Oh brrr! It’s much colder outside than I thought! I should have worn my heavy jacket! Squeaks, my friend, says he’s so cold that he feels like a “rat-sicle.” Have you ever said, “I’m freezing!” when you’re cold? I know I say that all the time, even though I’m not really frozen like an ice cube.
But did you know there’s an amazing animal that actually does freeze every winter? Yep! Wood frogs freeze when it gets cold. They really become “frogsicles”! Then, when it gets warm, they thaw out and hop away, perfectly fine. It’s a pretty sweet trick, and I’ll tell you all about it while we’re warming up!
For a lot of animals, staying out in cold weather for a long time can be bad news. That’s because bodies of living things have a lot of water in them. And what happens to water when it freezes? Yup! It turns into ice.
If we look at ice really closely, we can see that it’s made of tiny bits of frozen water stuck together in a fancy pattern. A pattern is something that repeats, like the hexagons in a beehive. In ice, the bits of frozen water stick together and make a special design that repeats again and again. We call this pattern a crystal.
Because it’s in that special pattern, water that’s frozen into ice crystals takes up more space than water that’s liquid. This is why it’s not a good idea to freeze water in glass bottles. As the liquid water gets colder and starts forming ice crystals, it gets bigger, so big that it can cause the glass bottle to crack!
If water is in an animal’s body when it freezes, it can cause a lot of damage—even if the animal eventually warms up and the water turns back into liquid.
But somehow wood frogs are able to freeze every winter and survive! In part, that’s because not all of the water in the frog’s body freezes. Only most of it does. So, even though the wood frog would feel hard as ice if you held it in your hands, parts of its body aren’t completely frozen solid! These parts are less like a popsicle and more like a slushie.
To keep from dying, the frog has to keep the water in some of its most fragile body parts, like its heart, liquid-y. And you might be wondering, how does it do that? Well, it fills those parts with sugar!
Yup, sugar! The same stuff that helps to make treats taste sweet can keep water from freezing quickly. You can even try this out yourself! Ask a grownup to help you get two identical plastic cups. You definitely want plastic here, so there’s no risk of broken glass!
Put the same amount of water in each cup. Then, mix several spoonfuls of sugar into one of the cups. Mark the cup with the sugar in it so that you don’t get the two cups mixed up, and put them both in the freezer. Check on the cups once every hour or so. You should see that the water without the sugar freezes much faster than the one with the sugar. Why do you think that is, Squeaks?
It’s OK not to know! It’s a tough question. Let’s think about what we do know: that ice forms when little bits of water get really cold and form a specific pattern called a crystal. So how might the sugar play into that?
Oh, that’s right! Sugar messes that pattern up! As the sugary water gets colder, the water part wants to form ice crystals. But the sugar literally gets in the way! Eventually, some of the water is able to make the pattern and make a small piece of ice. And these small pieces of ice manage to get together to make larger pieces of ice, basically pushing the sugar out of the way. But it does take longer.
As for our frozen frog, as long as enough water in the frog’s body stays liquid-y enough that its most fragile parts don’t form ice crystals, it can make it safely through the winter. Now, moving the sugar around its body is only one trick the frog uses to survive freezing. It also moves the water that does freeze into body parts that are tough enough to take it. And scientists think there’s even more to it than that, but they’re still trying to figure it out.
Ultimately, we know this frog’s super sweet tricks make it so that when the weather does warm up again, the frog can, too. And once the frog thaws out, it hops back to its usual life as if it was never frozen! Which I think is pretty… cool!
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Experiment with Freezing: Try the sugar and water experiment mentioned in the article. Ask a grownup to help you get two plastic cups. Fill both with the same amount of water, but add sugar to one of them. Place both cups in the freezer and check them every hour. Which one freezes first? Why do you think sugar affects the freezing process? Discuss your observations with a friend or family member.
Observe Nature: Go on a nature walk with a grownup and look for signs of animals preparing for winter. Can you find any frogs or other animals? Talk about how different animals might survive the cold. Do they migrate, hibernate, or use other strategies like the wood frog?
Creative Storytelling: Imagine you are a wood frog. Write or draw a short story about your adventure freezing in the winter and thawing out in the spring. What do you see and feel during this time? Share your story with your class or family.
