Genetic testing confirmed in 2016 that Nile crocodiles, a species native to Africa, have established a breeding population in the canals south of Miami. Researchers determined the animals were introduced through the exotic pet trade and have been living in the Florida wild for roughly two decades.

The discovery began with reports from the field. In March 2012, a patrol team near Homestead, south of Miami, encountered a large crocodilian that behaved differently from the native species. Instead of submerging when approached, it moved onto the bank and ran, reaching speeds of around 9 mph before disappearing into the sawgrass. At the time, the incident was filed as an anomaly.

Four years later, DNA analysis at the University of Florida provided a clearer answer. Tissue samples from animals captured in the area did not match the American alligator or the American crocodile. The genetic sequence matched the Nile crocodile, specifically a subspecies from the KwaZulu-Natal province of South Africa, approximately 7,000 miles away. The results were published in the Journal of Herpetological Conservation and Biology.

The presence of Nile crocodiles represents a shift in the region’s established wildlife hierarchy. The Florida Everglades have long been divided between two native species. The American alligator dominates freshwater areas, while the American crocodile, a shy and reclusive fish eater, is found mainly in coastal brackish waters. There has never been a confirmed human fatality caused by the American crocodile in the United States.

Nile crocodiles are a different matter. In their native range across Africa, they are responsible for an estimated 200 human fatalities per year. They are generalist predators that feed on large mammals and are known to be far more aggressive than the native American crocodile.

The first clear signs of a problem appeared in the mid-2000s. Fishermen in the Silver Bluff Creek area reported that large, dominant American crocodiles had abandoned basking spots they had held for decades. At the time, scientists attributed the disappearances to the Burmese python invasion, which was reducing mammal populations across the Everglades. Reports from local residents of unusually aggressive reptiles in the canals were initially dismissed as misidentifications.

Forensic evidence eventually suggested otherwise. Rangers found reptile carcasses that did not match the profile of a python kill. Pythons kill by constriction, leaving skeletons intact. These remains showed signs of a death roll, a rotational feeding technique used by crocodilians, but the bite radius was too wide for an alligator and the aggression level too high for an American crocodile.

The first captured specimen provided additional clues. A small juvenile was caught in the canal system near Miami in 2009. Researchers at the University of Florida noticed physical differences from native species. The dorsal armor, or osteoderms, were more rigid and geometrically aligned than the irregular pattern seen in American crocodiles. The animal also displayed sustained aggression during handling, rather than the passive response typical of native crocodiles.

Over the following years, additional specimens were captured in 2012 and 2014. These were subadults growing at an estimated 28 percent faster rate than native American crocodiles. This growth advantage allows an animal to reach maturity and predator size more quickly, giving it a competitive edge over local species.

Genetic analysis confirmed that the captured specimens were siblings, indicating that a mature breeding pair was living freely in the Everglades. Since Nile crocodiles take 10 to 12 years to reach maturity, researchers believe the original animals were introduced sometime in the late 1990s or around 2000. The most likely explanation is that imported hatchlings were released by owners once they outgrew their enclosures.

Kenney Krysko, collection manager at the Florida Museum of Natural History, was involved in examining the specimens. He noted that the animals displayed a high-walk posture when cornered, a stance that signals confidence, rather than the flight response seen in native crocodiles. However, visual observation alone was not enough to confirm the species. Mitochondrial DNA testing was required, and the results pointed definitively to South Africa.

As of the 2016 study, the full extent of the Nile crocodile population in Florida remains unknown. The confirmed specimens establish that a breeding colony exists, but the number of individuals and their range across the Everglades has not been determined. State and federal wildlife agencies have continued to monitor the area, though no comprehensive eradication plan has been announced.