PROJosh More, Flickr // CC BY 2.0

10 Slimy Facts About Hellbenders

PROJosh More, Flickr // CC BY 2.0

North America’s biggest salamander is a reclusive crayfish-eater with a compressed body and some rather unflattering nicknames.


Hellbenders have exacting real estate needs. Suited for a very specific habitat, they can only be found in clear, fast-moving streams with large, flat rocks at the bottom. An adult male hellbender will usually defend a territory of about 1000 square feet that is centered around its favorite rock—under which the animal sleeps.


There’s just one recognized species of hellbender, which scientists have dubbed Cryptobranchus alleganiensis. Wild ones may be encountered as far north as New York State, as far south as Alabama, and as far west as Missouri.

The hellbender grows up to 29 inches long, making it earth’s third-largest salamander. Number one is the appropriately-named Chinese giant salamander (Andrias davidianus). Exceeding even some humans in size, this Asian monster can reach 5.9 feet in length and weigh 110 pounds. Right across the Sea of Japan lives the Japanese giant salamander (Andrias japonicus), which grows to be about 5 feet long and maxes out at around 55 pounds.

Together, these three juggernauts form the Cryptobranchidae family. Fossils reveal that the group once invaded Europe and western North America. The hellbender’s ancestors most likely evolved in Asia before migrating to the U.S. via land bridge.


“Hellbender” is an intense name for such a harmless amphibian. How did this word come about? Nobody knows. Perhaps—as herpetologist C.M. Bogert once wrote—early settlers thought that the animal looked like “a creature from hell where [it was] bent on returning.” Or maybe its wrinkled skin reminded someone of the tortures said to take place in Satan’s domain. Both theories seem plausible.

Hellbenders have gone by other nicknames as well, including devil dogs, mud-devils, lasagna lizards, and Allegheny alligators. Yet another nickname refers to their texture: Grasping a hellbender is quite difficult because of the slimy mucus that coats its skin, so they're sometimes known as snot otters.


Though they also feed on insects, earthworms, and small fish, crayfish represent 90 percent of a hellbender’s natural diet. Upon gulping one down, the salamander uses sharp, tiny teeth to pierce its shell. (These chompers can also break human skin.)


USFWSmidwest, Flickr // CC BY 2.0

There are some unfortunate hellbender myths floating around out there. For instance, fishermen have long accused them of driving away bass and other game fish by eating their eggs—or even the fish themselves. However, scientists have yet to find any such foodstuff inside of a hellbender’s stomach [PDF].

Another common misconception is that the salamanders have venomous fangs. People who believe this often kill them on sight—even though this accusation has no merit. In fact, no one has yet discovered any amphibian with such a bite.


Like many amphibians, these stream-dwellers primarily breathe through their skin, extracting oxygen from water. This process is made easier thanks to folds running along their sides, which increase the skin’s surface area.

Hellbenders do have lungs, but they definitely aren’t vital organs. Consider this: As part of a 1967 experiment, both lungs were surgically removed from one individual [PDF]. The animal survived, and its ability to process oxygen was unaffected by the ordeal. So does this mean that a hellbender’s lungs are useless? Not quite. They may not be used for respiration, but the organs probably help regulate buoyancy underwater.


Nighttime is when these creatures do most of their hunting. Between dawn and dusk, hellbenders can usually be found hiding under rocks. On cloudy days, however, they tend to get a bit more active and may leave their haunts well before nightfall [PDF].

Come mating season, the amphibians get particularly bold. Most hellbenders reproduce in either August or September. During those months, they’re far more likely to be active in broad daylight—especially before noon.


A male prepares to breed by digging a tunnel under some nearby rock. Once finished, he curls up inside and pokes his head out. Ideally, a passing female will spot him and swim on over. The male then guides her into the hole, where she’ll release anywhere from 150 to 450 eggs. As she lays them, he sprays semen all over the clutch, fertilizing it.

Following this, the male chases his mate away and proceeds to spend the next few weeks protecting their unborn offspring. Ordinarily, hatching takes place somewhere between 64 and 80 days later. By then, there’s a good chance that the father will have eaten a few of the eggs—though never more than 20 or 30.


Brian Gratwicke, Flickr // CC BY 2.0

If placed ashore by some disruptive human, hellbenders can crawl back into the river, but unlike many amphibians, they almost never leave the water voluntarily. In the water, the salamanders mainly get around by crawling over submerged rocks—though the animals are decent swimmers as well.


Two subspecies are out there—and they’re both in trouble. The Ozark hellbender (Cryptobranchus alleganiensis bishopi), native to southern Missouri and northern Arkansas, has grown frighteningly scarce. Recent estimates indicate that there may be as few as 590 individuals left in the wild. Since the 1980s, the Ozark hellbender population has gone down by roughly 75 percent.

Elsewhere, the eastern hellbender (Cryptobranchus alleganiensis alleganiensis) isn’t faring much better. Previously widespread throughout their New York State range, they now exist in only a few streams and rivers. Similar reports have been made about the animal’s fading presence in West Virginia, Tennessee, Missouri, and Georgia [PDF].

Why are these creatures dying out? Siltation is the main culprit. Whenever a forest is torn down, huge amounts of soil and sand are disturbed. These later get washed into nearby waterways—including the streams that hellbenders call home. Unwelcome sediments muddy up their habitat, bury their tunnels, and suffocate their eggs.

Still, hope remains. Zoos from Toledo to St. Louis have launched captive breeding programs designed to lend snot otters a helping hand. If all goes well, these efforts will rejuvenate our ailing hellbender populations with a surge of young, healthy sub-adults. Keep your fingers crossed.

