Taricha granulosa
rough-skinned newt

Taricha granulosa is found along the Pacific coast of North America, with a range extending from Santa Cruz County, California, south of San Francisco Bay, into southeastern Alaska north to Juneau. Within this range, it is found at elevations from sea-level to 2743 m, or 9000 ft, and is found on many islands off the coast, including Vancouver Island. In northern California rough-skinned newts are found as far east as Shasta County, extending into northern Butte County. Isolated populations of T. granulosa occur in Latah County, Idaho and Saunders County, Montana. The Idaho population, at least, is probably introduced. ("Native Amphibians--Introduction", 2007; Behler and King, 1979; Jones, Leonard, and Olson, 2005; Petranka, 1998)

Taricha granulosa inhabits both aquatic and terrestrial environments. Though they generally spend more of their time on land, they must return to the water to breed. Many become temporarily aquatic during the summer months due to dry weather. It is possible for a newt to spend its entire life in an aquatic habitat. In the water, T. granulosa prefers areas of little or no current, such as ponds, lakes, and slow-moving streams, and sometimes small ephemeral wet areas such as ditches. Aggregations of adults have been discovered as deep as 12 meters underwater. On land, newts can usually be found under pieces of rotting wood on forested hills or mountains. They occasionally occur in open areas such as fields. (Bishop, 1943; Jones, Leonard, and Olson, 2005; Petranka, 1998)

The eggs of T. granulosa are each separately encased in a gelatinous substance, around 3 to 4 millimeters in diameter. The ova are generally light-brown on top and cream colored on the bottom. (Jones, Leonard, and Olson, 2005)

Larvae are aquatic, with a faint dorsal stripe on either side of the body that fades as they mature. Larvae have a dark stripe that extends from the eye to the nostril as well as two rows of spots. One row is near the limb insertions and the other is near the fin. The fin is speckled with dark spots. Larvae measure around 18 mm in total length. (Jones, Leonard, and Olson, 2005; Petranka, 1998)

Adults range from about 12.7 to 21.6 cm in total length. They have rough, grainy skin that is dark-colored dorsally and orange to yellow-orange ventrally. Their textured skin has earned them the common name "rough-skinned newts." Their eyes are relatively small and do not extend beyond the edges of the head. The irises are yellow, and the lower eyelids are orange. The vomerine teeth are arranged in a V-shaped pattern. Costal grooves are absent. Males are larger than females, with longer vents. During the breeding season, males and females become temporarily aquatic. Males develop smooth, spongy skin that is lighter-colored than usual. Their vents are strongly pronounced and swollen. The tail crests become more pronounced, as do the nuptial pads on the tips of their toes. The appearance of the females does not change, though their vent becomes cone-shaped. (Behler and King, 1979; Jones, Leonard, and Olson, 2005; Petranka, 1998)

Some adults living at high elevations retain their gills and are totally aquatic, though they do not exhibit genuine paedomorphosis. Aquatic females can sometimes be confused with breeding males, because they have lighter, smoother skin, tail crests, and larger vents than do terrestrial females. However, these features are less pronounced than in breeding males. (Jones, Leonard, and Olson, 2005; Petranka, 1998)

Taricha granulosa exhibits an aquatic larval stage. Eggs hatch 3 to 4 weeks after being laid, and these newts spend 4 to 5 months as aquatic larvae before metamorphosing into juvenile adults. In some high elevation areas, newts overwinter as larvae and emerge in the spring or summer. They spend a couple of years as juvenile adults before returning to the water to breed. At high elevations, some adults retain their gills and spend their entire life cycle in the water. Adults reach sexual maturity at 4 to 5 years of age. (Jones, Leonard, and Olson, 2005)

Little is known about the longevity of T. granulosa, but marked specimens have been recaptured after 17-18 years. (Ridenhour, Brodie Jr., and Brodie III, 2007)

Adult T. granulosa usually spend some portions of their lives in terrestrial habitats and some portions in aquatic habitats. They are known to migrate to and from mating sites, possibly using celestial cues as well as olfaction to navigate. Diurnality and nocturnality vary according to population. Rough-skinned newts produce a powerful toxin, tetrodotoxin, from granular glands located in the skin. The amount of toxin per newt varies geographically, with some regions bearing newts with extreme toxicity and some regions with newts of low toxicity. When provoked, rough-skinned newts will display the unken reflex, in which the head is bent back and the tail curled up to expose the animal’s bright-colored belly as a warning to potential predators. (Jones, Leonard, and Olson, 2005; Petranka, 1998)

Home Range

Not much is known about territory size, but aquatic adults seem to prefer shallow water during the beginning of the year (spring) and deeper water during the latter part of the year.

It is unclear how T. granulosa individuals communicate with one another, but there is evidence that rough-skinned newts navigate using celestial cues, olfaction, and darkened areas caused by vegetation at the edges of water bodies. (Jones, Leonard, and Olson, 2005; Petranka, 1998)

Larvae eat small aquatic invertebrates. Aquatic adults have been known to eat a variety of organisms, from snails and insects to other amphibians. (Petranka, 1998)

Adult terrestrial T. granulosa appear to be opportunistic carnivores, with insects making up a large portion of their diet. (Packer, 1961)

Because of the extreme toxicity of rough-skinned newts, they have only one known predator, common garter snakes (Thamnophis sirtalis), which seem to be immune to tetrodotoxin. It has been proposed that these two species are competing against each other in an evolutionary arms race, in which a predator species and a prey species co-evolve, each developing greater defenses against the other. In this case, as the newts evolve greater toxicity, garter snakes evolve greater resistance to the toxicity. (Brodie III and Brodie Jr., 1990)

Since T. granulosa is mainly an insect eater, it is important in keeping insect populations in check, possibly including some nuisance insect species, such as mosquitoes (Culicidae). Taricha granulosa is also an important food source for common garter snakes, which are in turn eaten by other animals. (Brodie III and Brodie Jr., 1990)

There are no known adverse effects of T. granulosa on humans, unless ingested. These newts contain enough toxin to kill several humans. (Brodie III and Brodie Jr., 1990)

Taricha granulosa is of particular interest to biologists because of its evolutionary arms race relationship with common garter snakes. This species is also exploited for the pet trade.

Rough-skinned newts are not listed as threatened or endangered, but like many amphibian species may face such a distinction if their habitat is extensively threatened by human development.