Some common ways to kill spiders include essential oils, salt water and diatomaceous earth. Removing outdoor clutter, such as wood, mulch, garbage and weeds, sometimes prevents spiders from nesting in the home.
To kill spiders with essential oils, add one drop of peppermint, citronella or cinnamon essential oil to a quart of water, and spray the mixture onto the spider. Shake the mixture well before each use to ensure the oils and water are combined. To use salt to kill spiders, mix 1/8 cup of salt into a gallon of warm water, and spray the mixture onto the spider. Salt water is also useful in treating spider nests.
To use diatomaceous earth to deter and kill spiders, sprinkle food-grade diatomaceous earth around baseboards, windows and other areas where spiders may enter the home. Freshly crushed chestnuts also work well. Replace the powder as needed to maintain its effectiveness, particularly after sweeping or vacuuming the area.
To make an insecticide spray from diatomaceous earth, combine 1 cup of food-grade diatomaceous earth in a gallon of vinegar, and pour the mixture into a spray bottle. Use the spray to kill live spiders, or spray the mixture around areas where you have seen spiders to keep them away.