Hellbenders are completely aquatic salamanders that live in freshwater streams with large flat rocks at the bottom to use for shelter and avoiding predation. Hellbenders use large rocks, logs, and even some manmade objects to hide under during the day. Streams appropriate for hellbenders are between 9 to 22.5 degrees Celsius and are free-flowing to provide more dissolved oxygen and prey (fresh-water invertebrates). Stream substrates are gravel, as opposed to mud, which gives larval hellbenders more protection from predators. The highest elevation at which they have been observed is 838 meters above sea level. Hellbenders stay at depths between 0.16 and 0.56 meters below the surface. (Bishop, 1994; Keitzer, et al., 2013; Pauley and Green, 1987; Wilson, 1995)
Hellbenders are the largest aquatic salamanders in North America, ranging from 295 to 686 millimeters in length. Mass is between 405 to 1010 grams. The body is flat with loose folds of skin that increase skin surface area for cutaneous respiration, which is vital for extraction of oxygen from their freshwater habitats. The head is very flat and broad with a short nose and, unlike other aquatic salamanders, they lack eyelids and feathered gill slits. They have five digits on each of the back feet and four digits on the front. All digits have webbed skin between them. The tail is very muscular and is used as the main source of propulsion. They have small and stubby limbs. Hellbenders do not vary in appearance between the sexes. Both have deep brown or black skin with occasional dark orange spots found on either the top of the back or along the underside. The ventral body is lighter. Rarely, individuals display an albino and red variant. Hatchling larvae are 25 to 33 millimeters long, does not have limbs, and are darkly colored. Lightly-colored gill slits are present in the juvenile stage that are lost once fully matured. (Bishop, 1994; Duellman and Trueb, 1994; Harding, 2000; Miller and Miller, 2005; Pauley and Green, 1987; Petranka, 1998; Wilson, 1995)
Hellbenders hatch out of their eggs at 20 to 33 millimeters in length. The egg is about 20 to 30 millimeters in diameter and connected to other eggs in a long strand. Hatchling larvae have no functional limbs and have gills. As they age, they develop stubby limbs and a muscular tail, the gills close and form two very small indentions to serve as small circular gill openings. This transition is considered a partial metamorphosis due to the gills circular openings still remaining in the adult form of the hellbender. The loss of gills in young larvae is reached when they are 100 to 133 millimeters long and 2 years old. Larvae grow at a constant rate until reaching 30 centimeters in length, at which point maturity is reached. Individuals continue to grow and can reach lengths of 73.66 centimeters. This species exhibits indeterminate growth.
Larval hellbenders reaches sexual maturity at about 5 to 8 years old and the only way to distinguish male and female at the adult stage is that the male has swollen cloacae during the breeding season. (Harding, 2000; Petranka, 1998; Wilson, 1995)
At the beginning of the mating season, male hellbenders designate an area for egg-laying. Males find a large rock and burrow a saucer-shaped indention beneath the rock. After the male has dug an area for the eggs to be deposited, he will wait in the burrow with his head sticking out to attract female mates. Once a female with eggs finds a male at the egg-laying site, she is guided into the burrow by the male. If the female tries to leave the egg-laying site the male will prevent her from leaving until she has deposited her eggs. The female then begins to lay her eggs into the burrow. As she is depositing the eggs, the male positions himself above her and releases stringy seminal fluid that fertilizes the eggs. While releasing the seminal fluid, the male will sway back and forth ensuring the sperm is deposited on the entire clutch of eggs.
