The first time Mason Polencheck BSx’25 met a mudpuppy, he was nine years old, on a fishing trip in the waters of Lake Superior. It’s an experience he’ll aways remember, one that spawned his fascination with these timid little amphibians. Ten years later, fate put Polencheck in the vicinity of mudpuppies once again.

In summer 2022, he had just completed his freshman year at UW and was working as an intern at the university’s Trout Lake Station. During a training event, he learned that mudpuppies had been found in local lakes. It rekindled his curiosity.

Mudpuppies (Necturus maculosus), also known as waterdogs, are freshwater salamanders with external gills that float around their necks like frilly red scarves. They are fully aquatic (their limited lungs are for emergencies only), and they come in various shades of brown or gray. An average adult mudpuppy is around 10 inches long, but Polencheck has seen some over 16. Each of their appendages ends in four little round toes.

“They are kind of like axolotls, if you know what those are,” says Polencheck, who is majoring in microbiology and zoology with a certificate in biology core curriculum honors. “Axolotls are pretty big in pop culture. I know they’re in [the video game] Minecraft. Mudpuppies are very distantly related, but they look very similar.”

Because they are so reclusive, most people have never seen or even heard of mudpuppies. And, as far as Polencheck knows, they are understudied in Wisconsin. So, he decided to make understanding them his own personal mission.

“People don’t realize we have our own kind of axolotls right here in our backyards,” he says. “And they are so neat.”

When he first came to UW, Polencheck joined a research lab, where he was introduced to bench work. It didn’t last long.

“I grew up out in the woods — fishing, hunting, all that stuff,” says Polencheck, who is from Ashland in far-northern Wisconsin. “I really enjoyed [the lab work], and I learned a lot, but it wasn’t me. I couldn’t sit in a lab all day.”

That’s what prompted him to apply for a summer internship at Trout Lake Station, a university research facility located near Minocqua, Wisconsin, only about a 90-minute drive to the southeast of his hometown. The position involved collecting water samples from bogs for microbial analysis to support the work of a graduate student in the lab of Trina McMahon, professor in the Department of Bacteriology at CALS and the Department of Civil and Environmental Engineering in the College of Engineering.

The topic of mudpuppies came up in passing during an outreach event held at the station. Polencheck was hooked. From that point forward, he devoted his free time to searching for the elusive creatures. He even tagged along on other people’s research outings, providing fieldwork assistance, so he could scout for mudpuppies in new places.

“I just got interested in them,” Polencheck explains. “Whenever I could, I would go out looking for them just to see what they looked like and where they lived. Natural history kind of stuff.”

But mudpuppies aren’t easy to find. They’re known as “winter salamanders” because they are most active during the coldest months. The only people who tend to see mudpuppies are ice fishers who accidentally catch them. In summer, mudpuppies need to avoid a variety of predators — fish, water snakes, aquatic mammals, birds — so they hunker down in safe, secret places under rocks and logs. And, being nocturnal, they only come out at night, which can make them seem even more scarce.

By the end of that special summer, Polencheck knew he wanted to study mudpuppies formally, even though no UW scientists were researching them at the time. Although perhaps understudied, mudpuppies are important members of the food web: They consume countless invertebrates while providing sustenance for many species of fish.

They are considered a bellwether species — they have sensitive skin that makes them vulnerable to toxins, so they can alert scientists to environmental problems. Mudpuppy populations are in decline in some areas, and they are listed as endangered, threatened, or a species of special concern in 19 of the 26 states where they naturally occur. This all served as further motivation for Polencheck.

“There’s a 40-year knowledge gap on how the populations are doing in Wisconsin,” he says. “So, I just wanted to look at where they are, how many there are. Plus, I wanted to develop better capture methods because there weren’t good methods available.”

Back on campus for the fall of his sophomore year, Polencheck started casting out feelers to faculty in hopes one would consider taking on a research project with a muduppy focus. He finally got a bite when McMahon was lured in.

