Why most 'spider bites' aren't
The 'spider bite' diagnosis is one of the most overused misdiagnoses in emergency medicine. Studies at US emergency departments consistently show that 40–80% of lesions diagnosed as spider bites are actually MRSA (methicillin-resistant Staphylococcus aureus) skin infections. MRSA produces a distinctive presentation: a red, warm, swollen area that progresses toward a central necrotic-looking wound — exactly what popular culture associates with spider bites. The problem is that MRSA and a brown recluse bite (not established in BC) look nearly identical, and clinicians who aren't thinking about MRSA default to the spider bite narrative.
The BC context matters here. Brown recluses (Loxosceles reclusa) — the spider actually capable of producing necrotic bites — are not established in British Columbia. The range ends in the south-central United States. The occasional 'brown recluse bite' report in BC is almost always either MRSA, a reaction to something else, or a misidentified specimen. If your doctor says you have a brown recluse bite and you've been in Metro Vancouver, question that diagnosis.
The differential diagnosis: what else it could be
| Condition | Typical presentation | Key distinguishing features |
|---|---|---|
| MRSA skin infection | Red, warm, swollen, central ulcer developing | Gets worse over 24-48h; fever common; doesn't itch like a bite |
| Bed bug bites | Clustered, linear, on exposed skin | Multiple bites in a pattern; appear overnight; no systemic signs |
| Flea bites | Small, grouped, often around ankles | Multiple; intense itch; outdoor animal exposure |
| Allergic dermatitis | Diffuse rash, often bilateral | Contact history; doesn't have central puncture; responds to antihistamine |
| Impetigo | Honey-coloured crusting lesion | Secondary skin infection; may follow scratched insect bite |
| Actual spider bite | Single puncture, mild swelling, resolves in 1-3 days | Rare; specific incident; no systemic symptoms in most BC species |
When it is a real spider bite: what to expect
For the vast majority of BC spider species — giant house spiders, European house spiders, cellar spiders, wolf spiders, jumping spiders, crab spiders — a bite produces a mild, local reaction equivalent to a small bee sting. You'll feel a brief sharp sensation, see minor swelling and redness within minutes, and the reaction will resolve within 24–72 hours without treatment. These spiders don't bite to feed on humans — they only bite when trapped against skin (in a shoe, glove, or clothing) or when handled directly.
The false widow (Steatoda grossa and Steatoda nobilis, both present in Metro Vancouver) is a step up from house spiders — it can produce a more significant local reaction, sometimes with prolonged pain lasting a day or two. False widow bites are not medically serious, but they're uncomfortable enough that some people seek care. Treatment is supportive: clean the wound, apply cold compress, oral antihistamine if itching is severe, and ibuprofen for pain.
The exception: western black widow
Western black widow (Latrodectus hesperus) bites are the meaningful medical exception in BC. Black widow venom is neurotoxic — it doesn't produce local necrosis but causes significant systemic effects through a mechanism called latrodectism. Symptoms develop within 20 minutes to an hour of a confirmed bite: intense pain at the bite site, muscle cramping that spreads from the bite area, abdominal rigidity, sweating, and sometimes nausea, fever, and elevated blood pressure. The syndrome is dramatic and distinctive. It's not fatal in healthy adults, but it warrants emergency care — the treatment is antivenin in severe cases and supportive care (muscle relaxants, pain management) in moderate cases.
The black widow in Metro Vancouver is uncommon. It's primarily a species of the southern interior (Okanagan, Similkameen, Kootenays), where hot summers and dryer conditions suit it. In Metro Vancouver, confirmed encounters occur in wood piles, outdoor furniture, sheds, and occasionally in garages in warmer microhabitats (South Surrey, Delta, south-facing properties). The female is visually unmistakable: jet black, shiny, with a red hourglass on the underside of the abdomen. See our dedicated [black widow BC range article](/guide/black-widow-bc-range) for distribution and identification.
First aid protocol for spider bites in BC
Spider bite first aid — BC context
What to do after a suspected spider bite in British Columbia. Applies to bites from common BC species (house spiders, wolf spiders, jumping spiders). Black widow protocol differs — see the callout above.
- 1Wash the site thoroughlySoap and water or antiseptic wipe. Spider mouthparts carry bacteria; a clean wound reduces secondary infection risk. This is more important than any topical antivenin product.
- 2Apply cold compressIce pack wrapped in cloth, 10 minutes on, 10 minutes off. Reduces swelling and pain at the bite site. Direct ice contact can cause skin damage.
- 3Monitor for 24–48 hoursWatch the lesion. A normal BC spider bite gets better within 24–72 hours — less swelling, less redness, itching resolves. If it's getting worse after 12 hours (spreading redness, increasing warmth, developing ulcer), that's not a normal spider bite reaction.
- 4Seek care for warning signsGo to urgent care for: spreading redness beyond 5 cm from the bite, increasing pain after 12 hours, fever, developing central ulcer, or any systemic symptoms (muscle pain, sweating, nausea). Tell your doctor where you were when bitten and ask about bacterial skin infection as a differential.