Most spider bites are harmless. They cause a red, itchy bump that usually fades on its own within several days, according to the American Academy of Family Physicians (AAFP). Worry when the pain gets worse instead of better, the redness spreads, the bite turns into a blister or open sore, you get a fever or feel sick all over, or you think the spider was a brown recluse or a black widow.
Call 911 right away for trouble breathing or swallowing, swelling of the face, lips, mouth or tongue, chest tightness, a racing heartbeat, fainting or a seizure after a bite. These can be signs of a severe allergic reaction or a dangerous bite. For advice at any hour, call Poison Help at 1-800-222-1222.
In the video above, family physician Dr. Richard Honaker explains why the brown recluse and the black widow are the two spider bites that concern doctors most: brown recluse venom damages tissue at the bite, while black widow venom travels through the body and can cause severe muscle cramps, spasms and breathing problems that need a hospital visit as soon as possible. The video page covers both spiders in depth. This article focuses on a narrower question: how to tell when any bite needs a doctor.
What happens if you get bit by a spider?
Usually, not much. The Merck Manual explains that almost all spiders have venom, but the fangs of most kinds are too short or fragile to get through human skin. AAFP says most U.S. spiders are harmless and only two have venom that can cause serious skin and health problems: the black widow and the brown recluse. AAFP says black widows live mostly in the southern and western U.S. and brown recluses are most common in the Midwest and South, so both are a concern in Texas.
A typical bite may leave a set of tiny fang marks, a small bump or blister, mild swelling and redness, Cleveland Clinic says. Many people never feel the bite or see the spider. Cleveland Clinic notes that most people with spider bites have mild symptoms, such as pain and swelling, that gradually go away with home care.
Do spider bites go away on their own?
Most do. AAFP says the raised, red, itchy skin from most spider bites usually fades on its own within several days. The NHS says insect bites in general usually get better within a few days.
Even the more serious brown recluse usually heals without severe damage. A 2022 review in American Family Physician, the AAFP’s journal, says brown recluse bites typically clear up in one week or less, though an estimated 10% become necrotic (the tissue dies) 24 to 48 hours after the bite.
A bite that is getting worse, not better, after a day or two is the main reason to stop waiting it out. AAFP lists pain that gets worse 24 hours after the bite as a reason to contact your doctor right away.
Spider bite stages: what a bite does day by day
Sources give clear timelines only for the two dangerous spiders. Every bite is different, so treat these as rough guides, not a schedule.
| When | Most spider bites | Brown recluse (sources’ timeline) | Black widow (sources’ timeline) |
|---|---|---|---|
| At the bite | Often not felt; small bump, mild redness | May not be felt, or a sharp sting (MedlinePlus) | Pinprick-like pain, though some feel nothing (MedlinePlus) |
| First hours | Mild pain, itching, swelling | Red, sensitive area about 3 to 8 hours after the bite, sometimes bull’s-eye shaped or bruised (Cleveland Clinic) | Dull muscle pain spreading from the bite within 15 minutes to 1 hour (MedlinePlus) |
| First 1 to 2 days | Starting to fade | About 10% become necrotic after 24 to 48 hours (American Family Physician) | Muscle spasms and sweating come in waves and last 48 to 72 hours (American Family Physician) |
| Days 3 to 5 | Usually gone within several days (AAFP) | Mild bites settle; if venom spread, an ulcer may form (Cleveland Clinic) | Severe symptoms usually start to improve within 2 to 3 days (MedlinePlus) |
| Week 1 to 2 | Healed | Ulcer can keep growing for up to 10 days (AAFP); severe cases break down into a wound (Cleveland Clinic) | Milder symptoms may last several weeks (MedlinePlus) |
| Weeks to months | — | Most heal by about 3 weeks (Cleveland Clinic); a black scab (eschar) may separate after 2 to 5 weeks and leave an ulcer that takes months to heal (MedlinePlus) | — |
Red flags: when to worry about a spider bite
Contact a doctor right away if you notice any of these. This list combines warning signs from AAFP, Cleveland Clinic and MedlinePlus:
- Pain that gets worse, especially if it is worse 24 hours after the bite (AAFP)
- Redness that spreads away from the bite
- Fluid or pus leaking from the bite
- A bull’s-eye look, or the bite turning into a blister or open sore
- The center turning purple, blue, dark or black
- Fever, chills or body aches
- Nausea or vomiting
- Pain somewhere else in the body, such as a headache or belly cramping (AAFP)
- Severe muscle pain, cramps or weakness (Cleveland Clinic)
- A racing pulse, vision problems or a severe headache (Cleveland Clinic)
- You think the spider was a brown recluse or a black widow, even if the bite looks small. MedlinePlus warns that a brown recluse bite may look minor at first but can become severe over time.
