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Bites, snake


Snakes sometimes bite in self-defence if they are disturbed or provoked. Adders, or vipers, are the only wild venomous snakes in the UK.  The adder is the only venomous snake that is found naturally in the wild in the UK.

This article focuses on the bites of adders. See the Health topic about Snake bites (foreign) for more information about other types of snake bites.

Adders are found in:

  • mainland England
  • the Isle of Wight
  • Wales
  • Scotland
  • some of the Inner Hebridean Islands (a group of islands off the west coast of Scotland)

Adders sometimes bite without injecting any venom (toxins produced by the snake). This is called a ‘dry’ bite and may cause:

  • mild pain caused by the adder’s teeth puncturing the skin
  • anxiety

If an adder injects venom when it bites it can cause more serious symptoms including:

  • swelling and redness in the area of the bite
  • nausea (feeling sick)
  • vomiting
  • faintness

See Snake bites, adder - symptoms for more information.

How common are snake bites?

In the UK, the adder is the only venomous snake that is found naturally in the wild. See Snake bites, adder - causes for more information about adders.

Each year, approximately 100 cases of adder bites are reported in the UK. Most bites occur between February and October, with the number of bites peaking during the summer months.

Worldwide, there are around 5 million snake bites every year. 


Although adder bites can be painful, they are rarely serious. About 7 out of 10 adder bites only result in pain and swelling in the area that was bitten. Since records began in 1876 there have only been 14 reported deaths caused by adder bites, with the last death occurring in 1975.

Severe cases of adder bites are unusual, but they can be treated effectively in hospital using anti-venom medicine. See Snake bites, adder - treatment for more information.

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There are two different types of snake bite:

  • dry bites - where the snake releases no venom (toxins produced by the snake)
  • venomous bites - where the snake releases venom

The effects of venomous bites may be more severe in children, because they are smaller. 

Symptoms of dry bites

The symptoms of a dry bite are:

  • mild pain at the site of the bite caused by the snake’s fangs
  • anxiety

If there are no other symptoms, such as swelling, it is probably a dry bite.

Although dry bites require no medical treatment, if you are bitten by a snake you should visit your local accident and emergency (A&E) department.  This is because signs that venom has been injected might not appear until later, up to two hours or more after the bite.

Symptoms of venomous bites

The symptoms of a venomous snake bite include:

  • severe pain at the location of the bite
  • swelling, redness and bruising at the location of the bite
  • nausea (feeling sick)
  • vomiting
  • diarrhoea
  • itchy lumps on the skin (hives or nettle rash)
  • swelling of the lips, tongue and gums
  • breathing difficulties with wheezing, similar to asthma
  • mental confusion, dizziness or fainting
  • irregular heartbeat

Dial 999 to request an ambulance if someone who is bitten by an adder faints or develops any other symptoms that may indicate anaphylaxis.

Anaphylaxis (severe allergic reaction)

Symptoms of anaphylaxis include:

  • swollen face, lips, tongue and throat
  • swelling in the throat that can cause breathing difficulties
  • rapid heartbeat
  • itchy skin

Anaphylaxis can also cause a drop in blood pressure, which can lead to shock and cause symptoms of:

  • dizziness
  • cold and clammy skin
  • mental confusion
  • loss of consciousness (in some cases)

Anaphylaxis should always be treated as a medical emergency, regardless of how severe it seems. Left untreated, the most serious cases of anaphylaxis can be life-threatening.

See the Health topic about Anaphylaxis for more information.  

What should I do if I am bitten by an adder?

If you are bitten by an adder you should visit your nearest accident and emergency (A&E) department, even if your symptoms are only mild. Hospital staff will be able to check for any signs that venom has been injected through the bite.

You can use the local services search to find your nearest A&E department.

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Adder venom contains two kinds of toxins (poisons) which are designed to immobilise or kill the snakes prey:

  • haemotoxins, which attack the (heart and blood) circulation system,
  • cytotoxins, which attack the cells in the tissue near the bite.


