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Order: Caudata
Family: Cryptobranchidae
The hellbender is the only species in its genus Cryptobranchus, although some authors have suggested that the two currently recognised subspecies (the eastern hellbender and the Ozark hellbender) should be treated as separate species. This is because their ranges are apparently not contiguous and the morphological differences suggest reproductive isolation and absence of gene flow between the forms.
There are only 3 living species of giant salamander in the family Cryptobranchidae: the hellbender and the Chinese and Japanese giant salamanders. Ancestors of the Cryptobranchidae diverged from all other amphibians over 170 million years ago during the Jurassic Period, which makes this family of amphibians one of the longest unbroken lineages present amongst the modern species assemblages of caecilians, salamanders, frogs and toads. The genus Cryptobranchus is represented by only 1 currently accepted extant species.
Cryptobranchids are believed to be derived from hynobiid-like amphibians (relatively primitive small- to medium-sized salamanders found primarily in Asia) due to the retention of larval characters into adulthood (a process called “neoteny”). The fossil record of cryptobranchid salamanders begins with Cryptobranchus saskatchewanensis from the Upper Paleocene to the Lower Eocene (52-58 million years ago), Cryptobranchus scheuchzeri from the Middle Oligocene to the Upper Pliocene in Europe (2-33 million years ago), and Cryptobranchus matthewi from the middle Miocene to the Miocene-Pliocene boundary (14-21 million years ago). The American hellbender (Cryptobranchus alleganiensis) is also known from the Pleistocene of North America (up to 1.8 million years ago).
There are only 3 living species of giant salamander in the family Cryptobranchidae: the hellbender and the Chinese and Japanese giant salamanders. Ancestors of the Cryptobranchidae diverged from all other amphibians over 170 million years ago during the Jurassic Period, which makes this family of amphibians one of the longest unbroken lineages present amongst the modern species assemblages of caecilians, salamanders, frogs and toads. The genus Cryptobranchus is represented by only 1 currently accepted extant species.
Cryptobranchids are believed to be derived from hynobiid-like amphibians (relatively primitive small- to medium-sized salamanders found primarily in Asia) due to the retention of larval characters into adulthood (a process called “neoteny”). The fossil record of cryptobranchid salamanders begins with Cryptobranchus saskatchewanensis from the Upper Paleocene to the Lower Eocene (52-58 million years ago), Cryptobranchus scheuchzeri from the Middle Oligocene to the Upper Pliocene in Europe (2-33 million years ago), and Cryptobranchus matthewi from the middle Miocene to the Miocene-Pliocene boundary (14-21 million years ago). The American hellbender (Cryptobranchus alleganiensis) is also known from the Pleistocene of North America (up to 1.8 million years ago).
Hellbenders are the largest species of salamander (and amphibian) living in North America. This completely aquatic species reaches adult sizes of 24 to 40 cm snout to vent length (30-74 cm total length (TL) snout to tail). Hellbenders are excessively slimy with a flattened body and tail and have broad heads with very small, lidless eyes. The skin is loose, wrinkled and in adults is greenish, yellowish brown or slate gray with black spots or blotches. Adult hellbenders have a single gill slit on either side of the head and lack external gills. Hatchlings are of 25-33 mm TL. The juvenile hellbenders (or larvae) have small gills, a tail fin and limbs that are incompletely developed at hatching.
Two subspecies are recognized based on differences in geogrphic distribution and colouration. C. a. alleganiensis, the eastern hellbender, has small dark spots on its back and a uniformly coloured chin. C. a. bishopi, the Ozark hellbender, has larger black blotches on its back and a darkly mottled chin region. The spiracle opening (or ear hole) is also smaller in the Ozark hellbender.
Two subspecies are recognized based on differences in geogrphic distribution and colouration. C. a. alleganiensis, the eastern hellbender, has small dark spots on its back and a uniformly coloured chin. C. a. bishopi, the Ozark hellbender, has larger black blotches on its back and a darkly mottled chin region. The spiracle opening (or ear hole) is also smaller in the Ozark hellbender.