Who should be seen after any possible bite: AAFP says young children and older adults are more likely to have complications and should see a doctor after a possible bite. The Merck Manual says people younger than 16 or older than 60, and people with high blood pressure or heart disease, usually need a hospital stay after a black widow bite.
Infected spider bite: signs to watch for
Any break in the skin can get infected, including a bite you scratched open. MedlinePlus advises watching the bite over the next several days for increasing redness, swelling or pain. Signs of an infected bite include:
- skin around the bite that feels hot or looks red (NHS)
- swelling and pain that get worse instead of better
- pus or fluid coming from the bite (NHS); Cleveland Clinic mentions yellow or cloudy drainage
- a reddish streak spreading out from the bite, blisters or pus drainage, which Cleveland Clinic describes as signs of a skin infection called cellulitis
- fever
An infected bite needs a doctor. Your doctor may prescribe an antibiotic, AAFP says. The 2022 American Family Physician review advises antibiotics for brown recluse bites only if the wound is actually infected. Cleveland Clinic warns that untreated infections can spread and, in serious cases, become life-threatening.
Could it be a skin infection instead of a spider bite?
Very often, yes. The Merck Manual says skin infections, including MRSA (a type of staph that resists some antibiotics), are often mistaken for spider bites. American Family Physician says many suspected bites are caused by other conditions, such as staph infection. Cleveland Clinic also says MRSA skin infections can be mistaken for spider bites.
A staph abscess is a pocket of pus in the skin. MedlinePlus describes swelling, hardened skin, a raised or open sore, redness, tenderness, warmth and pus drainage, sometimes with fever or chills. Don’t squeeze or pop it. A doctor may need to drain it. If you never saw a spider and you have a painful, warm, swollen bump, see a doctor. To learn how bites and look-alikes differ, see What does a spider bite look like?
Go to the ER if
Go to the emergency room, or call 911, for any of these:
- trouble breathing, wheezing or shortness of breath
- swelling of the face, lips, mouth or tongue, or a feeling that the throat is tight or closing
- trouble swallowing
- chest pain, chest tightness or a racing heartbeat
- dizziness, fainting or a seizure
- severe muscle cramps, stiffness or belly pain after a bite (signs of a possible black widow bite)
- fever, vomiting or feeling very ill along with a bite that is getting worse
- a likely brown recluse or black widow bite in a child
Cleveland Clinic advises getting emergency care for severe spider bites and for a suspected brown recluse or black widow bite. If you can do it safely, bring the spider in a closed container, even if it’s dead, so it can be identified (AAFP).
When to see a doctor (not an emergency)
Make an appointment, or call your doctor, if:
- the bite isn’t improving after a few days, or symptoms get worse (Cleveland Clinic)
- itching or swelling is severe, or swelling spreads
- you see signs of infection
- you’re not sure what bit you and the sore is growing
- you’re not sure your tetanus shot is up to date. AAFP says your doctor may give a tetanus shot if you haven’t had one in the past 5 years.
For what to do while you wait, see Spider bite treatment and first aid.
Frequently asked questions
How do I know if a spider bite is serious?
Warning signs include pain that gets worse after 24 hours, spreading redness, a blister or open sore, a center turning dark, pus, fever, chills, vomiting, severe muscle cramps or trouble breathing. A bite you think came from a brown recluse or black widow should be checked by a doctor even if it looks small.
What does an infected spider bite look like?
The skin around it gets redder, hotter, more swollen and more painful over time, and it may drain pus or cloudy fluid. A red streak spreading from the bite or a fever are also signs of infection. See a doctor; you may need an antibiotic.
Do spider bites go away on their own?
Most do. AAFP says the red, itchy bump from most spider bites fades on its own within several days. Most brown recluse bites also heal, but some form an open sore that can take weeks to months.
What are the stages of a spider bite?
Most bites go from a small red bump to fading within several days. A brown recluse bite may turn red and sore within hours; in about 10% of cases the center starts to die after 24 to 48 hours, and a dark scab and ulcer can form over the following weeks.
What happens if you get bit by a spider and don’t treat it?
Most ordinary bites heal on their own. The risk of waiting comes from bites that get infected, and from brown recluse or black widow bites, which can get worse over hours to days. Wash the bite, watch it, and see a doctor if any red flag appears.
Find a doctor
A family physician can check a bite that’s getting worse and follow it as it heals. 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. Brown Recluse Spider Bite.
- Cleveland Clinic. Bug Bites and Stings.
- Cleveland Clinic. MRSA (Methicillin-resistant Staphylococcus aureus).
- MedlinePlus (U.S. National Library of Medicine). Insect bites and stings.
- MedlinePlus (U.S. National Library of Medicine). Brown recluse spider.
- 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.
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.
