These saunas and spas for frogs could bring a species back from the brink of extinction

At a park near Canberra, Australia, a series of small white pyramid-shaped boxes are part of a new experiment: Can “frog saunas” help bring back an endangered species?

The green and golden bell frog—an iconic Australian amphibian with a call that sounds like a cross between a power tool and a quacking duck—is already extinct in the area. Like other frog species around the world, it was a victim of a deadly fungus called chytrid that has been killing amphibians for decades. But scientists are reintroducing the vibrant frog with the hope that a design intervention can help it survive.

The “sauna” is a simple design, with bricks inside a plastic enclosure that heats up in the sun. The bell frog loves sitting in the heat—and conveniently the high temperatures kill the fungus.

“The technology we’re using is extremely low tech,” said Simon Clulow, a conservation ecology professor at the University of Canberra leading the research. “That’s good because everything we do in science and conservation, ideally, we want to be accessible, affordable, and scalable.”

A new intervention backed by years of research

Clulow started thinking about the idea as a doctoral student, when he noticed that frogs in a university enclosure liked to sit in the holes inside bricks, probably because they could hide away and feel warmer. At the same time, he knew that the chytrid fungus was most dangerous when frogs got cold. “That led to this idea: Could you create essentially pockets of disease refuge by creating little hot spots in the environment?” he said.

Along with other researchers, he initially tested bricks that were painted black, but they didn’t get quite warm enough, so the small plastic greenhouse was added to help keep the bricks hotter. Research has shown that this type of environment makes a difference.

“We know for sure if we hold the frogs in a temperature-controlled cabinet at those sorts of temperatures for even just a couple of days, it usually leads to complete clearance [of the fungus],” Clulow said. “But even just short-term spikes clearly have beneficial effects.”

The green and golden bell frog used to be common on Australia’s eastern seaboard. “It was widespread in every farm, in everyone’s ponds, and it was just one of those frogs probably nobody took much notice of because it was absolutely everywhere,” Clulow said. Universities often went out to collect the frogs for use in biology classes. Then, in the 1980s, the fungus devastated the population, along with other species of frogs. Only a few isolated pockets of the green and golden bell frogs were left on the coast.

The places where the frogs survived were a little warmer in the winter, with water that was slightly more saline. That led to the second part of the intervention in the new study—tiny ponds with slightly saltier water, which research has shown also kills the fungus without harming the frogs. (The salinity is only about two or three parts per thousand, not enough to taste salty if you drank the water.)

The scientists call the small saline ponds spas, and they’re set up next to the saunas. The new experiment is the largest of its kind. The research team installed 15 experimental wetlands sprawling over hundreds of square miles in Australia’s Capital Territory, with some areas acting as a control to see how well the interventions work. They’ve released around 450 frogs so far this year; the first generation was raised in captivity and given the extra boost of a vaccine against chytrid. The next generation, born in the wild, will rely on the saunas and spas to treat the fungus.

The real-world test

When we talked, Clulow had been up until 3 a.m. the previous night tracking the newly released frogs. They’re not hard to spot. “They have a really fantastic, obvious call, a little bit like a motorbike revving up,” he said, demonstrating the sound. The frogs have microchips so they can be tracked. So far, roughly a month after the first frogs were released, the population is thriving.

The first big test for the project will be in the upcoming Australian winter (during the North American summer), and then the following winter when the new generation of frogs will need to survive. The outside temperature can dip to negative 5 degrees Celsius, or 23 degrees Fahrenheit. Inside the tiny saunas, it can stay a toasty 77 to 86 degrees Fahrenheit.

The research team still needs to prove that the interventions work as well in the wild as they did in the lab, but the solution could potentially be replicated around the world. At least 90 species of frogs have gone extinct because of the fungus; hundreds of others are at risk.

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