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Species native to the United Kingdom
Introduced or alien species
Alien species that present a threat to wildlife

Adder or Viper - Vipera berus - Native



Reptile - Venomous Snake

Distinct "V" or "X" shaped marking on head, also occasionally described as a "M" or "H" shape.

Vertically slit pupil

Dorsal surface and flanks, Very characteristic indented or zigzag stripe on the back, flanks usually have a row of dark oval spots.

The background colour is variable, from whitish or pale grey through yellows and to brown or brick red.

May appear very dark before skin shedding (sloughing)

Ventral surface, usually black, though may appear grey/brown of bluish.

Adder - identification - head from above

Original Image © Tony Phelps
Reptile Research & Imagery
Adder - Male Adder - identification - head

Original Image © Tony Phelps
Reptile Research & Imagery

Some colour variation occurs, the most distinctive features of the Adder are the dark or black zigzag stripe along its back and its squat or heavy bodied appearance.

Length: Typically males reach 60 cm Females 75 cm in the UK. It is often stated by observers that Adders appear larger than they actually are.


Males typically have a grey, creamy white or steely grey background colour. Females range from browns and yellows to brick red. Females are larger than Males.

Male Adder guarding his mate, showing colour difference and larger size of the female.
Adder - pair
© Tony Phelps Reptile Research & Imagery

Breeding and young

Males appear from hibernation in early spring, the females follow approximately a month later. Mating occurs in the later part of April and the first half of May. Males are territorial at this time and may occasionally be seen to duel or "dance" as a show of strength. Adders do not lay eggs, but give birth in late summer to approximately 8 live young that measure 15 - 20 cm. The young are contained in a membrane that breaks immediately after they are born. Adders usually only reproduce every other year in the UK.

Male Adders dueling in the Spring.
Adder - males duelling
© Tony Phelps Reptile Research & Imagery

What else could it be?

This snake maybe confused with the Grass Snake (Natrix natrix). The Grass Snake is a far more slender species and lacks the characteristic zigzag stripe of the Adder. The Adder may also be distinguished by its vertically slit pupil.

Sometimes the Adder is confused with the Slow-worm (Anguis fragilis), which is a leg-less lizard and not a snake at all. The Slow-worm is a smaller creature (40 - 45cm) with a glassy grey/brown appearance.

© Alan Hyde

Where will I see an Adder and is it dangerous?

The Adder has a wide spread distribution throughout the UK. Usually associated with open heathland in the southern regions, it also often occurs in dense woodland and in particular open areas within wooded regions, where sunny patches occur.

The Adder is the UK's only native venomous snake. Seeing an adder is no cause for alarm, these snakes are very placid and retiring creatures. People are usually only bitten during attempts to catch or handle them.

The venom is rarely fatal, the bite should however be taken seriously, and one should seek prompt medical attention if bitten by an Adder. Symptoms such as dizziness, vomiting and painful swelling and loss of mobility of the affected limb are not uncommon within hours of the bite. Do not attempt any form of first aid either on yourself or a victim of an Adder bite. The only helpful action is to immobilise affected limbs if possible and keep the victim calm and reassured, whilst medical attention is sort.

Adder bites are sometimes though rarely fatal to pets. Recent evidence suggests that the snakes venom is more potent during March/April after the animals leave hibernation, so extra caution should be taken when walking dogs at this time. Wear suitable footwear, keep dogs on leads and take care when sitting down in areas where Adders are known to occur.

The Adder is not a common garden visitor, though occasionally if conditions suit them they will take up residence.


Adders are protected under the Wildlife and Countryside Act 1981.

It is an offence to kill, harm or injure them

sell or trade them in any way

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