The breeding season for hellbenders is generally in the late summer to early autumn (and sometimes as late as December–January depending on the location), when individuals start to form breeding aggregations in and around nest sites, such as streamside burrows or beneath large rocks and submerged logs. Of the two recognised subspecies eastern hellbenders may breed over two months earlier than Ozark hellbenders. During the mating season male hellbenders compete for access to mates in a similar manner to the mating behaviour observed in their close relatives, the Japanese giant salamanders. They leave their routine hiding places and move around the stream bottom, even during daylight, exploring cavities under flat rocks and crevices or holes in the bedrock. Eventually a male occupies a suitable site and may actively prepare a nest by moving gravel to create a saucer-shaped depression. The males lie at the opening of their nests waiting for egg-bearing females. Females may enter the nest sites voluntarily or they may be forced into the cavity by the male. Hellbenders breed by external fertilisation whereby the male releases sperm at the same time as the female releases her 138–334 eggs. Chemical cues are thought to be important to this species in both courtship and mating. Females may share oviposition or egg-laying sites and nests have been found containing over 1900 eggs from different females. Males tend the eggs after oviposition and fertilisation to guard against predation by other species and even other hellbenders. The eggs are yellow, round, approximately 6 mm in diameter (swelling to 18 mm in water) and are attached by a solid rope from egg to egg resulting in long egg strings. Eggs take 45–84 days to develop depending on time of year (or temperature) and location. Development of hellbender larvae is rapid and hatchlings double their size from 30 mm to 60 mm during the first year, feeding mainly on invertebrates. Larvae normally lose their external gills in the second summer after hatching (at 100–130 mm TL).
The diet of an adult hellbender is varied and includes items such as crayfish, small fish, mollusks, worms and frequently the eggs and larvae of conspecifics. Hellbenders forage for their prey at night and sometimes also on overcast days. They retreat to crevices under rocks during the day. Although the slime produced by these animals is noxious to many predators, they are occasionally preyed upon by large fish, turtles and water snakes. Man is also an important predator of hellbenders, whether collecting them for fishing bait and scientific study or carrying out total extermination projects in some waterways. Paul L. Swanson in 1948 reported taking over 650 individuals from a 4.8-km stretch of the Big Sandy River, Pennsylvania, and Chris L. Peterson recalled killing 108 hellbenders from the Niangua River, Missouri in 1974 and 62 from the Spring River, Arkansas, in 1985–86 for a study of their nutritional ecology. Hellbenders are fairly long-lived and may reach ages of 20-30 years in the wild.
Home range size in hellbenders may vary according to body size although estimates for home range size are 18.7 to 28 metres squared for females and 18.8 to 90 metres squared for males, with other calculations giving individual home range sizes of 346.4 metres squared. Home ranges of hellbenders overlap, but they apparently avoid being in the area of overlap at the same time and they are known to defend shelter rocks, only occurring in the same shelters during the breeding season. They do not share rock shelters with conspecifics but hellbenders have been observed in close proximity to each other at night without conflict between individuals. In most streams hellbenders are likely to become inactive during winter. Over-wintering sites in New York included deep pools greater than 2 m in depth, fast-flowing riffles that remained free of ice cover and deep water pockets within riffles 1.5–2 m deep. However, hellbenders sometimes breed in Missouri and Arkansas during winter. Sexual maturity is reached from 300–400 mm TL at an age of about 3–6 years, with males normally maturing at a smaller size than females.
The diet of an adult hellbender is varied and includes items such as crayfish, small fish, mollusks, worms and frequently the eggs and larvae of conspecifics. Hellbenders forage for their prey at night and sometimes also on overcast days. They retreat to crevices under rocks during the day. Although the slime produced by these animals is noxious to many predators, they are occasionally preyed upon by large fish, turtles and water snakes. Man is also an important predator of hellbenders, whether collecting them for fishing bait and scientific study or carrying out total extermination projects in some waterways. Paul L. Swanson in 1948 reported taking over 650 individuals from a 4.8-km stretch of the Big Sandy River, Pennsylvania, and Chris L. Peterson recalled killing 108 hellbenders from the Niangua River, Missouri in 1974 and 62 from the Spring River, Arkansas, in 1985–86 for a study of their nutritional ecology. Hellbenders are fairly long-lived and may reach ages of 20-30 years in the wild.
Home range size in hellbenders may vary according to body size although estimates for home range size are 18.7 to 28 metres squared for females and 18.8 to 90 metres squared for males, with other calculations giving individual home range sizes of 346.4 metres squared. Home ranges of hellbenders overlap, but they apparently avoid being in the area of overlap at the same time and they are known to defend shelter rocks, only occurring in the same shelters during the breeding season. They do not share rock shelters with conspecifics but hellbenders have been observed in close proximity to each other at night without conflict between individuals. In most streams hellbenders are likely to become inactive during winter. Over-wintering sites in New York included deep pools greater than 2 m in depth, fast-flowing riffles that remained free of ice cover and deep water pockets within riffles 1.5–2 m deep. However, hellbenders sometimes breed in Missouri and Arkansas during winter. Sexual maturity is reached from 300–400 mm TL at an age of about 3–6 years, with males normally maturing at a smaller size than females.
