Ever wondered how the UK’s amphibians and reptiles keep themselves from freezing in this icy weather? As ectothermic animals (i.e. they cannot generate their own body heat like mammals and birds), they have to find other ways to keep the winter weather at bay. Keep reading to discover some incredible adaptations that three of our native species have evolved.

Unfrozen blood

Common lizards have “anti-freeze blood”! Glucose molecules have cryoprotectant properties that help to ensure these little reptiles do not freeze the water in their bodies when outside temperatures drop below zero. As the temperature drops, common lizards regulate their blood glucose levels which can increase two-to-five-fold. This helps them survive over particularly cold winters. A study found that they can maintain a body temperature of −3.5°C for at least 3 weeks.

Under the ice

Common frogs can be found overwintering at the bottom of ponds that have frozen over. As frogs (as well as other amphibians) have the ability to obtain oxygen through their skin, they can quite happily spend colder months at the bottom of ponds. However, this is a risky strategy that can potentially lead to frogs being trapped if the water’s surface remains frozen for too long, or other factors lead reduce the oxygen in the pond. There are a number of potential benefits to this strategy which makes it worth the risk to some. Firstly, the risk of drying out or desiccation is removed, and due to the thermal stability of water, frogs are less likely to risk freezing than if they were on land. There’s also the added advantage of being the first frogs in the pond when the spawning season comes around! See more about this in our "Where do frogs go in winter" article. 

Cold resistance

The adder is the northernmost snake in the world with a few sightings north of the Arctic Circle. This snake exhibits seasonal patterns of behaviour that help to keep it safe in these colder climates. This behaviour that helps the adder achieve optimal temperature even in cooler climates is likely achieved through altered circadian rhythms of activity and differences in the use of cover to that of its more southern relatives. In the UK, the adder hibernates between 150 - 180 days, with males generally emerging before females.

How you can help amphibians and reptiles this winter:

Making a space for them in your garden

Providing them with a garden pond

Submitting records to our monitoring programmes 

Creating habitat for them on your land


Relevant articles:

J Grenot, C., Garcin, L., Dao, J., Hérold, J-P., Fahys B., Tséré-Pagès, H., 2000. How does the European common lizard, Lacerta vivipara, survive the cold of winter? Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology. Volume 127, (1). Pp 71-80.

Inns, H., 2009. Britain’s Reptiles and Amphibians. Old Basing: WILDGuides

Beebee, T., 2013. Amphibians and Reptiles. Pelagic Publishing

Mallow D, Ludwig D, Nilson G (2003). True Vipers: Natural History and Toxinology of Old World Vipers. Malabar, Florida: Krieger Publishing Company.

Photo credits: Gillian Pullinger, Fred Holmes