Adder guide: how to identify, what they eat and how to avoid being bitten

The adder is the UK's only native venomous snake, and is actually the smallest snake species found here. Adders are more likely to flee than attack, unless they are stepped on or feel very threatened.

An 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.

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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.

Learn more about this beautiful and misunderstood species in our expert guide by herpetologist Steve Allain:


What is the scientific name of the adder?

The adder’s scientific name is Vipera berus and is closely related to 25 other species of vipers found across Europe and Temperate Eurasia. Three subspecies are recognised across the range of the species, with the nominate subspecies being the one that everyone is familiar with.

The adder’s common name comes from a mispronunciation of an old English word ‘nǣddre’ (pronounced nadder) meaning serpent.


How to identify adders

It may be a surprise to many to learn that adders are the smallest snake species found in the UK. They grow to an average length of 60 cm in length which is slightly smaller than smooth snakes and half the size of barred grass snakes, the other two snake species found in the UK. Larger individuals are known but these are few and far between.

Adders are sexually dimorphic meaning that males and females appear differently. Males are light grey or silver in colour with a black zig-zag running down their back. In contrast, females are light brown or copper colour with a dark brown zig-zag running down their back.

Both may have a ‘V’ or ‘X’ mark on the back of their head and possess vertical pupils. There is of course the chance that you may encounter a black adder, which are usually female. Adders are perhaps one of the most exotic looking native species found in the UK.

An entirely dark melanistic female lacking any apparent dorsal pattern. © Arterra/Universal Images Group/Getty
An entirely dark melanistic female lacking any apparent dorsal pattern. © Arterra/Universal Images Group/Getty

Where do adders live?

Adders are found throughout much of England, Scotland and Wales (but absent from Northern Ireland and the Republic of Ireland), and throughout most of Europe. They are the most northerly found snake with a distribution into the Arctic Circle. It may be argued that across the wider landscape that they have the largest distribution of any snake being found from the north-west corner of France all the way through to the Far East including north-east China.

Adders can be found in a large number of habitats such as heathland, open woodland, chalky downs, rocky hillsides, moors, meadows, coastal dunes, and stone quarries.


What do adders eat?

The diet of the adder can be varied depending on what habitat they are found in. In most, the diet consists mainly of small mammals such as voles and mice, however larger animals may even take rats. Other reptiles such as lizards and slow worms are often on the menu too.

The diet of adders not only depends on the location, but the size of the snake too. Generally speaking larger animals will take larger prey but this also gives them the ability to reach food sources that smaller snakes may not be able to including nestling birds and eggs.

A European nightjar at nest in threat display towards an advancing adder, in North Norfolk, England, UK. © David Tipling/Education Images/Universal Images Group/Getty
A European nightjar at nest in threat display towards an advancing adder, in North Norfolk, England, UK. © David Tipling/Education Images/Universal Images Group/Getty

On rare occasions adders have been recorded to each amphibians such as frogs and newts. As an opportunist, they will eat whatever comes their way although once they reach roughly half their adult size, the diet of younger snakes resembles that much more of larger and more mature adults.


What eats adders?

The flipside of the coin, what does eat adders? Surprisingly, adders are mainly predated on by birds such as corvids, birds of prey (like the buzzard) and pheasants. The smooth snake feeds primarily on other reptiles and so adders are sometimes on the menu. Other predators include mammals such as badgers, foxes and feral cats.


Are adders venomous, and are adder bites fatal?

Adders are infamous for being the only venomous snake found in the UK. This often creates a sense of fear and animosity surrounding them, which is completely misplaced. Adders are much likely to flee from a fight than envenomate a person, due to the expensive metabolic cost of producing the venom. They’re extremely unlikely to attack people just for the sake of it.

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

In those that are unfortunate enough to be bitten, these tend to occur on the feet and ankles where snakes have accidentally been disturbed as people are walking through a habitat and stood on a snake. This can also happen to dogs that are off the lead in areas where adders are to know to occur.

In both cases the fatality rate due to adder bites is low with the last death in the UK recorded in 1975. The young and old are at particular risk but as long as medical treatment is sought immediately after an envenomation (both human and canine), then the damage caused can be minimalised.

In most cases the bites cause no more pain or damage than a bee or wasp sting, however some people can have an allergic reaction. The same can’t be said for their prey, that often succumbs to the venom fairly quickly due to their much smaller body size.


How do adders deliver the venom?

