A stocky, medium to large salamander. Terrestrial adults have a brownish black dorsum and bright red venter. The skin is grainy in appearance. Aquatic males (breeding season only) have a brownish dorsum with bright red venter, and a broad, dark stripe across vent. The skin is smooth or slimy (Stebbins 1972; Petranka 1998). Snout to vent length of adults 5.9 to 8.1 cm (14-19.5 cm total length. Larvae are pond-type with incompletely developed or non-existent balancers and even, dark pigmentation on the sides and dorsum. A moderately high tail fin extends forward but does not reach the shoulders (Stebbins 1985; Petranka 1998).
Taricha rivularis may be distinguished from close relatives (T. granulosa and T. torosa) by relatively prominent eyes, brown iris, and bright red ventral coloration (Stebbins 1951; Petranka 1998).
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When full grown, the red-bellied newt measures between 2.75 to 3.5 in (70 to 89 mm) from its nose to its vent, and between 5.5 and 7.5 in (140 and 190 mm) from nose to tail. It has grainy skin, and is brownish-black on top with a tomato-red underbelly. It can be distinguished from other coastal newts by its red belly and a lack of yellow in its eyes. Breeding males develop smooth skin and a flattened tail.
The Red-bellied newt is found in California along the coast from Bodega in Sonoma County, inland to Lower Lake, and north to Honeydew, Humboldt County. It lives in coastal woodlands, especially in redwood forests.
Red-bellied newts lay their eggs in fast-flowing streams or rocky rivers. Newts begin their lives as aquatic larvae similar to tadpoles, though elongated and with external gills. Once they have matured into the adult form, which takes about four months, and usually happens in August, they leave the water until the fifth year of their lives. Then, as early as January or February, the males start congregating at stream banks. One to three weeks later, the females join them and the newts mate. The females lay their eggs in about 12 streamlined clusters with six to 16 eggs each. They usually lay them on the bottoms of rocks, or on branches leaning into the stream. When the adults leave the stream, instead of moving directly uphill, they move at an angle that leads them somewhat upstream. The females, unlike the males, do not breed every year. Red-bellied newts can live for up to 15 years.
Red-bellied newts have a remarkable homing ability. They make great efforts to always go back to the same spot on the stream. They find their way over several miles of rugged terrain to get back to the spot. Likely, smell is responsible for the homing ability.
Red-bellied newts have a brownish-black topside to avoid being noticed. When that fails, and they are seen and disturbed, they pull their heads and tails back to reveal their bright-red undersides. This serves as a warning to potential predators, as red-bellied newts have enough of a neurotoxin, tetrodotoxin, in their skin to easily kill an adult human, or 7,500 mice. Like other newts, red-bellied newts have the ability to regenerate several body parts, including their limbs, eyes, hearts, intestines, upper and lower jaws, and damaged spinal cords.
The range of red-bellied newts covers northwest California, including Sonoma, Mendocino, and Humboldt Counties. The habitat is characterized by coastal redwood forests and cold, rocky, forest streams with moderate to fast current (Petranka 1998; Stebbins 1972).
In 2014, several individuals were discovered in Santa Clara County, significantly south (ca. 130 km) from its previously known range (Reilly et al 2014). These adults were seen with egg masses so recruitment is likely. Reilly et al (2014) tried to determine the origin of this disjunct population by comparing a few molecular markers with populations from the north of San Francisco Bay. However due to the extremely low genetic diversity across its range it was inconclusive whether the population in Santa Clara County represents a previously unknown but natural range extension or an introduced population.
Adults appear above ground after the first few rains during the autumn months and begin to orient towards breeding sites in late January, with peak migration in early March. Movements are concentrated in the five hours following sunset on warmer, humid nights with moderate or no rain. Breeding occurs in fast-moving streams, and does not take place in standing water like related species of Taricha. Animals show philopatry and return to the same (or nearby) sites to breed each year. Courtship includes a period of amplexus where the male grasps the female and rubs her head with his. Eventually, the male deposits a spermatophore on the substrate and the female picks this up in her cloaca. Females deposit eggs in small, flattened masses, usually one layer thick. Masses contain 5-15 eggs, average 9. Egg deposition sites are in fast-flowing water on the undersides of stones or attached to rootlets. Eggs hatch after 20-30 days and larvae metamorphose after four months (by August). The juvenile stage lasts 5 years, during which time the animal is rarely seen above ground. Individual red-bellied newts may live as long as 15 years. See Petranka (1998) for references.
Diet is likely composed of terrestrial and aquatic invertebrates although this has been poorly studied (Petranka 1998). When attacked, T. rivularis assumes the characteristic "unken reflex" of all species of Taricha: the tail and head are raised to expose the bright red belly as a warning to predators (Brodie 1977). All Taricha produce the neurotoxin known as tetrodotoxin, which is toxic to their predators and humans (Brodie et al. 1974; Petranka 1998).
Taricha rivularis can be considered common. However, long-term population studies are lacking for this species (Petranka 1998).
Based on low genetic diversity, limited geographic range and potential habitat, and high potential for habitat disturbance, Reilly et al (2014) recommends conservation protection for this species.