A snake will sometimes bite in self-defence if disturbed or provoked.

Some snakes are venomous and can inject venom (toxin) as they bite. A bite from a venomous snake is a medical emergency as they can be deadly if not treated quickly.

In the UK, adders are the only venomous snakes found in the wild. People also keep foreign (exotic) venomous snakes, sometimes illegally.

Exotic snakes have been known to bite while being handled carelessly, or when they escape from their cages.

There’s also a risk of being bitten while travelling abroad to tropical countries.

Symptoms of snake bites

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

• pain, redness and swelling in the area of the bite
• nausea (feeling sick) and vomiting
• dizziness and fainting

A foreign snake that injects venom when it bites can also cause:

• extensive swelling, blistering and, eventually, gangrene in the area of the bite
• shock
• muscle paralysis (an inability to move one or more muscles of the body) leading to difficulties swallowing and breathing
• bleeding

Sometimes, venomous snakes can bite without injecting venom. This is called a ‘dry bite’ causing only:

• mild pain (from the snake’s teeth puncturing the skin)
• anxiety

Read more about the symptoms of snake bites.

What to do after a snake bite

Immediately after being bitten by a snake you should:

• remain calm and don’t panic; snake bites, particularly those that occur in the UK, are not often serious and rarely deadly
• try to remember the shape, size and colour of the snake
• keep the part of your body that has been bitten as still as possible to prevent the venom spreading around your body
• remove jewellery and watches from the bitten limb because they could cut into your skin if the limb swells
• do not attempt to remove any clothing, such as trousers, but loosen clothing if possible

Seek immediate medical assistance by dialling 999 to request an ambulance or visit your nearest accident and emergency (A&E) department.

You should give healthcare professionals a description of the snake to help identify it.

You may be admitted to hospital so the bite can be assessed and your condition closely monitored.

Read more about what to do if bitten by a snake and how snake bites are assessed.

Treating snake bites

In most cases of adder bites, the only treatment required is observation in hospital. As a precaution, you may be asked to stay in hospital for 24 hours to be monitored.

Antivenom medication is an effective antidote to snake venom and can be used to treat more severe snake bites.

In most cases, children bitten by an adder will make a full recovery in about one to two weeks. Adults usually require more than two weeks to recover fully, and a quarter of adults will take between one and nine months.

Read more about how snake bites are treated.

Why do snakes bite?

When a snake bites, it injects venom to immobilise its natural (food) prey. As humans are too large for a snake to eat, snakes bite only in self defence.

Snake bites usually occur when a person accidentally steps on a snake while out walking. However, sometimes people are bitten when they deliberately provoke a snake by striking it or trying to pick it up. 

Read more about the causes of snake bites.

Preventing snake bites

Follow the advice listed below if you are in an area where venomous snakes are found.

• look out for warning notices on heaths and commons
• wear boots and long trousers
• never pick up a 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 if you remain calm and still, the snake will escape without harming you

Adder and foreign snake bites can cause similar symptoms.

There are two types of snake bite:

• dry bites – where the snake injects no venom (liquid containing toxins produced by the snake)
• venomous bites – where the snake injects venom

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

Dry bites

Typical symptoms of a dry bite include:

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

If there are no other symptoms, such as swelling, it’s probably a dry bite. However you should still visit your nearest 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 an adder bite, or even longer after an exotic snake bite.

Venomous snake bites (adder and foreign)

Symptoms of an adder bite when venom has been injected include:

• severe pain at the location of the bite
• swelling, redness and bruising at the location of the bite, spreading up the bitten limb
• nausea (feeling sick) followed by 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

Foreign snake bites

For foreign snake bites, symptoms may also include:

• dizziness, mental confusion, faintness, collapse and shock
• bleeding from the mouth, nose and wounds
• vomiting blood or passing blood in urine or stools
• muscle paralysis, which can lead to breathing difficulties

In the most severe cases, a venomous snake bite may cause:

• extensive swelling, blistering and eventually gangrene (death of tissue) in the area of the bite
• paralysis, starting with drooping of the upper eyelids and progressing down the body to produce an inability to swallow, breathe or move
• shock and loss of consciousness
• kidney failure with little or no urine being passed
• massive blood loss, due to bleeding from the mouth, nose and wounds, vomiting blood and passing blood in urine or stools
• death

Dial 999 to request an ambulance if someone is bitten by a foreign snake or adder, and faints or develops symptoms of anaphylaxis (see below).

Anaphylaxis

In a small number of people a snake bite can trigger a severe allergic reaction, known as anaphylaxis or anaphylactic shock. This can occur immediately after a bite or several hours later.

