From USA Today Network:
Why iguanas are blamed for crocodiles missing teeth in Florida
A first-of-its-kind discovery has researchers probing whether a popular way to control an invasive pest is now threatening native Florida wildlife.
- Florida wildlife researchers documented the first known case of lead poisoning in a threatened American crocodile.
- Lead poisoning could be an emerging threat to the American crocodile population, which has recovered from endangered status.
- Researchers are concerned as crocodiles scavenge on invasive iguanas, which are legally hunted with lead pellets.
Goo spewed from the crocodile’s nostrils creamy and fetid, unnerving state wildlife researchers who were fitting the threatened species with a tracker.
Moments before, the prehistoric beast had been lounging in a Miami-Dade County pool on a clear-skied November afternoon.
Then, it was dead. Its teeth were missing. And it had black marbling in its mouth like when a printer is running out of ink.
Florida Fish and Wildlife Research Institute scientists believe the culprit was the croc’s dinner — an iguana, or multiple iguanas, shot full of lead pellets that ended up in its stomach, slowly leaching toxin into its bloodstream.
A report published this year in the journal Endangered Species Research says the demise is the first documented lead poisoning death in an American crocodile.
But after reviewing photos of other American crocodiles in South Florida without a full set of chompers, researchers don’t believe it is only vulnerable reptile suffering from the unusual gastric corruption. Absorbed lead replaces calcium and bone, weakening teeth.
“Lead poisoning is not mentioned as a threat to American crocodiles in the federal recovery plan for the species,” the report notes. “But it appears to be an emerging issue.”
In addition to the 23 individual air-rifle pellets in its stomach, the female crocodile also had ingested a lead fishing weight that was likely either attached to a fish that it ate or that it had eaten on its own. Crocodiles will eat rocks to aid in digestion and control buoyancy.
Lead poisoning is not mentioned as a threat to American crocodiles in the federal recovery plan for the species,” the report notes. “But it appears to be an emerging issue.”
In addition to the 23 individual air-rifle pellets in its stomach, the female crocodile also had ingested a lead fishing weight that was likely either attached to a fish that it ate or that it had eaten on its own. Crocodiles will eat rocks to aid in digestion and control buoyancy.
Conservation biologist and wildlife consultant Joe Wasilewski said he was surprised by the lead poisoning diagnosis but at the same time expected something to happen with the number of green iguanas becoming fodder for backyard target practice.
Iguanas are invasive in Florida and despite a 2026 winter freeze that culled the population, they are quick reproducers and have rebounded in number. Because they are invasive, it is legal to humanely kill them year-round without a hunting license.
“It was bound to happen,” Wasilewski said about the lead poisoning. “People can’t use ammunition with gun powder, so they use high-powered pellet rifles that use lead pellets.”
American crocodiles have learned to eat invasive green iguanas
While crocodiles will scavenge dead iguanas that may have been killed with lead pellets, Wasilewski said iguanas will often survive being shot, and sometimes survive being shot multiple times.
A crocodile will also “eat almost anything that moves”, according to the National Park Service.
“Every hunter thinks it’s just one shot in the head and they’ve killed it, but I’ve been with hunters who have shot them eight and nine times and they are suffering but still alive,” he said. “The crocs in South Florida have learned to feed on the iguanas and now the iguanas are full of lead.”
American crocodiles, distinguished from alligators by their grayish coloring and pointed snout, were named federally as an endangered species in 1975. Florida is the only state in the country where crocodiles live in the wild.
In 2007, crocodiles were downgraded from endangered to threatened as their numbers came up from a few hundred to an estimated 2,000 today. They prefer the same brackish waterways that humans live on at Florida’s fringes whereas alligators have vast amounts of freshwater resources to roam.
Most American crocodiles live in Everglades National Park, Florida Bay and Biscayne Bay, building nests in the soft Earthen berms of Florida Power & Light's Turkey Point cooling canals and the exposed shoreline of Florida Bay.
If a croc comes across a free meal, it will take it,” said Ryan Gradney, a reptile expert and owner of West Palm Beach-based Scales Exotics, about lead-filled iguanas becoming crocodile snacks.
Lead poisoning became such a problem for game birds, including ducks and geese, that the federal government banned the use of lead ammunition when hunting waterfowl in 1991.
Lead poisoning is the leading cause of death for California condors
Estimates of lead poisoning among waterfowl ranged from 1.6 million to 3.9 million birds per year prior to the ban, according to a 2023 paperpublished by Oklahoma State University.
Not only were the birds eating the seed-resembling lead ammunition — an estimated 2,700 tons of lead shot was deposited in wetlands each year — but the lead was also killing birds of prey. Lead poisoning is the primary cause of death in the wild for California condors.
An eight-year study by Conservation Science Global wildlife biologist Vincent Slabe found nearly half of 1,210 bald and golden eagles tested showed signs of chronic lead poisoning, likely from eating ammunition in deer and other carcasses.
The Florida report said tungsten and steel are alternatives to lead ammunition and fishing tacking, but that they are generally more expensive and have less desirable aerodynamic characteristics.
Wasilewski speculates that the reason there aren’t more alligators dying of lead poisoning is that crocodiles are more likely to live among iguanas in mangrove stands and brackish water estuaries. Or the alligators just aren’t being tested when there’s an unusual death. There are an estimated 1.3 million alligators in Florida.
The state has launched a project to more closely monitor toxins in Florida’s native crocodile population by collecting and testing tissue samples to better understand what kind of threat contaminants like lead pose on the population.
“If more of this happens, I could see Florida looking more closely at the laws regarding lead pellets,” Wasilewski said. “Crocodiles have rebounded to historic levels and we don’t want to throw that all away because now we are killing iguanas.”
Kimberly Miller is a journalist for the USA TODAY NETWORK FLORIDA. She covers weather, the environment and critters as the Embracing Florida reporter. If you have news tips, please send them to kmiller@pbpost.com. You can get all of Florida’s best content directly in your inbox each weekday by signing up for the free newsletter, Florida TODAY, at palmbeachpost.com/newsletters.
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