The preferred habitat is large streams and rivers with fast-flowing water and a rocky substrate. Individuals are most frequently found under large boulders, submerged logs or in rock crevices. The preferred water temperature tends to be cool (20ºC, although sometimes as high as 25-30ºC) and fairly constant throughout the year.
The hellbender occurs in the USA from southern Illinois (with a recent record from Wabash River), southern Indiana, Ohio, Pennsylvania, and south-western and south-central New York, to central and south-central Missouri, northern Arkansas (the Black River system and north fork of White River, and Eleven Point River), northern Mississippi, Alabama (Tennessee River drainage), northern Georgia, the western Carolinas, western Virginia, West Virginia (throughout, west of the Allegheny Front), and extreme western Maryland. In Kentucky, near the centre of its range, the hellbender is said to be most common in the upper reaches of the Cumberland, Kentucky, and Licking river systems. In Tennessee, no records exist for locations west of the Tennessee River.The secretive nature of hellbenders and their confusion with other species (such as the mudpuppy) means that the present range is not known with absolute certainty. They are no longer present in Iowa (if they ever occurred there), and they have almost certainly disappeared from the Ohio drainage in Illinois with the possible exception of the Wabash River in White County where there were verified sightings in 1991. Hellbenders have been eliminated from Indiana except for a small population in the Blue River and the lower portions of the South Fork of the Blue River. The hellbender has disappeared from the Miami River and its tributaries in the Ohio drainage system and some areas of the Tennessee drainage system. Records for the hellbenders in the Ohio River have not been reported since the first recorded sightings in 1916. No recent data are available for the Savannah drainage populations in Georgia and South Carolina.
The total adult population size is unknown. Although there are secure populations in many areas, many other populations have declined or been eliminated primarily due to the construction of dams, sedimentation of streams, water pollution, and over-collecting. There is an overall decline observed in the hellbender population. Where population estimates for localities have been calculated, hellbender densities have been estimated at over 400 animals per kilometre of stream, and up to 10 animals per 100 metres square of habitat.
Overall the hellbender is thought to be declining from across its range by the IUCN Red List of Threatened Species at a rate of less than 30% over the past 3 generations of the species. The only evidence of a decline in a hellbender population that has been documented rigorously in the literature is the case of sites surveyed by Stan Trauth and colleagues on the Spring River in the White River drainage system of Arkansas in 1991 that had previously been surveyed by Chris Peterson in the early 1980s. Stan Trauth did not encounter any hellbenders at a site where Peterson had previously marked 60 and encountered only 5 individuals where Peterson had marked 310 only a decade before.
The hellbender is listed as Near Threatened in the IUCN Red List of Threatened Species. This is because its population is in decline (but probably at a rate of less than 30% over three generations, assuming a generation length to be approximately ten years) because of widespread habitat loss through much of its range, thus making the species close to qualifying for a status of Vulnerable.Hellbenders also have a national conservation status according to which state they occur in within the United States of America. A summary is provided in the table below.
| STATE | STATUS | PROTECTION |
|---|---|---|
| Alabama | Protected as non-game species | No possession |
| Arkansas | Endangered | No collection |
| Georgia | Rare | No possession without permit |
| Indiana | Endangered | No possession |
| Illinois | Endangered | No Possession |
| Kentucky | Special Concern | Illegal to Sell |
| Maryland | Endangered | No Possession |
| Mississippi | S1 Species (extremely rare) | Insufficient information |
| Missouri | Endangered | No Collection |
| New York | Special Concern | Not Protected |
| North Carolina | Special Concern | No Possession without Permit |
| Ohio | Endangered | No Possession |
| Pennsylvania | None | None |
| Tennessee | Deemed in Need of Management | No Possession |
| Virginia | Special Concern | Can be used as bait, but not sold |
| West Virginia | Special Concern | Protected, except loophole as bait |
The hellbender is a habitat specialist with little ability to tolerate environmental change. As a result, the predominant threat to this species is degradation of its habitat. Hellbenders breath primarily (approximately 90%) through their skin and are therefore dependent on cool, well oxygenated, flowing water. Habitat degradation has occurred through a number of different factors. The construction of dams stops swift water flow and submerges riffles. Logging, mining, road construction and maintenance, channelisation and impoundment of streams and rivers and other habitat-altering activities can cause extensive sedimentation that covers the loose rock and gravel important for nest sites, shelter and food production. In former hellbender strongholds, such as Illinois, it has been said that most of the former rocky habitats have been buried under silt. Chemical pollutants and acid mine drainage are probably destructive, especially to eggs and larvae. Thermal pollution of water with consequent oxygen loss would also be detrimental. Several hellbender streams in Alabama have been polluted, impounded, or otherwise modified to the extent that they now seem to be incapable of supporting hellbender populations.
