Bats - Getting Them Out

In other articles I will discuss the benefits and hazards of bats in our urban environment, but the quick version is that bats are of tremendous benefit when it comes to their consumption of insects as they feed at night, but they also pose a distinct hazard to the health of humans in several ways. First, bats are one of the most common carriers of rabies, spread in their saliva from a bite or even from inhalation of their saliva as they cough or sneeze. Second, where bats inhabit structures in large numbers over a long period of time, they create an ever-growing accumulation of feces and urine, and most vertebrate experts would agree that this layer presents an excellent growth medium for bacteria and viruses. As it dries and becomes airborne it is hazardous to those who breathe the dust.

In addition to these actual health concerns, the presence of large accumulations of excrement just plain old smells bad. For these reasons, it would be considered prudent to attempt to discourage bats from living in the same buildings that people live or work in, and if the bats are already there it would be wise to encourage them to move on. In this article I would like to present some possible ways to accomplish this task without causing the bats any harm.

Throughout the world bats feed on a variety of things. The infamous vampire bats that live in Latin America feed on the blood of mammals. About one third of bats species feed on fruit or nectar, about one percent feed on small animals such as mice, fish, or frogs, but at least two thirds of the species eat almost exclusively insects, including those in the United States. In fact, a proper description of bats with respect to their feeding habits is that they are “insectivores”.

Bats are not rodents. They are mammals in a group of their own, and they are the only true flying mammals. Around 40 different species of bats live in the United States, but there are three species that are of the most concern with respect to pest management. These are the Big Brown Bat, the Little Brown Bat, and the Mexican Free-tailed Bat, and the three together often are referred to as “house bats” due to their common desire to nest or roost within structures. All three species are widespread and found throughout most of the states.

Because they are so mobile many species of bats can be found across wide areas. For example, there are around 18 different kinds along the eastern states and around 25 kinds in California. Many of them will migrate to warmer climates in the winter, where they can continue to find active insects to feed on, while some other species remain in the cold climate and hibernate, possibly in caves or hollow trees, or, unfortunately, within our homes and office buildings. All species are nocturnal, and are actively feeding only at night, so all day long they are holed up in their chosen dens. Movement into a new place may be most common in the spring or the fall, when they are choosing sites either for raising their young or for spending the winter.

Baby bats are usually born in mid to late spring, and into the early summer, and generally are capable of flying within a month. This is an important consideration in bat control, for you need to ensure you are not closing off all the access points into the building when you may be trapping the young bats inside. This could lead to problems as the bats then die within the building, leading to odor and fly problems that cause you even a greater headache. Similarly, you do not want to suddenly just block all the entry / exit points and not allow bats out. Ideally you identify all the openings they are using for passage into and out of the building, create a one-way door over these openings, and then permanently close it once you are confident all the bats have exited.

In some states there are species of bats that are protected by laws or local ordinances, and you need to check on this status within your local area. Good contacts may be the Fish and Wildlife Service, Department of Natural Resources, Department of Agriculture, or a university biology department. In Florida two species are classified as “endangered species”, so obtaining a proper identification of the bats you are dealing with can be important.

So, when it comes to bat “control” you have very few options. At this time there are no poisons registered for use against bats, so killing them in this manner is not allowed. That is probably just as well, for if the bats were poisoned and died within the walls of the structure there could be an immense odor problem. You also may have received advice about repelling them from the building with odors, and moth balls or moth crystals are the standard suggestion. The ingredient is naphthalene, and it can have an odor of its own that you or other people may object to, since several pounds of the material would be needed to have any effect on the bats. This may work as a temporary solution to move the bats out, but the physical exclusion is still the only long-term control solution.

You may also be tempted to try some of the various sound-emitting devices, commonly called “Ultrasonic” repellers, whose advertising claims to repel all manner of “vermin”, from roaches to rats to birds to fleas. I would suggest you save your time and money. Many studies have been conducted by qualified and impartial university researchers, and so far none of them has been able to support the claims made by the manufacturers of these little boxes. In some cases the Federal Government has even imposed hefty fines against the manufacturers of these devices, who could not substantiate the marketing claims they were making.

Where they are appropriate you might also try placing bright lights, since bats strongly prefer to spend their days in darkness. This may be most likely to be tried in buildings that are difficult to seal, such as warehouses or large barns. Where possible, permanent closure of openings will always be the best method and offer the longest control.

So, let’s look at the steps you should take in your bat control program, and these four important steps are:

  1. Inspection – to determine not only the openings the bats are using, but other openings that they may find and enter once the original ones are closed
  2. Physical exclusion – arranging for the bats to exit but not re-enter, and then permanently closing the opening
  3. Clean-up – elimination of the droppings left by the bats, as well as sanitizing the surfaces
  4. Follow-up – the bats may be very anxious to get back to their cozy hiding places, and will seek alternate routes to do this


Bats usually enter structures through openings that are well above the ground, so it will be very important to check the roof and the eaves, as well as vent openings leading into the attic. They are not capable of chewing material away to create an opening, as rats easily can do, and so they must use existing holes. However, it does not take much, for a small species of bat can squeeze through a crack only ¼ inch wide, or a hole that is about ¾ inch in diameter. If there are lots of bats then they likely have found openings larger than this. One excellent way to determine where these are is to go outside in the evening, sit down in a lounge chair with a cup of hot tea and a pair of binoculars…….and watch. You may substitute hot chocolate if you are not a tea drinker.

