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Black widow spider bite

What is a black widow spider?

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 1.5in long, but may be smaller.

Black widow spiders are frequently found in low-lying webs in garages, 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 and children may be more serious than bites to adults.

What are the signs and symptoms of a black widow spider bite?

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.
Chills, fever, nausea, or vomiting.
Sweating.
Severe abdominal, back, or chest pain.
Headache.
Stupor, restlessness, or shock.
Severe high blood pressure.

What should I do if a black widow spider bites me?

If you believe you have been bitten by a black widow spider:

Get medical help immediately. Call your health professional, hospital, or poison control center.
Remain calm. Too much excitement or movement will increase the flow of venom into the blood.
Apply ice to the bite area.
Do not apply a tourniquet. It may cause more harm than benefit.
Try to positively identify the spider or catch it to confirm its type.

How is a black widow spider bite 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. Your health professional will ask what your main symptoms are, when they began, and how they have developed, progressed, or changed since the bite.

How is it treated?

Medicine to counteract black widow spider venom (antivenom) is available in the United States, Mexico, and Canada. It is usually used if you have difficulty breathing, or high blood pressure, or are pregnant.

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 narcotics, such as morphine or fentanyl.
Antihypertension medicines for high blood pressure.

Author	Jan Nissl, RN, BS
Editor	Susan Van Houten, RN, BSN, MBA
Associate Editor	Tracy Landauer
Primary Medical Reviewer	William M. Green, MD - Emergency Medicine
Specialist Medical Reviewer	Sean P. Bush, MD, FACEP - Emergency Medicine and Envenomation Specialist
Last Updated	February 1, 2008

WebMD Medical Reference from Healthwise

Last Updated: February 01, 2008

This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.