Like other vipers, adders have hollow fangs that they use to deliver their venom deep into tissues and blood vessels where it can set to work. These are connected to their venom glands which help to deliver venom when the snake attacks prey.

Without any limbs to help immobilise it and being too stocky to effectively constrict their prey, vipers have opted for chemical warfare instead. There is evidence to suggest that venom in snakes evolved from saliva and has been acted upon by natural selection since to produce the wide variety we now see today.


Do adders hibernate?

Yes, adders like all of our native reptiles hibernate between around October and March. During this time, they congregate in areas known as hibernacula which act as a frost-free refuge until the following spring.

This means that inadvertent damage to a large hibernaculum, can be catastrophic for a small population especially if they are isolated from others.


When do adders breed and what is the adder dance?

Following hibernation, males are the first to emerge. It is crucial that males bask in the sun if they want to successfully breed that year. They spend up to two months basking in order to maintain their metabolism so that they can start to produce sperm after the winter slumber. Females will then emerge in late April-May with reproduction on their agenda, by which time the males should be ready.

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At this time, snakes may be seen ‘dancing’ with pairs of snakes entwining themselves around one another. This isn’t part of the courtship but is instead males fighting territorial disputes over females by wrestling, with the stronger and larger snakes winning over the smaller ones. The victor of the duel will then mate with the female and may spend a couple of days with her.

Two male adders fighting over a female, known as an adder dance. A male will try and push the rival male to the ground as they twist and rise together. Holt, North Norfolk, UK. © David Tipling/Education Images/Universal Images Group/Getty
Two male adders fighting over a female, known as an adder dance. A male will try and push the rival male to the ground as they twist and rise together. Holt, North Norfolk, UK. © David Tipling/Education Images/Universal Images Group/Getty

Do adders lay eggs or give birth to live young?

As a reptile, you’d expect adders to lay eggs. However only half of our native reptiles species lay eggs, including the grass snake.

The other half like the adder and the smooth snake give birth to live young, which is known as ovoviviparity and thought to be an adaptation to cooler climates. The name ‘viper’ is actually derived from the Latin for ‘live birth.’ Why risk leaving your eggs to fend for themselves when you can actively thermoregulate to incubate them internally?

Neonate adders are usually born in late August or early September and can be seen around this time. Most will not have their first meal until the following spring, which sounds like a long time to go without dinner. This behaviour is common in temperate reptiles. Shortly after birth, they find a location to hibernate to wait out the winter (just like the adults).


Are adders endangered?

Throughout their range, adders are listed as Least Concern by the IUCN Red List. This is mainly to do with the fact that they have such a large distribution range, however the story is different in the UK. As an island, snakes can’t naturally recolonise Great Britain from continental Europe and have unfortunately been declared extinct in a number of counties in England.

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

Habitat loss, persecution and agricultural intensification have all led to  population declines. Research published in early 2019 shows that in 20 years time adders may be restricted to a small number of sites as they are currently experiencing dramatic population declines. Smaller populations are most at risk of local extinction from the threats listed above with habitat fragmentation reducing genetic diversity, which creates further problems for smaller populations.

Adders are extremely sensitive to disturbance, particularly if they are males basking early in the season or females basking to incubate their internally developing young.

At no time should adders be handled or approached, this only increases the risk of being bitten. It is also illegal to kill, injure, harm or sell adders under the Wildlife and Countryside Act 1981.


Best places to see adders in the UK:

  • Carsegowan Moss, Dumfries and Galloway, Scotland
  • Feoch Meadows, Ayrshire, Scotland
  • Humberhead Peatlands, South Yorkshire, England
  • Wyre Forest, Worcestershire, England
  • Ash Woods, Surrey, England
  • Roydon Common, Norfolk, England
  • Winterton Dunes, Norfolk, England
  • Parc Slip, Glamorgan, Wales
  • Anglesey, Wales
  • Gower, Wales
  • Llyn Peninsula, Gwynnedd, Wales

Steven Allain is an avid herpetologist, photographer, researcher and science communicator. His research covers a range of topics, which most recently has involved investigating the population dynamics of grass snakes and the effects of ophidiomycosis. 

One of his main missions outside of his research is to communicate the growing need for interest in the conservation of amphibians and reptiles.

Steven also helps to engage members of the public through a number of different means such as via social media and podcasts, to answer their questions about amphibians and reptiles, whilst also reiterating whilst these two groups of animals are vital components of a healthy ecosystem.

Steven Allain
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Main image: An adder coiled up in moss. © Mark Smith/Getty