including in many countries where it’s still sold legally—use it to kill animals, rather than the insects it was invented to target. In Europe, gamekeepers defending pheasants at grouse-hunting estates poisoned hundreds of birds of prey, including Red Kites, Golden and White-tailed Eagles, and goshawks. Nearly 190 vultures in Kenya died after dining on the remains of an animal laced with carbofuran; a scientist studying the birds watched in horror as they dropped out of the sky within minutes of their meal. More than 230 Tundra Swan carcasses constituted a carbofuran crime scene at a lake in Inner Mongolia (authorities suspect poachers aimed to sell the birds to restaurants, some of which offer “swan feasts”).

Eagles have been an especially common target in the United States. Last May wildlife investigators offered a $10,000 reward for information related to a spree of carbofuran poisonings on Maryland’s Eastern Shore that had wiped out six Bald Eagles and a Great Horned Owl. A similar unsolved case three years ago left 13 eagles dead.

“Everyone knows this stuff works very, very well for killing animals,” says Mourad Gabriel, a research associate at the University of California One Health Institute in Davis and co-director of the Integral Ecology Research Center. In some parts of California, where Gabriel works, growers at illegal marijuana farms on public lands have been using carbofuran to protect their camps from bears and other wildlife. As a result, scientists there are finding entire food webs, from pollinators and rodents to raptors and coyotes, decimated by the pesticide.

And so, even as it has become more difficult to acquire, carbofuran’s popularity has grown. The once-mass-market pesticide has become a go-to poison for an active underground—and left wildlife officials grappling with the consequences.


or more than 40 years, carbofuran’s deadly nature has been its selling point. A 1980s TV commercial features a flannel-clad farmer in a flatbed pickup loaded with bags of the Pepto-Bismol-colored granules. “You’re a Furadan man because you know what’s best,” goes the bouncy jingle. “Cuz it saves more corn cuz it stops more pests.” Introduced with the U.S. trade name Furadan in 1967, carbofuran offered farmers the tantalizing prospect of greater crop yields. A broad-spectrum insecticide, it could wipe out insects, mites, and nematodes plaguing fields of corn, soybeans, alfalfa, and potatoes.

The chemical was an immediate and unequivocal success. Within a decade, domestic sales had soared to $100 million. In 1980 the Food Machinery and Chemical (later renamed FMC) Corporation, which patented Furadan, introduced carbofuran to European and Asian markets under the name Marshal. When FMC’s patent expired six years later, other companies started making and distributing carbofuran under different trade names, including Yaltox, Carbodan, Carbosip, Chinufur, Kenofuran, and Niagara.

Studies show a single granule, resembling a natural seed grain in size and shape, could kill a small bird.

Meanwhile, authorities had wisened to the fact that Furadan kills not just insects. Studies in the 1990s showed a single granule, resembling a natural seed grain in size and shape, could kill a small bird, according to Environmental Protection Agency scientists. In fact, the EPA reported that the insecticide was wiping out one to two million birds in the United States each year—more than any other pesticide in legal use, according to American Bird Conservancy scientists. The agency initiated a nationwide ban on the granular form of Furadan in 1991; liquid Furadan, considered less dangerous to birds, remained on the market. But then in 2006 it recommended restricting all uses due to grave concerns about the risks to ecosystems, drinking water and food, and the farm workers who handled it. The EPA announced a year later that it intended to prohibit liquid Furadan and block imports of any produce containing carbofuran residues.

At first FMC fought the decision in court. But in 2008 the company withdrew Furadan from U.S. markets and recalled products from stores, a step heralded as a win for the environment. Some observe, however, that FMC may have simply been executing a strategy commonly used by chemical companies. Preemptively withdrawing a pesticide creates a loophole to bring it back, says Drew Toher, community resource and policy director with the nonprofit Beyond Pesticides. He points to the example of aldicarb, trade name Temik, considered an “extremely hazardous substance” by the EPA. Facing a likely ban, Temik maker Bayer CropScience withdrew it from U.S. markets in 2010. Six years later, the EPA under the Trump administration began permitting farmers cultivating such crops as cotton, soybeans, and potatoes to once again use the chemical under a new trade name, AgLogic 15G. “When we have an EPA that’s more malleable to industry interests,” Toher says, “these half measures come back to bite us.”

And although Furadan left U.S. markets, FMC continued manufacturing and shipping carbofuran formulations for sale in other countries, including granular Furadan for use on rice fields in Asia. (U.S. laws do not prohibit chemical makers from exporting domestically banned pesticides.) It did so right up through December 2019, when Audubon contacted the company for this story. FMC spokesperson Emily Parenteau wrote that, as of January 1, 2020, FMC would no longer sell carbofuran products globally. Even so, she maintained, carbofuran does not harm humans or wildlife if used in accordance with label instructions.

