The wood frog is the only North American amphibian living north of the Arctic Circle.

Nature · Published 3 October 2026 Swipe more like this →

In short: This resilient creature survives the brutal northern winter by essentially turning into an ice cube. When temperatures drop, the wood frog freezes its own blood and tissues, halting its heartbeat and brain activity entirely, only to thaw out and hop away when the spring snow finally melts.

The wood frog, scientifically known as Lithobates sylvaticus, is a terrestrial member of the family Ranidae. Its range is remarkably broad, stretching from the boreal forests of Canada and Alaska down to the southern Appalachians. It is uniquely adapted to cold climates, holding the distinction of being the only North American frog species found north of the Arctic Circle.

To survive freezing temperatures, these frogs utilize a sophisticated biological mechanism. As winter approaches, they accumulate urea in their tissues and convert liver glycogen into glucose. These substances function as cryoprotectants, preventing excessive ice formation and protecting cells from shrinking. In this state, the frog exhibits no detectable vital signs, including no circulation or brain activity. While frogs in the American Midwest might tolerate temperatures down to -6 °C, those in Interior Alaska demonstrate even higher levels of freeze tolerance.

Beyond their cold-weather survival, wood frogs are known for their terrestrial lifestyle and reliance on ephemeral wetlands, or vernal pools, for breeding. They are typically diurnal and spend most of their time on the forest floor, where they hunt small invertebrates. Their life history involves significant migration, with individuals traveling hundreds of meters between their breeding sites and upland overwintering habitats. Research indicates a strong fidelity to their original breeding ponds, though a portion of the juvenile population will disperse to new locations.

As members of the order Anura, wood frogs share the evolutionary history of amphibians, a group that first appeared approximately 340 million years ago. While they are distinct from other ranids in their feeding strike—which contacts prey only with the tip of the tongue—they remain a classic example of the diverse reproductive and survival strategies that characterize the roughly 8,100 known species of living amphibians.

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