Female adder (Green)

Following a fantastic online talk by Suzie Collinson of Cumbria Amphibian and Reptile Group on Slow Worms and Adders, I was really interested to learn that Adders could be individually identified by their head scale pattern: like our fingerprints no two are the same. Unfortunately, it means that you need to take a photo at 90 degrees of their heads, luckily my local Adder hibernation site has lots of stony banks that sometimes allows good, close 90 degree views of them.


The Adder (Vipera berus) is the most northerly occurring snake in the world with their range extending into the Arctic Circle. They can be found almost across all of Britain (absent from Ireland, Orkneys, Shetlands, Outer Hebrides and the Isle of Man) in a number of habitats such as moorland, heathland and woodland edges. 

They hibernate through the coldest months (roughly October to March) emerging from their dry sleeping quarters, often a dry mammal burrow beneath rocks. Hibernacula (name of hibernating location) are usually located in areas of high ground, usually earthen banks with plenty of vegetation (bracken or heather). Adders usually emerge in March, although they can be seen as early as February if the weather is unseasonably warm. The males emerge from hibernation and stay for over a month, making them easier to find as they bask to build up their energy and produce sperm. This makes early spring the best time to see them during this period of relative inactivity. Adders slough (shed) their skins in April, this marks a change in behaviour as well as appearance and they become much more active.

Freshly sloughed male adder ‘blade basking’ (flattened at angle to get at close of 90 degrees to the sun’s rays and to increase their surface area to raise their body temperature more quickly.

So I started my survey on the 5th March, seeing only one male, then visiting for an hour almost every day, by the 2nd May I had 169 sightings and had managed to identify thirteen individuals, nine males & four females, all within a 150 metre radius. I was able to find five different hibernation sites within this area and was interested to see that the males and females hibernated separately, by the 18th April all of the males had abandoned their sites, some from across a beck and had moved to the two females sites.

Being a distinctively marked snake, they are not difficult to identify in the field, but can be very difficult to find when in dead bracken and the male and female adders can be separated by their different colouration. Male adders have a black zigzag pattern along the back, before they slough their skins they have a silver / grey body, but after they have sloughed and prior to breeding the body becomes a jewel like blue / green. Whereas, the larger females have a brown zigzag pattern and their body colour can vary between green, copper or brown.


Female Adders (Brown & Copper)    

On the 13th April I found my first of four sloughed skins and hopefully they can be DNA tested? Then on the 15th April I saw the first male of the year to emerge, which had just sloughed and he was mating with the brown female, avoiding having to be involved with any dancing. Amazingly I was then lucky enough to see a pair of males "dancing" on the 17th and another pair on the 19th.


Males dancing’ – Combat display.

This is when the males become entwined and can be seen ‘wrestling’, if an intruder male does not heed the warning signs, of hissing and aggressive lunges and backs off avoiding confrontation. During this combat I saw them travel over 15 metres and climb up vegetation to a height of 30cms. However, the snakes never made any attempt to bite each other and the victorious male (usually the larger snake) then chased the other male away at speed.

Adders only start to feed after mating has occurred and will travel some distance to hunt. They rely on a diet of small mammals, lizards, nestling birds etc but will also eat frogs. There have been high numbers of adders reported on the reserve this year, this is due to the very high numbers of voles last year (voles follow a natural cycle of peaks and crashes). The vole numbers are not looking very good so far this year, so this might affect next years’ numbers?

Like many people I always thought that Adders were "sun loving" however, I have seen them out in rain, hail & snow and the 23rd May was the only survey day when I did not see a single snake, as it was really hot with no wind whereas on the 30th April I saw eight individuals, when it was just warm.

The females only breed every other year and after spending the summer feeding the females will return to the hibernation site in late August / September to give birth. Depending on the female's size and food availability they will have between five to fourteen live young, as the eggs will break inside the female.

They do not use their nose to smell, but instead use their tongue and the Jacobson's organ in the roof of their mouth. Also, as they do not have an outer ear or eardrum, they are deaf. However, by placing their lower jaw on the ground they can transmit vibrations to an inner ear. This means that they can usually detect the vibrations of an adult human's footsteps, but can be surprised and strike out in defence if disturbed.    

So, although RSPB Geltsdale is a great place to see adders, it is recommended that people stick to the footpaths and to keep their dogs on leads. There are signs on the trails around the reserve alerting visitors to their presence, as most of the time the snakes can go undetected. If you have walked the trails around the office, it is likely you have been within metres of one these beautiful snakes!

Female adder (Green)

Adders are fully protected by law and it is illegal to harm or kill the snakes in any way. There are some great books about adders and lots of information on the internet if you want to find out more. Some information for this blog has been taken from Amphibians and Reptiles (New Naturalist) by Trevor Beebee and Richard Griffiths and The Adder by Peter Stafford.

Adam Moan May 2021