What are adders up to now?

Blog by Samuel Betts, Conservation Officer

An adder’s activity at this time of year, just like with their spring emergence, will vary with climatic conditions. From mid-September to October adders make their way back to their hibernation sites (known as hibernacula) and move underground to hibernate. Technically speaking, instead of hibernating adders brumate, sometimes emerging on warmer days from their hibernation sites to bask, but for the rest of this blog, I will use the term hibernating.

During the summer months, males, non-breeding females and juveniles explore their habitat and disperse to summer feeding grounds. These tend to be wetter areas where there is an abundance of prey. Gravid, or pregnant, females often avoid eating preferring to stay close to their hibernacula throughout the summer. When the live young are born in August or September, they follow secret scent trails left by the adults to locate a nearby hibernacula. From mid-September to October, is a key time for conservationists as adders return to hibernacula sites. This is an opportunity to discover more about adder populations because finding a snake at this time of year means that a hibernaculum could be close.

Over winter, adders will often hibernate communally, sharing the same hibernacula as Common lizards, slow worms, and sometimes small mammals. Hibernacula are typically located in the bases of trees, brash piles, under masses of decayed vegetation, in banks or disused animal burrows. Importantly, these areas must be frost and flood free. During hibernation, adders are vulnerable to predation, flooding and freezing. Hibernacula can be extremely difficult to find, sometimes appearing like just a small hole in the ground and, as a result, they are vulnerable to accidental destruction. Because a hibernaculum can be home to multiple adders and other species, it is important to identify these critical habitat features so they (and the adder population that depends upon it) can be preserved.

Once the adder has returned to the hibernaculum, it will move up and down within the depth of the structure, adjusting to the varying external temperatures – deeper when external temperatures are colder, and closer to the surface when external temperatures are warmer. Adders may emerge on warm, sunny, winter days – some individuals have even been observed basking on snow. Adders are the only snake species in the world that can move on snow.

Throughout Europe, including in parts of Britain, observations are showing that adders are now becoming active every month of the year in response to external temperatures. The impact of this trend on adder populations is currently unknown. It raises the question: how will adder populations function and/or survive in the landscape without the cues to hibernate?

Adders re-emerge from hibernation around the end of February and early March, depending on the weather. Males emerge first and bask for extended periods of time to develop sperm ready for mating. Females and juveniles emerge from the hibernaculum a few weeks later, and mating will begin, moving into another year and lifecycle for an adder.

As always, please submit any records of adders you see to iRecord.org.uk or email them to Samuel Betts (samuel@northpennines.org.uk), Conservation Officer.