Spider Bites: Symptoms, Causes, First Aid, and When to See a Doctor

Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: October 2026

Quick Answer: What does a spider bite look like, and when is it dangerous?

A spider bite usually looks like any other bug bite, a red, inflamed, sometimes itchy or painful bump, and most heal on their own in about a week. [1] [2] Only a few species, mainly widow and recluse spiders, can seriously harm humans. [1] Wash the bite and use cool compresses, but seek immediate care for severe pain, cramping or breathing trouble. [1] [2]

Black widow: shiny black body, red hourglass on the belly. Brown recluse: violin shape on the back and six eyes. Only a few species can seriously hurt humans.

What the research says

• "Spider bite" is often a misdiagnosis. A review in Canadian Family Physician concluded that spider bites are regularly misdiagnosed as the cause of skin necrosis, and that a working diagnosis of "spider bite" should be considered only when a spider is caught in the act of biting or otherwise reliably associated with the lesion (Bennett and Vetter, Can Fam Physician, 2004) [3].

• Where you live matters for recluse bites. Brown recluse populations range from abundant in states such as Arkansas and west and central Kentucky and Tennessee to absent in the Atlantic seaboard states, and the diagnosis of loxoscelism (recluse bite) should be restricted to areas where the spiders are both common and widespread (Vetter, South Med J, 2009) [4].

• The benefit of antivenom for widow-type bites is not clear-cut. In a randomized placebo-controlled trial of 224 patients with severe pain from redback spider (Latrodectus) bites, 34% of the antivenom group versus 23% of the placebo group had a clinically significant pain improvement at 2 hours, a difference that was not statistically significant (P = 0.10). Acute hypersensitivity reactions occurred in 3.6% of patients given antivenom (Isbister et al., Ann Emerg Med, 2014) [5].

Are Most Spider Bites Harmless?

Spider bites are usually harmless, and spiders don't usually bite unless threatened. [1] They bite only in defense, typically when trapped between your skin and another object. A typical bite looks like any other bug bite and may even go unnoticed. [1] Harmless bites usually don't produce any other symptoms. [1]

Many skin sores look the same but have other causes, such as a bacterial infection. [1] Unless you actually saw a spider bite you, it's difficult to be certain that your wound was caused by a spider. [1]

Worldwide, only a few species of spiders have fangs long enough to penetrate human skin and venom strong enough to hurt humans. [1] Among these are widow spiders, with about 30 species, and recluse spiders, with more than 140 species worldwide. [1]

What Do Spider Bites Look and Feel Like?

Typically, a spider bite looks like a red, inflamed, sometimes itchy or painful bump. [1] Bites from some spiders, notably widow and recluse spiders, might cause serious signs and symptoms. [1]

Widow spider bites

Signs and symptoms of a widow spider bite can include:

• Redness, pain, and swelling. Pain and swelling can appear around the bite and spread into the abdomen, back, or chest. [1]

• Cramping. Severe abdominal rigidity or cramping, which is sometimes mistaken for appendicitis or a ruptured appendix. [1]

• Nausea, vomiting, tremors, or sweating. These can occur alone or in combination. [1]

Symptoms can last 1 to 3 days. [1]

Recluse spider bites

Signs and symptoms of a recluse spider bite can include:

• Increasing pain over the first eight hours after the bite. [1]

• Fever, chills, and body aches. [1]

• A bite wound with a pale center that turns dark blue or purple with a red ring around it. [1]

• A bite wound that grows into an open sore (ulcer), with the skin around it dying. [1]

When Should You See a Doctor?

A spider bite needs immediate medical care if a dangerous spider may be involved or if warning signs such as severe pain, breathing problems or spreading redness develop. [1]

• You were bitten by a dangerous spider, such as a widow or recluse. [1]

• You're unsure whether the bite was from a dangerous spider. [1]

• You have severe pain, abdominal cramping, or a growing wound at the bite site. [1]

• You're having problems breathing or swallowing. [1]

• The area of the sore has spreading redness or red streaks. [1]

Seek medical care immediately if any of these warning signs apply. When in doubt, get it checked.

What causes spider bites, and who is at risk?

Severe spider bite symptoms result from the venom the spider injects. [1] How severe they are depends on the type of spider, the amount of venom injected, and how sensitive your body is to the venom. [1]

The main risk factors are living in areas where spiders live and disturbing their natural habitat. [1] Widow and recluse spiders like warm climates and dark, dry places. [1] Widow spiders can be found throughout the United States except Alaska, are more common in the rural South, and are also found in Europe. [1] Recluse spiders are found most commonly in the southern half of the United States and in South America, where they are known as brown spiders. [1] Both are most active in the warmer months. [1]

Spider	Where found	Preferred hiding spots	Most active
Widow	Throughout the U.S. (except Alaska), especially the rural South; also Europe	Sheds, garages, woodpiles, unused pots and gardening equipment, closets and cupboards	Warmer months
Recluse (brown spider)	Southern half of the U.S.; South America	Cluttered basements and attics, behind bookshelves and dressers, rarely used cupboards, under rocks, tree stumps	Warmer months

Recluse spiders sometimes get mixed up in bed linens and clothing, which is why many bites occur in the early morning. [1]

What Complications Can Spider Bites Cause?

