Hellbender Salamanders are one of the largest salamander species in the world, reaching lengths of 2.5 feet. They require cool, clear rivers and streams with little to no siltation in order to breathe and to inhabit sustainable microhabitats, and they are highly susceptible to pollution.
Hellbenders are currently divided into two subspecies: the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis) and the Ozark Hellbender (Cryptobranchus alleganiensis bishopi). The species was first described by Daudin in 1803. Cryptobranchus means “hidden gills”—in fact, adult Hellbenders completely lack gills. The species name alleganiensis refers to the Allegheny Mountain portion of the Appalachian chain, which is where the species was first discovered.
The distribution of the Eastern Hellbender is centered on the Tennessee and Ohio River drainages, with populations also occurring in the Susquehanna River. They range from southern New York to northern Georgia. Their eastern limit is the Appalachian Mountain range, and they range as far west as Missouri. Ozark Hellbenders are found in a smaller area of southern Missouri and northern Arkansas. Although Eastern Hellbenders have a broad historic range, their actual extent of occurrence is much more limited based on their reliance on free-flowing rivers and the documented and anecdotal declines across much of their range.
Hellbenders are restricted to cold rivers and streams with adequate flow, high dissolved oxygen and low levels of sedimentation. They spend much of their time under large rocks that have spaces underneath for the animal to take refuge and to use as egg-laying sites. Individuals are rarely found in the open. Larvae tend to use smaller rocks and cobble on the margins and rivers, and they often hide in spaces within the stream bottom. The presence of surrounding forest is also very important for Hellbender populations, which is likely related to reduced soil erosion into streams in these areas.
In general, Hellbenders do not move frequently and do not have large home ranges. Individuals can often be found under the same rock from year to year, and movements rarely range more than 100 to 200 meters along a stream, although in rare cases individuals have been found to move more than a kilometer.
Like all salamanders, Hellbenders are carnivorous and are capable of eating a wide variety of prey. However, crayfish make up the vast majority of their diet, and it is likely that other prey items are only taken when crayfish availability is low. Many fishermen believe that Hellbenders are detrimental to sport-fish populations which is untrue. Hellbenders rarely eat fish, and when they do, they are typically small fish like minnows and suckers. Hellbenders will scavenge, which is why they are sometimes caught by fishermen attempting to eat their bait. Finally, Hellbenders occasionally cannibalize on smaller individuals or eat other Hellbender eggs.
Hellbenders have external fertilization which is very unusual in salamanders. Hellbenders lay their eggs under large rocks (known as nest rocks) that males prepare and control. The breeding season typically occurs in late summer or early fall, and during this time male Hellbenders are especially aggressive while fighting for control of nest rocks. Females will go under nest rocks to lay eggs that are then fertilized by the attending male. The males fertilize eggs by releasing milt (which contains sperm) into the water and using their body to direct it towards the eggs. Once the female lays her eggs, she leaves the nest rock and the male remains to attend to the eggs. Multiple females will use the same nest rock, and there can be thousands of eggs at one nest rock. Eggs typically hatch in late fall. Hellbenders have a larval stage in which larvae have gills until age two, although individuals may not reach sexual maturity until eight years of age.
Hellbenders are important both symbolically and ecologically. They are one of the last survivors of an ancient group of salamanders—the loss of this species would mean the loss of a genus and the only members of its family that occurs in North America. They are important predators of crayfish, and while detailed studies are lacking, they likely play a role in keeping crayfish populations in control in streams.
Hellbenders are declining across their range and are petitioned for listing under the Endangered Species Act. To date, the southern Blue Ridge Mountains contain some of the best Hellbender populations remaining, yet there are still many historic sites where Hellbenders cannot reliably be found or are found at low densities.
Hellbenders are primarily threatened by river sedimentation and pollution that are causing declines of suitable habitat for these animals. Soil erosion leads to increased silt and sediment in rivers. Siltation leads to spaces being filled in along stream bottoms; therefore, Hellbenders cannot go under rocks for refuge, nests get filled in and larvae lack spaces in the stream bottom that are critical for survival at that young age. Increased erosion also tends to lead to increased pollutants into rivers that Hellbenders may absorb directly through their skin, and it reduces the dissolved oxygen in the water which is essential for them to breathe.
Dams and other alterations to rivers have also reduced habitat suitability for Hellbenders, not only by creating barriers to movement, but more importantly, by creating stretches of river that no longer have the flow necessary to maintain Hellbender populations. This eliminates habitat and isolates populations. Humans also exert some direct pressure on Hellbenders—for example, river recreation often leads to rocks that Hellbenders use being moved around, and humans will sometimes kill Hellbenders based on misconceptions and fear. Disease could also be a factor, although there is not yet direct evidence for this.
These threats are affecting Hellbender ecology. Survival rates of Hellbenders to adulthood are extremely low, so even small changes in their environment can cause them to not only lose their habitat, but it can also result in troubled breathing due to low oxygen levels and slow river flow. Many sites still have older adult Hellbenders but lack larvae or young individuals. Such patterns suggest that Hellbenders are most vulnerable at these early stages, and improving survival of young Hellbenders may be the most important conservation action. Hellbenders also probably have limited ability to respond or adapt to disturbance as they have very low levels of movement. It’s imperative that we work to conserve these microhabitats so that more Hellbenders are able to survive to adulthood and to reproductive age.