How Arctic Frogs Survive Being Frozen Alive

When you think about hardy arctic creatures bracing for a cold winter, you’re probably thinking of something huge and furry and possibly antlered. Odds are you’re not thinking of … wood frogs. (See a picture of a wood frog.)

But it may be time to cast that amphibian prejudice aside in light of a new study in The Journal of Experimental Biology that examines the astounding ability of Rana sylvatica to freeze—and live through it. R. sylvatica is a species of wood frog with a range that stretches from the state of Georgia all the way through Canada and into the Arctic Circle.

The study was led by Jon Costanzo of the Department of Zoology at Miami University in Ohio. Costanzo’s research interest in wood frogs goes back 25 years, to when he first learned of their extreme freeze tolerance. (Read about an octopus that survives in extremely cold temperatures.)

“I wanted to understand how the frog could do that on a physiological and chemical level,” he said.

Deep-Frozen Frogs

There are a number of creatures, from reptiles and insects to marine life, that possess some level of freeze tolerance, but few can perform the trick quite like Rana sylvatica. The tiny amphibians can survive for weeks with an incredible two-thirds of their body water completely frozen—to the point where they are essentially solid frogsicles. (Related: “Antifreeze-Like Blood Lets Frogs Freeze and Thaw With Winter’s Whims.”)

Even more incredible is the fact that the wood frogs stop breathing and their hearts stop beating entirely for days to weeks at a time. In fact, during its period of frozen winter hibernation, the frogs’ physical processes—from metabolic activity to waste production—grind to a near halt. What’s more, the frogs are likely to endure multiple freeze/thaw episodes over the course of a winter.

To test the freeze tolerance of Alaskan populations of Rana sylvatica specifically, the researchers compared them with frogs of the same species taken from the local Ohio population. While both exhibited impressive freeze tolerance, there were some obvious differences as well. While the Ohioan wood frogs could be frozen at -4 degrees Celsius (24.8 degrees Fahrenheit) and revived, the Alaskan wood frog was frozen at temperatures as low as -16 degrees Celsius (3.2 degrees Fahrenheit) before being thawed out and returning to its normal healthy state.

And Costanzo is convinced that the small but sturdy amphibians can survive even colder temperatures.

Avoiding Death

The way wood frogs avoid freezing to death is due to so-called cryoprotectants—solutes that lower the freezing temperature of the animal’s tissues. These include glucose (blood sugar) and urea and have been found in much higher concentrations in the Alaskan wood frogs than in their southern counterparts.

Increased levels of cryoprotectants help the frogs’ cells survive. In most animals, prolonged exposure to subzero temperatures causes cellular shrinkage—a process in which the formation of ice in the tissues pulls water from the body’s cells, essentially sucking them dry and eventually killing the cell.  (Related: “Champions of the Cold.”)

But cryoprotectants help the cells resist that shrinkage.

“The solutes tend to depress the freezing point [of tissue],” said Costanzo. “It limits the amount of ice that actually forms in the body at any part. The more of that cryoprotective solute you can accumulate, the less ice will form and therefore the less stress there is on cells and tissues.”

Costanzo and his team also detected the presence of an additional mystery solute in the northern wood frogs, not shared by the local Ohio frogs, and are planning future research to determine its exact nature.

Applications for Medicine

Beyond being fascinating science, the ability to freeze and unfreeze living organs and tissues without damaging them has potentially profound implications for areas such as organ transplantation.

“There’s an obvious parallel between what these frogs are doing to preserve all of their tissues simultaneously and our need to be able to cryopreserve human organs for tissue-matching purposes,” said Costanzo, noting that attempts to successfully freeze human organs for transplants have so far proved unsuccessful, perhaps due to their relative size and cellular complexity.

“If you could freeze human organs even for a short period of time, that would be a major breakthrough because then these organs could be shipped around the world, which would greatly [improve] the donor-matching process,” noted Costanzo.

And that, ironically, is a heartwarming thought.

Follow Stefan Sirucek on Twitter.


  1. chris c
    United States
    February 4, 10:14 pm

    Costanzo talking about cell shrinkage in the cold….that’s one letter off from being a Seinfeld episode

  2. Steve Novotny
    January 5, 7:56 pm

    Joseph and space enthusiasts! This would not work on the human body because we need to maintain a specific temperature to be healthy (98.7) even if we had a lower freezing point we would be long dead before we were frozen. Frogs are cold blooded wich means that their temperature as a whole changes with the enviornment. We are warm blooded witch means that we maintain our own temperature unless we are sick.

  3. joson joy
    August 27, 2013, 11:28 am

    if we are able to determine the mystery solute it will be a great about sythesising the solute,how it help humans? PLEASE I NEED A REPLY

  4. stay curious
    United States
    August 27, 2013, 4:51 am

    amazing…I wonder what happens to the brain, like can it stop like the other organs or drift into a hybernation.

  5. roel cagoco
    August 26, 2013, 6:21 pm

    how about the genetic formation of this wood frog,are there any similar genetic formation to human?try to find out

  6. joseph
    August 26, 2013, 1:58 pm

    this is great! how about a whole human body eh would it work on humans alive wahahha

  7. Orbitcoin
    August 26, 2013, 10:50 am

    This is great news for Orbitcoin and space colinization.

    We was planning to research moss as that can come back to life after 1000’s of years, guess a combination of the properties of moss and the properties the Arctic wood frog, Could be massive for cryogenics.

  8. Alex
    August 22, 2013, 9:08 pm

    Trying consanguinous experiments with a frog that is not freeze-tolerant could also be interesting to see if the cryoprotectants are transferrable (via blood)

  9. Alex
    August 22, 2013, 8:58 pm

    Enabling long-distance space travel could be killer app.

  10. Adeel Hasan
    August 22, 2013, 4:21 am

    i belive its crhoprotectants fluid in them, which lowers the freezing point.. How about these frog when the sunny season start, they may have different mechanism for this, when the begin to rise how fluid get cold, how they accomplished homeostasis..

    And my main point is about their heart beat activity,how thier heat acticity is reduced or stopped for a days, have u study or researched about the harmones that reduces or stop activity for days.. And what chemical that again starts heart activity..

    Looking forwad to your reply..
    At my email..