How Do Wood Frogs Survive Freezing in Winter?

A frog that survives a frozen winter

The wood frog (Lithobates sylvaticus) lives in parts of North America where winter temperatures drop far below freezing. Instead of retreating into a warm underground pool, it may spend winter in leaf litter with much of its body frozen. That sounds fatal because expanding ice can rupture cells, and circulation normally delivers oxygen and nutrients to tissues.

Wood frogs do not make ice harmless. They survive by controlling where ice forms and by preparing their cells for a long period of stress. Not every frog species can do this.

What happens when the frog begins to freeze?

The liver releases a protective sugar

As ice begins to form, the wood frog's liver breaks down stored glycogen and releases glucose into the bloodstream. Glucose accumulates in tissues and helps protect cells against extreme dehydration and freezing injury. The National Park Service describes this response in wood frogs living in Alaska, where the animals endure especially harsh conditions.

Glucose is often called a natural 'antifreeze,' but that nickname needs care. It does not keep the entire frog liquid. A substantial fraction of the frog's body water can freeze. Its most important benefit is helping cells remain viable despite ice forming in surrounding spaces.

Ice forms outside many living cells

When water freezes outside cells, it draws more water outward by changing the balance of dissolved substances. That can shrink cells dangerously. Glucose and other solutes help limit the damage. Urea, another compound that accumulates in wood frogs, also contributes to the protection of tissues and can reduce metabolic demand.

A useful analogy is packing delicate objects before a move: the frog cannot stop winter from arriving, but it can reduce the damage caused by the process. Unlike household packing, however, these protections are biochemical and finely regulated.

Does a frozen wood frog have a heartbeat?

While frozen, a wood frog may show no detectable heartbeat or breathing. Its metabolism slows dramatically. That does not mean it has died and come back to life. Its cells remain capable of recovery, and warming permits circulation and normal activity to resume. Researchers have observed that vital organs tend to freeze late and thaw early, an arrangement that helps restore function.

Survival has limits. The frog cannot endure unlimited cold or unlimited freezing. Temperature, duration, local adaptation, and the fraction of body water that freezes all affect the outcome.

Why this adaptation matters to science

Freeze tolerance gives researchers a living model for understanding cellular dehydration, oxygen deprivation, and tissue preservation. It does not mean scientists can immediately use wood frog biology to freeze and revive a human. Human organs differ profoundly in size, structure, blood supply, and response to ice.

The most interesting scientific question is not simply 'How does the frog avoid freezing?'—it often does not. It is 'How does the frog keep its cells alive while much of its body freezes?'

Explore other remarkable survival strategies in why animals hibernate and why deserts become cold at night.

Frequently asked questions

Do wood frogs freeze solid?

They can become largely frozen, with ice in extracellular spaces and no detectable heartbeat or breathing. Not every part of every cell becomes ice.

Can a frozen wood frog come back to life?

It can thaw and resume normal function, but describing this as resurrection is misleading because its cells remained viable.

Can people use the same method to survive freezing?

No. Wood frog adaptations cannot be transferred directly to humans, and severe freezing is dangerous to human tissues.

The takeaway

Wood frogs survive winter freezing by protecting cells with glucose and other compounds while allowing much of their body water to freeze in less damaging locations. The biology is remarkable precisely because the animals manage freezing rather than avoiding it altogether.