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Spider Bites

Reactions From Spider Bites

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Updated August 19, 2012

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Spider Bites

Black widow spider.

© US Dept of Agriculture
Spiders are commonplace in our daily lives. We see them in our homes, in our yards, and they are common subjects in horror films. While people have much anxiety about spiders causing significant injury from a bite, the reality is that the majority of spiders are harmless to humans.

The exception to this is three species of spiders (at least in the United States) whose bites can result in skin lesions, neurological toxicity, and other systemic systems. These spiders include the black widow spider (Lactrodectus species), brown recluse spider (Loxosceles species) and tarantulas. While allergic reactions to spider bites are possible, it is most likely that the toxin delivered by the spider bite is the reason for any symptoms that may occur.

Black Widow Spiders

The black widow spider is common in the United States, and is often found in dark, cool places such as garages and outdoor woodpiles. The female has the characteristic red-orange hourglass on their abdomen, and is larger and more venomous than the male. Most bites from black widow spiders cause immediate pain at the bite site, with very little inflammation or redness present. However, the toxin injected from the bite can result in neurologic symptoms within 30 minutes to 2 hours, and may include muscle spasms, abdominal pain, fever, high blood pressure, seizures, nausea and vomiting, and possibly respiratory failure.

Treatment of black widow spider bites includes local wound cleansing, ice pack application, tetanus prophylaxis, and over-the-counter pain medicines (such as ibuprofen or acetaminophen). People experiencing severe symptoms, including neurologic and systemic symptoms, as well as children, elderly people and pregnant women all require immediate medical attention. Antivenin is available for severe symptoms, and muscle relaxants, anticonvulsants, and hospitalization may be required.

Brown Recluse Spiders

Brown recluse spiders are commonly found in the Southwestern United States and in the southern part of the Midwestern United States. They are active at night and during the warmer months. They are characterized by the presence of a dark brown pattern on the middle of their backs that resembles a violin, which is bordered by three pairs of eyes. They are often found in bedding, linens and piles of clothing and often bite people when they are trapped between fabric and the victim’s skin.

Their bites are initially painless or cause minimal pain, but results in a necrotic, inflammatory skin lesion within a few days. Systemic symptoms may occur, including body aches, fever, chills, nausea and vomiting. Less common complications include seizures and kidney failure. Treatment usually involves local wound care, tetanus prophylaxis, antibiotic treatment for secondary infections, and surgical debridement of necrotic tissues.

Brown recluse spider bites are often over-diagnosed, especially in areas where these spiders don’t live. Skin infections, such as carbuncles and furuncles, caused by methicillin-resistant staphylococcus aureus (MRSA), are frequently misdiagnosed as spider bites.

Tarantulas

Tarantulas are commonly found in the deserts of the Southwestern United States. Bites are usually minimally painful without significant inflammation or necrosis as a result. Tarantula bites are more dangerous for pets, however, especially dogs. Treatment includes local wound cleansing, tetanus prophylaxis and pain control with ibuprofen or acetaminophen.

Many tarantula species can release hairs from their abdomen that can cause hives when they come into direct contact with a person’s skin. These reactions can be particularly severe and bothersome if the hairs become lodged in the eye. Treatment by an ophthalmologist is required if eye symptoms and complications occur as a result of tarantula hairs becoming lodged in the eye.

Prevention of Spider Bites

Prevention of spider bites is accomplished by wearing long-sleeved shirts, gloves, pants and shoes when cleaning any area where spiders may live, such as the garage or woodpiles. Using a bug repellant, such as those containing DEET (N, N-diethyl-m-toluamide), can help prevent spider bites. Cleaning of cobwebs and the use of insecticides (preferably by a professional exterminator for indoor use) can also reduce the chance of being bitten by a spider.

If a spider is found on a person’s body, it is important to gently brush off or flick the spider away, rather than smashing the spider against the skin. Doing so may result in the spider biting the person as it is being crushed.

If a tarantula is kept as a pet or handled, it is important to wear gloves and eye protection, and to avoid getting the spider near the face. Cleaning a tarantula’s terrarium should be done while using good eye protection, a face mask, and gloves.

Sources:

Diaz JH, Leblanc KE. Common Spider Bites. Am Fam Physician 2007;75:869-73.

Kemerer JJ, Reitz M. Diagnosis of Brown Recluse Spider Bites is Overused. Am Fam Physician. 2007;76:943-7.

DISCLAIMER: The information contained in this site is for educational purposes only, and should not be used as a substitute for personal care by a licensed physician. Please see your physician for diagnosis and treatment of any concerning symptoms or medical condition.

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