Amphibians
California Newt
Taricha torosa · also called orange-bellied newt, coast range newt
A California newt looks unremarkable, a stocky brown salamander with a warm orange belly, but it is one of the most poisonous animals in North America. Its skin holds tetrodotoxin, the pufferfish nerve poison, in quantities that could kill a person who ate it. And that toxicity is not fixed: it is locked in a slow evolutionary arms race with the garter snakes that have learned to eat it anyway.
Overview
The California newt, Taricha torosa, lives in the Coast Ranges of California, in oak woodland, chaparral, grassland, and mixed forest. It spends most of the year on land, under logs and leaf litter, hunting worms, slugs, snails, and insects, and it migrates back to a stream or pond to breed in winter and spring, when the males grow smooth skin and a swimming tail.
The poison and the arms race
The skin secretes tetrodotoxin — harmless to touch briefly, dangerous if the newt is swallowed. A threatened newt on land arches into a warning posture, showing the orange underside. In places where common garter snakes have evolved resistance to the toxin and eat the newts anyway, the newts have evolved even more toxin, which has driven the snakes to become more resistant still — a coevolutionary loop studied for decades.
Migration and roads
Adults return to the exact water they hatched in, so thousands move downhill together in the first rains, and any road in the way becomes a killing zone. In the San Francisco Bay Area, one road beside a reservoir is now closed to cars for months each winter just to let the newts cross.
Status
Least Concern overall but decreasing, and the southern populations are a California species of special concern. The threats are drying streams, post-fire sediment, introduced crayfish, mosquitofish, and bullfrogs eating the larvae, and road mortality.
California Newt: common questions
How poisonous is a California newt?
Very. Its skin contains tetrodotoxin, one of the most potent natural poisons known, the same toxin found in pufferfish, and a single adult California newt carries enough to be lethal to a person if the animal is eaten. Handling a newt is not dangerous in itself, because the toxin cannot pass through intact skin in a harmful dose, but it can cause numbness and irritation if it gets into the eyes, the mouth, or a cut, so you should wash your hands after touching one and never put fingers near your face. The real danger is ingestion. In 1979 a man in Oregon died after swallowing a rough-skinned newt, a close relative with similar toxicity, as a bar dare.
What is the newt and garter snake arms race?
It is one of the best-studied examples of coevolution, meaning two species evolving in response to each other. Most predators cannot eat a Taricha newt because of its tetrodotoxin, but common garter snakes in some regions have evolved changes to their nerve channels that make them resistant to the poison, letting them eat newts that would kill other animals. Where snakes are resistant, natural selection favours newts with even more toxin, since only the most poisonous survive being eaten, and those more toxic newts then select for even more resistant snakes. Over many generations this back-and-forth has produced newts in parts of California and Oregon with toxin levels far higher than needed to deter any ordinary predator, matched by local garter snakes that can shrug them off.
Why do California newts cross roads in huge numbers?
Adult California newts spend most of the year dispersed across the hills on land, but to breed they must return to water, and they show strong fidelity to the specific stream or pond where they themselves hatched. So in the first heavy rains of winter and through spring, large numbers of newts set off downhill toward the same breeding sites at the same time, and any road between the hills and the water becomes a crossing point where many are killed by traffic. In the Bay Area, the movement is so concentrated on one stretch of Alma Bridge Road beside Lexington Reservoir that the county now closes that road to vehicles for several months each winter to reduce the death toll.
Can you keep a California newt as a pet?
It is possible but discouraged, and in California it is illegal to collect them without a permit. Taricha newts are hardy in captivity and can live 20 years or more, but they need a cool setup that never gets warm, a land area and a water area, clean dechlorinated water, and live or frozen invertebrate food, and their potent skin toxin makes them a poor choice around children or other pets. The southern populations are a species of special concern, so taking animals from the wild adds pressure to declining groups. Anyone keeping newts should use captive-bred animals of a legal species and handle them as little as possible.