I work in the pest control industry. Kalidurga is right, the only way to make sure more don't come in is to seal up the entryways. The usual suspects are crawl space vents with holes in the mesh, wiring coming out of your house that has a hole bigger than the wire, and garage doors that are missing the seal from the bottom. You can usually tell where they're getting in from their droppings. A cheap, temporary fix is steel wool. Push some in any holes that are suspect.