That's kind of like taking the leash off of your living-room-dwelling dog, giving the old boy a pat on the back and telling him to enjoy his new life of freedom out in the wild. Like pets, zoo animals and newly married husbands, spiders become domesticated pretty quickly. That includes common house spiders who have adapted to like the inside over many generations. You may feel like you're setting the little fella free, but you're probably handing him a one way ticket to a quick ending.
Less than 5 percent of all house spiders have ever been outside [source: Crawford]. Even fewer are adapted to the outdoor life of changing temperatures and conditions, not to mention a whole new world of predators. "Human property rights mean nothing to other species," The University of Washington's Burke Museum arachnid curator Rod Crawford wrote on the museum's website. "There was spider habitat for millions of years where your home is now. My advice is, just wave as they go by."