Complications are uncommon, but they matter. Rarely, a bite from a widow or recluse spider is deadly, particularly in small children. [1] A severe wound from a recluse spider can take weeks or months to heal and leaves large scars. [1]

How Can You Prevent Spider Bites?

Preventing spider bites focuses on avoiding contact with spiders, since they usually bite only in defense.

• Learn and recognize. Learn what dangerous spiders look like and their preferred habitats. [1]

• Dress for protection. 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. [1]

• Inspect before use. Inspect and shake out gardening gloves, boots, and clothing before use. [1]

• Use repellent. Use insect repellents such as DEET, carefully following the directions on the package. [1]

• Seal the home. Install tight-fitting screens on windows and doors, seal cracks where spiders can come in, and use safe indoor insecticides. [1]

• Clear the outdoors. Reduce debris or remove piles of rocks or lumber from around your home, and avoid storing firewood against the walls. [1]

• Arrange the bedroom. Keep beds away from the wall with only the legs touching the floor, don't store items under the bed, and don't let bedding drag on the floor. [1]

• Remove spiders and webs. If a spider is on your skin, flick it off with your finger rather than crushing it against your skin. [1]

• Be careful with tarantulas. When cleaning tarantula enclosures, wear gloves, a surgical mask, and eye protection. [1]

How Is a Spider Bite Diagnosed?

Spider bites can be mistaken for other skin sores that are red, painful, or swollen. [2] Many skin sores attributed to spider bites turn out to be caused by bites from other bugs, such as ants, fleas, mites, mosquitoes, and biting flies. [2] Skin infections and other skin conditions, even burns, can also be mistaken for spider bites. [2]

Your doctor will likely diagnose a spider bite based on your history and your signs and symptoms. [2] This might involve determining whether anyone saw a spider bite you, having an expert identify the spider, and ruling out other possible causes. [2]

Feature	Black widow	Brown recluse
Color	Shiny black	Golden or dark brown
Marking	Red hourglass on the belly	Dark violin shape on the back
Eyes	Usual spider pattern	Six eyes (a pair in front and a pair on each side)
Size	About 1 inch (2.5 cm) including legs	Body about 1/2 inch (1.2 cm)

How Are Spider Bites Treated?

Most spider bites heal on their own in about a week. [2] A bite from a recluse spider takes longer to heal and sometimes leaves a scar. [2]

First aid at home

1. Clean the wound with mild soap and water. [2] Apply an antibiotic ointment three times a day to help prevent infection. [2]

2. Apply a cool compress over the bite for 15 minutes each hour, using a clean cloth dampened with water or filled with ice, to help reduce pain and swelling. [2]

3. If possible, elevate the affected area. [2]

4. Take an over-the-counter pain reliever as needed. [2]

5. If the area is itchy, an antihistamine such as diphenhydramine or cetirizine might help. [2]

6. Watch the bite for signs of worsening or infection. [2] Antibiotics might be needed if the bite develops into an open wound or becomes infected. [2]

Six first-aid steps for most spider bites. See a doctor for open wounds or signs of infection.

What a doctor may provide

For pain and muscle spasms, your doctor might prescribe pain medicine, muscle relaxants, or both. [2] You might also need a tetanus shot. [2] For black widow bites causing severe pain or life-threatening symptoms, your doctor might recommend antivenom, usually given through a vein. [2] Symptoms usually ease within about 30 minutes of receiving antivenom, but it can cause serious allergic reactions and must be used with caution. [2]

Treatment	Used for	Key details
Soap, water, and antibiotic ointment	All spider bites	Ointment applied three times daily to prevent infection
Cool compress	Pain and swelling	15 minutes each hour with a damp cloth or ice
Elevation	Swelling	Raise the affected area if possible
Over-the-counter pain reliever	Pain	Taken as needed
Antihistamine	Itching	For example diphenhydramine or cetirizine
Prescription pain medicine or muscle relaxants	Widow-bite pain and spasms	Prescribed by a doctor
Tetanus shot	When indicated	Given if needed
Antivenom (IV)	Severe or life-threatening black widow bites	Used with caution because of the risk of serious allergic reactions

How Should You Prepare for the Appointment?

If you've been bitten by a spider you suspect is dangerous, call your primary care doctor or go to an urgent care center. [2] If your doctor offers online services, you may be able to email a photo of the spider. Bring the spider or a photo of it if you can do so safely, list your symptoms, and write down your questions. [2] Your doctor is likely to ask when your symptoms began, what you were doing in the hours before they started, whether they have gotten worse, and what relieves or worsens them. [2]

Conclusion and Next Steps

The overwhelming majority of spider bites are harmless: a red, inflamed bump that looks like any other bug bite and heals within about a week. The exceptions are bites from widow and recluse spiders, whose venom can cause serious symptoms such as spreading pain, muscle cramping, fever, and wounds that darken into open sores.

