The rough-skinned newt is locked in a lethal evolutionary arms race with garter snakes.

Nature · Published 3 October 2026 Swipe more like this →

In short: This unassuming Pacific Northwest amphibian packs enough neurotoxin to kill several adult humans. Yet, it faces a singular predator: the common garter snake. Through a process of co-evolution, these two species have engaged in a biological standoff, constantly escalating their respective defenses and resistances in a high-stakes survival game.

The rough-skinned newt (Taricha granulosa) is a stocky, granular-skinned creature found from Alaska to California. Its primary defense is tetrodotoxin (TTX), a potent neurotoxin that acts like a cork in a bottle, blocking voltage-gated sodium channels in nerve cells. This mechanism halts electrical signals, leading to paralysis and death by asphyxiation. While the toxin is primarily a deterrent against ingestion, it is so powerful that a single 29-year-old man in Oregon died after consuming one in 1979.

This toxicity has triggered an evolutionary arms race with the common garter snake (Thamnophis sirtalis). Certain populations of these snakes have developed genetic mutations that alter the configuration of their sodium channels, preventing the toxin from binding effectively. This resistance allows them to prey on the newts, though they often test the newt's toxicity level by partially swallowing it before deciding whether to commit to a full meal. Even resistant snakes may experience temporary slowing after consuming a newt, as the toxin still exerts some physiological cost.

The newt is not immune to its own poison; it has evolved a protective mechanism through a single amino acid substitution in its sodium channels, similar to the adaptation found in pufferfish. Interestingly, this toxicity extends to the newt's eggs, suggesting that high toxin levels are under selective pressure to protect offspring. Newts have even developed a sophisticated chemical avoidance behavior, detecting the chemical signature of snakes that have recently consumed their kin to gauge whether a predator is resistant or sensitive, allowing them to minimize their risk of being eaten.

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