Certain bat species, such as the little brown or big brown bat, will sometimes roost in houses – generally in the attic. Buildings may be their only alternative owing to the loss of many of their natural roosting sites like snags (dead or dying trees) or large old trees. If roosting bats are causing serious problems, the only solution is exclusion, which essentially means evicting them. Repellants and poisons do not give long-term results and often cause as much harm to the human inhabitants of the building as to the bats themselves.
Exclusion should not be attempted during May to August when young bats may be present. Unable to fly, the young will be left to starve. Not only is this cruel to the bats, but it will also cause further problems when the dead bats begin to smell.
There are a number of companies that will do the work for you. Some are reputable while others make money by fuelling people’s fears. Choose only those companies that follow the general principle of exclusion at an appropriate time of year.
Before excluding the bats, consider putting up a bat house to provide evicted bats with a place to go. Locate the box on the side of the house near their entrance to the attic so that it is easy for them to find.
To exclude bats, look for their entrance(s) to the attic by watching for them to emerge at dusk and searching for stains from their droppings. Once an entrance hole is located, bird netting, available at some garden centres, can be attached above the hole and left to hang loosely below it so that bats can leave but not return. Leave the netting to hang for one week to ensure that all bats have been allowed to exit. Then seal and caulk entrances to prevent future problems.