Life Science

Is it true that some frogs can survive being frozen?

Asks Emily from Dwight, NE

June 23, 2008
This frozen wood frog is one of five species that tolerate freezing. [Credit: Janet Storey]
This frozen wood frog is one of five species that tolerate freezing. [Credit: Janet Storey]

Warm weather brings thoughts of spring peepers and leaping bull frogs. But what happens to frogs in the winter? If they can’t dig down far enough into the soil to avoid the ice or aren’t lucky enough to live in warmer climates, some actually freeze.

Fortunately for them, they don’t freeze to death: Most survive to mate another spring.

There are five known species of freeze-tolerant frogs in North America, including the well-studied wood frog, as well as Cope’s gray tree frog, the eastern gray tree frog, spring peepers and the western chorus frog. In the fall, these frogs bury themselves under the leaves on the forest floor—but not deeply enough to escape the icy fingers of Jack Frost.

Frogs are “cold blooded” (or more precisely, ectothermic), so their body temperature closely tracks the temperature around them. Temperatures have to dip slightly below 32 degrees Fahrenheit to freeze a frog, and ice begins to grow when an ice crystal touches the frog’s skin. Like falling dominoes, the ice triggers a cascade of particles that form as the temperature drops.

But these amphibians don’t just turn into a block of ice. A chain of events occurs to protect the freezing frog. Minutes after ice starts to form in the skin, a wood frog’s liver begins converting sugars, stored as glycogen, into glucose. This sugar is released from the liver and carried through the bloodstream to every tissue where it helps keep cells from completely dehydrating and shrinking.

As the wood frog is freezing, its heart continues pumping the protective glucose around its body, but the frog’s heart slows and eventually stops. All other organs stop functioning. The frog doesn’t use oxygen and actually appears to be dead. In fact, if you opened up a frozen frog, the organs would look like “beef jerky” and the frozen water around the organs like a “snow cone,” says Jon Costanzo, a physiological ecologist at Miami University in Ohio who studies freeze-tolerance.

When in its frogcicle state, as much as 70 percent of the water in a frog’s body can be frozen, write researchers Jack Layne and Richard Lee in their 1995 article (pdf) in Climate Research. Frogs can survive all winter like this, undergoing cycles of freezing and thawing.

If it gets too cold, though, they’ll die. Frogs in Ohio, in Costanzo’s neck of the woods, can survive about 24 degrees Fahrenheit. But frogs farther north can live through lower temperatures.

When the weather gets warmer, the frog melts. “The frog has to go through a repair process,” says Costanzo. It can be sluggish when it first thaws out, and its body needs to replace some damaged cells. Scientists, however, aren’t sure what tells the heart to start beating.

Researchers are still studying this and the mechanisms that protect the frog, aside from glucose. Urea, a waste that frogs get rid of in their urine, was recently shown to help them survive freezing. And proteins may bind to the inside and outside of the cells to keep them from shrinking too much, suggests Kenneth Storey, a professor of biochemistry at Carleton University in Ottawa, Canada, who also studies freeze-tolerance.

While humans aren’t going to survive being frozen any time soon, Storey does say that studying these methods may help preserve human organs longer for transplantation. “We’re on the edge of what you might call nature’s mechanism of transplants,” he says.

About the Author



Hmmm, …no comments in three and a half years. Thanks very much Rachel, I enjoyed it very much.

Tyler says:

How long can they remain in a frozen state and still survive?

Doc Brown says:

why don’t they just gene splice humans with frogs?
seems stupid not to

Vikas Vishwakarma says:

Amazing post… But even I have the same question as Tyler has…

Chris says:

Can someone help? A tiny little tree frog made its way into our home last night. (They sometimes like our sliding glass door- only this year I haven’t seen many). It got cool and quick. Husband saved it from being a puppy snack and said he felt bad about putting it out in the cold. We live in IL and temps dropped like 20 degrees in a day. We put it in our turtle’s cricket box and my intention was to put it out when it warmed today. I did, but it is so cool, it looks like it might have died :( I can’t tell for sure. I put him in the “safe box” with my kids’ box turtle under the lamp. Is there are way to know if it is dead or just hybernating? If it does survive, what can I do to give it its best chance? I feel bad the little thing took a wrong turn. If it is not dead, I will turn it out if it is safe. Crazy that I cant tell if it is dead or not…. Thanks

Cait says:

the article says people can’t survive being frozen, Lol. Ever heard of Jean Hilliard?

Jake says:

Well nice post ken!My thought is, if you need to sueccss; you need to master your own niche market first then only expand step by step and master each steps.I am at oldtown white coffee right now thinking about how they made it.It starts from Ipoh old town by selling coffee powder for many years and made a little fame via mass production coffee powder thru retail shop nation wide and now come out chain-coffee shop where you can find it almost everywhere. I heard soon they will expand to hongkong market to compete with those char chan teng. What’s their niche? Ipoh White Coffee! goodluck pal =p

Susan Poaps says:

In southern Ontario, we heard and saw many frogs this week. Today however, the temperature dipped to 4 Celsius and we didn’t hear them. Have they hibernated again or are they dead?

Bryan says:

Hi everyone, I work in Dr. Storey’s lab.

Tyler: Quite a long time, they can do the whole winter naturally! If someone manages to adapt this strategy to human donor organs, it can really help hospitals with organ transportation. Often times, the most ideal worldwide organ-patient pairings are not performed due to geographical barriers.

Doc Brown and Vikas: It’s not that easy. There’s no “one gene” that allows the frog to do what it does with respect to freeze tolerance. Even if we tried multiple genes to do a “cumulative effect”, it can have unwanted secondary effects.

Susan: If they were wood frogs and the temperature dropped to 4 Celcius, they are likely alive as they can withstand 0 Celcius.

Jackpot says:

Amazing post…

Sarah reazer says:

Very informative information I have a frog living down at the bottom of my outside basement steps. It’s been cold and thought it was dead. It’s been moving around to different spots so now I know he’s looking for shelter.

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