Which animal can survive being frozen?
Quick answer
The wood frog of North America can survive being frozen for weeks or months in winter. Up to about two-thirds of its body water turns to ice, its heart stops and it stops breathing. It survives by flooding its cells with glucose and urea, natural “antifreeze” substances that protect them. In spring, it thaws and hops away.
Key facts
- Animal
- Wood frog (Lithobates sylvaticus)
- Range
- North America, including Alaska and northern Canada
- Ice in body
- Up to about 65–70% of body water
- Survives
- Temperatures down to about −16 °C in some populations
How a frog freezes and survives
| Stage | What happens |
|---|---|
| Ice touches the skin | The frog’s liver quickly releases large amounts of glucose into the blood |
| Freezing | Ice forms in spaces between cells, but sugar-rich cells resist freezing inside |
| Frozen state | No heartbeat, no breathing, no brain activity |
| Thaw | The heart restarts and the frog revives within hours |
The danger in freezing is ice forming inside cells, which bursts them. By keeping ice outside the cells and protecting their contents, wood frogs avoid fatal damage.
Champions of the cold
Wood frogs in Alaska can survive temperatures as low as about −16 °C and stay frozen for months, longer than populations farther south. Scientists study them to improve ways of preserving organs for transplants.
Other freeze-tolerant animals
| Animal | Survival trick |
|---|---|
| Gray tree frogs | Use glycerol as antifreeze |
| Painted turtle hatchlings | Survive freezing in their nests over winter |
| Arctic woolly bear caterpillars | Freeze each winter and may take years to become moths |
| Tardigrades | Tiny animals that survive extreme cold in a dried-out state |
Antifreeze without freezing
Some animals avoid freezing altogether. Antarctic fish make antifreeze proteins that stop ice crystals from growing in their blood, letting them live in water below 0 °C. Insects such as some beetles do the same.
Winter survival strategies compared
| Strategy | Examples |
|---|---|
| Freeze tolerance | Wood frogs |
| Freeze avoidance (antifreeze) | Antarctic fish |
| Hibernation | Bears, ground squirrels |
| Migration | Many birds |
Water freezes at 0 °C, but dissolved substances lower its freezing point; see what temperature water freezes at.
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