Garter Snakes in Winter

In winter, garter snakes are supposed to be hibernating. This presents some challenges when one turns up in your basement, or when you’re keeping them as pets over the winter.


Winter is not a time of year that people normally think about reptiles. In the northern hemisphere, at least, reptiles are out of sight during the winter months, and (at least in theory) ought to be out of mind. It’s no surprise to me, for example, that gets much less traffic during this time. And yet reptiles — and in particular snakes — can nevertheless make their presence known, even to those who don’t keep them in cages, in ways that can be baffling.

For example, once or twice each season, I get e-mails from people who encounter snakes in their basements. Usually they’re garter snakes, but not always. They have two questions for me: What is this snake doing down there, and what do I do with it? Or garter snake keepers write in to ask what to do with a snake that has mysteriously stopped eating.

Garter snakes do not go on hiatus during the winter. Whether in the wild, in your basement by mistake, or in their cages, there is still something going on.

Hibernation in the Wild

Reptiles in temperate climates hibernate. They have no choice.

But hibernation in reptiles — more properly called brumation1 — is quite different from hibernation in mammals. Reptiles do not sleep the winter away, nor do they live off their fat reserves. They are alert, if sluggish, and if it’s cold enough, they don’t even lose weight during the winter. How does this happen?

It comes down to their cold-bloodedness (or, more precisely, ectothermy).1 A cold-blooded animal’s body temperature depends on its surroundings: when it’s warm, its metabolism is high; when it cools down, its metabolism slows down. When a reptile hibernates, its metabolism has slowed down so much that it hardly uses any energy over the course of the winter. It doesn’t eat for months, but it doesn’t starve either.

Not hibernating is not an option. For one thing, there’s nothing for them to eat. Imagine a garter snake, magically able to withstand the cold, trying to find food in the winter. The ground is frozen, so there are no earthworms. The ponds are frozen, so fish and frogs aren’t available either. And even if it could eat, because it’s so cold out, a reptile’s cold-blooded metabolism is so low that its digestive system has shut down: even if it could find something to eat, it wouldn’t be able to digest it. The food would sit in its stomach and rot, with fatal consequences.

One advantage of being cold-blooded is that you don’t have to burn much energy over the winter. (In comparison, bears that don’t fatten up before the winter will be awfully skinny in the spring.)

But a reptile must do more than slow down its metabolism enough that it won’t starve. It must also avoid freezing to death. That means getting below the frost line. This is more difficult in the north than in the south. Snakes in the southern United States, for example, may only have to get into an animal burrow or a tree stump to get below the frost line. Here in Canada, though, it’s a bit more complicated. Snakes have to go a lot deeper to get below the frost line, and there aren’t that many choices for them. Where decent hibernating sites are few and far between, you get a lot of snakes hibernating at a given site — sometimes thousands of them. (This is why there are so many garter snakes at the Narcisse snake dens in Manitoba: there really isn’t anywhere else for them to go in winter, so all the local snakes end up there.)

Winter mortality among garter snakes is high — which is to say that a lot of hibernating garter snakes don’t make it through the winter. One Manitoba study pegged the winter mortality rate at as much as one-third to one-half of the population (Rossman, Ford and Seigel 1996, 79). (Now you know why garter snake litters are so big — they have a lot of catching up to do.) The problem is that some winters are colder than others, and that, as a result, a denning site that was safe for years may suddenly be lethally cold. This happened in 1999, when a major die-off of the Narcisse garter snake population was discovered. Because hibernating snakes are still active and conscious, they do have the option of going deeper as needed — assuming that that’s even possible at their den site.

Winter Visitors

So, when those snakes start showing up in your basement in the late fall and early winter, what are they doing? They’re trying to find a way to get below the frost line. For better or for worse, they’ve stumbled across your basement during their search. And here they are.

If you don’t want snakes (or other animals) in your basement, this is probably a sign that you have some cracks or other openings in your house that need filling. But in the meantime, you have a live, wild snake on your hands. Now what? You could release it outside, but it might be too late in the season for it to get to a proper hibernation site in time — in which case, you may be setting the snake free so that it can freeze to death.

But keeping it in captivity may not be possible either, especially if it’s a protected species or it’s not legal to keep in your area. If it is, however, you have a couple of options: keep it active during the winter, or hibernate it artificially. I’ll talk about both options later on in this article.

If you’re in this situation, it’s not necessarily easy or straightforward, and I’m sorry I can’t give you more clear-cut answers.

But what I can do is tell you about an experience I had a few years ago, when an Eastern Garter Snake (Thamnophis sirtalis sirtalis) was found in a snowbank and turned in at a local wildlife rehabilitation centre. Because the centre focused on mammals, they didn’t have any reptile expertise, and so, through intermediaries, the snake ended up in my hands.

Ken Storey, who has been researching the ability of reptiles and amphibians to withstand subzero temperatures, reports that some garter snakes can tolerate subzero temperatures for a few days, which is probably what happened here. My guess at the time was that this snake had been somehow flushed from her hibernaculum.

Because we didn’t know whether she’d been frostbitten by her experience, we made the decision not to hibernate her artificially. Instead, we kept her at regular temperatures, fed her (worm-scented mice and nightcrawlers; she showed no interest in fish), and released her in a conservation area the following May.

