Insect and spider bites often cause minor swelling, redness, pain, and itching. These mild reactions are common and may last from a few hours to a few days. Home treatment is often all that is needed to relieve the symptoms of a mild reaction to common stinging or biting insects and spiders.

Some people have more severe reactions to bites or stings. Babies and children may be more affected by bites or stings than adults.

Examples of problems that are more serious include:

• A severe allergic reaction (anaphylaxis). Severe allergic reactions are not common but can be life-threatening and require emergency care. Signs or symptoms may include:
  • Shock, which may occur if the circulatory system cannot get enough blood to the vital organs.
  • Coughing, wheezing, difficulty breathing, or feeling of fullness in the mouth or throat.
  • Swelling of the lips, tongue, ears, eyelids, palms of the hands, soles of the feet, and mucous membranes (angioedema).
  • Lightheadedness and confusion.
  • Nausea, diarrhea, and stomach cramps.
  • Hives and reddening of the skin. These symptoms often occur with other symptoms of a severe reaction.
• A toxic reaction to a single sting or bite. Spiders or insects that may cause this include:
  • Black widow spider.
  • Brown recluse spider.
  • Scorpion.
  • Puss caterpillar (woolly slug).
• A toxic reaction to multiple stings or bites from a bee, wasp, or fire ant.
  • A bee leaves its stinger behind and then dies after stinging. Africanized honeybees, the so-called killer bees, are more aggressive than common honeybees and often attack together in great numbers.
  • Wasps, including hornets and yellow jackets, can sting over and over.
  • A fire ant attaches to a person by biting with its jaws. Then, pivoting its head, it stings from its belly in a circular pattern at multiple sites.
• A large skin reaction at the site of the bite or sting.
• A skin infection at the site of the bite or sting.
• Serum sickness, a reaction to the medicines (antiserum) used to treat a bite or sting. Serum sickness may cause hives and flu-like symptoms in about 3 to 21 days after the use of antiserum.
• A virus infection. Infected mosquitoes can spread the West Nile virus to people, causing an inflammation of the brain (encephalitis). For more information, see the topic West Nile Virus.
• A parasite infection. Infected mosquitoes can spread malaria. For more information, see the topic Malaria.

Review the Emergencies and Check Your Symptoms sections to determine if and when you need to see a doctor.