Injuries and deaths occur through angling when the salamanders are hooked by fishing rods. Some fishermen still believe that hellbenders are dangerously poisonous and destroy game fish and their eggs (both of these beliefs are false), and therefore kill them at every opportunity. In the past, there were even attempts by organized sportsmen's groups in West Virginia to eradicate them. Hellbenders are also sometimes killed and used as bait in states such as Virginia and West Virginia where this activity is not illegal. There is some collecting of hellbenders for sale as live animals or as preserved specimens. Over-collection has been considered a serious threat in Arkansas where a decline was noted in the early 1990s, apparently due to harvesting hellbenders for various reasons. Other additional factors that are suspected to have negatively impacted local populations of hellbenders include gigging (hunting of the species at night), heavy canoe traffic, dynamiting of large boulders to enhance commercial canoe traffic, and riverside cattle and pig pens. Hellbenders are also generally intolerant to any heavy recreational use within their habitat.
Injuries and deaths occur through angling when the salamanders are hooked by fishing rods. Some fishermen still believe that hellbenders are dangerously poisonous and destroy game fish and their eggs (both of these beliefs are false), and therefore kill them at every opportunity. In the past, there were even attempts by organized sportsmen's groups in West Virginia to eradicate them. Hellbenders are also sometimes killed and used as bait in states such as Virginia and West Virginia where this activity is not illegal. There is some collecting of hellbenders for sale as live animals or as preserved specimens. Over-collection has been considered a serious threat in Arkansas where a decline was noted in the early 1990s, apparently due to harvesting hellbenders for various reasons. Other additional factors that are suspected to have negatively impacted local populations of hellbenders include gigging (hunting of the species at night), heavy canoe traffic, dynamiting of large boulders to enhance commercial canoe traffic, and riverside cattle and pig pens. Hellbenders are also generally intolerant to any heavy recreational use within their habitat.
Although listed as Near Threatened on the IUCN Red List of Threatened Species, at a state scale in the USA hellbenders are classified as Endangered in Illinois, Indiana, Maryland, and Ohio; Rare in Georgia; Of Special Concern or Species of Concern in New York, North Carolina, and Virginia; on the Watch List in Missouri; and Deemed in Need of Management in Tennessee. The degree of protection given to the hellbender varies according to the state but, in general, Endangered status requires that a permit be secured before a hellbender can be captured and provides penalties for possessing hellbenders without a permit. The other categories listed above do not afford this level of protection, but do allow for some acknowledgment that the future of the species within their state boundaries is not totally secure. Other states such as Alabama, Arkansas, Kentucky, Mississippi, South Carolina and West Virginia track hellbender distribution records in a database, but do not generally forbid their capture. Pennsylvania apparently neither tracks hellbender records nor protects them from being taken from the wild.
The U.S. Fish and Wildlife Service performed a status review of Ozark hellbenders (C. a. bishopi) in the early 1990s. This review concluded that "populations of the Ozark hellbender in the majority of its range (in Missouri) are apparently stable and new populations of the species have been found during the recent status surveys." The final recommendation was that the Ozark hellbender did not warrant protection at the time.
As early as 1957, it was noted that the hellbender's range was rapidly shrinking as a result of human modification of stream habitats. However, many of the presently known populations are in national parks, national or state forests, and other public lands, where there is good potential for protecting habitat. There are still some very good hellbender streams remaining, mainly in Georgia, Tennessee, North Carolina, Virginia, and West Virginia. Several good streams also remain in some parts of Pennsylvania but populations in the Ozark Mountains are nearly gone, or have drastically declined. Also, Saint Louis Zoo's Ron Goellner Centre for Hellbender Conservation in Missouri has been involved in an active conservation project for this species. The Saint Louis Zoo's Center for the Conservation of the Hellbender is a new program whose goal is to find the cause of the hellbender’s decreasing wild populations and, if possible, reverse these declines. As part of this effort, the conservation center will assist and support researchers who are studying the water quality of the hellbender’s native habitat in Missouri and Arkansas.
