Preparing to be a “popsicle” in winter? Meet the wood frog!

Hi everyone!  This is Kelly from the Herpetology Department.  Y’all have probably noticed that the weather is getting cooler and the days shorter, which means winter is right around the corner.  If you are like me, and like going for hikes during this cooler time of year, you may notice you see fewer amphibians and reptiles (or “herps” as we like to call them).  Have you ever wondered how they stay warm in the winter?  Our native herp species have many “cool” adaptations to do this. 

As you may know, amphibians and reptiles are ectothermic, or “cold-blooded.”  This means their body temperatures are regulated by their environment, and they need external forces (like the sun) to maintain their normal body functions such as digestion, respiration, circulation, etc.  In the winter, it is too cold most days for them to maintain these functions, so most go into brumation, or a period of inactivity, until the weather warms up again.  They can shut down most of these functions, so they don’t need to burn up energy moving around looking for food.  They can just hunker down underground under a nice log, crevice, or burrow where they are protected from the elements and temperatures remain more stable, like a nice cozy blanket.  These winter hideaways are often referred to as hibernacula.  Sometimes, you might find a bunch of animals living all together in one hibernaculum.  Gopher tortoise burrows are notorious for housing not only the tortoise, but frogs, indigo snakes, mice, etc., all in one burrow!  Some snake species, like garter snakes, may have hundreds or even thousands of individuals brumating together in one location.  It’s a sight to behold in springtime when they all start to emerge out of the hibernacula together! 

One of the most fascinating adaptations, in my opinion, belongs to the wood frog (Lithobates sylvaticus).  These guys become literal popsicles in the winter!  They stop breathing, their heart stops beating, and their abdominal cavity fills with ice which surrounds their cells and internal organs.  As this is happening their liver starts producing a lot of glucose that floods into their cells and organs, acting like a type of antifreeze, which protects their cells from freezing.  Hidden right under the leaf litter, they can stay frozen like this for six to eight months.  Then in spring as the weather starts to warm, they will slowly start to thaw from the inside out. Beginning with their heart starting to beat again, then brain activity initiates, and finally the arms and legs will start to move.  It’s truly remarkable and one of my favorite adaptations! 

If you are interested, there are many amazing videos and timelapse footage examples.  My recommendations are from the Smithsonian Institute and the BBC’s A Perfect Planet with Sir David Attenborough. Thanks for reading!  And if you’re not under your cozy blanket all winter, come stop by Scaly Slimy Spectacular and learn more about other incredible herp species!

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(photo: Kelly G.)

Kelly G.
Lead Keeper, Herpetology