Black Widow Spider Bite

What is a black widow spider?

Black widow spiders are found throughout North America. 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 hourglass-shaped marking on the belly. Female black widows are usually about 0.5 in. (1.3 cm) long, but they may be smaller.

Black widow spiders live in webs in garages or sheds, in barbecue grills, around swimming pools, and in wood or brush piles. Most bites occur in warmer months. These spiders tend to bite when their webs are disturbed. Bites to babies, children, and older adults may be more serious.

What are the symptoms of a black widow spider bite?

Symptoms for most black widow spider bites include:

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

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

• Muscle cramps and spasms that start near the bite and then spread through the body.
• Nausea and vomiting.
• Sweating, fever, or chills.
• Belly, back, or chest pain.
• Headache.
• Anxiety or restlessness.
• High blood pressure.

What should you do if you think you've been bitten by a black widow spider?

Follow these steps if you believe you have been bitten by a black widow spider.

• Get medical help immediately. Call your doctor, hospital, or poison control center for treatment information.
• Remain calm. Too much movement will increase the flow of venom into the blood.
• Wash the bite area with soap and water.
• Apply a cool, wet cloth or ice pack to the bite area to reduce swelling.
• Elevate the bite area if it is on a limb, such as your arm or leg.
• Try to positively identify the spider or try to take a picture of it. If you are able to safely capture and transport the spider, bring it with you to show your doctor.

Your doctor may recommend a tetanus vaccine as part of your treatment.

How is it diagnosed?

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. (If you are able to safely capture and transport the spider, bring it with you to show your doctor.) Your doctor will ask what your main symptoms are, when they began, and how they have changed since the bite.

How is a black widow spider bite treated?

Treatment includes:

• Medicine for pain and spasms. Pain and spasms may be severe enough to need muscle relaxants or opioids, such as morphine or fentanyl.
• Antihypertension medicines for high blood pressure.
• A tetanus vaccine if the person is not up to date on vaccinations.

Medicine for black widow spider venom (antivenom) is available but is rarely needed. It is usually used if a person has trouble breathing, has high blood pressure, or is pregnant. Children and older adults with some medical conditions may also be given the medicine if their symptoms are serious.