The U.S. Fish and Wildlife Service performed a status review of Ozark hellbenders (C. a. bishopi) in the early 1990s. This review concluded that "populations of the Ozark hellbender in the majority of its range (in Missouri) are apparently stable and new populations of the species have been found during the recent status surveys." The final recommendation was that the Ozark hellbender did not warrant protection at the time.
As early as 1957, it was noted that the hellbender's range was rapidly shrinking as a result of human modification of stream habitats. However, many of the presently known populations are in national parks, national or state forests, and other public lands, where there is good potential for protecting habitat. There are still some very good hellbender streams remaining, mainly in Georgia, Tennessee, North Carolina, Virginia, and West Virginia. Several good streams also remain in some parts of Pennsylvania but populations in the Ozark Mountains are nearly gone, or have drastically declined. Also, Saint Louis Zoo's Ron Goellner Centre for Hellbender Conservation in Missouri has been involved in an active conservation project for this species. The Saint Louis Zoo's Center for the Conservation of the Hellbender is a new program whose goal is to find the cause of the hellbender’s decreasing wild populations and, if possible, reverse these declines. As part of this effort, the conservation center will assist and support researchers who are studying the water quality of the hellbender’s native habitat in Missouri and Arkansas.
The overall IUCN status of the hellbender is currently Near Threatened so there is currently no urgent need to take actions to prevent the species from becoming extinct in the near future. Because many populations occur in protected areas there are plenty of theoretically safe habitats that can act as strong-holds for this species.
There is potentially a need for a broad public education project, aimed at fishermen and people who regularly use hellbender habitat, to provide information about the species. Killing of hellbenders by fishermen is still a problem in some heavily fished areas. Hellbenders are wrongly thought to be poisonous, or they are thought to eat large amounts of game fish. Both of these ideas are purely myths. In fact, in the early 1920's and 30's, there were actually bounties on hellbenders. These bounties, usually about 25 cents per hellbender, were aimed at eliminating hellbenders from "trout streams." A well-organised education project could act to encourage fishermen to not kill hellbenders, not to use them as bait and generally to behave in a more responsible way towards this species. An education programme may also be used to address the numerous other threats that are affecting wild populations of hellbender by influencing industry, agriculture and recreational land uses to plan with hellbender conservation in mind.
Saint Louis Zoo's Ron Goellner Centre for Hellbender Conservation in Missouri is also creating a captive breeding program for hellbenders in case individuals are required for re-release initiatives in the future. This may be especially important in the case of the Ozark hellbender (especially in the Ozark mountains), which is generally more endangered than the Eastern hellbender.
There is potentially a need for a broad public education project, aimed at fishermen and people who regularly use hellbender habitat, to provide information about the species. Killing of hellbenders by fishermen is still a problem in some heavily fished areas. Hellbenders are wrongly thought to be poisonous, or they are thought to eat large amounts of game fish. Both of these ideas are purely myths. In fact, in the early 1920's and 30's, there were actually bounties on hellbenders. These bounties, usually about 25 cents per hellbender, were aimed at eliminating hellbenders from "trout streams." A well-organised education project could act to encourage fishermen to not kill hellbenders, not to use them as bait and generally to behave in a more responsible way towards this species. An education programme may also be used to address the numerous other threats that are affecting wild populations of hellbender by influencing industry, agriculture and recreational land uses to plan with hellbender conservation in mind.
Saint Louis Zoo's Ron Goellner Centre for Hellbender Conservation in Missouri is also creating a captive breeding program for hellbenders in case individuals are required for re-release initiatives in the future. This may be especially important in the case of the Ozark hellbender (especially in the Ozark mountains), which is generally more endangered than the Eastern hellbender.
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Phillips, C.A. and Humphries, W.J. 2005. Family Cryptobranchidae. M. Lannoo (ed.). Amphibian Declines: The Conservation Status of United States Species. University of California Press, Ltd. London, England. pp. 648-651.
