Excluding bats from buildings
In some instances bat colonies in a building may not cause any real
problems and can be left undisturbed.
In fact, a small colony of bats may go unnoticed for years.
If bats become a nuisance for a home or building owner a
bat exclusion has proven
to be the only successful method of permanently removing them.
An exclusion is conducted by positioning one-way devices at
the locations where the bats are emerging from the roost.
The one-way devices allow the bats to exit, but prevents them
Physically capturing bats and relocating them is almost never
successful because bats are often hiding in areas of the building
that are not accessible.
Even if bats are in an open area, attempts to capture them will
likely cause them to flee into inaccessible places.
Trapping bats as they exit a building does not work either
because bats are frequently injured or die in the process of being
captured and transported to a new location.
Furthermore, bats moved to another location will almost
always return to their old roost, even if it requires flying many
miles. Trapping bats is
illegal in Florida.
Do not attempt to poison or exterminate bats.
Bats are protected under Florida wildlife laws and it is
illegal to willfully kill bats in Florida.
Don’t just plug the holes.
A lot of people think they can cover the holes the bats are
using at midnight to keep the bats from getting back in.
All of the bats in a roost do not necessarily exit each
night, and in Florida, bats have often been observed returning to
their roost early in the evening, long before midnight.
Do not conduct a bat exclusion during the maternity season. It
is also illegal to conduct a bat exclusion during the maternity
season, which in Florida is defined as April 16 through August 14.
The maternity season is the period of time that mothers give
birth to their young and nurture them to adulthood.
Conducting a Bat Exclusion.
Exclusion techniques have been developed over the years and,
when properly applied, are almost always successful on the first
attempt. If it is later
discovered an entrance point was missed, an exclusion can be
re-conducted for that area.
More detailed information on bats in buildings and the
exclusion process can be found in the book, “Bats
Step 1. Find the
entry points. This
can be done by observing the building during emergence time.
Bats emerge from their roost shortly after sunset, so it is
best to observe the building from sunset until dark.
If there may be multiple emergence points you can watch
different areas on different nights, or have other people assist
you. A closer look at a
hole or crevice that the bats are using will likely reveal staining
around the edges from their body oils and a scattering of bat
droppings on the wall.
Step 2. Bat-proof all
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 where they might get back in.
Once the exclusion is
conducted, the bats will frantically look for other entrances back
into the building. Bats
can enter any hole ¾ inch in diameter, or any crevice of ½ inch or
Step 3. Install
Several exclusion methods have been developed over the years.
Since every situation is a little different, we have found
the most flexible approach is to use an industrial quality bird
netting. A known
supplier is Industrial
Netting of Minneapolis, Minnesota.
Netting with a 1/4 inch mesh seems to work the best.
Although many hardware and
gardening stores sell bird netting, the larger weave and lighter
weight of these products will often entangle the bats, and a smaller
weave may enable them to crawl on it and possibly re-enter the
Attach the netting above the opening using staples or duct tape.
The netting should extend about a foot below the bottom of
the hole or crevice. The
sides of the netting are attached in a way that puffs the netting
out and creates an open space over the hole or crevice, allowing the
bats to drop out and fly underneath the netting.
If you can easily slide your hand up under the netting, it
should provide sufficient space for the bats to exit freely.
When the bats return, they will attempt to fly directly to
the hole or crevice, but it will be blocked by the netting.
They will not land below the netting and climb up behind it
to reach the hole, nor will they fly vertically up the narrow space
between the wall and netting. Although
the bottom remains open, the netting must be securely fastened at
the top and on both sides.
The exclusion netting can then be attached during the day
when there is plenty of light.
It is a good idea to watch the emergence the first night
after the exclusion system is in place to make sure it is working
properly, and that bats are not failing to emerge or getting trapped
behind the netting. If a
bat becomes tangled in the netting, it can be carefully removed
while wearing heavy leather work gloves.
If you are ever bitten by a bat you need to keep the bat for
testing and seek medical attention immediately.
Click here to see photos of exclusion examples
Step 4. Allow time
for the bats to leave.
Before removing the netting, the area should be observed
carefully at emergence time to make sure no bats are exiting.
Florida regulations require that the netting be left up for
at least four clear, warm nights 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
Consult exclusion regulations for
details. 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 the
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
Step 5. Permanently
seal the openings.
After the bats have been successfully excluded, the netting or
exclusion devices 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 opening 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 basically made up of undigested insect particles
and can usually be left undisturbed, if it is in a dry area of the
building that is not used, or is inaccessible.
There is, however, a fungus that can grow in soil enriched by bat or
bird droppings that may cause a respiratory illness referred to as
histoplasmosis. Cases of histoplasmosis due to bat guano have only
been reported in Florida due to bats in a cave environment. If
you wish to learn more about histoplasmosis we recommend you visit the
Centers for Disease Control (CDC)