Spider bite vs MRSA: how to tell?
Last updated September 3, 2026.
Unless you saw the spider, it is probably not a spider bite: the CDC notes most suspected spider bites are staph or MRSA skin infections, a red, swollen, painful, warm, pus-filled bump that grows over 24-48 hours. Real significant spider bites are rare: most spiders cannot pierce skin, black widow bites cause body-wide muscle cramping more than a skin lesion, and brown recluse ulcers are region-specific and take days to develop. The behavioral tell: infection worsens, heats up, and may add fever or red streaks; a simple bite stays stable and fades. The rules: never squeeze or pop it (that spreads bacteria), cover it, wash hands, and see a provider, urgently if worsening fast, not improving in 48 hours, or feverish, because MRSA often needs drainage plus specific antibiotics. While it heals: no shared towels, razors, or gym gear, and wash bedding, since MRSA spreads person to person. The ER version: spreading infection with fever, confusion, or racing heart, or a bite followed by severe cramping or breathing trouble.
What to do
- No spider seen: assume infection, not bite.
- Never squeeze or pop it; cover and wash hands.
- Not improving in 48 hours or feverish: see a provider urgently.
- No shared towels or razors: MRSA spreads.
- Fever with spreading infection, or severe cramps: ER.
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