Researchers at the University of Florida have found a man-eating African species of crocodile among native populations in the state’s swamps and Everglades.

It is unclear how the Nile crocodile, Crocodylus niloticus, which can grow up to 5.5 metres (18 feet) in length and was blamed for at least 480 attacks on people and 123 fatalities in Africa between 2010 and 2014, arrived in the state.

But DNA analysis has confirmed that three juveniles have been identified in the state, including one that was relaxing on a house porch in Miami. The local alligators do not prey on humans, but the unwelcome imports have unsurprisingly made headlines in the state.

Kenneth Krysko, a herpetology collections manager at the Florida Museum of Natural History, confirmed that the specimens are linked to native populations in South Africa. He told the journal Herpetological Conservation and Biology that the species can survive and potentially thrive in sub-tropical Florida.

“The odds that the few of us who study Florida reptiles have found all of the Nile crocs out there is probably unlikely. We know that they can survive in the Florida wilderness for numerous years, we know that they grow quickly here and we know their behaviour in their native range, and there is no reason to suggest that would change here in Florida.”

Crocodylus niloticus is considered a generalist, unfussy predator, and has clearly adapted to the local food supply, from native birds, fish and mammals, including domestic pets, to the state’s native crocodile and alligator. The researchers looked at one juvenile specimen that grew nearly 28% faster than wild Nile crocodile juveniles.

The three captured specimens were genetically identical, suggesting they came from the same source. But that source remains mysterious – the reptiles do not match with any Nile crocodiles currently housed in US zoos.

However, the study noted that large groups of Nile crocodiles have been imported from South Africa and Madagascar, both for display at places such as Disney’s Animal Kingdom, and to supply Florida’s pet trade. Pet owners are the most likely source of introduction.

Florida has the world’s largest number of invasive species. The spiny lionfish, believed to have been released during Hurricane Andrew in 1992, has caused devastation to native populations of reef-dwelling fish across the Caribbean. There is also the Cuban tree frog, which has been found as far north as Jacksonville.

Short of the latest visitor, the invasive species that attracts the greatest attention is the Burmese python. These monsters are now common enough for authorities to organise and license python hunts.

The Miami Herald reported in March that biologists bagged more than 2,000 pounds of Burmese pythons – in just one county. One snake, measuring almost 5 metres and weighing about 63kg (140 pounds), set a new record for males caught in the wild in Florida. Using radio trackers, scientists found the snakes like to occupy gopher tortoise burrows, and found six males and a female squeezed into a “mating ball”. They are so numerous they have become one of the region’s top predators. Research suggests the pythons are responsible for a sharp decline in the population of Everglades marsh rabbits and for a decrease in deer.

“The ecological impact of these animals is just over the top,” said Ian Bartoszek, a biologist at the Conservancy of Southwest Florida. “We’re starting to get a sense they eat bigger up the food chain.”

But now the state has new worries. According to the University of Florida study, its Atlantic coast and the entire Gulf of Mexico coastline are favourable for Nile crocodiles.

“My hope as a biologist is that the introduction of Nile crocodiles in Florida opens everyone’s eyes to the problem of invasive species that we have here in our state,” Krysko said. “Now here’s another one, but this time it isn’t just a tiny house gecko from Africa.”

However, Allyson Gantt, a spokeswoman for Everglades National Park, where one of the reptiles was found, rejected the idea that any Nile crocs were still roaming in the park.

Some Everglades visitors might not be aware of the differences between crocodiles and alligators, complicating efforts to confirm any remaining crocs. Crocodiles have angular snouts, and their lower teeth are exposed when their mouths are closed. Alligator snouts are rounded, with few exposed lower teeth. Nile crocs are usually bronze or brownish yellow; by contrast, alligators are blackish green.