Invasive, noxious Cuban treefrogs that eat smaller frogs and grow as big as a human fist have established a population in New Orleans, and officials say they could soon pose a threat to native frogs across the Mississippi river.

The US Geological Survey says frogs caught at the Audubon zoo in the city and at a nearby riverfront park are the first established population of Cuban treefrogs on the US mainland outside Florida, where they’ve been multiplying at least since the 1950s.

The captured frogs probably arrived on palm trees from Florida that were planted in the zoo in 2016, USGS research ecologist Brad Glorioso wrote in a study published in the April issue of the journal Biological Invasions.

“They have noxious skin secretions, lay their eggs in bird baths and fish ponds, and they can clog plumbing and cause power outages by short-circuiting utility switches where they seek refuge,” he said in a news release.

They could easily cross the river on vehicles, boats, barges or debris and prey on smaller frogs, he wrote in the article.

Local treefrogs are considerably smaller than Cuban treefrogs, said Jeff Boundy, a herpetologist with the Louisiana Department of Wildlife and Fisheries’ Natural Heritage Program.

“The natives are about a quarter- to half-dollar-size on your kitchen window at night. These guys get up to five and a half inches (14cm) in body length. You’re talking about a fist-sized frog now,” Boundy said in a phone interview.

The geological survey has been using acoustic monitors since 2014 to check for Cuban treefrog calls in the Barataria Preserve of the Jean Lafitte National Historical Park and Preserve, across the river just a few miles south of New Orleans, Dusty Pate, the park’s natural resource program manager, said.

He said they’re the latest in a long list of invasive species, including Chinese tallow trees, nutria and feral hogs, threatening the park.

“The park spends a lot of time and effort trying to manage invasive plant and animal species,” he said.

Pate said a smaller Cuban treefrog, called the greenhouse frog, is already in the park, but is not considered such a threat. “They eat insects, not other frogs,” he said.

Soon after palm trees from Florida were planted in the zoo’s elephant exhibit, elephant keepers “began noticing unusual treefrogs,” the study said. Not knowing what they were, they caught the frogs and released them at the nearby fence line until being told in October 2016 that they were invasive Cuban treefrogs and should be euthanized.

Individual frogs have been found here and there in Louisiana at least since 1990, but there weren’t enough to establish populations, Glorioso wrote.

Four surveys of the zoo and park in late 2017 found 370 Cuban tree frogs: 58 in the zoo and the rest in the park. The park survey also found about 450 tadpoles in a tire rut, with 1,600 more in a pool only about a meter (3.3 feet) long and half that wide, the report said. Water was emptied from both pools to kill any tadpoles not caught.

Boundy said invasive Cuban treefrogs in Florida seem to be found mostly in cities and suburbs.

But he agreed that they could easily get to the Barataria Preserve.

“Somebody goes to visit the zoo for a day and they get one up in their wheel well and go to Jean Lafitte the next day, they could end up driving it down there. And of course one doesn’t make a population. But if that repeats itself over and over ... it could become established.”