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Insect and spider bites

Bees, wasps and ants are often the cause of bites during the British summer. Less common are spider bites, while bites are also possible from mosquitoes, fleas, flies, bedbugs and harvest mites.

Unless a person has an allergy to insect bites, the symptoms are usually itching, swelling and discomfort.

Yellowjacket wasp

However, on holiday abroad, mosquitoes may transmit diseases such as West Nile virus, dengue and malaria.

For people allergic to insect or spider bites, these bites can cause severe trauma and even life-threatening anaphylactic shock. Also, the bites of a few spiders, ticks and insects are poisonous or associated with specific diseases.

Ticks. While most tick bites are harmless, several species can cause life-threatening diseases such as Rocky Mountain spotted fever and Lyme disease. Ticks may also transmit tularaemia, relapsing fever, and a potentially fatal condition called ehrlichiosis. On rare occasions, a bite may trigger tick paralysis, which starts with numbness and pain in the legs and can result in respiratory failure.

Spiders. Bites are seldom fatal; infants, the elderly and people with allergies are at greatest risk. In the UK, the most dangerous is the false widow spider, now found in southern England, but originally from the Canary Islands. The bite itself can pass unnoticed, but within hours, intense pain, tingling and burning sensations may begin, occasionally followed by muscle spasms, abdominal pain, chills, nausea and heart problems.

The bite of a funnel spider is painless but may cause a spreading, necrotising (tissue-killing) wound. Occasionally, reactions to a funnel spider bite include raised temperature, chills, joint pain and convulsions.

There are no recorded deaths from any spider bites in the UK, however in most other parts of the world, some spider bites can be dangerous or fatal if left untreated.

Scorpions. Scorpion stings cause a sharp, burning pain, followed by numbness. In a small number of cases, scorpion venom produces shock, or even a life-threatening syndrome of rapid breathing, difficulty speaking and muscle spasm. Fewer than 1% of stings are fatal; these are usually with very young and elderly victims.

Fire ants. Although not found in the UK, fire ants produce small, fluid-filled bites that may ulcerate. The ants bite into the skin and then sting repeatedly in an arc around the bite. The venom is capable of causing severe reactions and even, in some cases, death. Most incidences of bites are in North America and Mexico.

What are the symptoms of insect and spider bites?

Most insect bites produce only minor irritation, with symptoms such as:

  • Swelling at the site of the bite.
  • Itching or burning.
  • Local numbness or tingling.

Bites of poisonous spiders and scorpions may produce these symptoms:

  • Intense pain at the site of the wound.
  • Stiffness or joint pain.
  • Muscle spasms.
  • Abdominal pain, nausea or vomiting.
  • Raised temperature or chills.
  • Difficulty breathing or swallowing.
  • A spreading, ulcerated wound or tissue death.
  • Dizziness, impaired speech or convulsions.

An insect or spider bite can, on rare occasions, cause a potentially fatal allergic reaction known as anaphylactic shock. Its symptoms include:

  • Rapid swelling of the lips, tongue, throat or around the eyes.
  • Difficulty breathing.
  • Wheezing or hoarseness.
  • Severe itching, cramping or numbness.
  • Dizziness.
  • A reddish rash or hives.
  • Stomach cramps.
  • Loss of consciousness.
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