There are thousands of species of spiders in Canada of which very few present health risks. Spiders are actually helpful in keeping the numbers of other pests down in the home or garden. The most common household spiders in Toronto are the Black-footed Spider, the House Spider and the Zebra Spider. There are two species of spiders that can be considered harmful. These are the Brown Recluse and the Black Widow. Both these species have venomous bites.
The Black-Footed Spider (Cheiracanthium mildei) was introduced from southern Europe. This spider is alternately known as the Yellow Sac Spider. It is between a sixth and a third of an inch in length and can have a leg span up to an inch across. It is pale yellow in colour and has dark markings on its jaws and feet. It builds small silk nests in which it lays its eggs but it does not use the web for trapping its victims. Instead, the black-footed spider actively hunts its prey. They are nocturnal and their bites can be painful but not harmful to humans.
The House Spider (Achaearanea tepidariorum) is responsible for most cobwebs found in buildings. This brown spider that is less than half an inch long has a spherically shaped abdomen which is white to brown in colour and has several dark markings. The smaller male has orange legs while the female's are yellow. House spiders are common throughout the world and their webs are found in corners, basements, under furniture and around windows. Their bites can cause localised wounds that may be slow to heal, though House Spiders rarely bite despite their aggressive nature.
The Zebra Spider (Salticus scenicus) is a small jumping spider that is less than a tenth of an inch in length. They are often seen on walls and doorways. They do not make webs but stalk their prey using their silk thread as an anchor. When in striking distance they leap and bite their victims, paralysing them with their venom. Their 360 degree vision is considered the best in the spider kingdom.
The Brown Recluse (Loxosceles reclusa) is half an inch in length and is poisonous. This light brown spider has violin markings on its thorax (the middle section of the body) and is sometimes known as the fiddleback spider. Unlike most spiders that have eight eyes, the Brown Recluse has only six. Its sticky web is used for shelter rather than trapping. Adults are found in dry reclusive places such as behind baseboards and in garments that have been left hanging for some time. Bites often occur when the spider is trapped in shoes or clothing. Bites are rarely fatal and usually are not felt. A stinging sensation develops and becomes intense in pain. The bitten area will have a white blister that grows to the size of a silver dollar. The affected tissue will die and leave an ulcerated sore. If bitten medical attention should be sought immediately.
Black Widow Spider
The female Black Widow Spider (Latrodectus hesperus) has a round, shiny, black abdomen with red markings that resemble an hourglass on the underside. The body is half an inch wide and 1 1/2 inches long. They live generally outdoors under rocks and trees but can also be found in wood piles, basements and crawlspaces. They feed on insects that are trapped in their webs. They are not aggressive but may bite if handled or accidentally touched. Their bite causes pain and serious illness in humans. Bite reactions include increased body temperature and blood pressure, sweating, dizziness, blurred vision, nausea and pain and swelling around the bite. Medical attention should be sought immediately if bitten. If promptly treated bites are rarely fatal, though small children are at greater risk.