A typical spider bite looks like a single small red bump, sometimes with a tiny blister, mild swelling and redness around it. You may see a set of tiny fang marks where the spider broke the skin, Cleveland Clinic says. Most bites are raised, red and itchy and fade on their own within several days, according to the American Academy of Family Physicians (AAFP).
But many sores people blame on spiders are something else. The Merck Manual says skin infections, including MRSA, are often mistaken for spider bites, and you can’t identify a spider from the bite mark alone.
Get care now for trouble breathing or swallowing, swelling of the face or mouth, chest tightness or a racing heartbeat after a bite (call 911), and see a doctor promptly for a bite that is spreading, turning dark or into an open sore, draining pus, or coming with fever. See When to worry about a spider bite for the full list.
In the video above, family physician Dr. Richard Honaker describes the two spider bites that concern doctors most. He says a brown recluse bite generally starts as a small puncture wound that turns dark brown and then black, and the dark area can keep spreading, while a black widow bite does little at the bite itself apart from some pain. The video page covers those two spiders in depth. This article is about recognizing a bite, and the common things mistaken for one.
Signs and symptoms of a spider bite
Most spider bites cause only local symptoms. Cleveland Clinic and MedlinePlus list:
- a small bump or blister
- redness or other skin discoloration (redness is harder to see on brown or black skin, the NHS notes, so you may need to feel for a lump)
- mild swelling
- pain, burning, numbness or tingling at the bite
- itching
- sometimes tiny fang marks
The 2022 review in American Family Physician, the AAFP’s journal, says typical spider bites show up as a single bump, a small pus bump or a raised welt. One bite, not a group of them, is the usual pattern.
Many people never feel the bite. Cleveland Clinic notes that most people don’t see the spider, and some think an insect bit them instead.
Are spider bites itchy?
Often, yes. AAFP describes most spider bites as raised, red and itchy. Cleveland Clinic lists itching as a sign of a brown recluse bite, either at the bite or all over the body, and an itchy rash as possible with black widow bites. Bug bites itch because the body releases a chemical called histamine at the bite, Cleveland Clinic explains.
That said, itching doesn’t tell you it was a spider. MedlinePlus says mosquito, flea and mite bites are more likely to itch than to hurt. A crop of very itchy bumps points more toward those bugs than toward a spider.
Spider bite vs. MRSA, mosquito, bed bug and flea bites
This table shows how sources describe each. A doctor may still need to look at the spot, and sometimes test the fluid, to know for sure.
| Spider bite | MRSA or skin abscess | Mosquito bite | Bed bug bites | Flea bites | |
|---|---|---|---|---|---|
| How many | Usually a single spot (American Family Physician) | A single pocket of pus in the skin (MedlinePlus) | A single raised bump (Cleveland Clinic) | Several, in a line, zigzag or random pattern, or grouped (Cleveland Clinic, NHS) | Several, in a straight line or a cluster (Cleveland Clinic) |
| Look | Small bump or blister, mild swelling, redness; maybe tiny fang marks (Cleveland Clinic) | Red, swollen, painful area that may be filled with pus or fluid (Cleveland Clinic); hardened skin, raised or open sore (MedlinePlus) | Small, raised bump; sometimes a tiny dark dot in the center (Cleveland Clinic) | Slightly swollen bumps with a reddish bruise in the middle (Cleveland Clinic) | Small, discolored bumps, sometimes with a ring or halo; smaller than mosquito bites (Cleveland Clinic) |
| Where on the body | Anywhere | Anywhere (MedlinePlus) | Any exposed skin | Skin exposed in bed, such as face, neck, arms, back and legs (Cleveland Clinic, NHS) | Mostly feet, calves and ankles; rarely above the knee (Cleveland Clinic) |
| Main feeling | Pain or itch, often mild | Pain, tenderness and warmth (MedlinePlus) | Itch | Itch, sometimes intense (NHS) | Itch |
| Pus or fever | Not usual; pus or fever suggest infection | Pus drainage common; fever or chills sometimes (MedlinePlus) | Not typical | Not typical; scratched bites can turn into red, oozing sores (Cleveland Clinic) | Not typical; scratching can break the skin and let infection in (Cleveland Clinic) |
| How long | Most fade within several days (AAFP) | Warm compresses may help it drain; a doctor may need to cut it open and drain it (MedlinePlus) | A few days (Cleveland Clinic) | Usually heal within about a week (Cleveland Clinic, NHS) | A few days (Cleveland Clinic) |
The big one to know is MRSA. Cleveland Clinic, the Merck Manual and American Family Physician all warn that staph skin infections, including MRSA, are often mistaken for spider bites. A skin abscess is a pocket of pus, MedlinePlus explains, usually caused by staph. If you have a painful, warm, swollen lump that keeps getting bigger or fills with pus, and you never saw a spider, it’s more likely an infection. Don’t squeeze or pop it. MedlinePlus says a doctor may need to drain it and may prescribe antibiotics.
