Hellbender

Appearance

''C. alleganiensis'' has a flat body and head, with beady dorsal eyes and slimy skin. Like most salamanders, it has short legs with four toes on the front legs and five on its back limbs, and its tail is keeled for propulsion. The hellbender has working lungs, but gill slits are often retained, although only immature specimens have true gills; the hellbender absorbs oxygen from the water through capillaries of its side frills. It is blotchy brown or red-brown in color, with a paler underbelly.

Both males and females grow to an adult length of 24 to 40 cm from snout to vent, with a total length of 30 to 74 cm, making them the third-largest aquatic salamander species in the world and the largest amphibian in North America, although this length is rivaled by the reticulated siren of the southeastern United States .

An adult weighs 1.5 to 2.5 kg, making them the fourth heaviest living amphibian in the world after their Chinese and Japanese cousins and the goliath frog, while the largest cane toads may also weigh as much as a hellbender. Hellbenders reach sexual maturity at about five years of age, and may live 30 years in captivity.

The hellbender has a few characteristics that make it distinguishable from other native salamanders, including a gigantic, dorsoventrally flattened body with thick folds travelling down the sides, a single open gill slit on each side, and hind feet with five toes each.

Easily distinguished from most other endemic salamander species simply by their size, hellbenders average up to 60 cm or about 2 ft in length; the only species requiring further distinction is the common mudpuppy.

This demarcation can be made by noting the presence of external gills in the mudpuppy, which are lacking in the hellbender, as well as the presence of four toes on each hind foot of the mudpuppy . Furthermore, the average size of ''C. a. alleganiensis'' has been reported to be 45–60 cm, while ''N. m. maculosus'' has a reported average size of 28–40 cm in length, which means that hellbender adults will still generally be notably larger than even the biggest mudpuppies.

Naming

The origin of the name "hellbender" is unclear. The Missouri Department of Conservation says:
The name 'hellbender' probably comes from the animal's odd look. One theory claims the hellbender was named by settlers who thought "it was a creature from hell where it's bent on returning."

Other vernacular names include ''snot otter'', ''lasagna lizard'', ''devil dog'', ''mud-devil'', ''grampus'', ''Allegheny alligator'', ''mud dog'', ''water dog'', ''spotted water gecko'' and ''leverian water newt''.

The genus name is derived from the Ancient Greek ''kryptos'' and ''branchion''. The subspecific name ''bishopi'' is in honor of American herpetologist Sherman C. Bishop.

Distribution

Hellbenders are present in a number of Eastern US states, from southern New York to northern Georgia, including parts of Ohio, Pennsylvania, Maryland, West Virginia, Virginia, Kentucky, Illinois, Indiana, Tennessee, North Carolina, South Carolina, Alabama, Mississippi, Arkansas, Missouri, and even a small bit of Oklahoma and Kansas.

The subspecies ''C. a. bishopi'' is confined to the Ozarks of northern Arkansas and southern Missouri, while ''C. a. alleganiensis'' is found in the rest of these states.

Status

Research throughout the range of the hellbender has shown a dramatic decline in populations in the majority of locations. Many different anthropogenic sources have helped to create this decline, including the siltation and sedimentation, blocking of dispersal/migration routes, and destruction of riverine habitats created by dams and other development, as well as pollution, disease and overharvesting for commercial and scientific purposes.

Behavior

Once a hellbender finds a favorable location, it generally does not stray too far from it—except occasionally for breeding and hunting—and will protect it from other hellbenders both in and out of the breeding season.

While the range of two hellbenders may overlap, they are noted as rarely being present in the overlapping area when the other salamander is in the area. The species is at least somewhat nocturnal, with peak activity being reported by one source as occurring around "two hours after dark" and again at dawn. Nocturnal activity has been found to be most prevalent in early summer, perhaps coinciding with highest water depths.

Habitat

The hellbender salamander, considered a "habitat specialist", has adapted to fill a specific niche within a very specific environment, and is labeled as such "because its success is dependent on a constancy of dissolved oxygen, temperature and flow found in swift water areas", which in turn limits it to a narrow spectrum of stream/river choices.

As a result of this specialization, hellbenders are generally found in areas with large, irregularly shaped, and intermittent rocks and swiftly moving water, while they tend to avoid wider, slow-moving waters with muddy banks and/or slab rock bottoms.

Reproduction

The hellbenders' breeding season begins in late August or early- to mid-September and can continue as late as the end of November, depending on region. They exhibit no sexual dimorphism, except during the fall mating season, when males have a bulging ring around their cloacal glands.

Unlike most salamanders, the hellbender performs external fertilization. Before mating, each male excavates a brood site, a saucer-shaped depression under a rock or log, with its entrance positioned out of the direct current, usually pointing downstream. The male remains in the brood site awaiting a female. When a female approaches, the male guides or drives her into his burrow and prevents her from leaving until she oviposits.

Female hellbenders lay 150–200 eggs over a two- to three-day period; the eggs are 18–20 mm in diameter, connected by five to 10 cords. As the female lays eggs, the male positions himself alongside or slightly above them, spraying the eggs with sperm while swaying his tail and moving his hind limbs, which disperses the sperm uniformly.

The male often tempts other females to lay eggs in his nest, and as many as 1,946 eggs have been counted in a single nest. Cannibalism, however, leads to a much lower number of eggs in hellbender nests than would be predicted by egg counts.

After oviposition, the male drives the female away from the nest and guards the eggs. Incubating males rock back and forth and undulate their lateral skin folds, which circulates the water, increasing oxygen supply to both eggs and adult. Incubation lasts from 45 to 75 days, depending on region.

Hatchling hellbenders are 25–33 mm long, have a yolk sac as a source of energy for the first few months of life, and lack functional limbs.

Food

''C. alleganiensis'' feeds primarily on crayfish and small fish. One report, written by a commercial collector in the 1940s, noted a trend of more crayfish predation in the summer during times of higher prey activity, whereas fish made up a larger part of the winter diet, when crayfish are less active.

There seems to be a specific temperature range in which hellbenders feed, as well: between 45 and 80 °F. Cannibalism—mainly on eggs—has been known to occur within hellbender populations. One researcher claimed perhaps density is maintained, and density dependence in turn created, in part by intraspecific predation.

Predators

Hellbenders are preyed upon by diverse predators, including various fish and reptiles. Cannibalism of eggs is also considered a common occurrence.