Anaphylaxis should always be treated as a medical emergency. Left untreated, anaphylaxis can be life-threatening.

Symptoms of anaphylaxis include:

• itchy skin with hives and redness
• swollen face, lips, tongue and throat
• swelling in the throat that can cause breathing difficulties
• wheezing and difficulty breathing 
• rapid heartbeat
• nausea, vomiting and diarrhoea

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

• dizziness or mental confusion
• faintness, loss of consciousness or collapsing 
• cold and clammy skin
• blindness

Read more about anaphylaxis.

There are a number of misconceptions about what to do immediately after being bitten by a snake. For example, you should never try to suck or cut the venom out.

Follow the advice below if you or a companion is bitten by a snake.

Immediate action

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

What you should not do

If you or someone you are with is bitten by a snake you should not:

• try to suck the venom out of the bite
• try to cut the venom out of the bite
• rub anything into the wound or apply ice, heat or chemicals
• leave someone who has been bitten on their own
• put anything around the bitten limb to stop the spread of venom, such as a tight pressure band, tourniquet or ligature – it will not help and can cause swelling, even if no venom has been released by the snake; it could also damage the limb, leading to the need for amputation
• try to catch or kill the snake

Medical attention

If you are bitten by a snake you should visit your nearest accident and emergency (A&E) department, or dial 999 to request an ambulance if it’s a medical emergency.

If a snake bites you while you are abroad, you should assume it’s a medical emergency and contact the relevant emergency medical services.

In most cases, following a bite, you will need to stay in hospital for a short period. This is so that staff can keep you under observation in case you develop symptoms that suggest venom has been injected.

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

Antivenoms are antidotes to snake venom and are used to treat more severe snake bites.

Antivenoms

Antivenoms 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. Antibodies are proteins that stick onto toxins and are capable of neutralising their effects. The antibodies are then taken from the animal (without harming it), purified and stored until needed.

In some people, antivenoms can trigger a severe allergic reaction called anaphylaxis, so it is important you are closely monitored after receiving this treatment.

Due to the risk of anaphylaxis, antivenom should only be given by a qualified healthcare professional.

In cases where a snake bite is severe, and your blood pressure has fallen significantly, you may need intravenous fluids (into a vein in your arm). You may also need a blood transfusion if you have lost a lot of blood.

Recovery

Recovery times for snake bites can vary depending on the species of snake involved.

In most cases, children bitten by an adder will make a full recovery in one to two weeks. Adults usually take more than three weeks to recover fully, with a quarter taking between one to nine months.

During the recovery period, you may experience episodes of pain and swelling in the area of your body that has been bitten. These symptoms can usually be controlled by taking over the counter painkillers, such as paracetamol and continuing to exercise the limb.

When a snake bites and injects venom, usually its aim is to immobilise its natural (food) prey.

As humans are far too large for a venomous snake to eat, most snake bites occur when the snake is provoked into acting in self-defence.

In most cases, the snake is provoked by accident – for example, when a person accidentally steps on a snake while out walking. However, sometimes a snake bites after being deliberately threatened and frightened by someone:

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

Snake bites that involve foreign (exotic) snakes kept as pets usually occur when someone handles or ‘plays’ with them, often after drinking too much alcohol or taking recreational drugs.

Snake venom

Snake venom contains many different toxins (poisons) evolved to kill or immobilise the snake’s prey. There are four main types of snake venom toxins:

• haemotoxins – affect the circulatory system (heart and blood)
• neurotoxins – affect the nervous system at the places where nerves connect to muscles
• cytotoxins – damage and kill tissue cells (such as skin) causing blood and plasma (the clear fluid in blood) to leak into the tissue near the bite
• myotoxins – destroy muscle tissue both at the site of the bite and generally throughout the body

The four types of toxins are discussed in more detail below.

Haemotoxins

Haemotoxins destroy red, oxygen-carrying blood cells, damage the lining of blood vessels and disrupt the blood’s ability to clot.

They can also cause a drop in blood pressure, which can result in tissue and organ damage, loss of consciousness and death.

Neurotoxins

Neurotoxins block or damage nerves where they connect to muscles, preventing the nerve signals getting through.

This causes paralysis and symptoms such as muscle weakness throughout the body and swallowing and breathing difficulties that can lead to lack of oxygen (respiratory failure) and death.

Cytotoxins

Cytotoxins cause swelling, bruising, blistering and gangrene (death of tissue cells) near the location of the snake bite. This may require plastic surgery or, in severe cases, amputation.

Myotoxins

Myotoxins damage muscle cells, causing pain and muscle weakness.

They may also damage your kidneys, which filter waste products from your blood, causing the flow of urine to decrease or even stop. The urine may become dark brown or black.