Not the forgotten part of Avatar: The Last Airbender or an abandoned Hellraiser title, as part of our look at weird animals over April we’re looking at North America’s largest amphibian, the hellbender. A species of salamander, it spends its entire life in the water and was seen as something bent on returning to Hell by European colonists.
Taxonomy and Evolution
The hellbender is the only member of its genus having the scientific name Cryptobranchus alleganensis. There are two subspecies: the eastern hellbender, C.a. alleganiensis, and the Ozark hellbender, C.a. bishopi. Hellbenders are salamanders and belong to the family Cryptobranchidae, or the giant salamanders, which also contains the massive Chinese and Japanese giant salamanders. First appearing at the end of the Cretaceous the giant salamanders filled a very specific niche in the rivers of the world with hellbenders being a recent member. The oldest known fossils belonging to hellbenders date to around 850,000 years ago.
Biology and Behaviour
Hellbenders are big amphibians reaching between 30 and 74 centimetres in length making them one of the largest amphibians in the world and the largest in North America. A species of siren is longer, but hellbenders are much heavier reaching between 400 and 1000 grams, which makes them by far the heaviest amphibian in North America. Being black or dark brown in colour with several dark orange spots one of the potential origins for the name ‘hellbender’ is that they had escaped the fiery torture of Hell. A hellbender certainly wouldn’t want to be near the fires of Hell as they are adapted to life in shallow, fast-moving water. Unlike other entirely aquatic salamanders, like mudpuppies, hellbenders do not have external gills upon reaching adulthood – capillaries in the folds of the skin instead absorb oxygen from the water. Even though they have lungs the capillary method means they can use their lungs for buoyancy instead. Hellbenders have a flat head with folded skin at the sides of their bodies to increase their surface area, and with it the amount of oxygen that can be absorbed. Having long legs is detrimental to them, so hellbenders have short legs ending in webbed feet. A long paddle-like tail is not used for swimming as would be expected, but instead for clinging onto rocks. It can be used for propulsion if they do detect a predator. Special pads on their feet allow them to better grip rocks and gravel so they don’t have to swim.
Hellbenders, like many amphibians, start out life as eggs, but they do differ from other salamanders. Most salamanders do internal fertilisation, whereas hellbenders do external fertilisation. In September and October males build a burrow to attract females who will lay their 150 to 450 eggs in it, and then the males will fertilise them. The male will then protect the eggs for the next 68 to 75 days until the eggs hatch, and the tiny, legless babies hatch. Measuring just 33 millimetres at their longest these hatchlings can instantly fend for themselves – all the better as dad might quickly turn them into a meal. The babies will have gills until they reach two years of age, and by then they should measure between 100 and 133 millimetres in length. From there the hellbender growth is slow with them not reaching sexual maturity until aged 7 or 8. If they do reach that lucky hellbenders will mate every year. Wild hellbenders have been known to reach 20 years old, although captive ones can far exceed that if well kept after.
Despite having lidless eyes hellbenders have poor eyesight. Living on river and stream bottoms, and being nocturnal means that good eyesight is a waste of energy. Instead, their skin is covered in photoreceptors that can detect light changes which allow them to ‘see’. Hellbenders also have a superb sense of smell, a sense so good that they can detect the smell of different fish to determine which are a danger or not. The only time hellbenders meet is to breed, and receptive ones release pheromones to indicate that they are willing to reproduce. Finally, the folds in their skin have another purpose. Like the lateral lines in fish, the folds in hellbenders can detect water movement which is essential for finding prey, avoiding predators, and navigating a watery environment.
