Dusky salamanders are small but robust salamanders with 14 grooves on their body and hind limbs that are larger than the front limbs. They have a knife-like tail that is less than half the body length. The upper body is brown or reddish brown to gray or olive, with slightly darker markings on the top and sides. The base of the tail is olive, yellow, or bright chestnut. The belly is whitish with some dark speckles. Adults are 6.4 to 14.2 cm in length. Males are typically longer than females. The average length for males is 9.4 cm, and the average length for females is 8.6 cm. Dusky salamanders are in the lungless salamander family and have no lungs. They “breathe” by absorbing oxygen through the skin. Also, members of this family have a groove that runs from the nose to the upper lip which may aid in smelling, which is important when finding prey and identifying potential mates.
Northern dusky salamanders occur from southern New Brunswick and Quebec, along the East Coast to North Carolina, and west to Ohio, southern Indiana, Kentucky, and Tennessee. Over most of their range, dusky salamanders are common in appropriate habitat. A breeding population of northern dusky salamanders has been found at one site in eastern Michigan; whether this population is introduced or a natural population has not yet been determined.
Northern dusky salamanders prefer wooded or partially wooded moist habitats with running or trickling sources of water. Most often, they are found under flat rocks or logs near rocky or hillside streams or seeps, or in the moist, misty habitat near waterfalls. They may go into the water to find cover under rocks or substrate if disturbed. If the stream substrate does not freeze, they can remain active year-round. In extremely cold conditions, they will burrow under gravel until they are below the frostline. Dusky salamanders can survive at a variety of altitudes, ranging from sea level to high in the Appalachian Mountains.
Upon hatching, dusky salamander larvae are about 1.6 cm long and have well-developed legs. The larvae may stay with their mother for several days or even weeks before going to the water. Because they are aquatic, they have gills, which are small and white. However they can survive in moist terrestrial environments for some time if required, and might even go through metamorphosis on land. After spending 7 to 11 months in the water they undergo metamorphosis (in the spring or summer after hatching). Newly transformed salamanders are 2.8 to 4.4 cm long.
Dusky salamanders, like other salamanders, reproduce in a unique way. The male deposits a jellylike glob (called a spermatophore) onto the ground. The female then climbs over it to push it into her cloaca. The sperm is stored in her until the fall or the next spring.
Courtship in dusky salamanders occurs near streams in spring and fall. Mating occurs on land. A male will approach a female while doing a "butterfly walk," rotating his front limbs similar to a swimmer doing a butterfly stroke. He will wag his tail and nudge the female with his snout in order to identify and stimulate her. Then the male will press his chin onto the female’s back and arch his body. With a quick snap, he will straighten his body. The snap is so violent that the male may be thrown 5 to 10 cm away from the female. He will repeat this activity, slowly moving until he is under the female’s head. He reaches back, snaps at the female's neck, and drags his teeth across her back to rub pheromones on her. Next, the female will straddle his tail, while touching her chin to the base of his tail. Then the male will produce a spermatophore to be picked up by the female.
In summer, females produce 12 to 51 eggs, which are deposited under rocks, logs, mosses or debris near water in the summer. Larger females typically produce larger numbers of eggs. Females stay with the eggs until they hatch, after 40 to 80 days. In most successful nest sites, 70% or more of the eggs will hatch. After two or three years, males will be reproductively mature. For females, three or four years are required.
Females care for eggs from deposition to hatching, leaving the nest sometimes at night to feed. Brooding females aggressively defend their clutch from predators. In one study, brooding females returned to their nests after being displaced as much as 32 meters. If females don't care for their eggs, the eggs often die as a result of predation and fungal infection.
No specific information is available on longevity in this species. Related salamander species can be relatively long lived (i.e. several years to a decade or more) for such small animals. (Petranka, 1998)
Dusky salamanders are mainly active at night, when they leave the log or rock that gives them protection during the day to find food along a steam or waterway. On moist evenings, salamanders are active from dusk to dawn. While mostly terrestrial, dusky salamanders can sometimes climb up vegetation or rock faces. These salamanders can be active throughout the year if in a spring or spring-fed habitat, but often are inactive in winter. They are generally solitary except during courtship and mating.
