Natural anti-freeze? – How Ontario’s frogs & toads survive the winter 

During the summer, we are likely to see many frogs and toads hopping around ponds and wetlands. Come wintertime, they seem to disappear. So, where do these critters go? 

Similar to turtles, most frogs brumate at the bottom of ponds, where the water is cold but not frozen. Unlike turtles, frogs cannot bury themselves in mud underwater as this will clog their skin, which they use as one big lung! Amphibians have thin skin with lots of blood vessels, which allows oxygen to diffuse through the skin and into their blood vessels and carbon dioxide to diffuse into the water.  

Frogs can survive this way during winter as long as there is enough oxygen in the water to “breath”. As a refresher, cold-blooded animals like frogs have decreased metabolisms when they brumate, meaning they need less oxygen than they would in warmer temperatures. Luckily for frogs, cold water contains more dissolved oxygen than in warm water. When water is at higher temperatures,  the water molecules move faster, which causes more oxygen to escape from the water than when water molecules are cold and slow moving.  

Green frog underwater. Photo taken by Tharusha Wijewardena. 

Do all frog species spend winter underwater? The answer is: no! Some of Ontario’s frogs spend more time in forests than in ponds, and these species have a different approach for winter – their body freezes!

One example is the wood frog, which you can identify by the tan or reddish body and dark mask across its eyes. They brumate under tree bark, logs on the forest floor, or under leaf litter. When it starts to get cold, they produce special anti-freeze proteins in their blood. This allows their body to freeze and safely thaw in the spring without damaging delicate tissue. Shockingly, the wood frog can withstand 60% -70% of water in their body freezing, and a consistent temperature of -6°C.

A frozen wood frog. Photo taken by Janet M. Storey & retrieved from Royal Ontario Museum 

The wood frog isn’t the only species to use this approach. Other species in Ontario that do this are the three treefrog species: the gray treefrog, spring peeper, and chorus frog. It’s no wonder that these are some of the first frogs to begin calling in the spring!  

Spring peeper 

Now we know what frogs do to survive the winter, but what about toads? Toads spend more time on land than frogs, so you can imagine they might spend winter on land as well. While this is true, they don’t have the same ability to freeze their body like wood frogs.  

Toads have a yet another approach! American toads will dig deep underground using their hind feet, which have hardened knobs that act like shovels. They must dig over 50cm, or below the frost line   to ensure they don’t freeze. This is a similar strategy to overwintering snakes, which you can read about in our next blog!  

American toad 

All these methods of winter survival are pretty neat, but there are ways that humans can help these critters out. Since we know frogs can use leaf litter and old logs to brumate, we can help them by simply doing less yard work! That’s right, all the energy put into cleaning up the yard during fall can be put elsewhere. By doing nothing, you are actually saving many critters’ lives! So, sit back and relax this season, nature will be sure to thank you! 

Thick snow also helps to insulate the creatures hibernating on (or under) the ground. Unfortunately, climate change has been reducing the amount of constant snowfall in southern Ontario. By taking action to help tackle climate change, you’ll also be helping these critters survive the winter!