What is black widow spider bite?

After being bitten by a black widow spider, you may have painful swelling around the bite. You may also notice cramps, muscle spasms, and achiness, and you may be sick to your stomach.

These symptoms may get worse for up to about 12 hours after you were bitten. Then they should start to go away. It may take a few days or weeks before all the pain goes away.

Black widow spiders are usually found throughout the United States, Mexico, and southern Canada. They live in low-lying webs in garages, in barbecue grills, around swimming pools, and in wood piles. Most bites occur in rural and suburban areas between the months of April and October. These spiders tend to bite when their webs are disturbed. Bites to babies and children may be more serious than bites to adults.

Medicine to counteract black widow spider venom (antivenom) is available, but it is rarely used.

In most cases of a black widow spider bite, symptoms consist only of:

• Minimal to sharp pain followed by swelling and redness at the site of the bite.
• One or two small fang marks like tiny red spots.

In some cases, severe symptoms appear within 30 to 60 minutes. These include:

• Muscle cramps and spasms that start near the bite and then spread and increase in severity for 6 to 12 hours.
• Seizures.
• Chills, fever, nausea, or vomiting.
• Sweating.
• Severe belly, back, or chest pain.
• Headache.
• Stupor, restlessness, or shock.
• Severe high blood pressure.

Medicine to counteract black widow spider venom (antivenom) is available in the United States, Mexico, and Canada. It is usually used if you have trouble breathing, have high blood pressure, or are pregnant. Children and older adults with some medical conditions may also be given the medicine if their symptoms are serious.

Treatment also includes:

• Medicine for pain and spasms. Pain and spasms may be severe enough to require benzodiazepines, such as lorazepam (Ativan) or diazepam (Valium), or opioids, such as morphine or fentanyl. Calcium may also be used.
• Antihypertension medicines for high blood pressure.

A black widow spider bite is diagnosed through a physical examination and questions about the bite. You should be prepared to describe the spider, where and when the bite took place, and what you were doing at the time. Your doctor will ask what your main symptoms are, when they began, and how they have developed, progressed, or changed since the bite.

• If the doctor gave you a prescription medicine for pain, take it as prescribed.
• Take an over-the-counter antihistamine, such as fexofenadine (Allegra) or loratadine (Claritin), to calm the itching and reduce the swelling. Read and follow all instructions on the label.
• Put ice or a cold pack on the bite for 10 to 20 minutes at a time. Put a thin cloth between the ice and your skin.
• If your doctor told you how to care for the bite, follow your doctor's instructions. If you did not get instructions, follow this general advice:
  • Wash the bite area with clean water 2 times a day. Don't use hydrogen peroxide or alcohol, which can slow healing.
  • You may cover the bite with a thin layer of petroleum jelly, such as Vaseline, and a nonstick bandage.
  • Apply more petroleum jelly and replace the bandage as needed.

Black widow spiders (Latrodectus mactans and Latrodectus hesperus) are found throughout the United States, Mexico, and southern Canada. A female black widow is much more likely to deliver more venom than a male spider. Female black widows are long-legged, shiny, coal-black spiders with an orange, red, or yellow shape on their underside that usually looks like an hourglass but may be another shape. Female black widows are usually about 1.5 in. (3.8 cm) long, but they may be smaller.

Black widow spiders are frequently found in low-lying webs in garages, in barbecue grills, around swimming pools, and in wood piles. Most bites occur in rural and suburban areas and occur between the months of April and October. These spiders tend to bite defensively when their webs are disturbed. Bites to babies, children, and older adults may be more serious.