Our only venomous snake, adders tend to like places also favoured by walkers and climbers. They may be more scared of you than you are of them, but what should you do if someone is bitten? Cory Jones of First Aid Training Co-operative explains.

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If you spend time walking or climbing in the British countryside, particularly in upland areas, there's a slim but real chance you may come across an adder—the UK's only venomous snake. They're not aggressive and rarely pose a threat to humans, but knowing what to do in the event of a bite is vital.

Spotting an adder

Adders are easily identified by the dark zigzag marking running along their back. Adults grow to between 40 and 70 centimetres in length and vary in colour from silvery grey to reddish-brown. A completely black form also exists, though it's much less common.

These snakes prefer basking in warm, open spots such as sunlit paths or rocks. If you see one, simply stop, observe from a safe distance, and let it retreat undisturbed.

Bites: When and why they happen

Adders will only bite if they feel threatened—usually when stepped on or cornered. Most human encounters end without incident, but curious dogs are more frequently bitten, sometimes with serious consequences.

First aid for adder bites: a calm, measured response

If someone is bitten, your priority is to remain calm and reduce their movement. Venom, if injected, spreads more rapidly when the heart is pumping harder, so keeping the casualty still can limit its circulation.

Here's what to do:

1. Reassure and immobilise

Encourage the person to sit down and keep the bitten limb still and positioned lower than the level of the heart. This helps to slow the spread of venom. Remove tight clothing, boots, or jewellery near the bite site in case swelling develops.

2. Clean, but don't interfere

Gently clean the area using water or antiseptic wipes. You can apply a cool, damp cloth to ease discomfort—but don't use ice, cut the wound, or attempt to suck out the venom.

3. Monitor and assess

Keep an eye on the casualty's breathing and responsiveness. Look out for signs of an allergic reaction or shock—such as difficulty breathing, rapid heartbeat, or fainting. These require urgent medical attention.

If symptoms worsen, call 999 or 112 and be ready to guide responders to your location using a grid reference or phone app like What3Words or OS Locate.

4. Leave the snake alone

Do not waste time trying to identify or catch the snake. It will have moved off quickly. While useful, a description isn't essential—doctors can run tests to confirm the cause of symptoms.

5. What next?

Keep the casualty sitting down for 10-20 mins. Once they have rested, and assuming they are able, walk them slowly out to the road. Then go to A&E to get them checked out.

Common signs of an adder bite

The effects of a bite can vary depending on the individual, the amount of venom injected, and the site of the bite. Typical symptoms include:

• Visible puncture marks (often two, but not always)
• Swelling, bruising or pain around the bite
• Tingling or numbness
• Nausea, dizziness or drowsiness
• In rare cases, anaphylactic shock

Note that adders sometimes give a "dry bite," where venom isn't injected. But since you can't tell immediately, always follow the same first aid steps.

Children and vulnerable adults

You should be especially cautious if a child, older adult, or someone with a pre-existing condition is bitten. Their bodies may be less able to tolerate the venom. In these cases, don't hesitate—call emergency services right away and clearly explain their age or condition.

How dangerous are adder bites?

Fatalities from adder bites in the UK are exceptionally rare. The last recorded death occurred in 1975. Today, improved awareness and faster emergency response mean that most bites result in little more than swelling and discomfort. Nonetheless, always treat a bite seriously.

Not sure it was an adder?

If you're uncertain whether the snake was an adder, don't worry. Medical staff can determine the cause of the bite with hospital tests. Other reptiles you might encounter include:

Slow worms – harmless legless lizards, smooth and shiny with a bronze tint.

Grass snakes – larger than adders and easily identified by their yellow and black collar; harmless.

Smooth snakes – rare and confined to southern heathlands, with subtle grey-brown patterns.

Escaped exotic pets are another possibility, though they're unlikely to be venomous.

Why first aid training matters

Incidents like adder bites highlight the value of good outdoor first aid knowledge. Knowing how to manage rare emergencies without panic helps everyone stay safe. If you spend time in the hills, getting trained in practical, scenario-based first aid is a smart move.

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About the Author

Cory Jones has been an International Mountain Leader for two decades and is a wilderness first aid trainer. He is a founder member of First Aid Training Co-operative which offer comprehensive first aid courses tailored to outdoor environments—whether you're a dog walker, a mountaineer, or a mountain leader. A little preparation can go a long way when the unexpected happens.