Spider bites
Spider bitesArticle Sections
DefinitionSpider bites are uncommon. Often, people mistake a skin infection or a bite by another insect as a spider bite. Only a few spiders have fangs strong enough to pierce your skin and enough venom to cause a reaction. In the U.S., these include the black widow spider and the brown recluse spider. Even these types of spiders tend to bite only when threatened. Spider bites are rarely lethal. Treating the site of the spider bite is generally all that's necessary. In a few cases, symptoms may be severe and widespread enough to require antivenom treatment and hospitalization. Black widow spiderThe black widow spider is known for the red hourglass marking on its belly. ...  Brown recluse spiderThe brown recluse spider is known for the violin-shaped marking on its top. ...  SymptomsTypically, a spider bite looks like any other bug bite — a red, inflamed, sometimes itchy or painful bump on your skin — and may even go unnoticed. Harmless spider bites usually don't produce other symptoms.
Symptoms of a black widow spider bite
Other systemic signs and symptoms — ones that affect the whole body — that sometimes occur include:
Pain usually persists for the first eight to 12 hours. Signs and symptoms diminish and go away after several days, although you may still feel weak and experience residual spasms and restlessness for next few weeks or months.
Symptoms of a brown recluse spider bite
Over the course of several days, other less common signs and symptoms may appear:
When to see a doctor CausesSevere spider bite symptoms occur as a result of injected spider venom circulating through your bloodstream. The severity of symptoms depends on the type of spider, the amount of venom injected and how sensitive your body is to the venom. Risk factorsAlthough dangerous spider bites are rare, your risk of being bitten increases if you live in the same areas that the spiders do and you happen to disturb their habitat. Both black widow and brown recluse spiders prefer warm climates and dark, dry places.
Location and habitat of black widow spiders They generally prefer to live outdoors, in places such as:
Location and habitat of brown recluse spiders Recluses are so named because they like to hide away in undisturbed areas. They mostly prefer to live indoors, in places such as:
Outside, they seek out dark, quiet spots, such as under rocks or in tree stumps. Spiders in general, including the black widow and brown recluse, bite only as a last defense when being crushed between your skin and another object. ComplicationsVery rarely, a bite from a black widow or brown recluse spider may lead to serious complications, such as a coma, kidney failure or death. People who are more susceptible to severe complications include:
Preparing for your appointmentIf you've been bitten by a spider that you suspect is a black widow or brown recluse, call your primary care doctor or go to an urgent care center. If your doctor has online services, an option may be to email a picture of the spider to your doctor.
What you can do
Some basic questions you might want to ask include:
What to expect from your doctor
What you can do in the meantime Tests and diagnosisYour doctor may suspect a spider bite based on your history and your signs and symptoms, but a specific diagnosis is difficult to confirm. Confirmation requires:
The black widow spider is a shiny black spider about a half-inch (12 to 13 millimeters or mm) long with a red hourglass (or two triangles) marking on the underside of its abdominal area. The brown recluse spider is a brown, nondescript spider about a quarter-inch to three-quarters of an inch (6 to 19 mm) long. It has a dark violin shape on top of the leg attachment region but this can be hard to identify. Another characteristic of the brown recluse is that it has six eyes — a pair in front and a pair on both sides — rather than the usual eight eyes in two rows of four. Black widow spiderThe black widow spider is known for the red hourglass marking on its belly. ... Brown recluse spiderThe brown recluse spider is known for the violin-shaped marking on its top. ... Treatments and drugsIf a spider has bitten you, try to identify the spider and, if possible, collect it and place it in a bag for later confirmation. If you think it was a black widow or brown recluse spider, stay calm and call your doctor, a hospital or 800-222-1222 to access your local poison control center.
Primary treatment for all spider bites
Your doctor may also recommend a tetanus booster shot if you haven't had one in the last five years. Antibiotics may be prescribed if a bacterial infection develops in the bite. Both black widow and brown recluse spider bites generally heal without leaving any scar.
Treatment for black widow spider bites
If you have severe symptoms, your doctor may recommend an antivenom, which may be injected into a thigh muscle or given through a vein (intravenously). The antivenom works for up to 36 hours after the bite and helps to reduce pain and the need for hospitalization. There is a risk of an allergic reaction to the antivenom, so it should always be given in a setting of continuous monitoring by staff equipped to treat a severe reaction.
Treatment for brown recluse spider bites In a very few cases, surgical removal of ulcerated tissue may be performed. This is usually done only after the ulceration has stabilized. PreventionTo prevent spider bites:
RelatedLast Updated: 2010-10-08 © 1998-2013 Mayo Foundation for Medical Education and Research (MFMER). All rights reserved. A single copy of these materials may be reprinted for noncommercial personal use only. "Mayo," "Mayo Clinic," "MayoClinic.com," "Mayo Clinic Health Information," "Reliable information for a healthier life" and the triple-shield Mayo logo are trademarks of Mayo Foundation for Medical Education and Research.
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