How do adders hibernate?

Our blog today is written by Bethia, one of this year’s NatureScot student placements who will be spending a year based across the Stirling NNRs: Flanders Moss, Blawhorn Moss and Loch Lomond. Growing up on the doorstep of the Abernethy Forest NNR, she has always held a love for nature, following this passion to university where she graduated with a degree in zoology. Throughout this placement, Bethia hopes to increase her employability within the sector, with a focus on gaining practical conservation skills, developing an understanding of how nature reserves operate, and furthering her general knowledge of Scottish ecology and conservation.

We saw the first of our adders appearing on the Flanders Moss in March. But how do these cold-blooded creatures survive winter in the first place? Unlike hibernating mammals, reptiles can’t 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 Arctic 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. Hibernaculums 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.

Adders rarely bite humans. They are shy animals whose first line of defence is to simply get away. However, if they are disturbed suddenly, or trodden on, they can bite. Being Britain’s only native venomous snake arguably earns them a degree of notoriety. Although adder bites can be painful and have unpleasant side effects, they are rarely life-threatening. Nevertheless all snake bites require prompt medical attention.

This entry was posted in biodiversity, Flanders Moss NNR, Reptiles, Uncategorized and tagged , , , , . Bookmark the permalink.