This decision was made based on this snake’s unique circumstances, about which you can read more here. What you should do in your situation will depend on a number of things. Is it early enough in the year that the snake can find another hibernation site? Is a known hibernation site nearby? Is the snake legal to keep? Is the snake dangerous? (I mean, it could be a copperhead instead of a garter snake.) Will the snake tolerate being in captivity? (Not every snake will; some will refuse to eat and starve rather than accept being in a cage.)

Hibernation in Captivity

Those who keep snakes deliberately have a different take on winter, and many snake keepers ask me whether they should hibernate their snakes artificially. Many authorities recommend it. Rossi and Rossi (2003) call hibernation

one of the most important things serious snake keepers do. This cool inactive period … is intricately tied to normal behavior, growth, feeding, and, of course, breeding of many reptiles. … We would strongly recommend either natural or artificial winter cooldown for all healthy, mature, temperate zone snakes. (37-38)

For breeding temperate zone snakes, hibernation is often an essential part of the reproductive cycle. But even if you’re not breeding your snakes, artificial hibernation may still be required.

As I mentioned before, a reptile’s metabolism practically shuts down over the winter. Among other things, it’s too cold for it to digest food; undigested food will sit in its stomach and putrefy. To prevent that from happening, reptiles go into hibernation on an empty stomach, and prepare for hibernation by stopping eating several weeks ahead of time.

While many reptiles ignore this biological imperative in captivity, some continue to go off their feed in the fall. They may be triggered by the fall’s cooler temperatures, but even if you keep them at a constant temperature, they may be triggered by the change in light levels or the length of the day. For whatever reason, they stop eating, requiring artificial hibernation to prevent them from starving over the winter.

This can be problematic for keepers who aren’t prepared for it. For most keepers, the decision to hibernate or not hibernate is largely based on whether they have the facilities to do it. Many of us simply don’t have access to a place cold enough for hibernation. If you have a fruit cellar or cold corner of the basement, a partially insulated garage, a drafty part of your home, or even an old refrigerator, you may be able to provide temperatures cold enough for your snakes to hibernate. Use a thermometer and see.

How cold is cold enough? Opinions vary, but 12°C (53°F) seems like a good starting point, give or take a few degrees. Northern snakes will probably want it colder yet; some Canadian snakes have been observed in the wild at single-digit temperatures. Southern snakes, on the other hand, may not need it quite so cold.

If you cannot provide these temperatures, you may not be able to hibernate your snakes successfully: too cold (for example, an outbuilding that gets below the freezing point), and your snakes will freeze; too warm, and their metabolisms won’t slow down enough, and they’ll lose weight.

Again, my own experience may help illustrate this point. I once lived in a drafty firetrap of an apartment in Ottawa’s Chinatown — a terrible place to live, except that it was perfect for reptile hibernation. My bedroom closet, for example, got as cold as 12°C — and that’s where I hibernated my garter snakes, the ones I was hoping to breed. Hibernation helps both male and female fertility, and my snake breeding attempts were successful when I was hibernating my snakes in that apartment. Ever since I’ve moved away, however, it hasn’t been the same. I couldn’t get the snakes cold enough to do any good (their fertility was reduced, and they lost weight), so I simply gave up and stopped hibernating them, figuring that it was better to feed them up over winter rather than hibernate them at too warm a temperature. Either way, I haven’t had a successful litter of snakes in more than two years.

I’ve been fortunate in that all of my snakes continue to eat throughout the winter: none of them are forcing me to choose between hibernating them or letting them starve. But there’s nothing more stressful for a snake keeper to have his or her snake suddenly stop eating when you don’t know how to hibernate it.

But hibernation may still not be required. If you’re keeping a garter snake and it suddenly decides to stop feeding, try resetting its appetite. A garter snake that has been trained to eat mice may sometimes refuse to eat them when fall comes, but it often turns out that it’s not that they’re not interested in eating, but that they’re not interested in eating mice. Changing its diet to fish or worms for a couple of feedings is sometimes enough to reboot its appetite, and it will be back on mice shortly afterward. I wrote that article three years ago, and what I wrote then still holds true: this past fall we were using the method to reset the appetite of several of our garter snakes.

If that doesn’t work, and you have a place you can hibernate your snake, then you will have to hibernate it artificially. See the Hibernation section of my garter snake care guide for more information.

Throughout this process, when you’re pulling out your hair trying to deal with a recalcitrant feeder, remember that garter snakes from temperate regions are hard-wired for winter survival. Not eating during winter is a means to avoid the putrefaction of its stomach contents, the same way that turning up in your basement is a means to avoid freezing to death. Garter snakes aren’t smart enough to be irrational.


  1. “Brumation” and “ectothermy” are the correct terms for reptile hibernation and cold-bloodedness, but I will use the latter, more familiar terms to keep things from getting too technical.


CBC News. 1999a. Concern Grows over Fate of Snakes.

———. 1999b. Tens of Thousands of Red-sided Garter Snakes May Be Dead in Dens.

Crowe, Jonathan. 2001. A Tale of Two Snakes. Chorus 18(10).

Rossi, John V. and Roxanne Rossi. 2003. Snakes of the United States and Canada: Natural History and Care in Captivity. Malabar FL: Krieger.

Rossman, Douglas A., Neil B. Ford and Richard A. Seigel. 1996. The Garter Snakes: Evolution and Ecology. Norman OK: University of Oklahoma Press.

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