Pough, F.H. and Wilson, R.E. 1976. Acid precipitation and reproductive success of Ambystoma salamanders. Proceedings: First National Symposium on Acid Precipitation and the Forest Ecosystem. 531-544.
Redmond, W.H. and Scott, A.F. 1996. Atlas of Amphibians in Tennessee (Miscellaneous Publication Number 12). The Center for Field Biology, Austin Peay State University, Miscellaneous Publication Number 12. Clarksville, TN, USA. v + 94 pp.
Routman, E. 1993. Mitochondrial DNA variation in Cryptobranchus alleganiensis, a salamander with extremely low allozyme diversity. Copeia. 1993:407-416.
Routman, E., Wu, R. and Templeton, A.R. 1994. Parsimony, molecular evolution, and biogeography: the case of the North American giant salamander. Evolution. 48:1799-1809.
Smith, P.W. 1961. The amphibians and reptiles of Illinois. Illinois Natural History Survey. 28:1-298.
Swanson, P.L. 1948. Notes on the amphibians of Venago County, Pennsylvania. American Midland Naturalist. 1948:362-371.
Tobey, F.J. 1985. Virginia's amphibians and reptiles: a distributional survey. Virginia Herpetological Survey. vi + 114 pp.
Topping, M.S. and Ingersol, C.A. 1981. Fecundity in the hellbender, Cryptobranchus alleganiensis. Copeia. 1981:873-876.
Trauth, S.E., Wilhide, J.D. and Daniel, P. 1992. Geographic distribution: Cryptobranchus bishopi. Herpetological Review. 23:121.
Wiggs, R.L. 1977. Movement and homing in the hellbender, Cryptobranchus alleganiensis, in the Niangua River, Missouri. M.S. Thesis. 45 pp. Southwest Missouri State University, Springfield.
Williams, R.D., Gates, J.E., Hocutt, C.H. and Taylore, G.J. 1981. The hellbender: a nongame species in need of management. Wildlife Society Bulletin. 9(2):94-100.
Barbour, R.W. 1971. Amphibians and Reptiles of Kentucky. University Press of Kentucky. Lexington. x + 334 pp.
Behler, J.L. and King, F.W. 1979. The Audubon Society Field Guide to North American Reptiles and Amphibians. A.A. Knopf (ed.). New York. 719 pp.
Blackburn, L., Nanjappa, P. and Lannoo, M.J. 2001. An Atlas of the Distribution of U.S. Amphibians. Ball State University. Muncie, IN, USA.
Blais, D.P. 1996. Movement, Home Range, and Other Aspects of the Biology of the Eastern Hellbender (Cryptobranchus alleganiensis alleganiensis): A Radio Telemetric Study. Masters Thesis. S.U.N.Y. Binghamton.
Brandon, R.A. and Ballard, S.R. 1994. Geographic distribution: Cryptobranchus alleganiensis. Herpetological Review. 25:31.
Bury, R.B., Dodd, Jr., C.K. and Fellers, G.M. 1980. Conservation of the Amphibia of the United States: a review. Resource Publication. 134:34 pp. U.S. Fish and Wildlife Service. Washington, D.C.
Coatney, Jr, C.E. 1982. Home range and nocturnal activity of the Ozark hellbender. Unpublished Master's thesis. Southwest Missouri State University. Springfield, Missouri.
Collins, J.T. 1991. Viewpoint: a new taxonomic arrangement for some North American amphibians and reptiles. SSAR Herpetol. Review. 22:42-43.
Dundee, H.A. 1971. Cryptobranchus, and C. alleganiensis. Catalogue of American Amphibians and Reptiles. 101:1-4.
Figg, D.E. 1993. Missouri Department of Conservation wildlife diversity report, July 1992 - June 1993. 75 pp.
Firschein, I.L. 1951. The range of Cryptobranchus bishopi and remarks on the distribution of the genus Cryptobranchus. American Midland Naturalist. 45:455-459.
Frost, Darrel R. 2006. Amphibian Species of the World: an Online Reference. Version 4 (17 August 2006). Electronic Database accessible at: http://research.amnh.org/herpetology/amphibia/index.php. American Museum of Natural History, New York, USA.
Frost, D.R. Frost, D.R.,editor. 1985. Amphibian Species of the World: A Taxonomic and Geographic Reference. Allen Press and the Association of Systematic Collections. Lawrence, Kansas. 1-732.
