Living With Bats

What is Bat Exclusion?

Bat exclusion is a multi-step technique where all potential bat entry and exit points in a building are identified. One-way exit devices are installed to allow bats to leave the structure but not re-enter. Finally, all potential bat entry points are permanently sealed to prevent re-entry by bats.

Step by Step Instructions for Completing a Bat Exclusion

This exclusion information is based on instructions from the Florida Bat Conservancy, Bat Conservation International, Bat Conservation and Management, and Fly By Night Inc.

Step 1. Find the entry points for bats.  A closer look during daylight at a hole or crevice bats are using will likely reveal staining around the edges from their body oils and a scattering of bat droppings on the wall.   After locating potential emergence point, watch for bats emerging from the building. Bats emerge from their roost shortly after sunset, so it is best to observe the building from sunset until dark. If there are multiple emergence points, watch different areas on different nights, or have other people assist you.

Step 2.  Bat-proof all other openings.  Carefully survey the exterior of the building during the daytime.  Now that you know which holes or crevices the bats are using, you can seal up any other areas not currently being used by bats where they might get back in. Entryways currently being used by bats must remain open until the end of the maternity season, and until the exclusion has been conducted.  Once the exclusion is conducted, the bats will look for other entrances back into the building.  Bats can enter any hole that is ¾ inch in diameter or any crevice of ⅜ inch or more.

Step 3.  Install exclusion devices.  Several exclusion methods have been developed over the years, and no one method is best for every situation.  Methods cited here are based on recommendations from the Florida Bat Conservancy, Fly By Night Inc., Bat Conservation International or IFAS/University of Florida. 

Step 4.  Allow time for the bats to leave.  Before removing the netting or tubing, the area should be observed carefully at emergence time to make sure no bats are exiting. Florida regulations require the netting or tubing be left up for at least four warm nights without rain or high winds to assure all of the bats have left. Bats tend not to forage on cold or rainy nights, so if the weather turns bad, it will be necessary to extend the exclusion an additional four consecutive nights.  If bats are still coming out after four nights, then they have either found another way back in or the exclusion system is not working and needs to be revised. If exclusion materials become loose or detached, the bats will be able to re-enter, so make sure it remains secure throughout the process. Bats will be checking continually to see if they can re-enter their roost.

Step 5.  Permanently seal the openings.  After the bats have been successfully excluded, the netting or tubes can be removed during the day and the openings permanently sealed. Do not leave the netting down without sealing the openings, or the bats will move back in the following night. If the openings cannot be sealed immediately, the exclusion devices may be left up longer, but there is a risk that wind, storms or failure of fasteners could allow the bats to re-enter. Another approach is to take the netting down and temporarily cover the openings with plywood or hardware cloth until permanent repairs can be made.

Step 6.  Cleanup.  If a colony of bats has been in a roost for a long time there will likely be an odor and an accumulation of bat guano. In most cases, the odor is actually from the scent gland, not the guano, of Brazilian free-tailed bats, a bat commonly found in Florida buildings. This odor should disperse shortly after the bats are gone. Bat guano is made up of undigested insect particles and usually can be left undisturbed without concern for human health, if it is in a dry area of the building that is not used or is inaccessible. Unfortunately, bat guano left undisturbed over time can attract insect pests such as cockroaches, so should be removed if the threat of pest infestation is possible. When disturbing the guano, it is important to take precautions due to a fungus that can grow in soil enriched by bat droppings that may cause a respiratory illness known as histoplasmosis. Cases of histoplasmosis due to bat guano in a building have never been reported in Florida; they have only been reported from bats in a cave environment. However, the Centers for Disease Control recommends wearing respirators whenever an individual is in a confined space with bat guano.

Step. 7 Bat Houses. Once bat are displaced, they need to find another location to serve as a roost.  Providing a bat house nearby before the exclusion begins can provide a potential roosting location for displaced bats. If you wish to erect a bat house, it is a good idea to determine the flight paths of the bats as they exit the building. Once the flight path is known, it is best to erect the bat house while the original roost is still active and to locate it in the flight path of the bats, or as close to the existing roost as possible. This way the bats will see the option exists and be aware of its presence. Experts also recommend that bat houses be painted tan or brown and be erected on a pole or building and not a tree to increase the amount of sunlight the bat house receives. Additional information regarding bat houses can be found on the Bat Conservation International website. After the exclusion begins, you may want to monitor the bat house to determine if bats are relocating to it. Remember however that bat houses will not always attract bats. Also, putting up a bat house is not a substitute for exclusion because bats are highly unlikely to leave an occupied building to begin using a bat house unless forced out of that building

What if you don’t follow the guidance on exclusions?

