Raisin' Hellbenders: How Scientists Are Saving North America's Largest Salamander

Sherri Doro Reinsch stands in the river and bends over one of the gray coolers filling the canoe. She reaches inside and untwists a long plastic bag containing a mottled brown creature submerged in water—an eastern hellbender. Under the burning Tennessee summer sun, Reinsch and her colleagues prepare to release 11 of these native salamanders, each implanted with a transmitter allowing the team to track them.

Once commonly found in the eastern United States, these salamanders—which are the largest in North America—are now struggling to survive. Yet, unlike their relatives, the Ozark hellbenders, eastern hellbenders as a whole are not listed as federally endangered; only a specific population in Missouri is protected.

Reinsch—the Nashville Zoo’s lead amphibian and reptile keeper—and her colleagues from the zoo, Tennessee State University, and the Tennessee Wildlife Resources Agency are trying to save the eastern hellbenders through an innovative program in which they raise the animals from eggs until they’re old enough to be returned to the wild.

An Amphibian Advantage

From egg cluster to fully grown amphibian, hellbenders spend their entire lives in the water. A female can lay up to 500 eggs at once, and after the eggs hatch, the animals stay with their father (known as the denmaster) before the tiny young hellbenders spend a year living in the gravel of the riverbed feeding on insect larvae. They then metamorphose into adult hellbenders. 

But too many hellbenders aren’t surviving these early life stages. The process where the young grow and join the adult population, replacing the old, is known as recruitment—and hellbenders suffer from a lack of recruitment. Dale McGinnity, a hellbender expert and Nashville Zoo curator of insects, amphibians, reptiles, and fish, believes hellbender populations began declining in the middle of the 1980s. Over a decade later, populations outside of national parks had shrunk by 90 percent. 

Scientists aren’t entirely sure what’s causing the lack of recruitment, but they do know what’s not. “We're quite sure that it’s not the sperm or the eggs because we can find viable nests,” McGinnity tells Mental Floss, “which is really nice, because we can collect eggs and head-start them—which is what we’re doing.”

The head start program began in 2015. The 11 hellbenders scientists are preparing to release today, which were captured as eggs in central Tennessee, are part of the second class. Scientists take a portion of a female hellbender’s egg clutch from a local waterway, hand-raise them past the point where they’d die in the wild, and then release them to the same area.

For almost seven years, the scientists cared for these hellbenders at the zoo, preparing them for life in the river they’re now standing in (its name and location are kept secret to protect the animals). They regularly introduced river water to their tanks and fed them crayfish—their main food source—from the same waterway. Now the biologists hope these amphibians, which can grow over 2 feet long and weigh five pounds, can complete their full lifespan here. Hellbenders in captivity have lived for almost 30 years, but it’s thought they might live 50 years or more in the wild. 

After getting in the river, Reinsch tested the water’s temperature, a factor in the hellbenders’ ability to breathe. “Colder water has more dissolved oxygen in it … so it makes [it] easier to breathe because they absorb oxygen through their skin,” Reinsch tells Mental Floss. To allow the hellbenders to adjust to their new home, the scientists pull each hellbender in its bag of tank water out of the coolers and hold the bags by their sides in the current, like pets on a leash. Eventually, they let a little water inside, slowly introducing the hellbenders to the new temperature.

And about that name: There’s no definitive consensus on its origin. Some scientists believe it’s because of their appearance, because they are active at night, or because they can bend from side to side. Their even more evocative nickname, “snot otters,” stems from the mucus they produce all over their bodies to ward off predators. 

The Case for Clean Water

Because they need clean, flowing water to survive, many consider hellbenders “canaries in the coal mine”: Their wellbeing is an indication of the overall health of the waterways on which other species also depend. And that could provide a clue as to what’s causing hellbenders’ lack of recruitment. 

Chemicals polluting these waterways may be a cause of their decline. One theory is that agricultural chemicals could be flowing into the water and harming the hellbenders as they metamorphose, preventing them from reaching healthy adulthood. The harmful substances could also be accumulating in the young insects that the larval hellbenders eat, which also might affect their metamorphosis. 

Sediment flowing into rivers is another possible obstacle to recruitment among hellbender populations. Hellbenders are extremely picky about their nest rocks: They must be several feet wide and completely embedded on all sides except for a small hole leading to a space underneath the rock. If too much sediment enters the water, it can fill up this entranceway, and eggs inside that space won’t survive. Suitable nesting habitat can also be damaged or destroyed if humans move or stack rocks in rivers.

The Next Generation

In addition to its head start program, the Nashville Zoo has a hellbender breeding program as part of its conservation efforts. In 2012, the zoo was the first to successfully breed eastern hellbenders. McGinnity and his team are now working on finding the most cost-efficient methods for this work—including cryopreserving sperm and artificial fertilization—that also promote genetic diversity, a key to a healthy population. One day they hope to perfect the process of hatching and raising hellbenders so they can supplement wild populations with strong, genetically diverse babies. “It’s a tough thing to figure out because they only breed once a year, and we have a really limited number of animals to work with,” McGinnity says. “But we’ve made a lot of headway.”

Sometimes the hellbenders don’t actually go along with this plan, though. Usually, after a female lays the eggs and the male fertilizes them, only he stays to ensure the flow of oxygen-rich water over the nest. McGinnity remembers a particular male hellbender guarding eggs in their lab; the researcher was hopeful he’d end up with a healthy batch of hellbenders until the male ate the eggs. (This sometimes happens in the wild, too, for unknown reasons.)

Into the Wild

Reinsch and her colleagues have chosen an idyllic new home for their hellbenders. A tall bluff, its gray rock peeping through the green of the trees and vines growing in its crevices, guards one side of the river, and lush forest hugs the other side as the sun shines down on the sparkling clear water. It’s fitting that these last moments with the creatures they raised are surrounded by such natural beauty; from then on, they would only be connected by technology, as the scientists depend on radio signals from the hellbenders’ transmitters to find them again.

Donning snorkeling gear, the scientists take turns releasing the hellbenders. Each lifts one out of its bag, cradling it gently before sinking below the water’s surface, holding the hellbender up to a specially chosen nest rock, and releasing it into the entrance hole. Thirty-four hellbenders were released this way during the summer of 2022, and months later, over half of the released amphibians have survived, an improvement over the previous year.

Before they release another group of hellbenders, the team will review what they’ve learned and what they should change. Reinsch likes to share their knowledge with any interested party. “We all want to do … what will work out to be the best [practice],” she says. “We all have the same passion for hellbenders.”