“Mason contacted me about his very specific interest in mudpuppies,” says McMahon, whose research focuses on predicting and modeling microbial behavior. “I had never worked on vertebrates before and was hesitant to say yes, but Mason’s enthusiasm and level of preparedness blew me away, so I invited him to join the lab. I am so glad that I did.”

Polencheck spent fall 2022 developing a detailed plan for a research project to look at the skin microbiome of mudpuppies. Then, back home in Ashland for winter break, he began his fieldwork, which involved trapping mudpuppies, taking microbial samples from their skin, and then immediately releasing them back into the wild. He and his dad set up traps on a few frozen lakes near their house, and they needed to check them daily — whatever the conditions — for a week. The weather soon turned foul.

“The first week was probably the worst in my entire life sampling because we placed the traps, and then, like two days later, it got to minus 20 [degrees] with the wind chill,” Polencheck says. “Then we got a foot of snow, so it was a rough start.”

Finally, on the fifth or sixth day, their efforts were rewarded with their first catch. “When we saw it in the trap, we were both hooting and hollering,” Polencheck recalls.

After his holiday visit home, Polencheck spent the rest of winter break at Trout Lake Station trapping for more mudpuppies. He caught 20 that first winter. When he returned to Madison for the spring 2023 semester, he used the same trapping methods on frozen lakes Monona and Mendota ahead of the coming thaw. After six weeks of trying, he’d only nabbed one mudpuppy.

“We went back to the drawing board at that point,” says Polencheck, who spent the rest of that semester searching for a better way.

Polencheck returned to Trout Lake Station in summer 2023 to continue the bog water sampling work he’d done the previous summer. This time he also had a Sophomore Research Fellowship — an award that supports undergraduate research conducted in collaboration with UW faculty or staff — to help fund his mudpuppy project with McMahon. Again, he used work interludes to search for mudpuppies, but this time he approached the hunt in a more assertive and systematic way: He put on a snorkel and wetsuit and started to explore their environs, flipping rocks along his floating path. Over time, he found some mudpuppy hot spots on Trout Lake and a couple other bodies of water and developed a true knack for predicting where to uncover them.

“When I’m snorkeling, it’s like, you just get the feeling, ‘that’s a perfect rock,’ and you slowly lift it up, and there’s one sitting there,” Polencheck says. “Rocky areas are best, and there needs to be sandy substrate so they can dig out a cavity to hide.”

As rocks are upended, sometimes mudpuppies will spook and take off — but they don’t swim far. They jet away about 15 feet or so and then freeze, so it’s easy to just float over and net them. Taking a sample involves wiping their skin with a cotton swab to collect microbes for analysis in the lab. When mudpuppies are caught and handled, their skin starts to exude a clear slime, making them slippery — a natural defense mechanism. Polencheck puts them back where he finds them.

Polencheck’s trial and error convinced him that it’s easiest to catch mudpuppies at night — with the aid of a special technique. Given their nocturnal habits, mudpuppies typically come out to find food when it’s dark. After the sun sets, all Polencheck has to do is put on waders and walk out into a lake. Using a waterproof light attached to a pole, he can easily scan the underwater terrain as he slowly walks along. There’s a menagerie to see — from frogs to fish to, of course, mudpuppies. He was taught this technique — called “shining” — by a pair of citizen scientists interested in amphibians.

“Man, the first time I went out shining with [then citizen scientists], I think we found six or seven mudpuppies, which was crazy for me because, at that point, I’d only caught [so few],” Polencheck says.

With snorkeling and shining in his toolbox, Polencheck made swift progress on his research project. But then he hit a snag — a big one. Turns out his cotton swab sampling protocol was missing a step. To get usable data, he should have been rinsing each mudpuppy with sterile water before swabbing to wash away the microbe-laden lake water. His samples were contaminated. He had to throw away his data and start over to get a true picture of the microbes that live on the skin of mudpuppies.

