On the day Brad Glorioso and his fellow scientists began their hunt for the invasive Cuban treefrog, they weren’t sure what they’d find. They’d come to Audubon Zoo in New Orleans after the curator of reptiles and amphibians informed them that several suspicious frogs had been spotted on the premises. The bulky frogs appeared to be an invasive species that had—until now—been confined to Florida.
Cuban treefrogs, which can grow as big as the palm of your hand, compete with native treefrogs for shelter and are create a number of nuisances for people. “They get into the plumbing sometimes and people will find them in their toilets, which is always a surprise,” says Glorioso, an ecologist at the U.S. Geological Survey’s Wetland and Aquatic Research Center in Lafayette, Louisiana.
Concerned that the frogs may have taken root in Louisiana, he decided to investigate the zoo and surrounding parklands last fall. His fears were confirmed even before the first search was officially underway. While waiting to meet with their collaborator from the zoo, Glorioso and his team discovered 23 Cuban treefrogs wedged behind a utility box on a bathroom wall. “I brought him a whole bucketful,” Glorioso says. “I was like, ‘we got a problem.’”
The researchers went on to capture 367 Cuban treefrogs on just four sweeps of the park between September and November. They had found the first-known breeding population of Cuban treefrogs to invade the mainland United States outside of Florida. The most likely explanation is that the frogs were stowaways on palm trees the zoo ordered from the Sunshine State.
“This is just the beginning,” says Glorioso, who reported the findings April 21 in the journal Biological Invasions. “Once they take over you can pretty much say bye-bye to seeing a lot of native treefrogs.”
It’s only a matter of time before these skilled hitchhikers colonize other parts of the Gulf Coast as well. So Glorioso and other scientists are trying to learn as much as they can about Cuban treefrogs and the dangers they pose to native wildlife. They don’t expect to stop the invasion, but it may be possible to slow it down and prepare homeowners for the coming onslaught of amphibians.
Unwelcome neighbors
Cuban treefrogs hail from Cuba, the Bahamas, and the Cayman Islands. They invaded the Florida Keys in the 1920s and had spread to the mainland by 1951, probably by hitching a ride on boats and other vehicles. The frogs have been found as far north as Jacksonville, and have traveled all around the country and even to Canada by hiding in horticultural shipments. In most of these places, the Cuban treefrog is unable to withstand the chilly climate. But the Gulf Coast is another story. Here the winters are mild enough that the frogs can survive by hunkering down in buildings and other manmade structures.
Cuban treefrogs have a number of qualities that make them great invaders. They will eat pretty much anything they can fit in their mouths, including other frogs and even the occasional snake. They also breed quickly. “These guys lay a whole bunch of eggs and they can come out of the aquatic tadpole stage pretty quick,” Glorioso says. And Cuban treefrogs thrive in suburban and even urban landscapes. Their habit of stuffing themselves into tiny spaces means they are rarely discovered while stowing away amongst plants or in cars. “They’re just masters at finding every little nook and cranny to go in,” Glorioso says. “Anyplace you can think of that’s a tight space, they’re going to be in there.”
For this reason, you really don’t want Cuban treefrogs anywhere near your home. They can clog your plumbing and have caused costly power outages in Florida by short circuiting utility switches. Cuban treefrogs have also been known to take over birdhouses and lay eggs in pools that haven’t been cleaned. And if they’ve been hanging out around your door, Cuban treefrogs will sometimes drop onto you as you try to get inside. “I have no idea why they do that,” Glorioso says. It could be that the frogs are seeking out warmer or more humid conditions, he speculates. On top of all this, Cuban treefrogs secrete a noxious slime that causes a painful burning sensation if you get it in your eyes, mouth, or any open cuts.
This secretion could spell trouble for native predators, too. When scientists fed gartersnakes a diet of Cuban treefrogs, they gained half the weight of those fed native prey and were more likely to regurgitate their meals or have trouble digesting them.
Even more troubling, Cuban treefrogs have been displacing the native treefrogs in Florida and are likely to do the same in Louisiana. Scientists aren’t quite sure why this is, but suspect Cuban treefrogs could be bad news for the locals on a number of fronts. The frogs may be competing for prey. That said, their food doesn’t seem to be in short supply, so this is unlikely to be the whole explanation, Glorioso says. Cuban treefrogs also gobble up native treefrogs, but they make up a pretty small part of the invaders’ diet. Another possibility is that Cuban treefrogs are so aggressive about jamming themselves into every refuge that they are leaving native treefrogs without any shelter from predators and the elements.
Cuban treefrogs can also carry the chytrid fungus that is plaguing amphibians around the world. Native green treefrogs actually don’t seem to be susceptible to the fungus, but Glorioso worries that Cuban treefrogs may spread it to more other more vulnerable amphibians. He and his team are testing the new invaders for chytrid fungus as well as several other pathogens that are lethal to amphibians.
Settling in
It’s likely that the invasion of New Orleans began in early 2016, when Audubon Zoo imported palm trees from Florida and planted them in the elephant exhibit. Lake Placid, where the trees were shipped from, lies well within the Cuban treefrogs’ range.
It wasn’t long before the elephant keepers began noticing treefrogs. Unaware of the frogs’ true identity, the keepers released them in a green space sandwiched between the zoo and the Mississippi River. This is where Glorioso and his team later discovered the densest clusters of frogs. There were probably even more stowaways that snuck out of the palms without being noticed by the zoo staff, though.