Haemotoxins can cause a drop in blood pressure, and prevent blood from clotting, which causes bleeding. This may result in:

  • tissue and organ damage
  • loss of consciousness
  • death


Cytotoxins cause blood and plasma (the liquid part of blood that contains antibodies and other proteins) to leak into the tissue near to the bite. This can damage and kill tissue cells and result in the affected tissue:

  • becoming severely swollen
  • bruising
  • blistering
  • scarring

Why do snakes bite?

As humans are far too large for a venomous snake to eat, nearly all snake bites occur when somebody provokes a snake into acting in self-defence.

In many cases, provocation occurs by accident, for example, when a person accidentally steps on a snake while out walking. However, sometimes snake bites occur when someone deliberately provokes a snake by:

  • kicking it
  • striking it
  • trying to pick it up

Where adders live

You can find adders in:

  • mainland England
  • the Isle of Wight
  • Wales
  • Scotland
  • some of the Inner Hebridean Islands (a group of islands off the west coast of Scotland)

Adders are not found in Ireland or in the:

  • Channel Islands
  • Scilly Isles
  • Isle of Man
  • Outer Hebrides
  • Orkney Islands
  • Shetland Islands


The adder is common throughout mainland Britain and some of the islands off the west coast of Scotland. It is not found in Ireland. Adders are the only snakes in Scotland.

Appearance of adders:

  • Adders have a distinctive, dark zigzag stripe down their back.
  • They are quite short, up to a maximum of 75cm (2ft 6in) long.
  • They have a large head and slit-shaped pupils.
  • Males are usually grey with black markings.
  • Females are usually brown with darker brown markings.
  • They can be silver, yellow, green or completely black.

Adders can be confused with:

  • Grass snakes. Grass snakes are longer (up to 120cm or 3ft 11in), greenish, grey or brown with black flecks or bands, fast moving and often found near water.
  • Slow worms (legless lizards). Slow worms are shorter (up to 50cm or 1ft 8in), have tails that break off easily, are uniformly brown or grey and sometimes have a straight dark line down their backs.
  • Smooth snakes. Smooth snakes are grey or brown with black dots down their back. They are only found in southern England and they are very rare.

Adders are not aggressive snakes and they will usually only bite if they are disturbed. Most adder bites occur when someone accidentally steps on an adder or tries to pick one up. 

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If you have been bitten by an adder or an unidentified wild snake in the UK, you should seek immediate medical attention (see Snake bites, adder - treatment).

The healthcare professionals who treat you may ask about the colour and size of the snake to identify which type of snake has bitten you.

You may be admitted to hospital, where the severity of a snake bite can be assessed by:

  • monitoring your symptoms, for example, any swelling or redness that appears 
  • monitoring your general condition, for example, your heart rate and temperature
  • carrying out blood tests, to check whether the venom is affecting your red and white blood cells, how your blood clots and your muscle and kidney function

In more serious cases of snake bite, an electrocardiogram (ECG) may be used to monitor your heart function.

An ECG records the rhythms and electrical activity of your heart. A number of electrodes (small, sticky patches) are placed on your arms, legs and chest. The electrodes are connected to a machine that records the electrical signals of each heartbeat. 

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There are a number of misconceptions about what to do immediately after a snake bite. In order to clear up these misconceptions, this section will provide advice about what to do and what not to do in the event of a snake bite.  If you or someone else has been bitten by a snake, you should follow the advice outlined below and seek medical attention by visiting the nearest accident and emergency (A&E) department or dialling 999 to request an ambulance if it is a medical emergency.

Immediate action

If you or someone else is bitten by a snake you should follow the advice listed below.

