How to Identify & Treat Poisonous Spider Bites

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Learn to differentiate between dangerous or harmless spider bites

Co-authored by Samuel Ramsey, PhD and Amber Crain

Last Updated: February 16, 2026 Fact Checked

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• Harmful Spider Bites
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• Mild or Harmless Bites
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• How do you know if a spider bite is dangerous?
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• Prevention
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• FAQs
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• Video

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Spiders tend to make people a little uncomfortable, but most of them aren’t actually dangerous. They’re much more afraid of us than we are of them! Spider bites happen, though, and it can be tough to tell what you’re dealing with–is the bite dangerous or harmless? In this article, we’ll explain which spider bites need medical attention, which are harmless, and how to tell them apart. We also spoke to scientists, medical professionals, and pest control experts for tips on how to treat spider bites (and prevent them altogether).

Note: Chances are, your spider bite is nothing to be worried about, but in the unlikely case you’ve crossed paths with a black widow or brown recluse, it’s important to get treatment right away.

Which spider bites are poisonous?

Most spiders are harmless, but there are a few poisonous ones to watch out for, including black widows, brown recluses, Brazilian wandering spiders, and yellow sac spiders. If one of these spiders bit you, seek medical attention immediately. The bite may not be lethal, but the venom can make you incredibly ill.

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Section 1 of 5:

Harmful Spider Bites

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   Black widow bite Black widow spiders (Latrodectus) have toxic venom. If you’re bitten, you’ll feel a sharp pain, almost like a pinprick. Black widows have long fangs, so you might see tiny red fang marks on your skin. The area will go numb, followed by muscle cramps, with redness and mild swelling around the bite. More serious symptoms will occur soon after.

   • Bite appearance: 1-2 tiny red puncture marks surrounded by red and swollen skin In some cases, a target-shaped lesion may develop.
   • Common symptoms: Numbness, severe pain, stiffness, muscle spasms, fever, nausea, excessive sweating, swollen or droopy eyes, headache, difficulty breathing.
   • Recommended treatment: Immediate medical attention for anti-venom and a tetanus shot. In the meantime, clean it with soap and water and apply an ice pack.
   • How serious is it? It won’t kill you, but it will make you very sick, especially if you don’t get treatment within 24-48 hours. After treatment, you’ll recover within 24-48 hours.
   • What black widows look like: Black widows have shiny black bodies ranging in size from ¹⁄₄–¹¹⁄₈ inches (6.4–34.9 mm) long. Only the females bite, and females have a distinctive red hourglass marking on their bellies.
   • Where black widows live: Southern and Western U.S., but they’ve been spotted in all states except Hawaii and Alaska.

   Meet the wikiHow Experts

   Samuel Ramsey, PhD, is an entomologist and a researcher with the United States Department of Agriculture.

   Julia Eze, NP-C, is a board-certified family nurse practitioner based in Atlanta, Georgia. She has over 10 years of experience in the field.

   Elmer Bensinger is a pest control specialist with Eden Advanced Pest Technologies in Spokane, Washington. He has over 20 years of experience.

   Luke Lewis is a pest management expert and the founder of Native Pest Management. He specializes in pet-friendly and eco-friendly pest control, termite control, and lawn care.

   Brandon Runyon is a board-certified entomologist based in Evansville, Indiana. He has over 18 years of experience as a pest control professional.
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   Brown recluse bite Brown recluse spiders (Loxosceles) are venomous. The initial bite is painless, so you may not notice it at first. The severity of your reaction depends on how deeply the venom penetrated. Typically, after 3-8 hours, you’ll feel pain and a burning sensation, and then a bullseye-shaped blister, bruise, or ulcer will develop. In the following hours and days, more serious symptoms may start to occur.

