Spider Bite Guide
Ontario has no spider capable of causing serious medical harm under normal circumstances. Here is what a real spider bite looks like, which species can bite, and when to seek medical attention.
Spider bites are far rarer than most people assume. Spiders do not bite humans as a feeding behaviour - they bite only defensively when pressed against skin or threatened. Most suspected spider bites in Ontario are misidentified: the wound is actually from another insect, a skin condition such as folliculitis or contact dermatitis, or an MRSA lesion that presents similarly to a spider bite.
A 2014 study found that less than 4% of wounds presented to emergency departments as presumed spider bites were confirmed as such after examination. Ontario has no established spider species capable of causing necrotic wounds (tissue death) or systemic toxicity under typical circumstances.
Important: If you have a wound that is rapidly worsening, developing a darkening or necrotic centre, or accompanied by fever, nausea, or muscle cramping - seek medical attention immediately regardless of whether you think it was a spider bite. Do not delay medical care based on the assumption that Ontario spiders are harmless.
Physically incapable of biting through human skin. Mouthparts are too small. Zero risk. If you are concerned about a bite, this species is not responsible.
Can bite if handled roughly but bites are rare and cause only minor, brief local irritation. Not a practical biting risk in a home environment.
Can technically bite but almost never does. Any bite causes only minor local irritation. Not medically significant.
Can bite when pressed against skin. Bite is painful (fang-puncture pain) but venom is not medically significant. Localized pain and redness resolve within 24 to 48 hours.
The most likely spider to bite in an Ontario home. Active at night, may bite if rolled against in bed. Produces a burning sensation, redness, and mild swelling. Symptoms resolve within 24 hours typically. Not medically significant for healthy adults.
Occasionally arrive via shipping containers or produce. Not established Ontario populations - cannot survive outdoors through winter. Confirmed sightings should be reported. If bitten by either, seek emergency medical attention immediately.
A confirmed spider bite typically has these characteristics:
Wounds that are expanding rapidly, developing a necrotic or dark centre, or accompanied by systemic symptoms (fever, nausea, muscle cramps, difficulty breathing) should be evaluated medically regardless of whether a spider was observed.
What spider bites are dangerous in Ontario?
No established Ontario spider species causes serious medical harm. Yellow sac spiders can bite and cause mild local irritation. Wolf spiders can bite and cause pain. Brown recluse and black widow are not established in Ontario - occasional arrivals via shipping, but not a population you encounter in a home.
How do I know if I was bitten by a spider?
Two close-set puncture marks, immediate sharp or burning pain, localized redness and swelling. Most suspected spider bites are actually other insect bites, contact dermatitis, or skin infections. Confirmed spider bites are significantly rarer than reported.
What should I do after a spider bite in Ontario?
For a harmless species: clean with soap and water, cold pack, monitor. If a wound is rapidly worsening, developing a dark centre, or accompanied by systemic symptoms, seek medical attention immediately - do not wait and see.
Can a wolf spider bite hurt you?
A wolf spider bite is painful due to fang size but venom is not medically significant for healthy adults. Local pain and redness resolve within 24 to 48 hours. Bites are uncommon - wolf spiders only bite when pressed against skin.
Reduce the Risk
The best spider bite prevention is keeping populations low. Call to book a treatment.
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