Spider Bite? What to Do (and How to Know It Was Really a Spider)
Updated July 27, 2026 · By the makers of Spider Identifier: Venom ID
First, a fact that surprises people: studies of patients arriving with "spider bites" find that most are something else, usually infected skin, other insect bites, or MRSA. Spiders bite humans rarely, defensively, and almost always when pressed against skin in clothing or bedding.
So this guide covers three things: sensible first aid, the red flags that mean medical care, and how identification, of the spider, if you actually saw one, changes the picture.
First aid for a suspected bite
For the overwhelming majority of bites, that is the whole story: a red bump that itches or stings for a day or two and fades like a mosquito bite.
- Wash the area with soap and water.
- Apply a cold pack wrapped in cloth, 10 minutes on, 10 off, for swelling.
- Elevate the limb if it is swollen.
- Do not cut, suck, or apply heat, folk remedies make it worse.
- Mark the edge of any redness with a pen and note the time, so you can see whether it spreads.
Red flags: get medical care
- Severe or spreading pain, muscle cramps, or abdominal rigidity (possible widow bite)
- A blister or ulcer that grows, darkens, or opens over 24 to 72 hours (possible recluse bite, or an infection either way)
- Fever, chills, nausea, or feeling generally ill after a bite
- Red streaks spreading from the site, classic infection sign
- Any suspected bite on a small child, or in someone immunocompromised
If you saw the spider, identify it
Identification transforms the decision. A confirmed harmless species means you can stop worrying and treat the bump like any insect bite. A confirmed widow or recluse means prompt medical care even before symptoms peak. If the spider is present and can be photographed safely, or captured under a glass, do it; emergency physicians genuinely appreciate a photo over a squashed smear.
Do not delay care to hunt for the spider, and never handle a live suspect with fingers.
If you never saw a spider
A bump you woke up with, no spider seen, is statistically unlikely to be a spider bite at all. Treat it with the basic first aid above and watch the red flags. If it worsens instead of fading over 48 hours, see a doctor and say "I do not know what this is" rather than "spider bite"; the honest framing gets better diagnosis.
Identify the spider with Spider Identifier
- If the spider is still there, photograph it from a safe distance, top-down.
- Read the species and the danger verdict.
- Open the bite and first aid section on the species page.
- Share the identification with whoever is treating the bite.
The app supports decisions; it does not replace medical care when red flags appear.
Download Spider Identifier on the App StoreSafety note: identification apps are decision support, not a medical opinion. If a bite shows spreading pain, an open wound, or fever, or you suspect a widow or recluse, seek medical care promptly.