   • Bite appearance: Red, swollen, and itchy (like a regular insect bite), then develops a blister or sore with a dark, sunken middle. In severe cases, the skin turns bluish or black.
   • Common symptoms: Pain, swelling, itching, blisters, muscle cramps, headaches, nausea, fever/chills, blackened skin around the bite (necrosis). Entomologist Samuel Ramsey, PhD, says most brown recluse bites won’t become serious necrotized wounds, though.
   • Recommended treatment: Immediate medical attention. No anti-venom exists for brown recluses, but you need medical intervention to manage symptoms.
   • How serious is it? Serious. You won’t get sick or die, but treatment is needed to prevent the skin from turning black and dying, which can cause serious scarring.
   • What brown recluses look like: These spiders are usually brown and about 1 inch (25 mm). According to Dr. Ramsey, they also have a distinctive violin-shaped mark that will help you recognize them.
   • Where they live: Southeastern and midwestern U.S.
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   Brazilian wandering spider bite Brazilian wandering spiders (Phoneutria nigriventer), also known as banana spiders, have highly toxic venom that immediately affects the nervous system. If you’re bitten by one, the pain will be intense and immediate. These spiders don’t build webs–instead, they creep along the forest floor at night hunting for prey. Unsettling to imagine, but bites are rare and you’re unlikely to run into this spider in the wild.

   • Bite appearance: Dark red and swollen bump, potentially with visible fang marks. The skin around the bite may blister or get purplish.
   • Common symptoms: Pain, sweating, drooling, irregular heartbeat, high blood pressure, and prolonged, painful erections (priapism) in men.
   • Recommended treatment: Immediate medical attention to get the antivenom administered to you.
   • How serious is it? Serious. While unlikely to kill an adult, it will make you very unwell and potentially put you in the hospital. The bite can be lethal for kids.
   • What Brazilian wandering spiders look like: Their hairy bodies can be up to 2 inches (51 mm) long, with a leg span of up to 7 inches (180 mm). They vary in color, but most are brown and gray.
   • Where they live: Mainly South America (especially Brazil, hence the name).
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   Yellow sac spider bite Yellow sac spiders (Cheiracanthium) are venomous, and their venom acts as a cytotoxin to humans (which means it destroys cells or impairs their functioning). This bite typically causes redness and swelling, and could potentially cause necrotizing (flesh-eating) lesions similar to brown recluses, but less severe.

   • Bite appearance: 2 small, red, swollen bumps (with visible puncture wounds) or 1 larger red bump. May develop a small blister, a dark spot in the center, or mild necrotic lesions.
   • Common symptoms: Pain, itching, redness, swelling, headache, nausea, vomiting, necrotizing lesions (severe cases).
   • Recommended treatment: Treatment varies depending on bite severity. Monitor your symptoms at home and see a medical professional if symptoms worsen or change.
   • How serious is it? It won’t kill you, but it can be very painful, and may occasionally cause necrotizing lesions.
   • What yellow sac spiders look like: They have pale yellow or light green bodies and long, thin legs (with the front legs being noticeably longer). Most grow to ¹⁄₄ inch (6.4 mm) and ³⁄₈ inch (9.5 mm).
   • Where they live: Throughout the United States, Mexico, and South America.
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Section 2 of 5:

Mild to Harmless Spider Bites

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1. 
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   Wolf spider bite Wolf spiders (Lycosidae) are venomous, but their venom isn’t super dangerous to humans. A wolf spider’s fangs will puncture the skin, so you might see two little red marks, but usually only result in mild redness, swelling, itching and irritation. However, symptoms can be more severe for immunocompromised individuals and those who are allergic to the venom.

   • Bite appearance: Red, swollen skin with tiny (but visible) puncture wounds where the fangs went in. Skin may look slightly damaged or torn.
   • Common symptoms: Mild redness, swelling, and itching. Rare but serious symptoms include a red line extending from the bite, a swollen bump that increases in size, facial swelling, difficulty breathing, dizziness or fainting.
   • Recommended treatment: Home treatment is fine. Clean it with soap and water, take an OTC pain reliever (if needed), and use an ice pack to manage swelling. Take an antihistamine if the area itches. Board-certified family nurse practitioner Julia Eze, NP-C, suggests applying aloe vera or witch hazel to calm itchy skin.
   • How serious is it? It’s not that serious–unless you’re immunocompromised or allergic. Get medical attention if you have symptoms other than redness, pain, and mild swelling.
   • What wolf spiders look like: Wolf spiders are dark brown or gray; some have stripes or markings down their backs. They’re about 2 inches (51 mm) long, and larger ones are hairy.
   • Where they live: Every continent on Earth (aside from Antarctica).
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   Hobo spider bite Hobo spiders (Tegenaria agrestis) are venomous, but it’s not toxic to humans. Misinformation has been spread about their potentially necrotic (flesh-eating) bites, but scientific evidence doesn’t back that up as a symptom. The CDC does not consider the hobo spider to be harmful humans.

