The hellbender is much larger than any other salamander in its geographic range, and employs an unusual adaption for respiration through cutaneous gas exchange via capillaries found in its lateral skin folds.

[7]In a study conducted in Indiana, informing the public about the rarity and locality of the hellbender resulted in more positive attitudes toward this species than were previously held.

[16] Only occasionally leaving the water, the hellbender makes little use of these lungs and the juveniles lose their external gills after around 18 months or about 125 mm in length.

They found three equally divergent genetic units within the genus: C. a. alleganiensis, and two distinct eastern and western populations of C. a. bishopi.

[25] Hellbenders are present in a number of Eastern US states, from southern New York to northern Georgia,[28] including parts of Ohio, Pennsylvania, Maryland, West Virginia, Virginia, Kentucky, Illinois, Indiana, Tennessee, North Carolina, South Carolina, Alabama, Mississippi, Arkansas, Missouri, and extending into Oklahoma and Kansas.

The subspecies (or species, depending on the source) 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.

[29] Some hellbender populations—namely a few in Missouri, Pennsylvania, and Tennessee—have historically been noted to be quite abundant, but several man-made threats have converged on the species such that it has seen a serious population decline throughout its range.

[31] Hellbender populations were listed in 1981 as already extirpated or endangered in Illinois, Indiana, Iowa, and Maryland, decreasing in Arkansas and Kentucky, and generally threatened as a species throughout their range by various human activities and developments.

[32] 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.

[28] One collector noted, at one time, "one could find a specimen under almost every suitable rock", but after years of collecting, the population had declined significantly.

[33] The same collector noted, he "never found two specimens under the same rock", corroborating the account given by other researchers that hellbenders are generally solitary; they are thought to gather only during the mating season.

The large amounts of gravel enable the hellbender to hide, cool water temperatures allow for more efficient cutaneous gas exchange, and low specific conductivity may indicate an undisturbed stream.

If a hellbender ends up in an area of slow-moving water, not enough of it will pass over its skin in a given time, making it difficult to garner enough oxygen to support necessary respiratory functions.

[37] In another study by Kenison & Wilson (2018), researchers found that young, captive hellbenders showed altered behavior in response to predatory fish nearby.

Because of their altered behavior, it was observed and concluded that hellbenders are capable of detecting kairomones, which are chemical cues emitted by predatory species.

[38] C. alleganiensis feeds primarily on crayfish and small fish, but also insects, worms, molluscs, tadpoles and smaller salamanders.

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.

[44] Studies have found that until the female successfully reproduces, the male hellbender will guard her in his territory until the reproduction is complete.

Incubating males rock back and forth and undulate their lateral skin folds, which circulates the water, increasing oxygen supply to both eggs and adult.

[46] Hatchling hellbenders are 25–33 mm (0.98–1.30 in) long, have a yolk sac as a source of energy for the first few months of life, and lack functional limbs.

Their flattened shape offers little resistance to the flowing water, allowing them to work their way upstream and also to crawl into narrow spaces under rocks.

They have a good sense of smell and move upstream in search of food such as dead fish, following the trail of scent molecules.

[2] Many different anthropogenic sources have contributed to 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.

[29] Due to sharp decreases seen in the Ozark subspecies, researchers have been trying to differentiate C. a. alleganiensis and C. a. bishopi into two management units.

This could be reason enough to ensure work is done on both subspecies, as preserving extant genetic diversity is of crucial ecological importance.

[52][53][54] The Ozark hellbender was successfully bred in captivity for the first time at the St. Louis Zoo, in a joint project with the Missouri Department of Conservation, hatching on November 15, 2011.

[55] Apart from the Ozark efforts, head-starting programs, in which eggs are collected from the wild and raised in captivity for re-release at a less vulnerable stage, have been initiated in Indiana, New York,[56] and Ohio.

[61] Youth members of the Chesapeake Bay Foundation's Pennsylvania Student Leadership Council were heavily involved writing and advocating on behalf of this legislation.