Upon reaching the zoo and surrounding park, the frogs got busy. “The fact that 2016 was a super mild winter probably didn’t hurt their [population] explosion,” Glorioso says. A few months later, the curator and keepers in the reptile house recognized the Cuban treefrogs for what they were.
When Glorioso and his colleagues came in to count the invaders, they removed as many adult frogs and tadpoles as they could find. They may well have culled enough frogs to slow the invasion, he says. But the frogs are such prolific breeders that it likely will not matter in the long run. The frogs could also have reached private property by now, where the scientists will be unable to follow. Glorioso also worries that the frogs will cross the Mississippi River and breach wilder areas that are strongholds for the native treefrogs.
It’s not clear yet whether Cuban treefrogs are displacing the native treefogs. However, Glorioso says, “We didn’t find any green treefrogs in the areas where we found the Cuban tree frogs—not one.” It turns out that green treefrogs hadn’t been found much in those parts of the park to begin with. But squirrel treefrogs, which had been a more common sight, were also missing from the part of the park where Cuban treefrogs were most rampant. The scientists found a few squirrel treefrogs hiding alongside Cuban treefrogs in PVC pipes stored in the zoo. The native frogs were greatly outnumbered by the invaders, though.
It’s not surprising that the frogs evaded detection while nestled among the palms. “At the base of every one of those fronds is a nice little tight space,” Glorioso says. “They’re just impossible to find, they’re way down in these palm trees.”
Additionally, it would be difficult to examine every nook and cranny on the palms without damaging the plants, says Joel M. Hamilton, the vice president and general curator at Audubon Zoo and the collaborator who Glorioso once presented with a bucketful of frogs.
“In the future, Audubon will carefully review the source of our palms and other landscape materials in an effort to avoid bringing in plants that originate in areas where Cuban tree frogs or other invasive species are known to be established,” Hamilton said in an email.
A constant battle
Scientists have predicted that Cuban tree frogs could find suitable habitat in most of the coastal areas along the Gulf of Mexico. As climate change ushers in warmer temperatures, the frogs could potentially reach as far as North Carolina.
In the meantime, there’s a good chance that Cuban treefrogs have settled into other locales beyond Florida but have not yet been recognized, says Steve Johnson, an associate professor of wildlife ecology at the University of Florida in Gainesville. “I wouldn’t be surprised at all if there’s some maybe in southeastern Texas that just haven’t been described yet, or coastal Alabama.”
He and his colleagues have also been tracking Cuban treefrogs off the coast of Georgia on Jekyll Island. The frogs likely arrived on imported palm trees and in cars visiting from Florida, and have been popping up frequently enough to suggest that they settled in.
“I think what we’ve learned is that they are going to continue to arrive elsewhere and when they get to places where the climate is suitable…that they’re likely to establish, unfortunately,” Johnson says.
If you are traveling out of Florida and are worried about transporting frogs, you can check your vehicle for stowaways; one place the frogs like to hide is behind the sideview mirror. But ultimately it’s pretty much impossible to stop the frogs from hitchhiking, Johnson says. “There are countless numbers of places to hide in a car.”
It’s important to examine plants such as bromeliads that have been shipped from Florida for the frogs, Glorioso says. Even so, some will slip through unnoticed.
Once the frogs have arrived in an area, capturing them and humanely euthanizing them when possible is our best bet for combatting the invasion, Glorioso says. “I think the most we can do is kind of knock it back a little…and make people more aware that this is probably coming to a city near you along the Gulf Coast.”
State and federal agencies have dedicated programs to deal with some of Florida’s more notorious invasives such as the Burmese python. There’s no similar effort for Cuban treefrogs, Johnson says. Still, the situation is not hopeless. “It doesn’t mean we should give up, but we have to be in it for the long haul,” he says. “It’s a constant battle; we’re never going to get rid of them…but we can do our best to manage them locally.”
Frog-proofing 101
If you are concerned that Cuban treefrogs may have arrived on your property, you can check for them on a warm night near the lights of your house, where their insect prey tends to gather. Recognizing these frogs can be difficult, as their color can range from pale, ghostly gray to dark brown and even occasionally bright green. To identify a Cuban treefrog, you can try gently rubbing a gloved finger over the frog’s head. On a native treefrog, the skin will move back and forth. But the skin on a Cuban treefrog won’t budge because it is fused to the top of the frog’s skull.
One way to get rid of the frogs is to leave out a PVC pipe and trap the frogs that come to hide, Johnson advises. But this technique does run the risk of capturing native treefrogs as well.
However, there are also a few steps you can take to keep the frogs at bay. One is making sure your pool is clean and well chlorinated and that there aren’t any other pools of standing water where the frogs can lay their eggs. “You really don’t want these guys breeding around your house; you’ll wind up going from just a few to thousands,” Glorioso says.
You can also check any ponds on your property after it rains for eggs and scoop them out with a little aquarium net. “It looks like a bunch of little black dots floating on the surface of the water,” Johnson says.
You also want to eliminate potential hiding spots for the frogs as much as possible, such as stacks of wood. And you can cover the vent stacks on your roof with a cap or hardware cloth to prevent Cuban treefrogs from sneaking in and reaching your plumbing. Finally, turn off any lights you don’t need at night around your house, since they attract insects that in turn lure the frogs to your doorstep.
And once you’ve done all that…get ready to frog-proof your house again. Because if the frogs have reached your property, they are almost certainly visiting your neighbors as well and will recolonize your house before long. “You can’t do it one time and be like, ‘problem solved!’” Johnson says. “You just have to be persistent at it.”