“That was a major blow, but that happens in research,” he says. “It’s one of the best lessons I learned from this, that not everything goes according to plan. It was very disappointing, but at least I knew where to look for them. I had these different ways to sample — snorkeling, shining. I had the methods down, so it wouldn’t be horrible to restart.”

During the fall of 2023, his junior year, Polencheck traveled around the state in a mad dash to get new samples, and he ended up catching more than 200 mudpuppies in two months. For his research project, he grouped his mudpuppy data into three categories: mudpuppies found living in lakes, those living below dams with a lake situated above, and those living below dams with no lake. Then he compared the microbial communities living on the skins of mudpuppies existing in these three different scenarios.

Skin serves multiple vital functions for amphibians: They use it to breathe, sense their environment, and stay hydrated. It’s also an important part of their immune systems. Mudpuppies, like other amphibians, rely on their skin microbiome — the bacteria and fungi that live on their flesh — to serve as a first line of defense against pathogens.

“We found that, within these different water bodies, the microbiome on mudpuppies varies quite a bit,” Polencheck says. These variations include the total number of microbes present and also the specific types of microbes. He has since shared his findings at several meetings and conferences.

“Mason is working at the level of a senior graduate student in many respects,” McMahon says. “He is extraordinarily driven and passionate about his science, and he gets things done. There are days when I tell myself to just get out of his way because I don’t want to slow him down!”

Over the course of the entire project, Polencheck says he learned another important lesson: Collaboration is a huge part of scientific research. He ended up sharing information, ideas, and effort with Trout Lake Station staff, UW faculty, Wisconsin Department of Natural Resources employees, and researchers from other universities around the nation.

As an outcome of such collaboration, Polencheck developed a second research project with Jessica Hua, associate professor in the Department of Forest and Wildlife Ecology, who studies aquatic ecotoxicity. Their study focuses on amphibian chytridiomycosis, an infectious fungal disease that has led to significant declines in amphibian populations worldwide, including the extinction of approximately 90 species. It’s caused by the microscopic fungus Batrachochytrium dendrobatidis, known as Bd, which grows on the skin of amphibians and disrupts its normal functions. Their results didn’t follow the usual pattern.

“Almost all of the mudpuppies had high levels of Bd, but they didn’t display any signs of disease, and we’re not sure why,” he says. It’s a surprising and significant finding.

He and Hua are wondering if mudpuppies are serving as a kind of reservoir for the Bd fungus. Could mudpuppies be inadvertently spreading the disease to other, more susceptible amphibians? Polencheck hopes to answer these and other related questions in graduate school. He’s currently exploring options in wildlife ecology and other programs that will allow him to continue to focus on mudpuppies. If he or other scientists can figure out how mudpuppies with Bd manage to stay healthy, this line of research could one day reveal treatments for impacted species.

“If there were something in the microbiome of the mudpuppies that prevents the pathogenicity of Bd, we could use it as a preventative measure for other amphibians,” Polencheck says. “It would be awesome to take something from here in Wisconsin, give it to amphibians that are struggling around the world, and help save them.”

Whether Polencheck pursues graduate studies at UW or elsewhere, his time at the university points to some good news for Wisconsin: The mudpuppy population appears to be widespread and healthy in the Badger state. And his findings are supported by a recent DNR survey (see“Mudpuppies in Wisconsin” below).

Polencheck can’t give a definitive total; but, anecdotally, in any given lake or stream — where the conditions are right — there can be hundreds or even thousands of mudpuppies. And now he knows how to find them.

Mudpuppies in Wisconsin

The Wisconsin Department of Natural Resources (DNR) led a survey in 2022–23 that found populations of mudpuppies in nearly all of the state’s 72 counties, including four counties where they had not been recorded previously.

You can add to the DNR’s mudpuppy databank by recording and sharing your own observations with the Wisconsin National Heritage Inventory.