Amphibians
Seal Salamander
Desmognathus monticola · also called mountain salamander
Kneel beside a cold Appalachian brook at night, shine a light along the mossy bank, and you may catch two points of reflected eyeshine at the mouth of a small tunnel. That is a seal salamander on station at its burrow, waiting for a beetle to blunder past.
Overview
Desmognathus monticola is a stout, medium-sized member of the dusky salamander group, reaching about 9 to 14 cm including the tail. The back is brown to grey with a scattering of darker blotches that fade with age; the belly is pale. It lives along shaded seeps, springs, and small streams in mountain forest, almost always within a metre or so of running water, and it breathes entirely through its skin and mouth lining because, like all members of the family Plethodontidae, it has no lungs.
Life at the water’s edge
The seal salamander is a burrow keeper. It occupies a shallow tunnel in the wet soil and gravel of the stream bank and uses the entrance as a hunting blind, sitting there after dark with its head exposed and darting back tail-first at any vibration. Prey is whatever invertebrate walks within reach — ground beetles, spiders, millipedes, worms, and insect larvae — taken in a fast forward lunge. Males compete for the best burrow sites and defend them from rivals.
Breeding follows the same tie to clean water. The female lays a grape-like cluster of eggs in a wet cavity near the stream and coils around it until it hatches. The larvae then live in the stream for one to two years, breathing with gills, before transforming into the terrestrial adult form.
One rung on a ladder
The southern Appalachians hold a remarkable stack of closely related dusky salamanders that divide the streamside habitat by moisture. The fully aquatic black-bellied salamander holds the splash zone, the more terrestrial mountain dusky salamander works the damp forest floor, and the seal salamander sits in between, on the wet bank itself. This fine partitioning is a classic example of how similar species avoid direct competition.
Status
The seal salamander is listed as Least Concern and remains common along suitable streams. Its weakness is its dependence on cold, clear, well-oxygenated water and an intact canopy. Sediment from logging, roads, and mining smothers the stream bed and drives the salamanders out, which is why biologists use them as an indicator of headwater stream health.
Seal Salamander: common questions
Is the seal salamander related to seals?
No. The two share nothing but a name. The seal salamander is a small lungless amphibian of Appalachian streams, and its closest relatives are the other dusky salamanders in the genus Desmognathus. Nineteenth-century naturalists applied the word seal to it, and the most common explanations are that the smooth, wet, faintly mottled skin has a seal-like sheen or that the blunt, rounded head recalls a seal's profile. Whatever the reason, the name is now fixed in field guides even though it describes an animal that fits in the palm of a hand and never leaves the forest.
How does a salamander breathe without lungs?
It uses its skin and the moist lining of its mouth and throat as the gas-exchange surface. Oxygen from the air or water dissolves into the thin film of moisture on the skin, diffuses through into a dense mesh of blood vessels just below the surface, and carbon dioxide passes out the same way. This works only while the skin stays wet and only across a fairly small body, which is why lungless salamanders are confined to cool, damp, shaded habitats and tend to be slender. It also means the animal effectively drowns in dry air and overheats quickly in sun.
What does the seal salamander do at its burrow?
The burrow is its home base, refuge, and hunting blind. During the day the salamander stays deep inside, in saturated soil where humidity is total and predators such as snakes, shrews, and birds cannot easily reach. After dark it moves to the entrance and sits with just the head and shoulders showing, watching the ground nearby. When a beetle, spider, or worm passes within range it lunges forward, grabs the prey, and often reverses straight back into the tunnel. Males defend the area around a good burrow against other males.
Why do biologists watch seal salamanders?
Because they are picky about water quality and easy to survey, they serve as a barometer for the condition of mountain headwater streams. A healthy population signals cold, clear, well-oxygenated water and an intact streamside forest. When the salamanders thin out or vanish, it usually means sediment is smothering the stream bed, the canopy has been opened and the water has warmed, or acid drainage has entered the system. Long-term counts of these and related salamanders are a standard part of monitoring logging effects and stream restoration across the southern Appalachians.