What do they look like?

The only poisonous snake in Britain is the adder. It is recognisable by the black, zig-zag stripes along its entire back and its red eyes with a vertical slit.

Why are they dangerous?

About 100 people in Britain get bitten by adders each year. The last time someone died was in 1975, but many of the people who are bitten have to be treated in hospital and take several weeks to recover. Some of them have to have the bitten arm or leg amputated. 

Adders will only use their venom as a last means of defence, and this is usually if the snake is trapped or trodden on. Many of the people bitten by adders in Britain are men who have foolishly picked them up! Most of the snakes in Britain are fairly harmless. Even though their bites can hurt a lot, they do not contain dangerous venom.

With proper and rapid treatment, the worst effects of adder bites are nausea and drowsiness, followed by severe swelling and bruising in the area of the bite.

Some symptoms of adder bites include:

  • Severe pain at the location of the bite.
  • Swelling, redness and bruising at the location of the bite, spreading up the bitten limb.
  • Feeling sick (nausea) followed by vomiting.
  • Diarrhoea.
  • Itchy lumps on the skin.

Any sign of drowsiness is a sign of more serious danger. 

As time passes, the site of the bite will become severely swollen and bruised. 

How can I avoid them?

Adders are relatively common in areas of rough, open countryside and are often associated with woodland edge habitats. They are less inclined to disappear into the surrounding undergrowth when disturbed and so are probably the most frequently seen of the three British snakes. The best time to see them is in early spring when they emerge from their hibernation dens. By mid April, the males have shed their dull winter skin and are ready to mate. There is a lot of frenzied activity on warm days, with males looking for females and occasionally wrestling with other males for supremacy.

  • You should regard all snakes as dangerous even if they are not adders. Even the bite of a non-venomous grass snake can be extremely painful and can lead to an infection.
  • Look out for warning notices on heaths and commons.
  • Wear boots and long trousers.
  • Never pick up any snake, even if you think it’s harmless or it appears dead.
  • Never put your hand in a hole or crevice (for example, between rocks) – if you need to retrieve something, stand well back and use a stick to reach it.
  • If you find yourself very close to a snake, stand completely still – most snakes only strike at moving targets, so the snake will escape without harming you if you remain calm and still.

What do you do if it bites you?

  • Call an ambulance. 
  • If you have been bitten by a venomous snake, anything that raises your heart rate will spread the venom around your body more rapidly. Staying calm will improve your likelihood of survival. Remember that snake bites, particularly those that occur in the UK, usually aren’t serious and are only very rarely deadly.
  • Keep the part of your body that’s been bitten as still as possible, to prevent the venom spreading around your body.
  • Remove jewellery and watches from the bitten limb as they could cut into your skin if the limb swells.
  • Do not attempt to remove any clothing, but loosen clothing if possible.
  • Wash the area of the bite very thoroughly while waiting for medical help, if this is possible.
  • Try to remember the shape, size and colour of the snake.

More information

For more information please visit:

NHS Choices – Snake bites for emergency advice in case of snake bites

Forestry Commission England website for general information on adders

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