Bats are beneficial to humans in many ways.  For instance, a single Little Brown Bat can consume up to 600 mosquitoes an hour.  In fact, bats are the only major predators of night-flying insects.  Additionally, nectar-eating bats gather pollen as they travel from flower to flower, helping ensure the continuance of plant life.

Locate your bat house near a permanent source of water, ideally within a mile of a stream, lake or marsh.  Place 12-15 feet above the ground on a building, tree or pole.  A building will offer the most stable temperature.  In cooler parts of the country, orient your bat house to get maximum warmth, especially in the morning (southeast exposure.) 

$10-$28 plus S&H