Black widow spider

Definition

The black widow spider (Latrodectus mactans) has a shiny black body with a red hourglass-shape on the belly area. The bite of a black widow spider is poisonous.

This is for information only and not for use in the treatment or management of an actual poison exposure. If you have an exposure, you should call your local emergency number (such as 911) or the National Poison Control Center at 1-800-222-1222.

Alternative Names

Poisonous Ingredient

The venom of the black widow spider contains poisonous chemicals that make people sick.

Where Found

Black widows are found throughout the United States but predominantly in the South and West. They are usually found in barns, sheds, stone walls, fences, woodpiles, porch furniture, and other outdoor structures.

Symptoms

This first symptom is usually pain similar to a pinprick. This sensation is felt when the bite is actually made. Some people may not feel it. There may be minor swelling, redness, and a target-shaped lesion.

Fifteen minutes to an hour later, a dull muscle pain spreads from the bite area to the entire body.

• If the bite is on the upper body, you will usually feel most of the pain in your chest.
• If the bite is on your lower body, you will usually feel most of the pain in the abdomen.

The following symptoms can also occur:

• Anxiety
• Difficulty breathing
• Extremely painful muscle cramps
• Headache
• High blood pressure
• Increased salivation
• Increased sweating
• Light sensitivity
• Muscle weakness
• Nausea and vomiting
• Numbness
• Restlessness
• Seizures (usually seen just before death in children)

Pregnant women may have contractions and go into premature labor.

Home Treatment

Seek immediate emergency medical treatment. Wrap ice in a washcloth or similar material and place it on the bite area. Leave it on for 10 minutes and then off for 10 minutes. Repeat this process. If the person has circulatory problems, decrease the time that the ice is on the area to prevent possible skin damage.

Before Calling Emergency

Determine the following information:

• Patient's age, weight, and condition
• Time the bite occurred
• Area where the bite occurred
• Type of spider, if possible

Poison Control, or a local emergency number

The National Poison Control Center (1-800-222-1222) can be called from anywhere in the United States. This national hotline number will let you talk to experts in poisoning. They will give you further instructions.

This is a free and confidential service. All local poison control centers in the United States use this national number. You should call if you have any questions about poisoning or poison prevention. It does NOT need to be an emergency. You can call for any reason, 24 hours a day, 7 days a week.

See: Poison control center - emergency number

What to expect at the emergency room

The health care provider will measure and monitor the patient's vital signs, including temperature, pulse, breathing rate, and blood pressure. Symptoms may be treated with a variety of therapies, including:

• Blood pressure drugs
• Muscle relaxers
• Pain medicines

In severe cases, antivenin medication to reverse the effect of the poison will be given. However, this drug can cause serious allergic reactions and must be used carefully.

Expectations (prognosis)

Severe symptoms usually start to improve within 2 to 3 days, but milder symptoms may persist for several weeks. Death in a normally healthy individual is very rare. Young children, the extremely ill, and the elderly may not survive a bite.

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References

Collier BR, Riordan WP Jr, Nagy RJ, Morris JA Jr. Wilderness trauma, surgical emergencies, and wound management. In: Auerbach PS, ed. Wilderness Medicine. 5th ed. Philadelphia, Pa: Mosby Elsevier; 2007:chap 20.