Gates, J.E., Stouffer, Jr., R.H., Stauffer, Jr., J.R. and Hocutt, C.H. 1985. Dispersal patterns of translocated Cryptobranchus alleganiensis in a Maryland stream. Journal of Herpetology. 19:436-438.
Green, N.B. and Pauley, T.K. 1987. Amphibians and Reptiles in West Virginia. University of Pittsburgh Press. Pittsburgh, PA, USA. xi + 241 p.
Guimond, R.W. 1970. Aerial and aquatic respiration in four species of paedomorphic salamander: Amphiuma means means, Cryptobranchus alleganiensis, Necturus maculosus maculosis, and Siren lacertina. Dissertation. University of Rhode Island.
Hammerson, G. & Phillips, C. 2004. Cryptobranchus alleganiensis. In: IUCN 2006. 2006 IUCN Red List of Threatened Species. <www.iucnredlist.org>. Downloaded on 08 December 2006.
Harding, J.H. 1997. Amphibians and Reptiles of the Great Lakes Region. University of Michigan Press. Ann Arbor, Michigan. xvi + 378 .
http://www.hellbenders.org/" target="_blank">Hellbenders.org
Hillis, R.E. and Bellis, E.D. 1971. Some aspects of the ecology of the hellbender, Cryptobranchus alleganiensis alleganiensis, in a Pennsylvania stream. Journal of Herpetology. 5:121-126.
Hulse, A.C., McCoy, C.J. and Censky, E. 2001. Amphibians and Reptiles of Pennsylvania and the Northeast. Comstock Publishing Associates and Cornell University Press. Ithaca, New York, USA.
Humphries, W.J. and Pauley, T.K. 2000. Seasonal changes in nocturnal activity of the hellbender, Cryptobranchus alleganiensis, in West Virginia. Journal of Herpetology. 34:604-607.
IUCN, Conservation International and NatureServe. 2006. Global Amphibian Assessment. <www.globalamphibians.org>. Accessed on 08 December 2006.
Johnson, T.R. 1977. The Amphibians of Missouri. University of Kansas Museum of Natural History. Lawrence, Kansas.
Johnson, T.R. 1987. The amphibians and reptiles of Missouri. Missouri Department of Conservation. Jefferson City. 368 pp.
Johnson, T.R. 2000. The Amphibians and Reptiles of Missouri, second edition. Missouri Department of Conservation. Jefferson City, MO, USA.
Martof, B.S., Palmer, W.M., Bailey, J.R. and Harrison III, J.R. 1980. Amphibians and Reptiles of the Carolinas and Virginia. University of North Carolina Press. Chapel Hill, North Carolina.
Mattison, C. 2005. Encyclopedia of reptiles and amphibians: An essential guide to reptiles and amphibians of the world. Grange Books Plc. Kent.
McCoy, C.J. 1982. Amphibians and reptiles in Pennsylvania. Carnegie Museum of Natural History Special Publication. No. 6.
Minton Jr, S.A. 1972. Amphibians and Reptiles of Indiana. Indiana Academy of Science Monographs 3. Indianapolis, IN, USA. v + 346 pp.
Minton, S.A., Jr. 2001. Amphibians and Reptiles of Indiana, revised second edition. Indiana Academy of Science. Indianapolis , IN, USA.
Mitchell, J.C. 1991. Amphibians and reptiles. Virginia's Endangered Species: Proceedings of a Symposium. Terwilliger, K.,editor. 411-476. McDonald and Woodward Publishing Company. Blacksburg, Virginia.
Mount, R. H. 1975. The Reptiles and Amphibians of Alabama. Auburn University Agricultural Experiment Station. Auburn, AL, USA.
Nickerson, M.A. and Mays, C.E. 1973. A study of the Ozark hellbender, Cryptobranchus alleganiensis bishopi. Ecology. 54:1164-1165.
Nickerson, M.A. and Mays, C.E. 1973. The Hellbenders: North American "Giant Salamanders". Milwaukee Public Museum, Publ. Inbiol. and Geol. No. 1:106 p.
Noeske, T.A. and Nickerson, M.A. 1979. Diet activity rhythms in the hellbender, Cryptobranchus alleganiensis (Caudata: Cryptobranchidae). Copeia. 1979:92-95.
Obst, F.J., Richter, K. and Jacob, U. 1984. The Completely Illustrated Atlas of Reptiles and Amphibians for the Terrarium. T.F.H. Publication Inc., N.J., U.S.A.
