Description
A large, stout-bodied, terrestrial salamander. The dorsum is dark brown overlain with fine brown spotting or marbling. In some populations there is no marbling mid-dorsally. Adults reach sizes of 17 - 25 cm total length. The posterior half of the tail is laterally compressed. Some populations have both metamorphosed and gilled adults. Gilled adults may become mature at less than 11 cm total length (Nussbaum 1976). Larvae are the stream type with short, bushy gills and a low tail fin which extends forward to the hindlimb insertion. Larval D. aterrimus are darker than larval D. tenebrosus, with little mottling. A yellow stripe behind the eyes may be indistinct (Nussbaum 1976; Petranka 1998).

Distribution and Habitat

Country distribution from AmphibiaWeb's database: United States

U.S. state distribution from AmphibiaWeb's database: Idaho, Montana

	View distribution map in BerkeleyMapper.
	View Bd and Bsal data (5 records).

Dicamptodon aterrimus is found in the Rocky Mountains of north central Idaho and in western Montana (Mineral County), where it has recently been found to occur more widely than previously thought (E. A. Dallalio, pers. comm.). Larvae generally inhabit small streams (Petranka 1998), but have also been found in mountain lakes and ponds (Stebbins 1985). Adults are found under rocks and logs near streams in moist coniferous forests (Petranka 1998; Nussbaum et al. 1983); although this species has been found in larger streams and rivers, it is more common in first and second-order headwater streams (Sepulveda and Lowe 2009). D. aterrimus terrestrial adults may also be found under cover objects on rocky shores of montane lakes (Stebbins 1985). Paedomorphic (aquatic) adults are found in cold, shaded headwater streams that have unembedded cobble substrate (Bury et al. 1991; Roni 2002).

Life History, Abundance, Activity, and Special Behaviors
Breeding occurs in mountain stream headwaters, or in montane lakes (Stebbins 1985). Egg deposition occurs in submerged nest chambers under logs and rocks or in water-filled crevices within submerged rocks (Stebbins 1985). One female laid 185 eggs (in captivity) during the fall. She was captured 2 feet deep in a rock pile, a likely nest site (Nussbaum 1969). The diet of larval Idaho giant salamanders includes a variety of invertebrates and the larvae of tailed frogs (Ascaphus) (Metter 1963). This species is facultatively paedomorphic; populations may include both gilled, fully aquatic adults as well as terrestrial metamorphic adults (Sepulveda and Lowe 2009).

Trends and Threats
Although Reichel and Flath (1995) characterized D. aterrimus as extremely rare in western Montana, more recent surveys (2005-2008) by the USGS have found this species in twelve streams in Mineral County, Montana (E. A. Dallalio, pers. comm.).

Populations appear to be stable in undisturbed areas. Threats include habitat loss and degradation resulting from logging, the building of roads, and siltation of streams. This species is able to recolonize formerly disturbed areas once they have been restored. It occurs in several areas that are designated wilderness (Hammerson 2004; Sepulveda and Lowe 2009).

Comments
Until recently only two species were recognized in the genus Dicamptodon.Recent genetic research (Dougherty et al. 1983; Good 1989) has supported the division of D. ensatus into three species: D. aterrimus, D. ensatus, and D. tenebrosus. The species are also morphologically distinct (Nussbaum 1976). The genus Dicamptodon was historically included as a subfamily (Dicamptodontinae) in the family Ambystomatidae, and was placed in a separate family, Dicamptodontidae, based on features of the spinal nerves (Edwards 1976).

References

Bury, R. B., Corn, F. S., Aubry, K. B., Gilbert, F. F., and Jones, L. L. C. (1991). ''Aquatic amphibian communities in Oregon and Washington.'' Wildlife and Vegetation of Unmanaged Douglas-fir Forests. K. Ruggiero, B. Aubry, A. B. Carey, and M. H. Huff, eds., USDA Forest Service General Technical Report PNW-GTR-285, 353-362.

Daugherty, C. H., Allendorf, F. W., Dunlap, W. W., and Knudsen, K. L. (1983). ''Systematic implications of geographic patterns of genetic variation in the genus Dicamptodon.'' Copeia, 1983(3), 679-691.

Edwards, J.L. (1976). "Spinal nerves and their bearing on salamander phylogeny." Journal of Morphology, 148, 305-328.

Good, D.A. (1989). "Hybridization and cryptic species in Dicamptodon (Caudata: Dicamptodontidae)." Evolution, 43, 728-744.

Hammerson, G. 2004. Dicamptodon aterrimus. In: IUCN 2010. IUCN Red List of Threatened Species. Version 2010.4. . Downloaded on 13 January 2011.

Metter, D. (1963). "Stomach contents of Idaho larval Dicamptodon." Copeia, 1963, 435-436.

Nussbaum, R. A. (1969). ''Nests and eggs of the Pacific Giant Salamander, Dicamptodon ensatus (Eschscholtz).'' Herpetologica, 25, 257-262.

Nussbaum, R. A. (1976). "Geographic variation and systematics of salamanders of the genus Dicamptodon Strauch (Ambystomatidae)." Miscellaneous Publications of the Museum of Zoology, University of Michigan, 149, 1-94.

Petranka, J. W. (1998). Salamanders of the United States and Canada. Smithsonian Institution Press, Washington D.C. and London.

Roni, P. (2002). ''Habitat use by fishes and Pacific Giant Salamanders in small western Oregon and Washington streams.'' Transactions of the American Fisheries Society, 131, 743-761.

Sepulveda, A. J., and Lowe, W. H. (2009). ''Local and landscape-scale influences on the occurrence and density of Dicamptodon aterrimus, the Idaho Giant Salamander.'' Journal of Herpetology, 43, 469-484.

Stebbins, R. C. (1985). A Field Guide to Western Reptiles and Amphibians. Houghton Mifflin, Boston.

Species Account Citation: AmphibiaWeb 2011 Dicamptodon aterrimus: Idaho Giant Salamander <https://amphibiaweb.org/species/3864> University of California, Berkeley, CA, USA. Accessed Jul 3, 2022.

Citation: AmphibiaWeb. 2022. <https://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 3 Jul 2022.

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