Spiders

Thousands of species of spiders live in Canada, but only a few are a health threat. Spiders are actually good because they feed on other insects and spiders. Spiders usually will not bite unless accidentally trapped or grabbed. The venom of most spiders is not very toxic to humans, and usually causes only a slight swelling, inflammation, or itching feeling. Spiders rarely bite humans. Most spiders’ fangs are too weak and too small to puncture human skin.

Spiders are arachnids, with two body parts (cephalothorax and abdomen), eight legs and usually six to eight eyes. Most spiders live for one to two years, but some can live for five to twenty years. Spiders lay eggs in an egg sac that is hidden in a web, attached to a surface, or carried by the female. Spiders produce many egg sacs, each containing several hundred eggs. To grow, a spider sheds its skin (molts) four to twelve times before maturity.

All spiders secrete a liquid through the spinnerets. This liquid hardens in the air to produce silk which is used to make egg sacs, capture or hold prey, make shelters or retreats, and to transfer sperm during mating. Spiders are predators that feed on living prey, usually insects, mites, and other small arthropods. They inject venom through hollow fangs to immobilize the prey. Then they inject or regurgitate digestive fluids into the prey and suck in the digested liquid food.

Control

The simplest way to control spiders is to reduce the number of other insects inside the home so they leave to find food elsewhere. An integrated pest management (IPM) approach that includes preventive measures, exclusion, sanitation, and chemicals applied to targeted sites. IPM requires a complete inspection of the building to locate the spiders and their dwellings. The spider should be correctly identified to determine which strategy to use.

Preventive Measures

Shake out clothes and shoes
Inspect bedding and towels
Wear gloves when handling firewood, rocks, etc.
Move the bed away from the wall
Keep the space under the bed empty.

Exclusion

Install weather stripping and door sweeps
Install tight-fitting screens on windows and doors
Seal crevices where spiders can enter
Install screens in soffits, foundations and roof gables
Install sodium vapour light bulbs outside since these attract fewer insects
Turn off lights at night
Tape edges of cardboard boxes

Sanitation

Clean up outdoor areas such as wood piles, rock piles, trash and debris
Get rid of indoor clutter in closets, basements, attics, garages
Store items off the floor and away from walls to reduce harborage areas
Eliminate flies, ants and cockroaches that attract spiders
Don’t stack wood close to or against the house
Remove vegetation and leaves around the foundation
Use a high-pressure sprayer to wash spider webs off the building

Non-chemical control

Capture the spider and release it outside (Put a glass over the spider and slide a piece of cardboard underneath to trap it.)
Dust and vacuum often to remove spiders, webs and egg sacs. Spiders may move if their webs are regularly destroyed.
Sweep outside areas often to destroy webs
Use a fly swatter or newspaper to kill individual spiders
Use tape or glueboards
Reduce night lighting that attracts the spiders’ insect food source

Insecticides

Some pesticides are labeled for homeowner use, and some are labeled only for the licensed, certified pesticide applicator. Directions must be followed carefully. A nonresidual aerosol spray can be used to kill exposed spiders, but the egg sacs should be vacuumed. A nonrepellent insecticidal dust is used to treat webs, and areas where spiders may hide. A wettable powder or slow-release insecticide can be appled under furniture and in storage areas. Pyrethrins can cause spiders to move so they contact treated surfaces. Residual liquid sprays can be used on spider harborages. For all treatments, directions must be followed carefully. A pest professional is familiar with the safe use of insectides and may be the best way to control spiders safely.