[3][4] The dusky salamander lays its eggs close to water under moss or rocks, in logs, or in stream-bank cavities.

[3][4] The holotype for Desmognathus fuscus does not exist; Rafinesque (1820) described the type locality to be in the northern parts of the state of New York in small brooks.

[3][4] Juvenile colouring consists of five to eight pairs of dorsal spots or blotches located between the front and hind legs.

[3][4] As with all dusky salamander species, both juveniles and adults have a pale single stripe outlined in black that extends from the eye and runs diagonally to the rear of the jaw.

[3][4][11] Additionally, both have 14 costal grooves, larger hind limbs than forelimbs, and a keeled (knife-like) tail that is triangular in cross-section and compressed laterally at the base.

[3][11][12] The dusky salamander also has a naso-labial groove, which aids olfaction, and thus the ability to search out mates and prey through smell.

Distinguishing characteristics are that the dorsal spots of the Mountain dusky salamander are usually chevron-shaped and its tail rounded at the base rather than laterally compressed.

[3] Within its Canadian range, the northern dusky salamander usually occurs in forested habitat located in high elevation, low-order streams.

In the south, the northern dusky salamander can be found in upland streams as well as floodplains, sloughs and muddy sites.

[3][4] As a result of desiccation and predators, activity of the northern dusky salamander peaks in the morning, and the evening and early night.

During development while in the larval stage, the northern dusky salamander is strictly aquatic, its habitat the interstitial spaces between rocks of the streambed.

[3][21] Females normally deposit between 10 and 30 eggs under logs, moss or rocks located streamside where soil is saturated with water.

[3] Females remain with their eggs for an incubation period of six to ten weeks (45 to 60 days) in order to protect them from desiccation and predation .

This is because they are dominant vertebrates within headwater riparian forest ecosystems, with a biomass greater than that reported for fish, birds or small mammals.

[11][23][24] When prey is in excess, the northern dusky salamander does typically have a preference for the larger and fleshier terrestrial invertebrates, such as earthworms.

[24] The aquatic portion of the adult's diet is habitat specific and commensurate with the seasonal abundance and diversity of invertebrates.

[12] Resultantly, contamination of ground water or waterways through pollution from urban areas, industry, or agriculture, can be catastrophic to local populations.

[1] The disappearance of the species from the Acadia National Park in Maine is believed to be the result of heavy metal contamination.

Aquatic habitat can be degraded through siltation of streams, or the microhabitat conditions of the forest floor undergoing alterations.

[3] The northern dusky salamander is listed as endangered in Ontario[3][4] and is declining in many parts of the United States[26][27] yet some populations remain stable.

Likewise, Article 22 of the provincial Environmental Quality Act offers protection against unregulated degradation of the dusky salamander's environment.