  • Do not panic and try to remain calm. Snake bites, particularly those that occur in the UK, are rarely serious and very rarely fatal.
  • Keep the bitten body part as still as possible, this will prevent the venom spreading around your body. You may want to secure the bitten part with a sling (a supportive bandage) or a splint (a rigid support that helps keep the body part stable). However, do not make sling or splint so tight that it restricts your blood flow.
  • Try to remember the shape, size, and colour of the snake.
  • Remove jewellery and watches from bitten limb because they could cut into the skin if the limb swells. However, do not attempt to remove any clothing such as trousers.
  • Seek immediate medical attention (see below).

If you or someone else is bitten by a snake you should never:

  • Suck the venom out of the bite
  • Cut the venom out of the bite wound with a knife or other instrument
  • Apply any tight bandage around the bitten limb to stop the spread of venom, such as a tourniquet or ligature. This does not help and can cause swelling, even if no venom has been released by the snake. It can damage the affected limb and amputation of the limb may be required in extreme cases 
  • Try to catch or kill the snake

Seeking medical attention

If you are bitten by an adder in the UK, you should visit your nearest accident and emergency (A&E) department.  You can find the closest A&E department by using the Local Services search.

Hospital treatment

In most cases of adder bites, the only required treatment is observation in hospital, in case any symptoms develop that suggest venom has been injected.

You may be asked to stay in hospital for at least 24 hours as a precaution, so that your blood pressure and general health can be monitored.

In more severe cases of adder bites, an effective antidote to snake venom (anti-venom medication) can be used.


Anti-venoms are produced by injecting a small, non life-threatening amount of snake venom into a large animal, usually a horse. The animal's immune system (natural defence system) produces antibodies.  These are proteins that stick onto toxins and are capable of neutralising their effects. The antibodies are then taken from the animal, purified and stores in a refrigerator until they are needed.

In some people, anti-venoms can trigger a severe allergic reaction called anaphylaxis, so it is important that you are closely monitored after receiving your first dose. If you experience anaphylactic symptoms, such as an itchy rash, a fall in blood pressure or breathing difficulties this can be treated with adrenaline. See the Health topic about Anaphylaxis - treatment for more information.

Due to the risk of anaphylaxis, anti-venoms should only ever be administered by a qualified health professional.

In snake bite cases where there has been a significant fall in blood pressure, you may also need fluids given through a drip into your arm.


In cases of adder bites, most children will make a full recovery in about 1-3 weeks. Adults usually require more than three weeks to recover fully, and a quarter of adults will take between 1-9 months.

During the recovery period, you may experience episodes of swelling and pain in the area of the body that has been bitten. These symptoms can usually be controlled by taking the over-the-counter painkillers such as paracetamol.  Always read the manufacturer’s instructions to make sure that:

  • the medication is suitable for you
  • you are taking the correct dose


After an adder bite, a person may go into shock. Shock is a life-threatening condition that occurs when there is an insufficient supply of oxygen to the body.

Shock should be treated as a medical emergency and you should dial 999 to request an ambulance immediately.

Symptoms of shock include:

  • faintness or collapsing
  • pale, cold, clammy skin
  • sweating 
  • rapid, shallow breathing
  • weakness and dizziness
  • blindness
  • feeling sick and possibly vomiting

After calling for an ambulance, you should lie the person down and raise and support their legs. Use a coat or blanket to keep them warm. See First aid for shock for more information and advice. 

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If you are travelling in parts of the country and at times of the year when adders are around, the advice outlined below will help to prevent you being bitten.

  • Look out for warning notices on heaths and commons.
  • Wear long boots and trousers.
  • Never pick up a snake in the UK, even if you think it is a harmless grass snake or slow worm, and even if it appears to be dead.
  • Never place your hand down a hole or cavity for example, between rocks. If you need to retrieve a fallen object, stand well back and use a stick to reach the object.
  • If you find yourself close to an adder, stand completely still. Most snakes only attack moving targets and, if you remain calm and still, the snake will escape and will not harm you.
  • Remember that snakes are more active during warm weather. 
  • Do not sleep on the ground unless you are in a tent that has a sewn-in groundsheet.
  • Do not walk around barefoot on grassy lawns or in overgrown areas.
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