Get rid of squirrels under the house as soon as you notice them. Ground squirrels breed once a year and have up to eight babies that mature in six months. One family will attract more squirrels. Before you realize it, a large colony of squirrels will be living under your house. If the first attempt is not successful, use it with an additional method until you find a combination that works.
Crawl under your house with a powerful flood lamp and locate all the openings the squirrels use for entrances and exits. Use cement or caulking compounds to fill small openings, and close up larger openings with pieces of a 1/2-inch hardware cloth. Keep the lamp lit to discourage the squirrels from returning until the compounds or mixtures are thoroughly dry.
Spread a liberal amount of mothballs under the house. One mothball per square foot is effective. Mothballs contain naphthalene, a chemical that irritates the squirrel's olfactory senses. Additionally, other types of chemical squirrel repellents are available in many home centers and hardware stores. They include products that contain fox urine or coyote urine. Three drops of either liquid in every 10 square feet of space create a squirrel deterrent.
A catch-and-release commercial trap is a humane way to deal with squirrels. Wear latex gloves to block your scent and place bait like shelled peanuts, sunflower seeds or peanut butter inside the trap. Prepare the trap door according to the instructions of that particular trap. Set the trap under the house in a spot where squirrel tracks or pathways are the heaviest. If you're using more than one trap, set them at least 25 feet apart. Check the traps each morning. Release captured squirrels in woodlands or public parks far away from your home.
Toxic Bait Method
Toxic bait or, rodenticide, contains ingredients that compromise a squirrel's blood-clotting mechanism and leads to death. It is available at most home centers or hardware stores. Use the toxic bait in conjunction with a bait station, which often comes packaged with the bait product. Follow the directions for rodenticide use carefully as the bait represents a danger to pets and wild birds. Replace used bait over a period of five days.