Places to suspect might be where power or phone lines enter the structure through the walls, where holes have been punched for plumbing pipes or TV cables, possibly around roof-top vents and louvered fans, and around window framing that may have developed gaps. Wood shake roofs or tile or slate roofs may allow the bats entrance if there is not full sheeting under these roof materials.

You may find bat droppings on window sills or porches outside, and wonder if this means that bats are entering the structure above that point. This probably is not the case. Instead, what you likely have discovered is a site where bats will land to feed on their catch, clinging to the wall or some other object they can grip as they consume the bugs. They then defecate and move on. This may make you a little squeamish, but it is important to determine if the little black pellets you have found are from bats or from rats or mice, for they look very much the same. The difference is that bat droppings are shiny, and if you press on them with a stick they will easily crumble into

Physical Exclusion

Openings that you find that you know the bats are not currently using should be closed right away, so they won’t find these as alternatives once you have closed off the ones they currently use. Depending on the size of the hole and what kind of surface it is on you may use several options for this. For small cracks and holes a simple caulking gun and tube of caulk will work wonderfully. Vent screens should be replaced or repaired. Larger holes could be covered with metal sheeting, hardware cloth, or plywood. Unusual holes that are hard to cover in this manner could be filled with expandable foam, available in aerosol cans. A temporary fix could be done quickly by pushing in a wad of steel wool or copper mesh.

Holes that you identify as definite pathways for the bats should not be permanently closed right away. You would like to give all these unwanted residents of your building the opportunity to depart first, so some sort of one-way door needs to be placed over that hole. Just picture a “doggy” door that only goes one direction. The flaps could be made of sheet metal, wood, plastic, or stiff netting, but in all cases it allows the bat to push its way past the door to exit, but prohibits re-entry. These should be left in place until you are sure all the bats have left the building, usually in less than a week, although this will depend on the weather. If you are having extended rains the bats may just stay secluded until the weather is nice again and their foods will be flying.

Another one-way door that is used is a tube of heavy plastic sheeting, allowing the bats to go into the tube and work their way out of it to fly away, but they cannot return through the collapsed tube. Once you are sure your extended visitors have moved on the flaps can be removed and a permanent repair can be made to close off the openings. All of these methods ensure that you eliminate a well-documented health problem without harming the animals.


Bats that have resided within a structure for a period of time may be very determined to get back into it, so you need to spend time after the exclusion job simply observing the exterior. Watch for bats gathering near the sites they used to enter through, or for bats entering new, undiscovered openings.

A side benefit to this exclusion for bats is that it is also exclusion for most other kinds of pests, including insects, rats, spiders, etc. The wonderful array of unwanted house guests relies on finding hidden entrances to your home or office building, and the repair of these openings will be of great help in keeping them out.


This is a very important step, but it must be undertaken carefully. If there is a large accumulation of bat droppings, and therefore likely a lot of urine has fallen too, this can pose an ongoing health and odor concern for you. It needs to be removed. This can be a major undertaking if the bats were inside walls or other areas that need to be physically opened up, so contracting with a professional could be needed.

Whoever is chosen to manage the clean-up, though, needs to wear protective clothing, and this includes eye protection such as goggles, long sleeved shirt and long pants, rubber gloves, and – very important – breathing protection. The worst hazard would be for someone to inhale the dust stirred up in a cleaning process, for bacteria and viruses growing in this nutritious medium are then taken directly into the body. The proper protection would be a respirator that uses air-purifying cartridges, and the cartridges should be “HEPA” filters that are capable of removing the tiny pathogenic organisms from the air. Following the cleanup all clothing should be either thoroughly laundered or disposed of.

To reduce any chance of creating airborne dust that is contaminated the area should first be dampened with a disinfectant solution. Suggested materials have been a 1:10 solution of bleach, or a household disinfectant used according to its instructions. Washing things frequently to avoid dust and spread of contamination is important, and a very important rule is never use a vacuum cleaner to remove rodent, bird, or bat droppings. The filters in vacuums do not retain the pathogens that are now blown out the back end and are easily inhaled.

As you can see, bat exclusion can be a difficult and time-consuming process. Before you begin you should consider contacting a professional company with experience in removing and excluding animals from buildings. They will have the knowledge and equipment to take care of the problem in a manner that will prevent you from having to expose yourself to the difficulties and possible health consequences.

And finally, try to avoid doing exclusion work in the summer, say from the months of May through August, as it is very likely that young bats will be in the building at this time, unable to leave, and will be trapped inside to die.