Spiders in the home: how to identify and control these arachnids
Spiders are among the most feared home invaders but, for the most part, they are beneficial because of their role as predators of other bugs. Over 700 spider species live in or around our homes in British Columbia. Fortunately, it does not “rain spiders” here, as happened in Brazil last month.
Two spiders that are health risks in B.C. are black widows and hobo spiders. They are considered “poisonous” spiders, as their venom may cause a serious reaction in humans. Typically a spider bite is less dangerous than a bee sting, but some people may react severely to a spider bite.
Identifying spiders in the home
Spiders often are confused with insects, but they are arachnids and are close relatives of ticks and mites. Unlike insects that have six legs and three body parts, spiders have eight legs and two body parts.
Black widows (38 millimetres long) are notorious spiders identified by the coloured, hourglass-shaped mark on their abdomens. They are considered the most poisonous spiders in North America. They usually are found in dark, dry, relatively undisturbed places such as garages, sheds, barns, crawl spaces, utility meter boxes, and old animal burrows. The web of the black widow is an irregular, tough-stranded, sticky cobweb mesh in which the spider hangs with its underside up.
The hobo spider (12 to 18 millimetres long), also known as the aggressive house spider, builds funnel-shaped webs in dark, moist areas such as basements, window wells, and around the perimeter of homes. It is a fast-running brown spider with a herringbone or multiple chevron patterns on the top of the abdomen. The toxicity and aggression of the hobo spiders are debatable.
Another spider frequently found indoors is the common house spider, which makes a cobweb in corners of rooms, in windows, and in similar places. Another is the cellar spider, a long-legged spider that resembles a daddy long legs. These spiders are only marginally capable of biting humans because their fangs are too short to pierce human skin. Various kinds of small spiders may wander indoors and occasionally rather large hunting spiders (e.g. wolf spiders and tarantula) are also discovered in homes or garages.
Controlling spiders in the home
- The best approach for controlling spiders in and around the home is to remove hiding spots for secretive spiders such as black widows and regularly clean webs off the house. Also, eliminate insects that serve as a food supply, especially when large numbers exist.
- Seal cracks in the foundation and other parts of the structure and gaps around windows and doors. Good screening not only will keep out many spiders but also will discourage them by keeping out insects.
- Use tightly closed plastic bags to store all gardening apparel and sports gear in a garage that is used only sporadically. Clean up clutter in garage, shed, basement, and other storage areas. Be sure to wear gloves to avoid accidental bites.
- Capture and discard or remove individual spiders that have wandered inside.
- Sticky traps such as glue boards can be used to monitor for presence of spiders, and to achieve some level of control. Place traps along walls, under furniture and appliances, and in other undisturbed locations.
- Chemical control of spiders is difficult and rarely necessary. For current chemical control options, consult your local pest control representative. Follow closely the directions and cautions on the label.