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 spray kills spiders instantly?

Vinegar: Mix equal parts white vinegar and water in a spray bottle and spray it directly onto any spiders you see. Vinegar contains acetic acid which burns the spider upon contact.

Does Raid spray kill spiders?

Raid Max® Spider & Scorpion Killer kills spiders, black widow spiders, and scorpions on contact and can be used both indoors and outdoors. Available in 12 oz. size.