When bats are found in a building, the human residents typically want them out quickly, and pest or wildlife control companies benefit if they can complete a bat exclusion project quickly.  But it is critically important to make sure the bats have sufficient time to leave.  First, FWC rules require that any exclusion device must be left up for a minimum of 4 nights when the overnight temperature is forecast to be at least 50ºF.  Second, bats are capable of reducing their activity, especially in cool weather, and they may stay inside their roost for several days.  If they don’t leave before their exit is sealed, they will die inside the building.  Finally, if bats are trapped in building walls or attic space, they may find ways into the interior of the building where they directly encounter people. 

Can it really be that bad if all the bats don’t get out?

Yes, it can.  To help convey the potential consequences of sealing bats inside a building, here’s a true account of an incident that occurred in north Florida before the exclusion rules were in place.  In this case a modern county courthouse, 3 stories tall, had Brazilian free-tailed bats (Tadarida brasiliensis) in the upper walls. The bats had entered openings where the brick met the roof.  There were hundreds of bats and, as is characteristic with this species, the odor of bats was noticeable inside the building.   Unfortunately, a proper exclusion was not done; in fact, an experienced bat biologist was not even consulted.  Instead, the maintenance staff began sealing off the openings around the roof edge, over several days.  When the workers finished, they assumed that most of the bats had escaped and that those that didn’t would simply perish unnoticed inside the walls of the courthouse.

They were wrong -- at least about the unnoticed part.  At first, the only complaints were from people with offices on the top floor who said that the bats smelled stronger and were louder than they were, previously.   Soon some of the bats found their way out of the walls, to the interior of the building where they flew among the offices and hallways trying to find an exit.  Of course, bats flying in the courthouse halls didn’t set well with county administrators, and they contacted a local wildlife rehabilitator to capture the bats.  The wildlife rehabilitator caught dozens of bats each day, much to the relief of visitors and office staff.

But flying bats were the least of the problems.  A week or so after the bats’ exits were boarded and the flying bats were mostly removed, the courthouse staff started smelling an overpowering  odor.  Those with offices nearest the roosting bats sprayed deodorizers and even resorted to lighting candles in their offices to mask the stench.  Soon flies appeared and buzzed along the edges of the windows and trim, or anywhere that emitted the odor of dead and rotting bats.   In a few rooms the odor along the window seams was accompanied by fluids seeping down from the rotting carcasses.   That was enough.  The courthouse had to be closed for a week until the walls were cleaned and the odor reduced.

So yes, it is important to do an exclusion right and to give the bats plenty of time to move out.  Closing exclusion exits early or simply sealing bats in a building is not only illegal and inhumane, it can also expose people to sick or weakened bats.  And if that’s not enough of a deterrent, the example of the rotten courthouse should be. 

Can building repairs be done during bat maternity season?

In most cases, yes! If bats are occupying a building, and structural repairs are needed that will not impact the bats' ability to enter or exit, the repairs can proceed.  Some commonsense precautions to take:

1. Workers should be made aware of the bats presence to avoid being startled.
2. Avoid areas with bats, and immediately leave if bats appear to be disturbed (increased chattering or flying).
3. Use red lights if needed to navigate in attic spaces to limit disturbance to the bats. White lights in the work area should be okay, if not shining directly on bats.
4. Do not handle or pick up any bats.

There are bats hanging on the exterior of the house or structure during exclusion.  Is this normal?

When bats leave the roost site, they often forage for most of the night, using alternate night roosts and returning to the building or structure just before sunrise. When bats return to a roost with exclusion material in place, they may stay close to the roost – hanging on walls, under eaves or on netting over their entrance – for the first day. Although they may seem exposed, this is normal behavior and not something for concern. The bats will usually leave the next evening after dark and not return. Fidelity of bats to roost sites and their instinct to return there is a key reason why it is so important to bat-proof a building prior to exclusion. If other potential entrances that were never used before by the bats are left unsealed, these become more attractive to bats once the more desirable entrances are blocked.

