Spiders are beneficial because they feed on pests like mosquitoes and flies. Cobwebs are a common sight in the corners of dark, dry areas of your home. The common house spider may be one of a group of spiders, many of which are harmless. However, some species use venom to catch their prey and this can be harmful to humans as well if bitten
Most house spiders only bite when threatened and aren't considered dangerous. The most common house spiders include funnel weavers, cobweb spiders and sac spiders. Funnel weaver spiders are often mistaken for a brown recluse spider but are harmless. They have a darker brown body than a brown recluse and do not have the recluse's telltale violin-shaped marking. Cobweb spider species include the black widow, but most others are harmless. Sac spiders are pale in colour and spend daylight hours in a flattened sack. They're believed to be the most common source of spider bites in the home.
Hobo spiders are brown, measuring about 8 to 16 mm (1/3 to 2/3 inches) long with a long leg span. On its abdomen you'll see chevron-shaped markings. This spider will rarely climb on vertical surfaces and is commonly found in basements. The hobo spider's bite is painless, but after 24 hours, a blister forms that breaks open within 36 hours. Soon after the bite, symptoms may appear which include headache, nausea, fatigue, impaired vision, and short-term memory loss.
Black house spider
Black house spiders are about 12 mm (1/2 inch) long with a dark brown to black body. They inhabit secluded areas such as sheds, under eaves, in gutters and brickwork, and behind toilets. They also hang around light fixtures to attract prey like flies and mosquitoes. Their bite is venomous but not lethal. Symptoms from a black house spider bite include pain around the bite, sweating, muscle pain, vomiting, headache and giddiness. If you are bitten by one of these spiders, seek immediate medical attention.
Brown recluse spiders are typically around 12 mm (1/2 inch) long with violin-shaped markings on their midsection. They're often unnoticed because they hide in dark indoor spaces that are dry and undisturbed, like behind baseboards, in basements and crawlspaces, attics, and garages and sheds. The brown recluse may hide in sheets or linens that have been unused for a period of time as well. The venom of the brown recluse attacks skin cells which results in dead tissue. Often you won't feel their bite, but soon after, symptoms such as a stinging sensation begins, followed by pain. The bite results in a small white blister that enlarges to the size of a silver dollar. If you've been bitten, consult a physician immediately. There is no antitoxin available, but treatment can prevent severe reactions and reduce the damaged tissue and scarring.
The female black widow spider is about 12 mm (1/2 inch) wide and 36 mm (1 1/2 inches) long and is shiny black with reddish orange markings that look similar to an hourglass on its underside. Black widows hide indoors in basements and crawlspaces and outside in garages or sheds. When black widows bite, the resulting pain is immediate. Their venom attacks the nervous system and can cause severe pain and illness. Symptoms of a black widow bite include fever and raised blood pressure, sweating, dizziness, blurred vision, and nausea. There is an antitoxin available so if bitten, see a physician immediately.