   • Bite appearance: A tiny prick that develops into a small, red, swollen bump.
   • Common symptoms: Mild pain, redness.
   • Recommended treatment: Home treatment is fine. Clean the bitten area with soap and water and cover it with a sterile bandage.
   • How serious is it? It’s not serious at all. The mild pain and redness will go away on its own in a few days. Visit a doctor if you develop additional symptoms.
   • What hobo spiders look like: They have light to medium brown bodies with dark stripes down the center. They can grow up to 1 inch (25 mm) in diameter.
   • Where they live: Pacific Northwest.
3. 
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   Jumping spider bite The jumping spider (Salticidae) has fangs and produces venom, but their venom is not a medical threat to humans. That said, their bite can cause mild symptoms like redness and swelling. Jumping spiders are very shy, so you’re unlikely to be bitten by one.

   • Bite appearance: A tiny, red, swollen bump that itches (similar to a mosquito bite).
   • Common symptoms: Redness, itching, stinging, and swelling.
   • Recommended treatment: Home treatment is fine. Clean it with soap and water, apply an ice pack to manage swelling, and take OTC acetaminophen or antihistamines to relieve minor pain and itching. Symptoms should reduce within 24 hours.
   • How serious is it? It’s not very serious. Monitor your symptoms; if they get worse after 24 hours, contact your doctor.
   • What jumping spiders look like: They have short, hairy bodies ranging in length from ¹⁄₅–³⁄₄ inch (5.1–19.1 mm) in length. They tend to jump erratically from place to place.
   • Where they live: Throughout the United States.
4. 
   4
   Tarantula bite Tarantulas (Theraphosidae) are venomous, but they rarely bite and their venom is only mildly toxic to humans, causing symptoms like redness and swelling. That said, their fangs are strong and large enough to leave marks on your skin, so the actual bite can be painful. Tarantulas are hairy, and skin contact with the hairs can be mildly irritating, as well.

   • Bite appearance: Red, swollen bump with mild swelling (similar to a bee sting)
   • Common symptoms: Mild pain and throbbing, redness, itching, and swelling.
   • Recommended treatment: Home treatment is fine. Clean it with soap and water and monitor symptoms. Pain/throbbing may last a few hours; use OTC pain relievers.
   • How serious is it? It’s not serious. The bite will sting for a bit, similar to a bee sting However, if you experience fever, nausea, or vomiting, seek medical attention.
   • What tarantulas look like: Tarantulas look imposing with their large, hairy bodies and long legs, but they are quite docile. They are usually black, brown, or gray.
   • Where they live: Tarantulas are popular pets, so one might live at your buddy’s house! In the wild, they’re found in the American Southwest, Mexico, and Central and South America.
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   Camel spider bite There’s a lot of misinformation out there about camel spiders (Solifugids​). They’re classified as arachnids, but they’re really more of a cross between a spider and a scorpion–which admittedly, sounds creepy! They’re also aggressive, but will only bite when threatened, cornered, or handled. The bite will be about as painful as a bee sting. They aren’t venomous, but they have strong jaws.

