Eurycea bislineata

Northern Two-Lined Salamander (Eurycea bislineata)

The northern two-lined salamander, scientifically known as Eurycea bislineata, is a species of salamander native to Canada and the United States. It is a member of the Plethodontidae family, which are lungless salamanders.

Description and Habitat

This small salamander typically measures between 65 and 120 mm in total length. Its most distinctive feature is the presence of two black stripes running longitudinally along its yellow or yellowish-brown back, though these stripes may become fragmented further down the tail. The flanks are mottled with grayish or brown patterns, and the belly is a pale, almost transparent yellow. Adults possess four toes on their forefeet and five on their hindfeet, with 14 to 16 costal grooves visible along their sides.

The northern two-lined salamander exhibits a strong affinity for moist environments. Its natural habitats include temperate forests, shrublands, riverbanks, intermittent streams, freshwater marshes, and springs. While it can be found in areas far from running water, such as damp ground or even urban settings, it is notably more water-oriented than some related species. They are frequently observed in and around water bodies like rain puddles, streams, swamps, and damp stream beds, and sometimes along the stony shores of small lakes and rivers.

Reproduction and Life Cycle

Reproduction begins with a complex courtship ritual that can span from September in the southern parts of its range to May in the north. This courtship involves intricate behaviors, including a tail-straddling walk. Males possess specialized premaxillary teeth used to abrade the female's skin, facilitating the introduction of secretions from a mental gland on the chin, which stimulates mating.

Following courtship, the female seeks a suitable site for egg-laying, typically under rocks or logs in or near streams. She demonstrates a unique method of oviposition, often flipping onto her back to press her cloaca against the substrate to lay each egg. The eggs, measuring 2.5–3 mm in diameter, are white or pale yellowish when freshly laid and are surrounded by two membranes. Communal nesting has been documented in several locations.

Upon hatching, the gilled larvae are approximately 10 mm long and remain in slow-moving water or crevices. They begin feeding on benthic invertebrates after their yolk sacs are absorbed. The larval period is variable, with metamorphosis occurring around two years of age in southern regions and three years in the north, at total lengths of approximately 50 mm and 70 mm, respectively.

Adult Ecology and Behavior

Adult northern two-lined salamanders reach sexual maturity between three and four years old. Both adults and juveniles tend to inhabit the edges of streams, seeking shelter under rocks and debris during the day. Seasonal migrations can occur, with some adults moving into the forest after the breeding season.

Most above-ground activity by adults and juveniles takes place after dark, particularly during wet weather. They emerge from their retreats to forage along stream banks or the forest floor. Their diet is diverse, including a wide array of invertebrates. Adults can be territorial, and population densities vary with habitat quality. In colder climates, adults overwinter burrowed up to 80 cm deep into stream banks, while in southern regions, they may remain somewhat active and continue feeding.

Predators and Defense

Due to their size and habitat, northern two-lined salamanders are preyed upon by various animals, including birds, snakes, and other salamander larvae. Their defense mechanisms include remaining motionless or engaging in tail autotomy, a common adaptation that allows them to escape predators by shedding part of their tail.