Snakes are cold-blooded animals, or ectothermic, as they get their temperature from their environment and cannot generate their own body heat. While this can be beneficial, the downside of being a cold-blooded animal is the struggle to survive in a cold environment. Incidentally, if the outside temperature drops sharply, their body temperature can also drop to temperatures that are life-threatening.
Species that live in habitats where the winter months are inhospitable remain safe in the form of hibernation. Although reptilian hibernation is different from mammalian hibernation on a physiological level – in fact, it is often referred to by scientists with the term “brumation,” instead—follows pretty much all the same principles: If it’s too cold to prey and mate, you need to rest.
“Why waste energy? If you’re not able to feed and you’re not mating, you can also take advantage of the fact that you’re an ectotherm and that you can get really cold and still survive,” says Matt Good, assistant research scientist in the School of Natural Resources and Environment of the University of Arizona.
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Snakes hibernate depending on their habitat and geography
Not all species of snakes need to hibernate – it depends on where they live. Species living in tropical regions typically do not hibernate, according to Goode, although they may have periods of lower activity and dormancy related to other environmental factors, such as drought or dry seasons. This is the case with anacondas, for example, which are native to warm, tropical climates.
“But in temperate regions, snakes can spend many, many months underground,” says Good. His first research focused on prairie rattlesnakes in Wyoming, where temperatures can drop to 5 to 10 degrees Fahrenheit in the winter and the ground can freeze up to 5 feet deep.
“Snakes have to fall under that,” Goode says. “If they don’t, they might freeze and not make it through the winter.” Tiger rattlesnakes begin brooding in late October to early December, while western diamondback rattlesnakes, which are slightly larger, go into their dens a little later than that time.
How do snakes hibernate?
Since snakes derive their heat from external factors such as sunlight, when temperatures begin to drop, they will physiologically experience a drop in their body temperature as well. As colder days become more frequent, snakes will begin to eat less and will slow down their metabolism and heart rate to conserve energy. They will move less and stay as still and calm as possiblealmost grinding his body to a halt.
“Because snakes spend so much time not moving around, their heart rate goes down a lot, it goes down a lot, and their breathing rate, of course, goes down a lot,” Goode says.
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They then find a place to stay safe and warm throughout the cold and take a nap while the cold lasts. In fact, they rest more and take a nap than deep sleep, because they can still spawn outside the lair if needed – like basking in the sun to keep warm or fight off an infection. Their internal storage of glucose will help them jump back into action if needed in an emergency.
Where do snakes hibernate?
Snakes usually hibernate in what scientists call a hibernaculum, also known as a den. “[A snake is] hiding wherever it has the ability to buffer those cold temperatures from the outside,” says Good.
This is usually in holes deep underground, under frost and part of the ground that is frozen. But snakes can also hibernate in tree hollows and rotting logs, tree roots, burrows, tunnel systems dug by other animals, railroad embankments, water-filled cisterns, houses, basements, and sheds intended for humans. In some cases, smaller snakes would like to spend the winter deeper underground than larger snakes, and some snakes like to return to their den as they age.
Often these dens can house hundreds, if not thousands, of snakes at once throughout the winter – both adult snakes and young snakes, sometimes even of different species. In Canada, for example, Good explains, garter snakes have been known to hide in dens with over 20,000 garter snakes in one place.
“A limiting feature of their environment is finding that really good spot that allows them to get underground and avoid freezing,” Goode says. It is also beneficial to hibernate in large groups because this helps produce heat as a group of snakes intertwine and keep the group warm.
Scientists suggest that dens also serve a social function
“It may have some social function [hibernating in a den] too,” says Goode. He argues that the evolution of snake social systems, for example, may have come from the fact that large groups of snakes were essentially forced to congregate underground.
“It’s not like snakes want to hang out with each other, right,” Goode says. “But some species actually, when they come out of the den, they stay at the den site above ground, and then you see social interactions happening.”
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Diamond rattlesnakes do this for example. But other snakes, such as tiger rattlesnakes, hibernate completely alone. They have no interaction with other species or other individuals of their species until later after they have moved away from the lair.
Especially for snakes that live in places where it is cool for a long time, hibernation becomes a crucial part of their life cycle. It underlies many of the hormonal mechanisms that later allow them to reproduce successfully (this is why snake breeders will also subject their snakes to brumation, even if it is not required).
For example, brumation comes as an advantage to the longevity of ectotherms. Goode studies rattlesnakes are long-lived relative to their body size, particularly because they have evolved to be great at conserving energy.
“Being able to fall for extended periods of time like that really allows them to live longer lives and reproduce more,” says Good. “If we were ectotherms, with our large body sizes, we would probably live to several 100 years.”