Bats are insect eaters with large appetites, and when they take up residence in a garden, they can help to reduce the garden's population of mosquitoes and other insect pests. Bats feed at night and roost during the day, sleeping and raising their young in secluded cracks and crevices. Bat houses are structures designed to provide the kind of roosting spaces bats prefer, and installing one in your garden may convince bats make themselves at home.
Bat House Designs
Bats roost most readily in houses with tall but narrow cavities, with openings in the bottom through which they enter. Ideal designs are 13 inches wide, 3 inches deep and more than 24 inches high. The house's joints should be caulked to protect the interior from weather, and it should have a vent above the entrance to allow air circulation through the house.
Bat House Locations
Place bat houses up high, at least 15 feet from the ground, on a pole or the side of a building where bats can fly to it easily. An unobstructed space of 20 feet in front of the house provides a clear flight path.
Bats need their houses to be consistently warm, so houses are best placed in south-facing locations that get six to eight hours of sun exposure during the day. Building walls absorb heat during the day and radiate it to the bat house at night, so bat houses mounted on walls tend to stay warmer than those mounted on poles. Painting the exterior black can also help it to absorb and retain heat during the day.
Bats may be slow to move into new houses, sometimes taking as long as two years to take up residence, so give them plenty of time to discover and accept the new structure. If bats haven't moved into a house within a couple of years, however, try moving it to a different location.
Bats feed on insects that are active at night, so a garden designed to encourage night-time insect activity is more likely to attract bats. Choose plants for the garden that bloom at night or that have a pronounced night-time fragrance. One such plant is evening primrose (Oenothera macrocarpa), which is hardy in U.S. Department of Agriculture plant hardiness zones 3 to 7. Another is moonflower (Ipomoea alba), a night-blooming vine that produces 6-inch-wide white flowers; it is hardy in USDA zones 10 to 12.
Effectiveness for Mosquito Control
Attracting to bats to your garden may help to control some insects and bats may have some impact on the garden's mosquito population, but bats are unlikely to effectively control the pests on their own. Some species of bat, such as the big brown bat, prefer to eat larger insects such as beetles and moths, and although species such as the little brown bat do eat mosquitoes, other insects make up the majority of their diet.