A sit in the sauna can save endangered frogs

On warm, muggy evenings, conservation biologist Anthony Waddle and his students, along with local frog enthusiasts, venture into the wild and wet suburbs of Sydney, Australia, head torches on, searching for green and golden bell frogs (Litoria aurea). Then they frogmarch the captured amphibians into a small greenhouse made from nothing more than a stack of masonry bricks for a “luxury treatment” sauna — which might ultimately save their lives, he explains.

For many, the idea of a ‘frog sauna’ might sound bizarre. But when Waddle’s team published a study (A. W. Waddle et al. Nature 631, 344–349; 2024) showing that a simple sit in a warm enclosure could treat the deadly chytrid fungal infection plaguing the green and golden bell frog, it made waves — and resulted in him winning the 2025 Future for Nature award. Now, as a postdoctoral researcher at Macquarie University in Sydney, he’s collaborating with partners, training local communities and helping Australia to save its declining population of these glossy green-and-golden-streaked frogs that fit in your palm and croak with a muffled, motorcycle-like revving sound.

Chytrid fungus infections are a huge threat to the global frog population and have contributed to declines in more than 500 frog species and the extinction of more than 90 others.

The good news is that infections can be cleared easily in some frogs under the right conditions, because the fungus is sensitive to heat. “Around 28 °C is enough to really limit chytrid growth,” Waddle says. And the sauna treatment can pay off really fast: a few hours a day for a week or less is all that’s needed. Saving one female frog can markedly change the trajectory of a population, because a single adult can produce thousands of offspring in one season.

How the treatment came about was serendipitous. In 2013, researchers studying tree frogs in Queensland, Australia, noticed a pattern: in areas where chytrid fungus had spread, frog populations survived near large granite boulders and crevices, but disappeared from shaded, forested areas. The researchers hypothesized that the boulders acted as natural refuges that absorbed heat during the day and slowly released it at night. The process created warmer microhabitats that protected the frogs from the fungus.

However, not all habitats had these heating boulders. So Waddle and his colleagues wanted to finally “test this idea that people had been hemming and hawing about forever”, but that no one had tested by experiment.

Trying a new approach meant there was no standard blueprint. Waddle and his team had to test and adjust various sauna designs as they went. Their simple set-up consists of a small garden-greenhouse frame wrapped with translucent plastic and placed over a stack of masonry bricks, each with a series of openings for frog entry and exit. Their experiments found that the frogs readily find and enter saunas on their own.

So far, the researchers have placed about 70 frog saunas in three sites in greater Sydney and plan to use three more sites there in the next Southern Hemisphere winter, in 2026. They have also created how-to guides, educational videos and workshops to teach community members how to build the saunas (see ‘Quick-fire Q&A’). Several greenhouse suppliers have even listed the set-up on their websites as useful for creating frog saunas, as well as for growing plants.

Quick-fire Q&A

How do you capture the frogs for the treatment?

Capturing frogs is the fun part. You just go out at night with head torches and pick them up. We capture them by hand and bring them into a temperature- and environment-controlled facility. We either give them antifungal baths or increase their temperature for treatment, and then eventually release them. My students and I like capturing frogs the most, but it’s also the start of a lot of work, because the frogs are usually quite ill and need close attention.

What has been the main challenge of this project?

It’s mostly been about getting people on board with solution-driven research. I’ve worked on chytrid fungal infections for nearly 12 years — starting with an undergraduate project, then a master’s on chytrid and vaccines, a PhD focused on ‘vaccination’ in frog saunas, and now a postdoctoral position investigating synthetic-biology solutions for chytrid resistance.

We’re in a position to make a big impact, even with a small team. But sometimes it’s been hard to get the exposure and support we need to grow and to secure major funding — especially when we don’t have the CVs of more-senior researchers to back us up.

When someone develops a patent, or something for use during their PhD, it’s the responsibility of that person to make sure that the technology is used. So, I’m adopting an unconventional entrepreneurial spirit, doing citizen-science work, trying to secure partnerships with industry and going out to places where people don’t think to look for funding or support, to drive my research forwards. It’s been the secret to my success.

What’s a surprising question that you are asked about your job?

People often ask us to justify why we do our work or explain its broader benefit to society. I often retort with: “No one asks an accountant, or someone making money from money, what their greater purpose is.” Yet, someone like me working to conserve frogs is treated as if that’s not a real job. I’m not tired of justifying that what I do is important, because we are saving species from the face of extinction. But I do enjoy making people laugh with that joke, because it’s true.

The saunas are a low-cost garden habitat for the endangered frogs that live throughout southeastern Australia. Waddle has worked with other frog conservationists, encouraging local people to use apps such as FrogID. This lets users make audio recordings of frog calls and upload them to an online database, togeher with GPS data. Experts then identify the frogs and notify the users.

Jodi Rowley, a herpetologist at the Australian Museum Research Institute in Sydney and lead scientist for FrogID, says that tens of thousands of people across Australia use the app, and have put more than 1.3 million frog records on the map. The app has contributed to the discovery of 13 frog species and is actively used by communities to monitor local frog populations. Now, regular FrogID users can get frog-sauna information and updates. “We are hoping that communities are using the app to record their local frogs and potentially determine whether the frogs do better after the installation of frog saunas,” Rowley adds.

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