The lizard that survives by freezing solid and giving birth to live young

Nature · Published 3 October 2026 Swipe more like this →

In short: The viviparous lizard, Zootoca vivipara, thrives in climates no other non-marine reptile can tolerate. By mastering the art of subarctic survival, this small creature can endure being frozen solid for months at a time, only to thaw and continue its life once the harsh winter conditions finally subside.

Found across northern Eurasia, from the British Isles to Japan, Zootoca vivipara holds the record for the largest distribution of any lizard species. Its resilience is rooted in a unique physiological hardiness. In extreme subarctic environments, these lizards do not merely conform to the cold; they actively thermoregulate. When temperatures drop below −3 °C, they enter a state of supercooling, eventually freezing entirely. They remain in this state until warmer weather arrives, often two months later, relying on unfrozen groundwater and soil-heating effects to find microhabitats that prevent their body fluids from reaching lethal temperatures.

The species is named for its ability to give birth to live young, a trait that has sparked significant scientific debate. While some researchers argue that viviparity evolved from egg-laying only once, others suggest multiple evolutionary events across different clades. Evidence even points to the possibility of reversions to egg-laying, which may have occurred two to three times in the species' history. In the Italian Alps, reproductive isolation between viviparous and oviparous subpopulations has led some to suggest they should be classified as distinct species, as hybridization often results in embryonic malformations.

Beyond its reproductive complexity, the lizard displays fascinating social and physical traits. Females exhibit colour polymorphism—yellow, orange, or a mixture—which is maternally inherited and linked to reproductive fitness. Meanwhile, males are sexually selected for larger head sizes, which serve as weapons in aggressive encounters over mates. Despite their small size, typically 50 to 77 mm, these lizards are active hunters, feeding exclusively on insects like flies and spiders. Their survival is a testament to extreme adaptation, allowing them to occupy niches that would be impossible for their less hardy reptilian relatives.

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