Adult dusky salamanders have a small home range, and an individual may move only a couple of meters over a period of several months. The actual size of the home range varies between localities and geographic range, ranging from 1.4 square meters to 114 square meters. (Bishop, 1941; Gibbs, et al., 2007; Hulse, et al., 2001; Petranka, 1998)
It is thought that the groove between the nose and the lip in these salamanders helps them smell prey and potential mates. Odors may be transported along the groove and into the mouth, where the chemical is "tasted." Also, glands are used to communicate with mates when courting. The male will vigorously rub his chin on a female to expose her to his pheromones. If a brooding female is returning to her nest after feeding at night, she can recognize which clutch is hers with smells. Dusky salamanders may bite a threatening predator. Also, a male may attack a another male that is courting a female.
Dusky salamanders are carnivorous. They eat small invertebrates (both terrestrial and aquatic) including earthworms, slugs, snails, crustaceans, spiders, mites, flies and fly larvae, ants, beetles and beetle larvae, centipedes, moths, and mayflies. Dusky salamander larvae eat crustaceans, insect larvae, copepods, and mites. The diet is fairly nonspecific, and they tend to eat whatever is in abundance. Dusky salamander larvae or small juveniles are occasionally eaten by large adults.
Dusky salamanders have a number of predators, including raccoons, birds, striped skunks, shrews family, water snakes, garter snakes, spring salamanders and red salamanders. Dusky salamander skin is only mildly toxic, so they must rely on other defensive techniques. Dusky salamanders can move quickly and are good jumpers. They also have slippery skins which makes grasping them difficult. They may actually bite a predator. Like many of the lungless salamanders, they can drop their tails when attacked in order to distract the predator enough to make a quick escape. The tail will grow back later, though it may look slightly different than the original. Tail dropping is fairly common in northern dusky salamanders; about 50% of adults have missing or regrown tails.
Dusky salamanders are second and third order consumers that eat a wide variety of small terrestrial and aquatic invertebrates. They are opportunists and will eat whatever is available in high abundance. Dusky salamanders are prey to a number of animal species representing many vertebrate (and perhaps some invertebrate) groups, including mammals, snakes, birds, and larger amphibians. Dusky salamanders often share their habitat with other salamanders. Other species that have been found to coexist with dusky salamanders are seal salamanders, Allegheny Mountain dusky salamanders, southern dusky salamanders, and northern two-lined salamanders.
There are no known adverse effects of dusky salamanders on humans.
In the southeastern United States, salamanders are collected and sold as fishing bait for largemouth bass and other sport fish. Lungless salamanders are important in nutrient cycles in the forest ecosystem, which undoubtedly helps maintain the health of forest resources.
Dusky salamanders can be common where habitat is intact and abundant in areas such as shaded streamsides in moist woods. But they are threatened in some areas by tree removal, which exposes the area to sun, increasing the water temperature and decreasing the humidity. Pollution of waterways can also be a serious threat. The overall effects of bait collection are unknown, but this activity may certainly impact local populations, especially if collection techniques (such as rock turning) disrupt the local habitat.
Tanya Dewey (editor), Animal Diversity Web.
Hannah Edwards (author), Michigan State University, James Harding (editor, instructor), Michigan State University.
Bartlett, R., P. Bartlett. 2006. Guide and Reference to the Amphibians of Eastern and Central North America (North of Mexico). Gainseville, Florida: University Press of Florida.
Bishop, S. 1941. The Salamanders of New York. Albany: New York State Museum Bulletin, No. 324.
Bonett, R., K. Kozak, D. Vieites, A. Bare, J. Wooten, S. Trauth. 2007. The importance of comparative phylogeography in diagnosing introduced species: a lesson from the seal salamander, Desmognathus monticola. BMC Ecology, 7(7): Published Online. Accessed December 05, 2008 at http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=2020456.
Conant, R., J. Collins. 1998. Reptiles and Amphibians: Eastern/Central North America. New York: Houghton Mifflin Company.
Gibbs, J., A. Breisch, P. Ducey, G. Johnson, J. Behler, R. Bothner. 2007. The Amphibians and Reptiles of New York State: Identification, Natural History, and Conservation. New York: Oxford University Press.
Harding, J. 1997. Amphibians and Reptiles of the Great Lakes Region. Ann Arbor, Michigan: University of Michigan Press.
Hom, C. 1987. Reproductive ecology of female dusky salamanders, Desmognathus fuscus (Plethodontidae) in the Southern Appalachians. Copeia, 1987 (3): 768-777.
Hulse, A., C. McCoy, E. Censky. 2001. Amphibians and Reptiles of Pennsylvania and the Northeast. New York: Cornell University Press.
Petranka, J. 1998. Salamanders of the United States and Canada. Washington: Smithsonian Institute Press.