Spider bites are usually harmless. Many bites attributed to spiders turn out to have been inflicted by other bugs. Skin infections also have been mistaken for spider bites.
Only a few types of spiders have fangs long enough to penetrate human skin and venom strong enough to hurt humans. In the United States, these include the black widow spider and the brown recluse spider.
Spider bites can cause redness, pain and swelling, or you may not notice them at all. Black widow spider bites can also cause severe abdominal pain or cramping. Brown recluse spider bites can cause a sting or sharp pain, like a bee sting. With severe bites, surrounding skin may die within a few hours. Both types of spiders generally live in undisturbed areas, such as attics or sheds. They don't bite unless threatened.
Typically, 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 any other symptoms.
Black widow spider bites
Signs and symptoms of a black widow spider bite may include:
- Pain and swelling. You may have pain and swelling around the bite, which can spread into your belly, back or chest.
- Cramping. You may have severe stomach cramps, which are sometimes mistaken for appendicitis or a ruptured appendix.
- Sweating. You may experience chills, nausea or sweating.
Brown recluse spider bites
The pain associated with a brown recluse spider bite typically increases during the first eight hours after the bite. You may also have fever, chills and body aches. The bite usually heals on its own in about a week. Sometimes the skin at the center of the bite turns dark blue or purple, and then forms an open sore (ulcer) that gets bigger as the skin around it dies. The ulcer usually stops growing within 10 days after the bite, but full healing can take months.
When to see a doctor
Seek prompt medical care in the following situations:
- You are unsure whether the bite was from a poisonous spider.
- The person who was bitten experiences severe pain, abdominal cramping or a growing ulcer at the bite site.
- The person who was bitten is having problems breathing.
Your doctor may recommend a tetanus booster shot if you haven't had one in the last five years.
Severe spider bite symptoms occur as a result of the venom that the spider injects. How severe the symptoms are depends on the type of spider, the amount of venom injected and how sensitive your body is to the venom.
Risk factors for spider bites are living in areas where spiders live and disturbing spiders' natural habitats. Black widow spiders and brown recluse spiders like warm climates and dark, dry places.
Black widow habitat
Black widow spiders can be found throughout the U.S., except Alaska and the far north. They prefer to live in:
- Unused pots and gardening equipment
- Closets and cupboards during cold weather
Brown recluse habitat
Brown recluse spiders are found most commonly in the southern Midwest and in limited areas of the South. Recluses are so named because they like to hide away in undisturbed areas. They mostly prefer to live indoors, in places such as:
- The clutter of basements or attics
- Behind bookshelves and dressers
- In rarely used cupboards
Outside, they seek out dark, quiet spots, such as under rocks or in tree stumps.
Very rarely, a bite from a black widow spider or brown recluse spider may be deadly, particularly in children.
Spiders in general, including the black widow and brown recluse, bite only in defense, when being trapped between your skin and another object.
To prevent spider bites:
- Learn what dangerous spiders look like and their preferred habitat.
- Wear a long-sleeved shirt, hat, long pants tucked into socks, gloves and boots when handling stored boxes or firewood, and when cleaning out sheds, garages, basements, attics and crawl spaces.
- Inspect and shake out gardening gloves, boots and clothing before use.
- Use insect repellents, such as DEET, on clothing and footwear.
- Keep insects and spiders out of the house by installing tightfitting screens on windows and doors, sealing cracks where spiders can come in, and using safe indoor insecticides.
- Remove piles of rocks or lumber from the area around your house and avoid storing firewood against the house.
- Make sure beds aren't pushed against the wall and that only the legs of the bed touch the floor. Don't store items under the bed and don't let bedding drag on the floor.
- Vacuum spiders and spiderwebs and dispose of them in a sealed bag outside to prevent reentry into the house.
- If a spider is on your skin, flick it off with your finger rather than crushing it against the skin.
- When cleaning tarantula enclosures, wear gloves, surgical mask and eye protection.
Your doctor may suspect a spider bite based on your history and your signs and symptoms. The process might involve talking to someone who saw the bite, having an expert identify the spider and ruling out other possible causes of the symptoms.
Black widow identification
Some clues for identifying black widow spiders include:
- Shiny black body with long legs
- Red hourglass on underside of abdominal area
- Entire body, including legs, is about 1 inch (2.5 centimeters) across
Brown recluse identification
Some clues for identifying brown recluse spiders include:
- Golden or dark brown body with long legs
- Dark violin shape on top of the leg attachment segment
- Six eyes — a pair in front and a pair on both sides — rather than the usual spider pattern of eight eyes in two rows of four
- Central body is 0.25 to 0.75 inches (6 to 19 mm) long
Treatment for spider bites usually includes the following steps:
- Clean the bite with mild soap and water. Apply an antibiotic ointment to help prevent infection.
- Apply a cool damp cloth to the bite. This helps reduce pain and swelling.
- If the bite is on an arm or leg, elevate it.
- Take an over-the-counter pain reliever as needed.
- Observe the bite for signs of infection.
Your doctor may also recommend a tetanus booster shot if you haven't had one in the last five years. You may need antibiotics if the bite becomes infected.
Black widow antivenom
If a black widow bite is causing severe pain or life-threatening symptoms, your doctor may recommend antivenom, which may be injected into a thigh muscle or given through a vein (intravenously). Antivenom can cause serious allergic reactions, so it must be used with caution.
Preparing for an appointment
If 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 photo of the spider to your doctor.
What you can do
To help your doctor understand your symptoms and how they might relate to a spider bite, you can:
- Bring the spider or a photo of the spider with you
- List any symptoms you're experiencing
- List questions to ask your doctor
Some basic questions you might want to ask include:
- If this is a dangerous spider bite, what's the next best step?
- If this isn't a spider bite, what are possible causes for my symptoms or condition?
- Do I need any tests?
- How long will my symptoms last?
- What is the best course of action?
What to expect from your doctor
Your doctor is likely to ask you a number of questions. Being ready to answer them may reserve time to go over any points you want to spend more time on. Your doctor may ask:
- When did you begin experiencing symptoms?
- What were you doing in the hours before your symptoms started?
- Have your symptoms gotten worse?
- Does anything relieve your symptoms or make them worse?
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