Spider Bites: How to Identify Them and When to See a Doctor

When should you get medical care for a spider bite?

Call 911 or your local emergency number right away if someone has trouble breathing, wheezing or shortness of breath, swelling anywhere on the face or in the mouth, throat tightness or trouble swallowing, feels weak or turns blue after a bite or sting ^[1]. Also call 911 if you think a black widow bit someone. MedlinePlus calls black widow bites very toxic and says to seek medical help right away ^[2].

Get medical care promptly in these cases:

• You suspect a brown recluse. MedlinePlus says to seek emergency medical treatment right away, because the bite may not look serious at first but can become severe over time ^[3]. The University of Kentucky also says bitten people should seek medical attention immediately ^[5].
• Any spider bite causes an unusual or severe reaction, such as increasing pain or extreme swelling. UC IPM advises contacting a physician ^[4].
• You have a fever, a spreading rash, or a sore that gets worse after a few days instead of better. NC State says that whatever the cause of a suspicious wound, always seek prompt medical help ^[6].
• The bite might be from a tick. A rash that grows over several days, sometimes shaped like a bull's-eye, can be an early sign of Lyme disease. It usually starts 3 to 30 days after the tick bite ^[10].

For advice at any hour, call Poison Help at 1-800-222-1222. MedlinePlus says the line is free, confidential and open 24 hours a day anywhere in the U.S., and you do not need an emergency to call ^[3]. For pain or itching from a mild bite, ask a doctor or pharmacist what to do instead of guessing.

How common are spider bites, really?

Spider bites are uncommon. UC IPM explains that, unlike mosquitoes, spiders do not seek out people to bite them, and the jaws of most spiders are so small that their fangs cannot get through an adult's skin ^[4]. Spiders generally bite only when they are squeezed, lain on or otherwise trapped.

Even the brown recluse rarely bites. The University of Kentucky says bites are rare even in homes where brown recluses are abundant, and most happen when a spider is accidentally trapped against bare skin, for example when someone rolls over onto one in bed or puts on clothing a spider was hiding in ^[5]. NC State sums it up: for the most part, spider bites are insignificant ^[6].

That fits what most people see at home. The spiders that wander indoors, such as large, fast wolf spiders, may bite if mishandled or trapped against the skin, but Penn State says the result is usually pain and redness that fade within about a day ^[9]. For a broader look at the spiders you are likely to meet, see our spider profile.

Is it really a spider bite?

Often it is not. Many sores blamed on spiders are actually infections or bites from other animals. UC IPM warns that people and their physicians often blame spiders for skin lesions with no proof that a spider was involved ^[4]. It lists bites that can be mistaken for a spider bite: ticks, fleas, bees, wasps, bed bugs, mosquitoes, kissing bugs, deer flies, horse flies and water bugs. Scratching can also break the skin and let in bacteria.

Infections are the big lookalike. NC State says bacteria such as MRSA can create wounds that look like a brown recluse bite ^[6]. The University of Kentucky adds bacterial and fungal infections, diabetic and pressure ulcers, and outbreaks of drug-resistant staph infections to the list of conditions that have been mistaken for recluse bites ^[5].

You cannot identify a spider, or any bug, from a bite with certainty. The best clue is the animal itself. UC IPM and the University of Kentucky both suggest catching the spider, even if it is crushed, and having it identified; Kentucky notes that an expert identification helps the physician ^[4]. Never pick a spider up with bare hands. A jar, a sealed bag or a clear photo works.

If you woke up with itchy bites and never saw a spider, read our guide to bed bug bites as well, or try the bite identifier, which walks through the questions a doctor is likely to ask.

How do black widow and brown recluse bites differ?

The two spiders that matter most in the U.S. cause very different bites. Black widow venom acts on the nerves, while brown recluse venom can damage skin tissue at the bite ^[7]. The table summarizes what medical and extension sources describe. It helps you decide how urgent things are, not what bit you.

	Black widow (adult female)	Brown recluse	Most other house spiders
What it looks like	Shiny black, round abdomen, red hourglass on the underside	Tan to brown, dark violin mark on the front body section, no stripes or bands	Varies; many are brown, tan or gray
Body size	About 8 to 13 mm (Penn State)	About 6 to 13 mm (NC State)	Varies widely
First feeling	Like a pinprick	A sting, or nothing at first	Brief sharp pain, if any
What can follow	Dull muscle pain that spreads from the bite within 15 minutes to an hour; cramps, sweating, nausea, trouble breathing	Pain within several hours that may become severe; a blister and sometimes a slow-healing sore; fever or chills	Pain and redness that usually fade within a day (wolf spiders)
What to do	Seek medical help right away; call 911	Seek medical care right away	Watch it; see a doctor for unusual or severe reactions

Sources for the table: MedlinePlus on black widow and brown recluse symptoms ^[2]; Penn State on black widow size ^[8]; NC State on recluse size; CDC NIOSH on the white blister; Penn State on wolf spiders.

Serious outcomes are rare. Penn State reports that about 2,200 people a year in the U.S. are bitten by black widows, according to the American Association of Poison Control Centers, and no deaths have been recorded since 1983 ^[8]. Most brown recluse bites stay local and heal within about 3 weeks without serious complications ^[5]. Children may react more strongly, which is another reason to get them checked quickly ^[3].

Where do brown recluses and black widows live in the U.S.?

Where you live changes the odds a lot. The brown recluse is found in the south-central and Midwestern United States and is rare outside that range ^[5]. MedlinePlus names Missouri, Kansas, Arkansas, Louisiana, eastern Texas and Oklahoma as states where it is most common ^[3]. UC IPM says it does not occur in California; spiders occasionally arrive with household goods, but there are no breeding populations there ^[4].

If you live far outside the brown recluse range, a sore is very unlikely to be a recluse bite. That does not make it harmless, which is why a doctor should look at any wound that is getting worse.

Black widows are much more widespread. CDC NIOSH says they are found throughout North America but are most common in the southern and western United States ^[7]. Penn State notes that most widow bites happen in summer, when females guard their egg sacs ^[8]. Our black widow profile has more on the three main U.S. species.

How can you lower the chance of a spider bite at home?

Because most bites happen when a spider is pressed against skin, the best prevention is making that contact less likely. The University of Kentucky recommends these steps for brown recluse areas ^[5]:

1. Move beds away from walls and remove bed skirts so bedding does not touch the floor.
2. Keep shoes and clothing off the floor, or shake them out before you put them on.
3. Cut clutter and store seldom used items in sealed plastic containers instead of cardboard boxes.
4. Wear long sleeves and gloves when sorting through boxes or stored materials.

Outdoors, black widows hide in protected spots such as under rocks and boards, in dense plants and in dark, damp corners ^[6]. Wear gloves when you move firewood, stones or stored items in the garage or shed, and look before you reach. Our bedroom and garden pages cover the other pests you may find in those spots, and the brown recluse identification guide shows how to tell a recluse from harmless lookalikes.