9 things you never knew about the adder

Discover fascinating facts about the adder, Britain's only native venomous snake.

Adder coiled up in moss. © Mark Smith/Getty

With its highly distinctive, viscerally thrilling pattern of diamonds on its back, the adder is one of Britain’s most exotic native species.


The adder is, after all, our only venomous snake – and venomous animals are normally associated with the tropics. Paradoxically, though, it’s also remarkable for being the world’s only snake found within the Arctic Circle.


Where does the adder’s name come from?

The snake’s common name is the result of a historical pronunciation error. The old English “nadder” became “adder” by the same route that “a napron” became “an apron”.


Do adders lay eggs?

Like other members of the viper family, adders are ovoviviparous – the eggs hatch within the mother and the young are born live. Indeed, the name ‘viper’ is derived from the Latin for ‘live birth.’


Are adders aggressive?

These are very timid snakes that bite only in self-defence during attempted capture or handling or if actually stepped on. A Scottish National Heritage survey found that over 50 per cent of adder bites were to the hand, compared with 38 per cent to the feet.


How do adders deliver their venom?

Like their close relatives, the rattlesnakes, adders have the most sophisticated venom delivery systems of all snakes. Their hinged, hollow fangs are capable of delivering venom deep into their victims’ tissues.

Adder (Vipera berus)
Adders are the UK’s only native venomous snake. © Mike Lane/Getty

Do many people get bitten by adders?

Britain’s only venomous snake bites hundreds of people every year, but has caused only 14 fatalities since 1876 (and none since 1975).

Though seldom fatal, adder bites can have nasty effects, including swelling, drowsiness, vomiting and diarrhoea, so you should always see a doctor straightaway.

Always keep dogs on the lead at known or suspected adder locations, and if you’re a photographer never try to edge too close.


Where can adders be found?

Adders occur in England, Scotland and Wales, but not Ireland. They range across Europe and Russia to China and Mongolia, northwards into the Arctic Circle, and up to 3,000 metres in the Alps.

Adders are increasingly rare in the north and Midlands due to agricultural intensification and development, though good numbers survive in areas such as the south-west and Wales.

Adders like rough grasslands, heaths and moorland, but anywhere with sunny spots for basking, dense cover for shelter and plenty of prey – small mammals, on the whole – will do.

Some of the best places to see an adder in the UK:

  1. Carsegowan Moss, Dumfries and Galloway
  2. Humberhead Peatlands, South Yorkshire
  3. Parc Slip, Glamorgan
  4. Wyre Forest, Worcestershire
Adder (Vipera berus) amongst pink heather flowers in the rural countryside of the UK.
Adder showing its distinctive diamond pattern on its back. © Nature Picture Library/Getty

Do adders bask?

You will see many British animals sunning themselves – a blackbird or robin resting with its wings outstretched on a lawn, for example. But for a reptile such as an adder, basking is a matter of life and death.

“Adders lack any biological means of self-regulating their temperature, so instead rely on heat from their surroundings,” explains expert Nigel Hand.

“Rather than calling these snakes cold-blooded, it’s more accurate to refer to them as ectothermic, from the Greek for ‘outside’ and ‘hot’.

“Their daily challenge is to raise their temperature to 25–30°C before they can be fully active, and the way they do this is by moving between sun and shade, a behaviour known as thermoregulation.”

It’s the male adders that rouse first from hibernation in spring.

“Their priority is to form sperm ready for mating with the larger, later-emerging females,” says Nigel. “So they spend one or two months mostly basking.

“Their last meal, perhaps a field vole, was probably as long ago as September, yet in the British Isles it usually won’t be warm enough for them to start hunting again until May. It’s amazing how long they can go without feeding.”

During summer you may also see gravid (pregnant) female adders basking, as the warmth aids development of their babies. Males, meanwhile, become harder to spot.

“After May, males prefer to bask in dappled shade and seldom venture into the open,” Nigel says. “They like to bask under a patchy canopy of bramble stems or gorse, or among dead bracken.”

If they find a secure spot, it’s not uncommon to find adders of either sex basking with slow-worms and other reptiles.


How big are adders?

Though metre-long specimens have occasionally been recorded, adult adders are usually about 60cm in length. They hunt small mammals, birds, reptiles and amphibians.


What is the ‘adder dance’?

The famous adder dance, in which pairs of snakes entwine themselves around each other and wrestle energetically, is often assumed to be a courtship ritual but is actually a duel between territorial males.