Peterson, C.L. 1985. Comparative demography of four populations of the hellbender, Cryptobranchus alleganiensis, in the Ozarks. Ph.D. dissertation. University of Missouri, Columbia, Missouri.
Peterson, C. L., C. A. Ingersol, and R. F. Wilkinson. 1989. Winter breeding of Cryptobranchus alleganiensis bishopi in Arkansas. Copeia. 1989:1031-1035.
Peterson, C. L., D. E. Metter, and B. T. Miller. 1988. Demography of the hellbender Cryptobranchus alleganiensis in the Ozarks. American Midland Naturalist. 119:291-303.
Peterson, C.L., and Wilkinson, R.F. 1996. Home range size of the hellbender (Cryptobranchus alleganiensis) in Missouri. Herpetological Review. 27(3):126-127.
Peterson, C. L., Wilkinson, Jr., R.F., Topping, M.S. and Metter, D.E. 1983. Age and growth of the Ozark hellbender. Copeia. 1983:225-231.
Peterson, C.L. 1987. Movement and catchability of the hellbender, Cryptobranchus alleganiensis. Journal of Herpetology. 21:197-204.
Peterson, C.L. and Wilkinson, R.F. 1996. Home range size of the hellbender (Cryptobranchus alleganiensis) in Missouri. Herpetological Review. 27:126-127.
Peterson, C.L., Reed, J.W. and Wilkinson, R.F. 1989. Seasonal food habits of Cryptobranchus alleganiensis (Caudata: Cryptobranchidae). Southwestern Naturalist. 34:438-441.
Petranka, J.W. 1998. Salamanders of the United States and Canada. Smithsonian Institution Press, Washington, D.C.
Pfingsten, R.A. 1990. The status and distribution of the hellbender, Cryptobranchus alleganiensis in Ohio. Herpetological Review. 21:48-50.
Pfingsten, R.A. and Downs, F.L. 1989. Salamanders of Ohio. Bulletin of Ohio Biological Survey. 7(2):1-315.
Phillips, C.A., Brandon, R.A. and Moll, E.O. 1999. Field Guide to Amphibians and Reptiles of Illinois. Illinois Natural History Survey Manual 8. Illinois. xv + 282 p.
Phillips, C.A. and Humphries, W.J. 2005. Family Cryptobranchidae. M. Lannoo (ed.). Amphibian Declines: The Conservation Status of United States Species. University of California Press, Ltd. London, England. pp. 648-651.
Pough, F.H. and Wilson, R.E. 1976. Acid precipitation and reproductive success of Ambystoma salamanders. Proceedings: First National Symposium on Acid Precipitation and the Forest Ecosystem. 531-544.
Redmond, W.H. and Scott, A.F. 1996. Atlas of Amphibians in Tennessee (Miscellaneous Publication Number 12). The Center for Field Biology, Austin Peay State University, Miscellaneous Publication Number 12. Clarksville, TN, USA. v + 94 pp.
Routman, E. 1993. Mitochondrial DNA variation in Cryptobranchus alleganiensis, a salamander with extremely low allozyme diversity. Copeia. 1993:407-416.
Routman, E., Wu, R. and Templeton, A.R. 1994. Parsimony, molecular evolution, and biogeography: the case of the North American giant salamander. Evolution. 48:1799-1809.
Smith, P.W. 1961. The amphibians and reptiles of Illinois. Illinois Natural History Survey. 28:1-298.
Swanson, P.L. 1948. Notes on the amphibians of Venago County, Pennsylvania. American Midland Naturalist. 1948:362-371.
Tobey, F.J. 1985. Virginia's amphibians and reptiles: a distributional survey. Virginia Herpetological Survey. vi + 114 pp.
Topping, M.S. and Ingersol, C.A. 1981. Fecundity in the hellbender, Cryptobranchus alleganiensis. Copeia. 1981:873-876.
Trauth, S.E., Wilhide, J.D. and Daniel, P. 1992. Geographic distribution: Cryptobranchus bishopi. Herpetological Review. 23:121.
Wiggs, R.L. 1977. Movement and homing in the hellbender, Cryptobranchus alleganiensis, in the Niangua River, Missouri. M.S. Thesis. 45 pp. Southwest Missouri State University, Springfield.
Williams, R.D., Gates, J.E., Hocutt, C.H. and Taylore, G.J. 1981. The hellbender: a nongame species in need of management. Wildlife Society Bulletin. 9(2):94-100.
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