One of the most effective and environmentally friendly ways to reduce the mosquito population is to install a bat house. Most North American bats prefer to live in large groups, called colonies, so a mid-sized house (100-300 bats) is typically recommended. Bat houses mounted on poles or buildings tend to have a slightly higher occupancy than those mounted on trees. Mount the house 15-20 feet above the ground where it will not be exposed to bright lights. Place the bat house where it will receive at least 6 hours of sun in regions where average July temperatures range from 80-100 degrees.