Ted Cranford
Scientists Use a CT Scanner to Give Whales a Hearing Test
Ted Cranford
Ted Cranford

It's hard to study how whales hear. You can't just give the largest animals in the world a standard hearing test. But it's important to know, because noise pollution is a huge problem underwater. Loud sounds generated by human activity like shipping and drilling now permeate the ocean, subjecting animals like whales and dolphins to an unnatural din that interferes with their ability to sense and communicate.

New research presented at the 2018 Experimental Biology meeting in San Diego, California suggests that the answer lies in a CT scanner designed to image rockets. Scientists in San Diego recently used a CT scanner to scan an entire minke whale, allowing them to model how it and other whales hear.

Many whales rely on their hearing more than any other sense. Whales use sonar to detect the environment around them. Sound travels fast underwater and can carry across long distances, and it allows whales to sense both predators and potential prey over the vast territories these animals inhabit. It’s key to communicating with other whales, too.

A CT scan of two halves of a dead whale
Ted Cranford, San Diego State University

Human technology, meanwhile, has made the ocean a noisy place. The propellers and engines of commercial ships create chronic, low-frequency noise that’s within the hearing range of many marine species, including baleen whales like the minke. The oil and gas industry is a major contributor, not only because of offshore drilling, but due to seismic testing for potential drilling sites, which involves blasting air at the ocean floor and measuring the (loud) sound that comes back. Military sonar operations can also have a profound impact; so much so that several years ago, environmental groups filed lawsuits against the U.S. Navy over its sonar testing off the coasts of California and Hawaii. (The environmentalists won, but the new rules may not be much better.)

Using the CT scans and computer modeling, San Diego State University biologist Ted Cranford predicted the ranges of audible sounds for the fin whale and the minke. To do so, he and his team scanned the body of an 11-foot-long minke whale calf (euthanized after being stranded on a Maryland beach in 2012 and preserved) with a CT scanner built to detect flaws in solid-fuel rocket engines. Cranford and his colleague Peter Krysl had previously used the same technique to scan the heads of a Cuvier’s beaked whale and a sperm whale to generate computer simulations of their auditory systems [PDF].

To save time scanning the minke calf, Cranford and the team ended up cutting the whale in half and scanning both parts. Then they digitally reconstructed it for the purposes of the model.

The scans, which assessed tissue density and elasticity, helped them visualize how sound waves vibrate through the skull and soft tissue of a whale’s head. According to models created with that data, minke whales’ hearing is sensitive to a larger range of sound frequencies than previously thought. The whales are sensitive to higher frequencies beyond those of each other’s vocalizations, leading the researchers to believe that they may be trying to hear the higher-frequency sounds of orcas, one of their main predators. (Toothed whales and dolphins communicate at higher frequencies than baleen whales do.)

Knowing the exact frequencies whales can hear is an important part of figuring out just how much human-created noise pollution affects them. By some estimates, according to Cranford, the low-frequency noise underwater created by human activity has doubled every 10 years for the past half-century. "Understanding how various marine vertebrates receive and process low-frequency sound is crucial for assessing the potential impacts" of that noise, he said in a press statement.

Scientific Reports, Fernando Ramirez Rozzi
Stones, Bones, and Wrecks
Humans Might Have Practiced Brain Surgery on Cows 5000 Years Ago
Scientific Reports, Fernando Ramirez Rozzi
Scientific Reports, Fernando Ramirez Rozzi

In the 1970s, archaeologists discovered a site in France containing hundreds of cow skeletons dating back 5000 to 5400 years. The sheer number wasn't surprising—human agriculture in that part of the world was booming by 3000 BCE. What perplexed scientists was something uncovered there a few decades later: a cow skull bearing a thoughtfully drilled hole. Now, a team of researchers has released evidence that suggests the hole is an early example of animal brain surgery.

Fernando Ramírez Rozzi, a paleontologist with the French National Center for Scientific Research, and Alain Froment, an anthropologist at the Museum of Mankind in Paris, published their findings in the journal Nature Scientific Reports. After comparing the opening to the holes chiseled into the skulls of humans from the same era, they found the bones bore some striking similarities. They didn't show any signs of fracturing from blunt force trauma; rather, the hole in the cow skull, like those in the human skulls, seemed to have been carved out carefully using a tool made for exactly that purpose. That suggests that the hole is evidence of the earliest known veterinary surgery performed by humans.

Trepanation, or the practice of boring holes into human skulls, is one of the oldest forms of surgery. Experts are still unsure why ancient humans did this, but the level of care that went into the procedures suggests that the surgery was likely used to treat sick patients while they were still alive. Why a person would perform this same surgery on a cow, however, is harder to explain.

The authors present a few theories, the first being that these ancient brain surgeons were treating a sick cow the same way they might treat a sick human. If a cow was suffering from a neural disease like epilepsy, perhaps they though that cutting a hole in its head would relieve whatever was agitating the brain. The cow would have needed to be pretty special to warrant such an effort when there were hundreds of healthy cows living on the same plot of land, as evidenced by the skeletons it was found with.

Another possible explanation was that whoever operated on the cow did so as practice to prepare them for drilling into the heads of live humans one day. "Cranial surgery requires great manual dexterity and a complete knowledge of the anatomy of the brain and vessel distribution," the authors write in the study. "It is possible that the mastery of techniques in cranial surgery shown in the Mesolithic and Neolithic periods was acquired through experimentation on animals."

Either way, the bovine patient didn't live to see the results of the procedure: The bone around the hole hadn't healed at all, which suggests the cow either died during surgery or wasn't alive to begin with.


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