Found this online while looking for something else …
A Natural Spider Spray Formula for inside the house:
Dr Bronners Peppermint or Lavender Soap, or any other natural soap. 1 ounce of Neem oil You can also add 1 to 5 drops of any of these Essential Plant Oils (depending on your preference) to 1 quart of water:
Catnip Oil, Citronella Oil, Lavender Oil, Cinnamon Oil, Peppermint Oil, Citrus Oil, Tea Tree Oil, or other essential oils.
Add 5 tablespoons of the soap per quart water. Add one ounce of the Neem oil to the water which you have added the soap and label it. Shake well and spray inside house where spiders are seen.
Test for strength. May be done as often as needed. This is not a long term solution but will provide you immediate help.
Oils may stain some fabrics or light colored furnishings, test first.