Bat Exclusion: How to Get and Keep Bats Out of Your Home

Unlike most pests, such as rats, mice, ants, and wasps, bats are extremely beneficial to have around your home. Each night, bats eat a tremendous amount of mosquitoes, moths, and other flying insects. They work as your very own natural pest controller, helping to keep your home bug free.

However, while you want bats around your home, you don’t want them nesting in your home. Bat guano can contain the fungus Histoplasma Capsulatum which is known to cause lung disease Histoplasmosis in people. You definitely don’t want this in your house. In addition, bat urine is extremely stinky and will leave stains. In large amounts it can seep into the ceiling and walls staining and damaging the drywall. The key then is to get the bats out of your home as soon as possible while helping them to nest on your property.

The bats we have here in the foothills of Northern California are migratory. The most common bat is the Mexican Free-tail. They are a medium sized bat with reddish brown or grey fur. They migrate to Northern California in the Spring when the weather gets warm and head back south as the weather begins to cool. These bats can live up to 18 years, and because they return to the same nesting place every year, it means they will be working to keep your home mosquito free for a long time.

It also means that if action isn’t taken to remove them from your house, the bat guano will continue to build up each year. Bats give birth to their young in late May or early June and the young are unable to leave the nest until after August. Because of this, we do not exclude bats during the moths of June-August.

How to Identify if Bats are Nesting in Your House

Since bats come out at night, you may not always see them. However, they will leave behind noticeable signs such as piles of bat guano and urine stains. Because bats nest in the same spot each night, their droppings will accumulate in the same spot. Mice and rats leave their droppings more randomly. In addition, bat droppings tend to be less uniform and contain various bumps and dimples. Mice droppings are more uniform, similar to a grain of rice. Bat droppings are also sticky and you will often find their droppings stuck to the walls where they climb into their nests.

The other main sign of a bat nest is the white stains of their urine. Look for white staining on the walls and adjoining boards near the entry points to their nests. Bat urine is especially stinky and has a strong smell of ammonia. It is much more noticeable than the urine of rats or mice.

Excluding Bats (How to get bats out of your home)

As mentioned above, bats are beneficial for the environment and help eat many of the disease spreading pests, such as mosquitoes. We want them to stay around your home, we just need to relocate them. Getting them out of your home is a three step process:

1. Getting them to leave your house.
2. Sealing your house so they can't reenter.
3. Install other nesting areas around your home.

Using the above points to identify the entrances the bats are using, install netting over the entrances leaving an exit for them to crawl out several inches below the exit. This basically creates a one way door. They will crawl out the exit, but when they return they will try to enter the original entrance. Eventually they will give up. Do not exclude bats during the months of June-August as there may be young unable to leave the nest during this period.

After a couple of weeks, remove the netting and seal the holes to the entrances. This may require adding new material, caulking, or adding copper mesh. It is important to make sure that all holes are well sealed. You should also clean up any guano at this point wearing a respirator, gloves, and protective clothing. It is also important to use a HEPA filter when doing any vacuuming.

Finally, because you want to keep the bats around your home, we recommend installing bat enclosures around your property to give your evicted bats a new place to nest.