Cleveland Clinic notes that a doctor may test the fluid from a blister to rule out infections such as MRSA. There is no test that confirms a spider bite.
What does a brown recluse or black widow bite look like?
The video page has photos of both spiders and a full timeline. In short:
- Brown recluse: AAFP describes a bite that may not be felt at first, then pain after a few hours and possibly a bull’s-eye: a white blister with a red ring. The center may turn purple or blue. American Family Physician says a brown recluse bite is usually a single, flat spot without swelling, and most clear up in one week or less.
- Black widow: MedlinePlus says there may be minor swelling, redness and a target-shaped sore. The bigger signs are not on the skin: dull muscle pain spreading from the bite, cramps and sweating.
Spider bite rash: when the skin reaction spreads
A spider bite is usually one spot. A widespread rash is different. The Merck Manual and Cleveland Clinic list rash or itching all over the body as possible with brown recluse and black widow bites. MedlinePlus lists rash or flushing among the signs of a severe allergic reaction to a bite or sting, along with face or mouth swelling and trouble breathing. Call 911 for those.
Cleveland Clinic says a reddish streak spreading out from a bite, along with blisters or pus, can mean a skin infection called cellulitis. That needs a doctor.
Spider bite on the leg
A bump on the leg could be a spider bite, but legs are also where some look-alikes show up. Cleveland Clinic says flea bites mostly appear on the feet, calves and ankles, often in a line or cluster. A single painful, warm, swelling lump on the leg could be a spider bite or a skin abscess.
For a bite on an arm or leg, AAFP advises raising it above heart level to reduce swelling. See Spider bite treatment and first aid for the rest of the home care steps.
When to see a doctor
See a doctor for a bite or bump that:
- is getting bigger, more painful or more swollen after the first day
- has redness spreading away from it, or a red streak
- forms a blister, a bull’s-eye, a dark center or an open sore
- drains pus or fluid
- comes with fever, chills, body aches, nausea or vomiting
- you think came from a brown recluse or black widow
- is on a young child or older adult, since AAFP says they are more likely to have complications
If you can do it safely, bring the spider in a closed container, even if it’s dead (AAFP).
Frequently asked questions
What are the signs of a spider bite?
A single small red bump, sometimes with a tiny blister, mild swelling, pain or itching, and occasionally tiny fang marks. Many people don’t feel the bite or see the spider.
Are spider bites itchy?
Many are. AAFP says most spider bites are raised, red and itchy. But a group of very itchy bumps is more often from mosquitoes, fleas, mites or bed bugs.
Why do I have spider bites that itch and keep appearing?
New, itchy bumps that keep showing up, especially in lines or clusters, point toward bed bugs or fleas rather than spiders. Bed bugs bite skin exposed in bed, and flea bites cluster around the feet and ankles, per Cleveland Clinic.
Is it a spider bite or MRSA?
You can’t always tell by looking. A painful, warm, swollen lump that grows or fills with pus is more likely a skin infection such as MRSA, which sources say is often mistaken for a spider bite. See a doctor and don’t pop it.
What does a spider bite rash look like?
Most spider bites don’t cause a rash, just one spot. A rash spreading over the body can happen with brown recluse or black widow bites, and rash with swelling of the face or trouble breathing can mean a severe allergic reaction. Call 911 for those.
Find a doctor
A family physician can look at a bite or bump and tell whether it needs treatment. Doctors on Best Docs Network who can check a spider bite include:
- Dr. Richard Honaker, family medicine, Dallas-Fort Worth
- Dr. Michael Dotti, family medicine, Dallas-Fort Worth
- Dr. Cody Mihills, family medicine, Dallas-Fort Worth
Sources
- American Academy of Family Physicians, familydoctor.org. What Should I do if I Get a Spider Bite?.
- American Family Physician (American Academy of Family Physicians). Arthropod Bites and Stings (2022).
- Cleveland Clinic. Spider Bites.
- Cleveland Clinic. Bug Bites and Stings.
- Cleveland Clinic. MRSA (Methicillin-resistant Staphylococcus aureus).
- Cleveland Clinic. Mosquito Bites.
- Cleveland Clinic. Bed Bugs.
- Cleveland Clinic. Flea Bites.
- MedlinePlus (U.S. National Library of Medicine). Insect bites and stings.
- MedlinePlus (U.S. National Library of Medicine). Black widow spider.
- MedlinePlus (U.S. National Library of Medicine). Skin abscess.
- Merck Manual Consumer Version. Spider Bites.
- NHS. Insect bites and stings.
- NHS. Bedbugs.
This article is for general information only and is not medical advice. Talk with a qualified health professional about your own situation. If you think you may have a medical emergency, call 911.
