Spiders are abundant throughout Canada, inhabiting a wide array of environments from natural outdoor spaces to human dwellings. Most spider species found in Canada are harmless to humans and play a beneficial role within their ecosystems by preying on insects and other small invertebrates.
Common Spiders Across Canada
Many spiders commonly encountered in Canada pose no threat to people. House spiders, frequently found indoors, vary in color and construct irregular webs in dark corners and under furniture. Wolf spiders are ground-dwelling hunters, known for their speed and keen eyesight, actively pursuing prey rather than building webs. They often carry their egg sacs attached to their spinnerets.
Cellar spiders, sometimes called “daddy longlegs” due to their long, slender legs, prefer cool, damp areas like basements and cellars, where they weave loose, tangled webs. Orb weavers are recognized for their intricate, circular webs often seen in gardens and wooded areas, effectively trapping flying insects. Fishing spiders, which can be quite large, are typically found near water bodies, demonstrating an ability to walk on water as they forage for aquatic prey and insects. Crab spiders are ambush predators that rely on camouflage, often blending in with flowers as they wait for unsuspecting insects.
These common species are generally shy and will only bite if they feel threatened, such as when accidentally squeezed.
Spiders of Medical Concern
A very small number of Canadian spiders are considered medically significant due to their venom. The Western Black Widow (Latrodectus hesperus) is one such species found in southern regions across Canada, from British Columbia to Manitoba, and occasionally in southern and eastern Ontario. The female Western Black Widow is identifiable by her shiny black body, measuring around 14-16 mm, with a distinctive red or orange hourglass-shaped mark on the underside of her abdomen. These spiders typically build irregular, messy webs in protected, dark areas like woodpiles, garages, and outbuildings.
The venom of the Western Black Widow contains a neurotoxin that affects the nervous system, potentially causing muscle cramps, pain, sweating, and nausea in humans. Although bites can be painful, serious long-term complications or fatalities are rare, particularly for healthy adults.
The Brown Recluse (Loxosceles reclusa) is often discussed, though it is not considered native to or established in Canada, primarily residing in the south-central United States. Any reported sightings in Canada are typically due to accidental transportation, such as in cargo. This spider is light to dark brown and characterized by a violin-shaped marking on its cephalothorax, with the “neck” of the violin pointing towards its abdomen. Its venom is cytotoxic, meaning it can cause localized tissue damage and, in some cases, lead to open sores or necrosis. While bites can initially be painless, they may develop into painful, itchy lesions with potential systemic symptoms like fever or muscle pain, though fatalities are extremely rare.
Understanding Spider Bites
Most spider bites in Canada result in minor reactions. Common symptoms include localized redness, swelling, and mild pain or itching at the bite site.
For general spider bites, basic first aid involves washing the affected area thoroughly with soap and water. Applying a cold compress or ice pack to the bite can help reduce swelling and discomfort. Elevating the bitten limb, if possible, may also aid in reducing swelling.
Medical attention should be sought if symptoms worsen significantly, such as developing severe pain, spreading redness, or signs of infection like pus or red streaks. Systemic symptoms, including fever, headache, dizziness, or widespread muscle cramping, also warrant professional medical evaluation. To minimize the chance of bites, wear gloves when working in areas where spiders might hide, such as woodpiles or cluttered spaces. Shaking out clothing and shoes before wearing them and sealing cracks around homes can also help prevent encounters.