The Mendip serpent

Phil Bruss, Area Ranger Phil Bruss Area Ranger
Adders do not like to be disturbed

The Mendip Hills are home to the rare and secretive adder. Find out more about these amazing creatures from our Area Ranger Phil Bruss. Phil works on the Mendip Hills and looks after the places they call home.

An adder's year

Male adders are the first to wake in spring, braving the surface again in February, where they lie in the sun, known as basking, to get themselves back into condition, shedding their dull old skins to reveal a set of glistening new grey-white scales, with a black zigzag down the spine.

A few weeks after the males emerge, the females follow. The females too take to basking and, like the males before them, can flatten their ribcages to increase their surface area and soak up more sun.

Their breeding takes places from April to May after they have improved in condition after hibernating all winter. After the breeding season adders move away from their hibernation sites to feed, this prevents them from competing for food.

In September and October, the adders will return to the hibernaculum, and gain condition before the long sleep. Soon after, in October or November, the snakes disappear below ground again, becoming cold and dormant for the winter season.

Winter is a time that adders, and all our reptiles, sit out. They are cold blooded, meaning they rely on the sun and other external heat sources to up their temperature and keep their bodily systems functioning. Naturally, winter is not a time for great activity.


Females emerge ready to find a mate in March. To try and mate males will coil themselves around females, jostling for position to lie as her partner. If two males are equally matched, they may engage in what is known as the ‘dance of the adders’, in which the two males reach their bodies up vertically (snakes are known for their core muscles) and twine around each other, each trying to force the other to the ground and assert their superior strength, like the skinniest wrestlers you’ve ever seen.

In autumn, basking for females has another purpose. In the chilly climate of Britain, laying eggs would be a risky strategy, as they could easily chill and die. As such, her extra girth is not just a flattened rib cage, but a brood of between six and twenty baby snakes. The basking helps to develop the young, and allows them to be born, live, around August next year.


Adders more away from their hibernation sites to feed. This allows them to find areas with more prey and prevents them competing for food. The average adder will survive on around five to ten kills per year, so flesh hungry ravenous killing machines they are not. Most of the summer will be spent in cover, basking and digesting. Frogs, newts, mice, voles and chicks are all on the menu, but never very many of any. Reptiles are often masters of minimalism.


Adders are the only venomous snake in the UK. Britain is not a country of threatening creatures, with most species that posed a danger to people being exterminated in our distant past and adders are, to many, a reminder that the countryside is not always the green and pleasant land we want it to be. I love adders for this. The bite of the adder isn’t that threatening. The recommendation if you get bitten is to seek medical attention, but the bite has the potential to cause serious harm only if you have an allergy to the venom, much like a bee sting. It is true that it can cause more harm to dogs if they are unlucky enough to get bitten, but the snake is far more likely to slither away unless very seriously harassed. In any case, it takes a lot of energy to make venom, and the snake doesn’t want to waste it. In fact, if hunting an animal that poses no threat in return (a frog for example), an adder with withhold its venom rather than waste it.

My advice would be not to worry about them, and not to go looking for them unless you’re surveying them. Take pleasure in knowing they they’re in the undergrowth, coiled fragments of the wilderness we’ve largely lost, but leave them to exist in peace, as they have for millennia, atop our beautiful, carefully managed hills.


Somerset in general, and the Mendip Hills in particular, are good sites for adders. For a species that is disappearing in large swathes of the countryside, the population in our county is fairly strong. The rocks of the Mendips are perfect for them, with limestone scree piles leading to small chambers where adders gather to hibernate (known as a hibernaculum). In some places, individual snakes can even pass the winter in mouse or vole burrows.

Our volunteers carefully monitor our sites for adders where we know they occur, in an attempt to identify their winter refuges and manage them so they provide cover and optimum basking opportunities.

Because the adders are so elusive, and so tied to their hibernation sites, it is very easy to miss them and do a great deal of damage. If you remove their cover, even as they hibernate, they become easy prey for buzzards and crows while basking or get regularly disturbed so they cannot gain enough condition to complete their life cycle. We do not shout about where they are, because they benefit greatly from peace and quiet, living life in the slow lane, where each snake can survive for up to a decade.

Even if you know where they are, and the fieldcraft needed to find them, this is how many encounters with adders play out, with the snakes only becoming visible as they move to escape the unwanted attention. Far more often, the snakes go completely undetected, which is often for the best as many people still harbour their own suspicion of these wonderful, misunderstood creatures.