After the eggs are deposited, the parents sometimes prey on their own eggs as a food source, as confirmed by some hellbenders having eggs in their stomachs during mating season. The number of eggs ingested is never more than 20 to 30 eggs, so the bulk of the clutch presumably survives. The male will chase the female away after the eggs are deposited. The female may go to deposit more eggs in another burrow. Females exhibit polyandrous behavior by depositing eggs in several male burrows in one breeding season. (Bishop, 1994; Duellman and Trueb, 1994; Petranka, 1998; Stebbins and Cohen, 1995)
Hellbenders reproduce yearly, from mid-September to mid-October. The number of eggs produced by the female is from 150 to 450. The maturation period for the eggs is from 45 to 80 days. Young salamanders become fully mature anywhere between 5 to 8 years of age. Males reach maturity slightly faster and at a smaller size due to the higher energetic needs of females associated with reproduction. Females may mature a year later than males. Males fertilize eggs externally. Larvae are immediately independent to prevent being preyed on by the male parent hellbender. (Duellman and Trueb, 1994; Pauley and Green, 1987; Petranka, 1998; Stebbins and Cohen, 1995)
The only period of parental involvement is displayed by the male after the eggs are fertilized. Males occupy the burrow that the eggs were laid in to provide protection. If any other hellbender attempts to enter the burrow the male will become very aggressive to defend the fertilized eggs. The male also provides a higher oxygenated environment due to the the skin folds on his sides jostling the eggs to bring oxygenated water near them. There is no parental care provided to larvae after hatching. (Bishop, 1994; Duellman and Trueb, 1994; Pauley and Green, 1987; Petranka, 1998; Stebbins and Cohen, 1995)
Hellbenders can live up to 30 years, but commonly live between 12 and 15 years if they reach adulthood. Survival to adulthood is determined by predation on young. Survival rates to adulthood are low. Lifespan is also reduced by pollution and siltation of streams. There are just a few instances where adults are captured and raised in captivity and those individuals lived as long as 29 years. Captive breeding efforts are being attempted, including raising abandoned eggs. ("Virginia Department of Game and Inland Fisheries", 2015; Duellman and Trueb, 1994; Pauley and Green, 1987; Petranka, 1998)
Hellbenders are solitary and become aggressive if another hellbender enters their territory, except during breeding season. Hellbenders are fully aquatic and motile and are most active at night to hunt for prey along stream bottoms. Hellbenders become active at dusk and hunt until dawn. During the day, hellbenders burrow under large flat rocks at the bottom of streams. Hellbenders center their territory around the rock that it uses as shelter during the day. (Bishop, 1994; Duellman and Trueb, 1994; Petranka, 1998; Stebbins and Cohen, 1995)
Hellbender territories range from 32 square meters up to 346 square meters (average is 113 square meters). Home ranges can overlap with other members of the species, but hellbender populations are not densely concentrated. (Duellman and Trueb, 1994; Harding, 2000; Pauley and Green, 1987; Petranka, 1998)
Hellbenders use specific chemical cues to escape predation along with sensing movement in the water. Hellbenders have an olfactory canal located in the snout known as the Jacobson's organ, which is used to interpret chemical signals. Hellbenders also use a lateral line system of sensory receptors to detect stimuli from the water. These receptors allow for the interpretation of light detection, water pressure, and vibrations from movement that is occurring around them in the water. Hellbenders respond properly only to native species of predatory fish. When introduced species prey on them, hellbenders are unable to recognize the foreign chemical signals. As a reactionary response to predator chemical cues, hellbenders release a milky substance from glandular cells in the outermost layer of the skin that acts as a deterrent and aids escape.
Hellbenders have lidless eyes, but the eyes are poor at forming images. They rely on the lateral line system as well as the sense of smell to compensate for poor eyesight
Hellbenders are solitary species and only communicates with other hellbenders during breeding season. They use pheromones to communicate the intent to breed as well as physical motions to signal that they are ready to participate in reproduction. (Bishop, 1994; Duellman and Trueb, 1994; Harding, 2000; Mathis and Wilkinson, 2013)
Hellbenders primarily eat crayfish as adults, but will eat insects, fish, and smaller salamanders as well. In a survey of 34 individuals, over half had stomach contents made up of strictly crayfish remains. The remainder included fish, tadpoles, and insects in small amounts. Debris that could be found in the river sediment such as mud, twigs, and rocks was also found in the stomach contents. This suggests that hellbenders feed in the depths of the water as opposed to surface predation. This species typically forages for food at night and uses a suction feeding behavior to help uproot crayfish from the muddy substrate that they inhabit. (Duellman and Trueb, 1994; Pauley and Green, 1987; Petranka, 1998; Wilson, 1995)
