Answer: Spiders are considered beneficial because they feed on destructive insects. However, if it is necessary to reduce the number of spiders in and around your home, start with nonchemical methods including sanitation to prevent spiders from entering from the outside.
Remove piles of bricks, firewood, and other debris that may serve as suitable homes for spiders or move them further from your home.
Keep grassy or weedy areas near buildings cut short.
Trim back shrubs and other plants that directly contact your home.
Knock webs down with a broom or a hard spray of water.
Remove and destroy any egg sacs or spiders that are found.
Caulk or seal obvious cracks or spaces around the foundation, doors, and ground level windows.
Check to be sure screens fit tightly. Replace any screens that fit poorly or are damaged.
Change outside lights to reduce insect prey that can encourage spiders. Yellow lights are less attractive to insects than mercury or sodium vapor lights.
If it is necessary, supplement these methods with an insecticide application around the outside of your home. Spray under siding, in cracks and crevices, and other places where spiders may hide. General treatments on the siding or other surfaces are not as effective.
When treating the outside of a building, use ONE of the following insecticides:
chlorpyrifos as a liquid concentrate or a liquid ready-to-use product
diazinon as a liquid concentrate
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