Healthsheet

Black Widow Spider Bite

Black Widow Spider Bite

Most spiders are harmless to people. But there are 2 types of spiders in the U.S. that can cause harm: the black widow and brown recluse.

Black widow spiders are black and shiny. They are about a half-inch to 1 inch long. Only female black widows are dangerous. They have a red or orange marking on their bodies. Black widow spiders are found throughout the U.S. But they are most common in the southern and western states. They live outdoors in places such as woodpiles, porch furniture, and fences. They tend to avoid the inside of homes. But they can be found in dark corners of garages and outhouses. They are shy and do not bite unless disturbed.

When the black widow spider bites, it injects a small amount of venom. This can cause pain, numbness, tingling, redness, and swelling at the bite site. Other symptoms include muscle cramps all over the body and severe abdominal pain. Tremors (shaking), sweating, rapid breathing, weakness, headaches, nausea, and vomiting can also occur. In severe cases, the person may also develop a fast heart rate and high blood pressure. Symptoms most often appear within 30 minutes to 2 hours of the bite. They may last for 24 to 72 hours. Symptoms may be worse in children and the elderly.

The bite site will be cleaned. Cold packs may be used to ease pain and swelling. Medicine may be given to relieve pain and muscle spasms. A tetanus shot may also be given, if needed. For severe cases, antivenom may be given. This antivenom carries a small risk of allergic reaction. A delayed reaction to the antivenom called serum sickness can also occur 1 to 2 weeks later. This may cause symptoms such as rash, fever, and joint pain.

Home care

  • Apply cold packs to the bite site to ease pain and swelling. You can use a cool wet washcloth. Or make a cold pack by filling a plastic bag that seals at the top with ice cubes and then wrapping it with a thin towel. Do not apply ice directly to the skin.
  • To help relieve pain, you may use acetaminophen or ibuprofen. If needed, another pain medicine may be prescribed. Note: If you have chronic liver or kidney disease or ever had a stomach ulcer or GI bleeding, talk with your healthcare provider before using these medicines.
  • Medicines may be prescribed to relieve muscle spasms. Antibiotics may also be prescribed to prevent or treat infection. Make sure to take these medicines as directed. Also make sure to complete the medicines.
  • Watch for any signs of allergic reaction to the antivenom, if it was given (see below). If mild serum sickness occurs, you can treat this at home with medicines such as ibuprofen or naproxen. For more serious symptoms, contact your healthcare provider.
  • Check the bite site daily for signs of infection (see below).

Follow-up care

Follow up with your healthcare provider, or as advised.

When to seek medical advice

Call your healthcare provider right away if any of these occur:

  • Fever of 100.4°F (38.0°C) or above, or as directed by your provider
  • Abdominal pain
  • Chest tightness or trouble breathing
  • Muscle pain, cramping, and rigidity
  • Nausea and vomiting
  • Symptoms last longer than 3 days
  • Signs of allergic reaction to antivenom such as skin itching, redness, swelling of face or mouth, or problems breathing
  • Signs of serum sickness such as moderate to severe rash, fever or joint pain starting 1 to 2 weeks after treatment
  • Signs of infection at the bite site such as increased redness or streaking, swelling, pain, or foul-smelling drainage
  • Bleeding from the bite site that does not stop after 5 minutes of firm pressure
  • Bite site becomes black or blue
  • Bite site won't heal or becomes larger
  • An open sore (skin ulcer) forms at the bite site
  • A skin ulcer (open sore) forms at the bite site

Date Last Reviewed: 3/1/2017

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