1. Why a snake's weight stays the same when its body activity slows down
Animals like snakes are cold-blooded, meaning their body temperature changes with the environment. When winter temperatures drop, their body temperature drops too. This slows down chemical reactions inside the body and lowers metabolism, which is the rate at which energy is used [1]. For hibernating cold-blooded animals, this drop in temperature and metabolism acts as an energy-saving tool [1].
The experiment mentioned earlier shows this reduction in numbers. The standard metabolic rate (the minimum energy used while resting) dropped by 95% at 5°C (about 41°F) compared to 30°C (about 86°F). Furthermore, during the six-month hibernation period, the rate at 5°C dropped another 20% [2]. Because the body uses much less energy, it is thought that weight did not change even without food for half a year. However, this was a lab result with controlled temperatures and may not apply exactly to all snakes in the wild.
If slowing down movement is one way to save, what else happens inside the body?
2. Why a snake's gut shrinks when there is no food
When there is no food, the intestines have no work to do because they are not digesting or absorbing nutrients. In the same experiment, the weight of the small intestine decreased by 25% over several months of hibernation. The speed at which amino acids (nutrients that build proteins) were taken in dropped by half. When combining weight and absorption power, the gut's function fell by 65% [2].
These are different measurements: 25% refers to weight, and 65% refers to function. The researchers interpret this as the body lowering gut activity to save energy [2]. Keeping the gut active requires energy. By shrinking it while unused, the snake prepares for spring when food is available again.
So, snakes lower their movement power and shrink unused organs. This two-step process seems to keep their reserves from running out. But what are these reserves?
3. Do snakes use body fat or liver sugar as winter fuel?
Dictionaries explain that hibernation energy mainly comes from breaking down stored fat [1]. It is easy to assume snakes do this too, but research results are split.
A doctoral thesis studying Red-sided Garter Snakes in America reported that liver glycogen (stored sugar) was used before fat during hibernation. This contrasts with studies on mammal hibernation. The study also noted that when hibernated at temperatures higher than natural conditions, reserves decreased more [3].
On the other hand, a report on northern garter snakes found that body lipids (fats) decreased from autumn to winter, while water percentage increased [5]. Another study from 1985 stated that glycogen and protein in the liver and muscles made up most of winter energy, with no change in weight or fat. This contradicts the previous results. Since only summaries of these studies are available, specific numbers are not listed here [8].
There is also a study that is not about hibernation but about fasting. Three types of snakes, including ball pythons, were starved for about six months. They lowered their metabolism by up to 72%. They used fat first and did not start using protein until body fat reached about 5%. Many animals are considered at risk when body fat drops below 10%, so snakes are described as strong against fasting [4].
Fuel sources seem to change depending on the species and conditions. In hibernation studies comparing temperatures, reserves decreased more in warmer conditions than in natural ones. So, what really threatens winter snakes?
4. Why drying out may be a bigger winter danger than hunger
Until now, the discussion was about whether reserves would last. However, another experiment shows there is another threat to winter snakes.
In a study, Eastern Garter Snakes were kept in hibernation conditions (5°C or 12°C / about 41°F or 54°F) with varying humidity for up to 165 days. In this experiment, snakes placed in air died mainly from dehydration, while those submerged in water survived by keeping their moisture. According to the summary, weight loss in air was greater in warmer conditions [6].
This is an extreme experiment where snakes were kept until death, not a normal winter decline. The key takeaway is the direction of the results: in dry environments within this study, dehydration threatened life before starvation did, and it got worse as it got warmer. This is in the same direction as the finding in Section 3 that reserves decreased more at higher temperatures.
This paper was also read only in summary form. Checking the original text for experimental details is worthwhile.
5. How Japanese rat snakes hibernate in stable underground soil
What about snakes in Japan? Materials from Sapporo Maruyama Zoo state that Japanese Rat Snakes (Aodaisho) begin preparing for winter around September, burrow into the ground around November, and hibernate until mid-April. It is said they hibernate in soil where temperature changes are small [7].
Underground, temperature fluctuations are smaller, and protection from dryness is likely easier. This fits with the idea that temperature and moisture determine winter survival. Soil is a place where temperature does not change easily and dryness can be prevented.
However, these times are an example for Sapporo and may vary by region and species. The materials used here do not have numbers on how weight or fat changes during hibernation for Japanese species like the Japanese striped snake or Mamushi. The body changes discussed in this article are mainly based on overseas garter snake studies. Read with the understanding that it may not be the same for Japanese snakes.
6. Try it at home: compare how towels dry out with and without protection
You can test drying with towels. Wet two towels and wring them lightly. Leave one as is, and put the other loosely in a plastic bag. Touch them the next morning to compare. The one left outside will be drier. This is not a snake experiment, but it helps you understand that the towel inside the bag resists drying.
You can also look for resources. Check zoo materials or library books about snakes for sections on winter habits. If detailed changes in Japanese snakes' bodies are written there, you can compare them with the overseas studies in this article. If you see a snake outdoors in winter, do not approach or touch it.