Spiders aren't actually insects, they're arachnids, and this and the fact that they don't crawl as close to the floor as insects do makes them hard to get rid of with common bug sprays, which rely on an insect's body coming into contact with the poison.
To permanently rid your home of spiders you'll need to seal up possible entry points with caulk and frequently vacuum every corner, nook and cranny. If you're faced with a severe infestation, you may want to start with a thorough, careful application of a commercial pesticide product to eliminate at least most of your current eight-legged roommates.
Chemical Spider Control
Chemical pesticides that are effective in killing spiders are commonly sold in dust form or as powdered concentrates that can be diluted to make a spray. Look for products that contain the active ingredients deltamethrin or cypermethrin. Follow instructions carefully. Apply to cracks and gaps on the exterior and interior of your home, and in places such as basement and attic corners where spiders like to hide.
Avoid any contact with pesticides. Wear gloves and avoid breathing in powder or spray. Avoid contact with mucous membranes and keep pets and children away from treated areas.
Other Spider Control Tactics
Eliminating insect infestations will decrease the amount of spider food available. Spiders like to eat roaches, flies, earwigs, mosquitoes, clothes moths and other unappealing insects. The same tactics that eliminate these pests will reduce your spider population: eliminate food debris, dirty dishes, and crumbs. Clean up spills promptly. Avoid accumulating piles of papers, heaps of clothing, and other jumbles that serve to harbor prey insects.
Eliminating moisture may help. Spiders need water sources to survive; you'll often find them dwelling in bathrooms and basements, near plumbing that may sweat or leak slightly.
Placing glue traps in basements, attics, and seldom-disturbed corners, behind furniture or appliances, or under baseboards can eliminate a few of the critters and help you measure your success.
S**ealing up cracks and crevices** can be a daunting task. It's worth doing, though, as it will also decrease moisture, increase your home's energy efficiency, and make it harder for pests of any sort to invade. Spiders can fit through tiny spaces, so you'll need to do a thorough job.
Vacuuming for Effective Spider Eviction
Do a thorough vacuum cleaning both before and after your sealing campaign; if you live in a temperate climate, your spider control campaign will work best in spring as the weather is beginning to warm up, when spiders are about to lay their eggs.
Step 1: Use the right equipment.
Change the vacuum bag to maximize suction, and use a crevice tool to get into small spaces.
Step 2: Be extremely thorough.
Take care to get into all nooks and crannies: under radiators, behind fixtures, anyplace a spider could possibly hide. When at all possible, turn furniture over or get underneath it to vacuum its underside. Vacuum up all spiders, egg sacs and webs as you encounter them.
Step 3: Dispose of bag properly
Bring the vacuum out of doors, as far as possible from your doorstep, and dispose of the vacuum bag directly into a garbage receptacle.
The combined effect of sealing entry points, eliminating the insects they feed upon, and doing a thorough cleaning will eliminate the vast majority of eight-legged invaders; the more thorough you are with these measures, the fewer spiders you'll encounter.