Wash the bite, keep it cool and clean, watch it closely, and get medical help when warning signs appear. If you're unsure whether a bite came from a dangerous spider, treat it seriously and have it evaluated. Seek emergency care immediately for severe pain, muscle cramping, trouble breathing or swallowing, or rapidly spreading redness.

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Frequently Asked Questions

Are spider bites usually dangerous?

No. Spider bites are usually harmless, and spiders don't usually bite unless threatened. A typical bite looks like any other bug bite, a red, inflamed bump, and may go unnoticed.

How do I know it's a spider bite?

It's difficult to be certain unless you actually saw the spider bite you. Many skin sores that look like spider bites have other causes, including bites from ants, fleas, mites, mosquitoes, and flies, plus skin infections and even burns.

Which spiders can actually hurt people?

Worldwide, only a few species have fangs long enough to penetrate human skin and venom strong enough to hurt humans, mainly widow spiders (about 30 species) and recluse spiders (more than 140 species worldwide).

What does a black widow bite look like?

A black widow has a shiny black body, long legs, and a red hourglass shape on its belly, and is about 1 inch (2.5 cm) across including legs. Its bite can cause redness and swelling that spreads to the abdomen, back, or chest, severe muscle cramping sometimes mistaken for appendicitis, and nausea, vomiting, tremors, or sweating lasting 1 to 3 days.

What does a brown recluse bite look like?

A brown recluse is golden or dark brown with a dark violin shape on its back, six eyes instead of the usual eight, and a body about 1/2 inch (1.2 cm) across. Bite pain increases over the first eight hours, and the wound can develop a pale center that turns dark blue or purple with a red ring, sometimes growing into an open sore.

When should I see a doctor for a spider bite?

Seek medical care immediately if you were bitten by a dangerous spider, you're unsure whether it was dangerous, you have severe pain or abdominal cramping, you're having trouble breathing or swallowing, or the sore has spreading redness or red streaks.

How do you treat a spider bite at home?

Clean the wound with mild soap and water and apply antibiotic ointment three times a day, use a cool compress for 15 minutes each hour, elevate the area if possible, take an over-the-counter pain reliever as needed, and use an antihistamine if the area itches. Watch the bite for signs of worsening or infection.

How long does a spider bite take to heal?

Most spider bites heal on their own in about a week. A bite from a recluse spider takes longer and sometimes leaves a scar; severe recluse wounds can take weeks or months to heal.

Do you need antibiotics for a spider bite?

Not for a typical bite. You might need them if the bite develops into an open wound or becomes infected. Your doctor might also suggest a tetanus shot.

What is black widow antivenom?

For bites causing severe pain or life-threatening symptoms, a doctor might recommend antivenom given through a vein. Because antivenom can cause serious allergic reactions, it must be used with caution, and its benefit is debated.

How do I prevent spider bites at home?

Learn what dangerous spiders look like, wear protective clothing when cleaning storage areas, shake out gloves and clothing before use, use DEET repellent, install tight screens and seal cracks, clear debris from around the house, keep beds off the wall with bedding off the floor, and remove spiders and webs, flicking spiders off your skin instead of crushing them.

Are spider bites deadly?

Rarely, a bite from a widow or recluse spider is deadly, particularly in small children. A severe recluse wound can take weeks or months to heal and leave large scars.

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References

1. Mayo Clinic Staff. Spider bites: symptoms and causes. Mayo Clinic. July 30, 2021. https://www.mayoclinic.org/diseases-conditions/spider-bites/symptoms-causes/syc-20352371

2. Mayo Clinic Staff. Spider bites: diagnosis and treatment. Mayo Clinic. July 30, 2021. https://www.mayoclinic.org/diseases-conditions/spider-bites/diagnosis-treatment/drc-20352377

3. Bennett RG, Vetter RS. An approach to spider bites: erroneous attribution of dermonecrotic lesions to brown recluse or hobo spider bites in Canada. Can Fam Physician. 2004;50:1098–1101. PMID 15455808. https://pubmed.ncbi.nlm.nih.gov/15455808/

4. Vetter RS. The distribution of brown recluse spiders in the southeastern quadrant of the United States in relation to loxoscelism diagnoses. South Med J. 2009;102(5):518–522. PMID 19373143. https://doi.org/10.1097/SMJ.0b013e3181a0abb3

5. Isbister GK, Page CB, Buckley NA, et al. Randomized controlled trial of intravenous antivenom versus placebo for latrodectism: the second Redback Antivenom Evaluation (RAVE-II) study. Ann Emerg Med. 2014;64(6):620–628.e2. PMID 24999282. https://doi.org/10.1016/j.annemergmed.2014.06.006

Medical Disclaimer

This article is for informational purposes only and does not constitute medical advice. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or an injury.