Distribution and Habitat
Hellbenders fit a very particular niche in a very particular habitat. Not being the best swimmers you would imagine them preferring standing or slow flowing water, but hellbenders live in fast flowing water. Fast flowing water is richer in oxygen making it ideal for hellbenders. Hellbenders are also very reliant on rocks and gravel in their habitat so are only found in running bodies of water that have plenty of rocks, sediment, and gravel which they use for cover and to cling onto. As this is a very niche habitat collectors wanting to find hellbenders in the past had to just look for suitable habitats and they could easily find them. Hellbenders are only found in the United States, with the eastern hellbender having a much wider distribution. Being found as far north as southern New York and as far south as northern Georgia they are also found as far west as Illinois. The Ozark hellbender, as its name suggests, is confined to the Ozark mountains in Arizona and Missouri, which has meant that human activity has pushed them close to extinction (more below).
Diet and Predators
Like almost all salamanders, hellbenders are carnivores. Ambush predators, they wait patiently for crayfish, worms, snails, small fish, insects, and other salamanders to swim too close by. Then they will lash out and shake the prey in its jaws before swallowing them whole or into smaller chunks. Smaller hellbenders are not off the menu, and have been known to eat their own young. Male hellbenders will often eat 20 to 30 of their own eggs to sustain them during their months long defense of the burrow, but considering that there are often more than 150 eggs it is hardly a drop in the bucket. As hellbenders get larger the amount of animals that can hunt them is heavily reduced, but they do have predators. Mostly, fish like trout, bass, sculpin, and, in the most northern areas, pike pose a threat to adult hellbenders.
Conservation and Threats
It is once again an unfortunate story that the hellbenders are facing extinction. In 2021 the IUCN looked at hellbender populations and classified them as ‘Vulnerable’ with the US government, since 2011, covering the Ozark hellbender under the Endangered Species Act. It is estimated that there is perhaps just over 500 Ozark hellbenders left in the wild, and eastern hellbender numbers are sharply dropping. Most of the reasons why can be traced back to humans. Water pollution, dam construction, and silt accumulation have all reduced the available habitat for a species that needs very specific habitats to survive. Furthermore, the deadly chytrid fungus has deeply impacted hellbender numbers. This fungus has rapidly spread across the Americas and causes amphibian skin to dry out which eventually kills them, and it has already contributed to the extinction of several species. Climate change is also impacting them as not only does it help the spread of the chytrid fungus, but it also reduces oxygen concentration in the water. Colder water contains more oxygen, so as temperatures rise the rivers that hellbenders call home increasingly has less oxygen. Conservation methods have been implemented. Capturing wild hellbenders for the pet trade is now band and several institutes have developed a breeding programme. The Smithsonian National Zoological Park has been especially successful managing to breed hellbenders for potential release. However, until the US implements direct policies to address environmental destruction and climate change, hellbenders will creep closer and closer to extinction.
Bibliography:
- Chris Mattison, Snakes and Other Reptiles and Amphibians, (London: DK, 2014)
- Zeb Pike, ‘Hellbender’, Animal Diversity Web, (2015), [Accessed 13/04/2023]
- ‘Hellbender’, IUCN, (15/07/2021), [Accessed 10/04/2023]
- S. Conor Keitzer, Thomas Pauley, and Chris Burcher, ‘Stream Characteristics Associated with Site Occupancy by the Eastern Hellbender, Cryptobranchus alleganiensis alleganiensis, in Southern West Virginia’, Northeastern Naturalist, 20:4, (2013), 666-677
- R. David Williams, J. Edward Gates, Charles Hocutt, and Gary Taylor, ‘The Hellbender: A Nongame Species in Need of Management’, Wildlife Society Bulletin, 9:2, (1981), 94-100
- Catherine M. Bodinof, Jeffrey T. Briggler, Randall E. Junge, Tony Mong, Jeff Beringer, Mark D. Wanner, Chawna D. Schuette, Jeff Ettling and Joshua J. Millspaugh, ‘Survival and Body Condition of Captive-Reared Juvenile Ozark Hellbenders (Cryptobranchus alleganiensis bishopi) Following Translocation to the Wild’, Copeia, 1, (2012), 150-159
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