   • Bite appearance: Very red and swollen spot with two distinct puncture wounds.
   • Common symptoms: Pain, swelling.
   • Recommended treatment: Home treatment is fine. Clean it with soap and water, cover the bite, and monitor symptoms. Take OTC pain relievers for pain and swelling.
   • How serious is it? It’s not very serious, but it will sting quite a bit. Avoid touching or scratching the bite area to prevent infection.
   • What camel spiders look like: They’re usually light grey, tan, or reddish-brown, with their sizing ranging from ¹⁄₂–4 inches (13–102 mm). They have 8 legs and a hairy, segmented body.
   • Where they live: In deserts all over the world, including North American ones.
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Section 3 of 5:

How do you know if a spider bite is dangerous?

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1. 
   Symptoms like fever, chills, and vomiting indicate a more serious bite. Most common spider bites are harmless and only cause minor symptoms like temporary redness, pain, swelling, and itching. These symptoms go away on their own in a few days and don’t require medical treatment. If you develop more serious symptoms, it’s important to seek medical treatment.

   • Keep in mind most venomous spider bites aren’t lethal–but you need treatment for the serious ones. Antivenom needs to be administered (otherwise you will not be okay).
   • Do I need to call emergency services? Yes, get treatment ASAP if you’re experiencing fever, chills, and vomiting. If you’re having trouble breathing, suffering from intense headaches, or burning up with fever, call 911 immediately.

Section 4 of 5:

Preventing Spider Bites

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1. 
   Spiders have specific hiding places and behaviors that can be avoided to minimize the chances of being bitten. No strategy is 100% foolproof, though. Spiders live among us and we can’t avoid these creatures entirely. To prevent being bitten, these useful tips will help:

   • Use insect repellant registered with the U.S. Environmental Protection Agency (EPA).
   • Trim the vegetation in your yard. Pest control specialist Elmer Bensinger says many spider food sources live in overgrown bushes and shrubs. “If you can control their food source and trim back vegetation, you make it extremely undesirable for them to be there.”
   • Store firewood outdoors and check for spiders before bringing it inside.
   • Shake out your shoes, hats, gloves, etc. before wearing them.
     • Dr. Ramsey says brown recluses love to hang out in shoes, and the most common way people get bitten is by sticking their foot in without looking.
   • Wear gloves for outdoor chores like gardening, moving rocks or furniture, or carrying wood. Wear long sleeves and pants outdoors (especially in wooded areas).
   • Declutter your home and get rid of old newspapers, clothing, and unused furniture.
   • Seal all openings, cracks, and crevices in your home with caulk.
   • Turn off or minimize outdoor lighting. ​​Pest management expert Luke Lewis says, “Mosquitoes, midges, and gnats are attracted to lights at night and are a primary food source for spiders. By keeping exterior lights off or by replacing the lights with yellow or purple bulbs, there will be a significant reduction in flying insects which will in turn help keep spiders away.”
   • Avoid approaching or touching any spiders you do cross paths with. Entomologist Brandon Runyon says that most spiders only bite when they’re defending themselves. If you don’t threaten them, they typically won’t bite.
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Section 5 of 5:

FAQs About Spider Bites

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1. 1
   Are all spiders venomous? Almost all spiders are venomous because they use their fangs and venom to incapacitate their prey. However, most spider venom isn’t harmful for humans. Only a few species have venom that can hurt us or make us sick (black widow, brown recluse, etc.)
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   How long after a spider bite do symptoms begin? Most mild symptoms, like pain, itching, and swelling will begin right away. The one exception: brown recluses. Their bites are painless, and you may not even know you were bitten for hours.
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   Is it okay to touch or squeeze a spider bite? No, it’s not okay–try to avoid it as much as possible. Spider bites are tiny open wounds, and touching them could cause a bacterial infection. Board certified allergist & immunologist Farah Khan, MD suggests applying a calming lotion, chamomile oil, or a topical steroid like 1% hydrocortisone to prevent yourself from scratching. Another anti-itch option is taking an oral OTC antihistamine.
4. 4
   What can be easily mistaken for a spider bite? Many skin conditions can mimic the symptoms of a spider bite including other insect bites, rashes, bacterial infections, and sores. The symptoms of more dangerous spider bites, like black widows, can be very similar to the flu (at first). Be cautious and monitor your symptoms–if something seems unusual, don’t hesitate to call your doctor.
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