Adders hibernate between November and February. They usually have their first moult soon after they have emerged from hibernation. When an Adder moults, it sheds or loses its skin. The old layer of skin separates itself from a new layer of skin which has formed underneath. The old skin eventually splits at the head. The Adder then rubs itself against plants so that the old skin can be peeled back inside out. An Adder moults its skin on average three to four times a year.

Even though the Adder’s skin is dry and cold to touch, its body temperature varies with the temperature of its surroundings. The ideal outside temperature for an Adder is about ten to sixteen degrees Celsius.

During the night an Adder can become really cold so it needs to sunbathe first thing in the morning to gain heat for its body. The Adder’s body temperature needs to be high enough for the Adder to be able to digest food and function properly. The sun doesn’t need to be shining directly onto the Adder because some of the sun’s heat can penetrate through the clouds.

An Adder often sunbathes near to a safe refuge. It doesn’t like to be too far out in the open. When an Adder basks in the sun, it sometimes lies on the ground sideways to get the maximum sunlight on its body. On very rare occasions an Adder will lie on its back to expose its dark underside to the sun.

When an Adder is disturbed, it usually just slides away in a wave-like motion to a safe place. Adders try to avoid being aggressive. It is only when there is no escape or when they feel very threatened that they may bite.