How do adders hibernate?

Flanders Moss NNR

We have seen the first of our adders appearing on the moss this past week. But how do these cold blooded creatures survive winter in the first place? Unlike hibernating mammals, reptiles cannot regulate their own body temperature – so how do they not freezing during, well, freezing temperatures?

The answer is mostly physics, with a pinch of mystery! Adders are a relatively understudied species given their abundance – they have the largest global distribution, as well as the most northerly range, of any snake species – they have even been found within the Artic Circle! Yet due to their secretive nature and sensitivity to disturbance, they are rather difficult to research.

What we do know is that adders like to hibernate in sheltered spaces known as ‘hibernaculum’- such as within fallen trees or abandoned burrows – and that they will often share these spaces with each other, sometimes dozens at a time! After all, a small space filled with lots of bodies is much easier to keep warm and insulated. Snow, surprisingly, acts as a pretty good insulator, and many hibernating animals are known to take advantage of this. Not bad for semi-frozen water! However, semi-frozen is the key. Hibernaculum’s must remain frost-free, without being accessible to predators or at risk from flooding. This is likely why adders usually hibernate underground, rather than within above-ground structures.

By early spring – or, as we have already seen, late winter! – temperatures will start to rise and the first adders will begin to emerge. They need to bathe in direct sunlight to warm up enough to first be able to mate, and in later months hunt for food. To provide the best chance of rapid warming, most hibernacula sites will also be south facing – providing the best access to sun throughout the day.

Sound specific? Well, it kind of is! And it’s likely why we find that individual adders will often return to the same hibernation sites each year. If they’ve found the perfect spot to survive the winter, why risk trying somewhere new? This is also why we must take great care to not disturb or destroy known and potential hibernaculum sites – adder numbers are on the decline, and just one incident could cause a significant hit to local populations if several snakes are sheltering together.

A group of male adders
Photo taken by Ray Hamilton of the Amphibian and Reptile Conservation (ARC) free adder photo library.

So, when you’re out and about at this time of year and find yourself out on a mild, sunny day (yes – even in Scotland!), if you are lucky enough to spot an adder, keep an appropriate distance and enjoy the experience without scaring our scaly friends.

About Bethia Pearson

Stirling NNRs
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1 Response to How do adders hibernate?

  1. Anne says:

    Fascinating content – and what a marvellous sight to see so many adders at once!

    Liked by 1 person

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