Bat evictions/ exclusion can only occur from August 15 through April 15.

Maternity Season (April 16 – August 14)

During the maternity season, female bats are congregating and raising baby bats, known as pups. Pups are born hairless, and require high temperatures to stay warm, especially when their mother is out finding food. Pups aren’t able to fly for a few weeks after they are born, so any form of eviction during this time period will result in baby bats being trapped, along with adult bats that may not have emerged. Trapped bats will attempt to escape and may end up in the living space of buildings. Also, the decay process of dead bats can produce strong odors and could attract unwanted pests, such as cockroaches.

What can be done during the maternity season?

Bat-proofing inside the building. Preventing bats from entering the living space in your building is the single most important step to protecting yourself until bats can be excluded after the maternity season ends. If bats are roosting in the attic or walls, but some have come into the living space, there may be structural issues such as tears in ventilation or loose fitting fixtures. Bats are not capable of tearing and breaking fixtures, so any damage leading to bats entering living spaces will have been preexisting. Appropriate repairs should be made during the maternity season, so that when the exclusion devices are up, bats don’t find their way back into the home.

Note: In many cases, bats are forced further inside a building when exit sites on the outside are sealed. Wildlife control operators should ask if exclusion was attempted or if bat exits have already been covered. These obstructions need to be removed. (See Violations section). When young bats start to fly, some may enter open windows or have trouble navigating, so it may help to close unscreened windows and garage doors from dusk till dawn June through August.

If the smell of guano is strong, see if there are existing structural concerns with the building. Building codes usually require air handlers to keep attic air separate from living space air, and this should be checked. If moisture is getting into attic spaces and walls, it can increase odor. Check for areas that may be allowing water into the building, and if these areas are not an exit site for bats, repair immediately. Dehumidifiers or fans inside of buildings can also help reduce odors. Note: Strong smells are not a health hazard. They are a quality of life and aesthetic concern for persons living in a home, but the smell from bats (or their guano) is not, in itself, something that causes or creates health problems for most individuals. If the bat entrance or exit is the site of water entering a building, discuss ways to prevent water from entering while still allowing bats access until the end of the season.

Sealing and preparing areas outside of the building. Look for holes or crevices larger than one-half inch, make sure they are not the sites of bats entering and exiting, and go ahead and seal them, before the exclusion. The best way to identify the areas bats are using is to watch the bats emerge in the evening. Remember that these entrances cannot be sealed during the maternity season April 16 - August 14.

Consider putting up a bat house nearby or on the building before the exclusion begins. Bats are unlikely to switch and use a bat house but may use it after an eviction/exclusion. Bat houses have an increased chance of occupancy if they are placed in the flight route of the bats exiting the building. This way the bats will see the option exists and be aware of its presence. Experts also recommend that bat houses be painted tan or brown and be erected on a pole or building and not a tree to increase the amount of sunlight the bat house receives. Information regarding bat houses can be found on the Bat Conservation International website or in the bat house builders handbook.”

Remember: It is illegal to exclude or remove bats from April 16 to August 14!

If you have an emergency and cannot wait until after maternity season, please contact the FWC Wildlife Assistance Biologist at your regional FWC office.

What Diseases in Bats Affect Humans?

Bats can be vectors for diseases that can impact human health. The two most common of these are rabies and histoplasmosis.

Rabies

Rabies, a virus usually transmitted from a bite, affects a very small portion of bats — perhaps only one among every few hundred bats across all of the bat populations in Florida. In fact, although bats are rabies vectors, raccoons and foxes have a higher incidence of rabies than bats do. However, people should not handle bats, whether they are sick, injured or dead, due to the threat of this disease. While very rare, rabies is extremely serious. For more information about bats and disease, including what to do if a person makes contact with a bat, contact your county health department, the Florida Department of Health, or the Centers for Disease Control and Prevention (CDC).

Histoplasmosis

Histoplasmosis is an infection caused by a fungus called Histoplasma, which can live in soil that contains large amounts of guano, or bat droppings. Inhaling histoplasmosis spores can cause an infection in the lungs, with symptoms such as fever, coughing, and fatigue. However, most people that do inhale its spores do not get sick. For more information, contact your county health department, the Florida Department of Health, or the Centers for Disease Control and Prevention (CDC).