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Adder fact file

By George Wykes

Spring and early summer are important times for adders. Males need to maximise basking time to prepare for the mating season. If you come across an adder please don’t disturb it. This interrupts basking behaviour and reduces their ability to prepare for the mating season. 

© Image by James Common from Pixabay Fact File

Meet the UK’s only venomous snake, the Eurasian Adder

Latin name: Vipera berus

Size: Size ranges from 60-80 CM

Lifespan: Adders have a maximum natural lifespan of around 15 years with some reports showing this could even go as high as 30 years.

Diet: Adders are opportunistic predators and will take a range of prey including amphibians, lizards, small mammals, and even ground nesting birds.

Sexual dimorphism: In both male and female adders, the classic zig zag patterning on the back is present. The differences in sexes come from the coloration of the animals. Females can be distinguished from males due to a slightly reddish-brown coloration. Males in comparison, are greyish in colour.

Current legal protection: Adders are protected by 1981 Wildlife and Countryside Act and listed as a priority species under the UK Post-2010 Biodiversity Framework. This legislation however does not protect hibernaculums and as a result means it remains legal to destroy an area where adders are hibernating.

Distribution: Adders have been recorded across the majority of the UK however they are absent from the Scottish Isles, the Channel Isles, Northern Ireland, the Isle of Man and the Isles of Scilly.

Population trends: There is widespread concern for adder populations across the UK. A recent publication by Make the Adder Count has shown significant declines on known adder sites with small populations while larger populations showing a very minimal increase. This data suggests that unless this trend does not change within 15-20 years adder populations in the UK may be restricted to be a few large populations further heightening the risk of UK extinction.

Habitat: Adders have a preference for peat and light soils that are present in association with moorland grasses, bracken and gorse.

© Helen Williams

Yearly life cycle

Hibernation  - October- February/March. 

This is the hibernation period of adders however interestingly, unlike mammals, adders may not remain completely inactive within this time period.  If temperatures temporarily rise, adders may make a brief appearance above ground and reports of adders being spotted in the snow have been confirmed!

Emergence  - February/March- Mid May.

This is the time adders emerge from hibernation however the exact timing of this behaviour is entirely on temperatures. Males emerge first followed by females with the juveniles the last to emerge. Following emergence, a lot of activity takes place around the hibernaculum. In preparation for mating males bask at every chance they can, this helps to grow sex cells and encourages the growth of new skin. This is followed by shedding their skin (a process known as sloughing). At this time, the males have stunning coloration and need to be in peak condition in order to attract a mate.

Mate guarding and combat.

Having found a female, the male will coil around her and “guard” her for up to several days until mating takes place. During this time it is unlikely the male will remain unchallenged however and what follows has been named “The Dance of the Adders”.  This involves chasing and raising the front half of their bodies against each other. The aim of this behaviour is to force their competitor back to the ground. The victor, having seen of their rival, will return to his chosen female.

©Image by Meatle from Pixabay

Dispersal -Mid-Late May.

Following the mating season, the majority of adders will disperse to their summer feeding grounds. How far the individuals disperse depends on how suitable the habitat is around their hibernaculum. If basking sites and opportunities for cover are nearby, dispersal is close however if conditions are not suitable then dispersal may be up to 2k. Pregnant females are less likely to disperse, whereas females that have not mated may also move onto summer feeding grounds.

Returning to hibernation site September

In September, adders will return to their hibernaculums with the females incubating their eggs internally before three to twenty young adders make their first appearance into the world.

Hibernation -October

The final stage of the adder’s yearly cycle, with temperatures dropping, young adders are the first to enter hibernation soon followed by the adults. They will not emerge completely until the following Spring.


Threats: Pressure and disturbance from the general public has been identified as the predominant negative factor on adder populations. Habitat fragmentation and poor habitat management have also been identified as significant threats to UK adder populations.

How you can help:  March to the middle of May marks a crucial time for adders, in particular males who use the lying out period to bask as much as possible in preparation for the mating season. One of the main challenges they face during this time comes from well-meaning people intrigued by their beauty and hopeful of getting the perfect sighting or the perfect picture. Intentionally disturbing the adders with innocent intentions or not seriously disrupts male’s ability to bask and as a knock-on effect, may negatively impact breeding success rates.  We’re not saying don’t enjoy these beautiful animals but please if you see them give them plenty of space and appreciate them from a distance. For your own safety and their protection, do not attempt to move them for the perfect picture – a bite from an adder is serious and will require a hospital visit.

© Image by Ian Lindsay from Pixabay

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