Adders are the most commonly seen snakes in the UK, mostly because they are less likely to move into cover if disturbed. They hibernate through the winter and emerge in early spring.
Like other reptiles, adders are ectothermic, meaning that they cannot generate their own body heat. As a result, they need to raise their body temperature to 25℃ to 30℃ before they can become fully active and will bask in patches of sunlight to raise their temperature. Pregnant females bask in the sun to aid the development of their young inside their bodies. In the UK, it is often May before daytime temperatures are high enough for adders to being hunting for food.
Read More: Adders and humans