Diagnostic standard
A spider bite is only confirmed when the spider is observed biting, captured, and identified by a qualified arachnologist. Without all three steps the diagnosis is presumptive at best.
A 2011 study in the Annals of Emergency Medicine found that fewer than 20% of presumed 'spider bites' were verified; the majority were methicillin-resistant Staphylococcus aureus (MRSA) infections.
What most verified bites look like
Two small puncture marks within a few millimeters of each other, mild redness, and localized pain that resolves within 24–72 hours. Most spider species in North America cannot puncture human skin or deliver venom of medical consequence.
Systemic symptoms (fever, chills, muscle cramping, expanding necrosis) are not typical of common house spiders and warrant evaluation for infection or envenomation by a medically significant species.
When to seek care
Seek medical evaluation if you develop spreading redness, pus, fever, severe pain disproportionate to the lesion, or systemic symptoms - these suggest infection or, rarely, true envenomation by a widow or recluse.
References
- [1]Spider Bites: Updates and Misconceptions - American Family Physician. Accessed June 2026.
- [2]Verification and Reporting of Spider Bites - Annals of Emergency Medicine. Accessed June 2026.
Related in Bites and medical
- Brown recluse bite: symptoms and treatmentLoxoscelism - the syndrome caused by Loxosceles envenomation - is rare even within the brown recluse's native range and is over-diagnosed.
- Black widow bite: symptoms and treatmentLatrodectism is the syndrome caused by Latrodectus envenomation.
- Spider bite vs. MRSA infectionThe most common misdiagnosis for a 'spider bite' is community-acquired MRSA.
- Are spider bites dangerous?For the average person in North America, spider bites are very rarely dangerous.
- Necrotic arachnidism: scope and overdiagnosisNecrotic skin lesions attributed to spiders are overwhelmingly caused by other agents.
- Antivenom for widow envenomationLatrodectus antivenom (Antivenin Latrodectus mactans, Merck) is effective at relieving systemic latrodectism but is reserved for severe or refractory cases due to the risk of acute hypersensitivity and serum sickness..