Biologists refute that claim. “This product is inherently toxic. You can’t make it safe,” says Richards. And as long as people still have access to the chemical, they will continue using it to poison wildlife. Carbofuran’s reach is long and far, she says, and people who poison wildlife can be ruthless.


pecial agent Ken Dulik has witnessed so many carbofuran poisonings in his 30-plus years with the U.S. Fish and Wildlife Service that he can spot an eagle killed by the chemical. “When they go into convulsions, their tail and wings spread out and their head arches over the neck backwards,” he says. “It’s a fast and brutal death. Once you’ve seen it, you know what it is.”

In addition to the telltale appearance of a poisoned bird, carbofuran creates what’s often called “a circle of death,” detectable for miles. For example: A coyote feeds on a poisoned cow carcass, walks 100 yards away, and dies. Then another coyote feeds on that one. Because it received a lower dose, it might travel 400 or 600 yards before succumbing. A bird that feeds on the second victim might manage to fly a half mile. “The circle of death keeps moving outward,” Dulik says. “In one case, we had a four-square-mile radius that we kept finding animals in. Each time you find a carcass, your crime scene gets bigger and bigger. I’m never confident that we’ve found them all.”

In the United States, it doesn’t matter that carbofuran is no longer sold in stores; it’s common for farmers to have some of the banned chemical stashed away. “Plenty of people have kept a jar from back in the day,” Dulik says. “There’s no other purpose than for killing animals.” Doing so can carry a stiff penalty. People who violate wildlife laws such as the Migratory Bird Treaty Act and the Bald and Golden Eagle Protection Act can face serious criminal charges and fines. In extreme cases, even jail time.

The Bald Eagle on Kevin Hynes’s examination table back in 2015 had been discovered four days earlier in a cornfield in the small town of Addison in New York’s Southern Tier. After retrieving the carcass, Steven Farrand, an officer with the New York State Department of Environmental Conservation, learned that a sheep farmer had reported losing animals to eagles and allegedly talked­ about shooting the birds. The farmer, William Wentling, lived about 200 miles south in Lancaster County, Pennsylvania, and paid a local named Eli Byler to periodically check on his sheep outside of Addison. For his part, Byler claimed not to know anything about a dead eagle. 

Two weeks later, Farrand got a call from a man who came across two dead hawks while hunting coyotes on Wentling’s farm. Farrand collected the birds, a partial Rough-legged Hawk and a Red-tailed Hawk, plus another eagle, lying next to dead sheep and sent them to Hynes. He soon confirmed that they, too, had died from ingesting carbofuran.

With a warrant to search the property, Farrand found another Red-tailed Hawk adjacent to the sheep pile, a plastic bottle, and four discarded black latex gloves. All tested positive for carbofuran. With the evidence mounting, federal wildlife authorities joined the investigation. Another search revealed more black latex gloves.

The smoking gun was the huge jug of carbofuran hidden behind the toilet in the barn.

Then they searched Byler’s property. “The smoking gun,” says FWS senior special agent Lee Schneckenberger, “was the huge jug of carbofuran hidden behind the toilet in the barn.” Someone had written the word “Poison” and drawn a skull and crossbones on the bottle.

Confronted with this discovery, Byler confessed, but said he had simply been following Wentling’s instructions. He then agreed to call Wentling and allow the agents to secretly record the phone call. “Byler told Wentling he was very nervous and that he could not continue to lie about the poison,” Schneckenberger says, quoting from the tape recordings. “Wentling responded, ‘I don’t want you to lie, but if you let the cat out of the bag, we’re all going to hang.’ ”

In Wentling’s version of the story, he was innocent; Byler was the real criminal. “The man looking after the sheep told me that eagles were killing the lambs as they were being born,” Wentling told me over the phone. “I said, ‘We’ve got to get rid of them, but I don’t know how.’ I had corn insecticide on the shelf that I’d bought 8 or 10 years ago at a public sale. He poured that insecticide on the sheep—I didn’t know anything about it.”

Nonetheless, in June 2017, Wentling pleaded guilty to misdemeanor violations of the Bald and Golden Eagle Protection Act. Taking into account that he had no prior criminal history, the federal judge sentenced him to two years of probation and a $3,500 fine. Eli Byler and his son, who assisted him with the poisoning, were not prosecuted at the federal level; in New York, they pleaded guilty to reduced charges and were each sentenced to one year of probation and a $75 fine.

From Dulik’s perspective, every conviction is a helpful deterrent to other would-be poisoners. It sends a message, he says: “It’s not worth it.” Thus in rural areas, wildlife agents continue to methodically track down rogue farmers and ranchers who use the chemical to protect their livestock. In Northern California, meanwhile, authorities are facing an even more intractable problem: illicit pot growers toting semi-automatic rifles, operating in the remote wilderness.  


n California’s Emerald Triangle, the three-county epicenter of pot cultivation in the United States, an estimated 50,000 legal farms work to fill the commercial demand for cannabis, now permitted for recreational use in 11 states and for medical purposes in 33. On nearby public lands, drug cartels operate hundreds of thousands more plots that supply a black market. In 2019 alone, authorities in California removed more than 950,000 pot plants from 345 illegal sites. Called “trespass grows,” such sites are often difficult to find because they’re concealed within rugged old-growth forests, home to Spotted Owls, cougars, bears, and house-cat-size carnivores called Pacific fishers.