Larval stages of hellbenders are most vulnerable to predation. Their only defense is early detection. Hellbenders detect potential predators by sensing chemical cues of predators in the water and seeking shelter. The major predators on larva are large fish like smallmouth bass (Micropterus dolomieu), banded sculpin (Cottus carolinae), rainbow trout (Oncorhynchus mykiss), and introduced brown trout (Salmo trutta). Adult hellbenders also prey on larvae. Adult hellbenders are cryptic and have defenses against predators. They an escape more readily using the propulsion of their powerful tail and can secrete irritants from the pores in the skin if disturbed. Adult hellbenders are preyed on by other hellbenders and large fish (same species that consume the larvae). There are several reports of fisherman catching hellbenders while fishing close to dusk. (Crane and Mathis, 2013; Petranka, 1998)
Hellbenders play vital roles in their ecosystem as predators of crayfish and prey to large fish. Hellbenders are host to amphibian chytrid fungus (Batrachochytrium dendrobatidis) and this is thought to be responsible for, along with pollution, the decline of individuals in some areas. Hellbenders serve as hosts to leeches, nematodes, parasitic worms, and tapeworms. A partial list of parasites that are found in this species are: leeches (Placobdella appalachiensis) nematodes (Falcaustra cryptobranchi, Zanclophorus cryptobranchi, Spironoura mackini, Falcaustra waltoni, Zanclophoruis variabilis), tapeworms (Ophiotaenia cryptobranchi, Crepidobothrium cryptobranchi), and spiney-headed worms (Acanthocephalus acutulus). (Chatfield, et al., 2012; Dyer and Brandon, 1973; Hopkins, et al., 2014; Pugh, et al., 2013)
Hellbenders are biodindicators of stream quality, as their tolerance for poor water quality is low. There are reports of people keeping them as pets, although this is prohibited by law. (Pauley and Green, 1987; Petranka, 1998)
There are no known adverse impacts of hellbenders on humans. They will try to defend themselves with biting when handled. (Pauley and Green, 1987)
Hellbender populations are in a state of decline. This decline is mostly due to pollution and silt that accumulates in the freshwater streams they inhabit. Hellbenders are sensitive to pollution because they needs clean and well oxygenated water. Hellbenders may be affected by chytrid fungus, but are less likely to be fatally harmed because the cold water they inhabit is not optimal for fungal growth. Hellbenders are being studied to learn how to breed them in captivity successfully. There has been rearing in captivity due to the collection of abandoned eggs being brought to mature in an aquarium. This has provided many hellbender individuals to study and may be used to supplement populations in the future. The IUCN red list considers hellbenders to be "near threatened." They have no special status on the US Endangered Species List. CITES lists hellbenders under Appendix III, which is only given to a species that needs protection from unsustainable practices related in the international trade of this species. Hellbenders are protected at the state level throughout their range. ("CITES Appendices", 2013; "Virginia Department of Game and Inland Fisheries", 2015; Hammerson and Phillips, 2004; Petranka, 1998)
Zeb Pike (author), Radford University, Karen Powers (editor), Radford University, April Tingle (editor), Radford University, Emily Clark (editor), Radford University, Cari Mcgregor (editor), Radford University, Jacob Vaught (editor), Radford University, Tanya Dewey (editor), University of Michigan-Ann Arbor.
living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.
having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.
an animal that mainly eats meat
uses smells or other chemicals to communicate
having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.
animals which must use heat acquired from the environment and behavioral adaptations to regulate body temperature
fertilization takes place outside the female's body
union of egg and spermatozoan
mainly lives in water that is not salty.
having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.
Animals with indeterminate growth continue to grow throughout their lives.
An animal that eats mainly insects or spiders.
offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).
parental care is carried out by males
A large change in the shape or structure of an animal that happens as the animal grows. In insects, "incomplete metamorphosis" is when young animals are similar to adults and change gradually into the adult form, and "complete metamorphosis" is when there is a profound change between larval and adult forms. Butterflies have complete metamorphosis, grasshoppers have incomplete metamorphosis.
having the capacity to move from one place to another.
specialized for swimming
the area in which the animal is naturally found, the region in which it is endemic.
active during the night
reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.
chemicals released into air or water that are detected by and responded to by other animals of the same species
an animal that mainly eats fish
Referring to a mating system in which a female mates with several males during one breeding season (compare polygynous).
breeding is confined to a particular season
reproduction that includes combining the genetic contribution of two individuals, a male and a female
that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).
defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement
movements of a hard surface that are produced by animals as signals to others
uses sight to communicate
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