That’s easy – they’re formulated to kill insects, not arachnids. Most household “bug sprays” will sooner or later kill any spider that’s directly sprayed, but have little residual effect against spiders that come by later.

What is the best repellent for spiders?

Peppermint oil: Mix 20 drops of peppermint essential oil (not peppermint extract) into a 32-ounce spray bottle filled with water. Spray the mixture in corners, near entrances and along the floorboards around the whole house.

What kind of bug spray kills spiders?

TERRO Spider Killer Spray is proven to give you the protection you need against spiders including black widow, brown recluse, and hobo spiders. The spray also offers protection against ants, cockroaches, crickets, scorpions, bed bugs, and more.