A fisher provided the first clue to the extent to which carbofuran and other pesticides are damaging­ the ecosystem in Northern California, where the animal’s population may have dwindled to several hundred individuals. In 2009, Gabriel, of the Integral Ecology Research Center, necropsied a seemingly healthy-looking Pacific fisher whose body cavity was filled with blood from internal hemorrhaging. Cause of death: anticoagulant rodenticide, more commonly known as rat poison.

Baffled as to where the animal might have encountered rat poison so far from human development, Gabriel reexamined 58 carcasses he’d recovered in the past three years. More than 80 percent contained at least one type of rodenticide. When he reported this result at a wildlife conference in 2010, a pair of conservation officers approached him with a possible insight: They were frequently finding various chemicals on their raids of illegal marijuana grow sites.

Wanting to see the sites for himself, Gabriel accompanied an armed officer and two other researchers to a location known as Mill Creek on the Hoopa Valley Reservation. Winding along the banks of a salmon stream—deep in a gorge where Gabriel had once radio-collared gray foxes—they came upon a denuded patch of forest where 130-year-old tanoaks once stood. The growers had felled the trees and planted thousands of pot plants up to the creek’s edge. Now that police had confiscated the marijuana, all that was left was barren land littered with irrigation lines and refuse. The group found food, sleeping bags, tents, sprayers, trash pits, and stashes of toxicants—including rat poison and a bottle of carbofuran.

“It was a witches’ brew,” Gabriel says. “We were like, ‘Wow, this isn’t some little foray,’ like back in the day when a guy would hike down the trail, water his plants, and leave. People were living down here. Then we walked another trail and found another plot, and another. We didn’t even cover half of it all that day. There are hundreds of these sites.”

The scientists dress in camouflage and wear face paint; Gabriel carries a gun.

To document the problem, Gabriel and his colleagues now work side by side with officers as they raid plots guarded by armed growers. The scientists dress in camouflage and wear face paint; Gabriel carries a gun. “This isn’t bravado,” he says. “We want to go home at the end of the day.”

Often the teams encounter Gatorade bottles filled with carbofuran and tuna tins stuffed with carbofuran-tainted meat. The labels on jugs of chemical are frequently in Spanish, indicating they were smuggled from Mexico. Gabriel questions the growers on site, after they’ve been arrested, and some have admitted to using carbofuran to keep animals from rampaging their camps because, they say, it worked great for getting rid of jaguars preying on livestock back home in Mexico.

The scientists’ bold field work is paying off, if only to document a compounding problem. In 2013 they discovered carbofuran at 20 percent of the raided sites. Just six years later it’s been found at more than 80 percent of them. Gabriel suspects the growers are increasingly using carbofuran not just because of its potency with animals, but also with law enforcement: Media outlets have reported officers exposed to the chemical being hospitalized for nausea, blurry vision, and migraines.

Sheriff’s sergeant Nathan Trujillo, a member of the Trinity County Crimes Unit who has been working with Gabriel’s team for about seven years, has had some close calls on the raids. In 2015, for instance, he and his K9 Johnny were going into an area where a forester had reported an illegal grow site. “We kept seeing pink tuna cans along the trail,” he says. “In the camp, we found a bottle of carbofuran, open and empty.” After splashing through some water, Johnny seized up, started foaming at the mouth, and then vomiting. Trujillo rushed the dog to the vet. “I don’t know how they saved him, but they did,” he says. “You used to worry about getting shot or breaking a leg in a canyon. Now you have to worry about this almost invisible weapon these guys have.”

As the surge of pesticides in state forests continues to course through the ecosystem, water supplies, and even some marijuana smoked by consumers, government agencies and Gabriel’s organization are working to mitigate the contamination. But resources are limited, and the process is slow in remote backcountry that often requires helicopter access. Of 1,000 sites discovered so far, Gabriel and his team have cleaned fewer than 200.

“It’s going to take a collective of scientists and a lot more funding and logistics to address this,” Gabriel says. “We can’t leave these sites with chemicals in plastic bottles. If that bottle opens up 20 years from now, boom, you have another pulse of contamination.”

At press time the Mexican government was reportedly planning a ban on imports of carbofuran, which may help stem the tide of the chemical’s damage in California forests, says Gabriel. If it does, it would join the 63 countries (out of the 150 that report such information) that have already taken that step. Meanwhile, dozens of companies continue to make and sell carbofuran around the globe—including some, like FMC until it stopped exports this year, headquartered in nations where the pesticide can no longer be legally used.

Science doesn’t justify its sale at all. From Africa and Asia to Europe and North and South America, a global collective of biologists documenting animals killed by carbofuran say the sole condition under which it can be safely used—in accordance with label directions—is “if an area is completely devoid of wildlife.” As each successive poisoning illustrates, carbofuran may instead help create this circumstance. Even decades after environmental officials found the pesticide imperils people and birds, carbofuran’s toxic legacy, and its circle of death, still grows.

This story originally ran in the Spring 2020 issue as “Death Spiral.” To receive our print magazine, become a member by making a donation today.​