G1667

Bats In and Around Structures

The NebGuide describes common bats and their habitats in Nebraska, and provides recommendations for their exclusion, and removal from homes and structures.

Dennis M. Ferraro, Extension Educator
Scott E. Hygnstrom, Extension Wildlife Damage Specialist
Stephen Vantassel, Extension Wildlife Damage Project Coordinator

Figure 1.
Figure 1. Big brown bat, Eptesicus fuscus© Merlin D. Tuttle, Bat Conservation International, Inc.
Figure 2.
Figure 2. Big brown feeding on moth© Merlin D. Tuttle, Bat Conservation International, Inc.
Figure 3.
Figure 3. Red bat, Lasiurus borealis.
Figure 4.
Figure 4. Bat droppings: bat fecal material is shiny black with many insect parts.
Figure 5.
Figure 5. One-way door netting used to exclude bats. Black arrow points to hole.
Figure 6.
Figure 6. Cloth funnel trap.
Figure 7.
Figure 7. LaFrance’s Bat Trap is an example of a commercial bat trap.

Bats are misunderstood creatures. While some people perceive them as an evil menace, they actually are very gentle animals to be respected and not destroyed needlessly. Occasionally bats gain access to buildings where they are unwelcome. A bat that is flying around in a bedroom or church can be disconcerting. The droppings (guano) and urine deposited by a colony of bats in an attic can cause odor and damage. On rare occasions, bats can threaten human health because they are capable of carrying and transmitting rabies and histoplasmosis (extremely rare in Nebraska).

Thirteen species of bats occur? in Nebraska?. Most are uncommon, however, and rarely found in or near structures. The big brown bat, Eptesicus fuscus (Figure 1) is found throughout the state and is commonly encountered by the public. This bat is only about five inches long from nose to tail; but it appears larger in flight (Figure 2). As its name suggests, this bat is brown with black skin exposed on the nose, ears and wings. The underside is pale brown.

The red bat (Lasiurus borealis) (Figure 3) sometimes is encountered around structures and landscape. It is smaller than the big brown bat and is reddish-brown to rust colored on top with a paler red underside. It also has a cream or off-white patch on each shoulder.

The little brown bat (Myotis lucifugus) occurs in the eastern third of the state. This bat is three to four inches long and is glossy dark brown.

Bat Facts

Bats are not rodents, but mammals having flapping membranous wings supported by elongated fingers capable of true flight. Bats have small needle-like teeth that are excellent for capturing small insects. They do not chew wood, caulk or structural materials. Bats are nocturnal and seldom are seen in daylight unless disturbed. Bats have good vision yet they rely on their specialized sonar (called echolocation) and hearing for hunting at night. They scoop flying insects out of the air with their mouths or can use their wings to draw prey into their mouths. Nebraska’s bats feed exclusively on insects, devouring more mosquitoes than any bug zapper. A single bat is capable of consuming over 1,000 insects per night. They also drink while in flight by swooping over sources of standing water, including swimming pools.

Native bats have only one or two young per year. Some species mate in early fall and the female holds the sperm until late winter or early spring, when fertilization takes place. The young are born six to eight weeks later, and young stay in maternal roosts until late summer. Occasionally, adults and their young accidentally find their way into structures during their return trip to the roost. Under natural conditions bats normally live under loose bark or in hollow trees, caves, quarries and cracks of rocky ledges. In urban areas, however, they frequently use attics or areas behind shutters, downspouts, seams of bridges and even in storm sewers. Big brown bats live in colonies, some of which include hundreds of individuals in one attic. Many big brown bats stay in their Nebraska roosts (there may be several temporary summer roosts) all year. Some Nebraska species migrate southward for the winter.

Ecological and Economic Importance

A common misconception is that bats are disgusting, disease-ridden vermin responsible for massive human health problems. Only a very small percentage of bats are associated with rabies and histoplasmosis. In fact other common animals, such as skunks, raccoons, cats, dogs and animals with which humans often have more contact, are noted to have a higher incidence of rabies.

Bat rabies

Many of the deaths from rabies in the United States have been associated with the bat strain of rabies. Since bats are so small, some people don’t even know they were bitten. Therefore, Nebraska has adopted new recommended protocol for handling potential bat-human exposures.

Assume a person was bitten if:

  1. He/she awakens to find a bat in the room;
  2. A bat is found in the room with someone unable to communicate well (i.e. children, intoxicated or otherwise mentally impaired);
  3. The bat made contact with a person.

In these situations, do not release the bat. Take care not to damage the bat’s head (no tennis racquets, please). Contact local health officials to determine where the bat needs to be sent for rabies testing. If the bat is not found within a couple of hours, consult health professionals about needed treatment.

Bat guano

Only large amounts of bat droppings in a confined location can be considered a threat for developing histoplasmosis. Bat guano (Figure 4) has been prized for years by many gardeners as the finest organic fertilizer. Guano typically includes 10 percent nitrogen, 3 percent phosphorous and 1 percent potassium. Sun-dried guano from natural outdoor settings unlikely includes histoplasmosis fungi.

Bats consume one-quarter to one-half of their body weight in insects each night. An average colony of big brown bats may eliminate over 100 tons of insects in one season! Several studies recently have shown that populations of bats can effectively control corn rootworm moths, therefore reducing the need for applications of agricultural insecticides in some areas. Just imagine what these creatures could do in your garden.

Bat Signs

Droppings are the most commonly viewed sign left by bats. Individual droppings are small (1/8- to 1/4-inch long), black and shiny. Under magnification they are full of shiny insect parts (legs, wings, etc.). Droppings often are found on attic and porch floors under eves and shutters. Dropping and urine accumulate beneath a colony of bats over time, leading to staining and a rather pungent odor in enclosed spaces.

Bats frequently move in and out of a structure though the same opening every evening. Repeat movements at these entry points leave smudges of oil and dirt from the bat’s fur, called rubmarks. Look for rubmarks at entry points near eaves, vents, chimneys, cracks and other openings. Occasionally the squeaking and scratching of individual bats can be heard in a wall void, ceiling and other spaces.

Preventing Entry/Exclusion

Bats accidentally find their way into houses in the early evening hours, when they are seeking shelter or feeding on insects attracted by doorway lights. They can enter through openings as small as 1/4- to 3/8-inch in diameter. Bats are incapable of making their own entry holes. Therefore it is important to plug all holes and use good screens and tight fitting doors prior to having a problem. Hardware cloth, aerosol foam insulation and weatherproof foam strips are excellent materials for excluding bats. Foaming insulation will degrade under UV light, so coat it with exterior caulk for long term. Replace doorway light bulbs with yellow “bug lights” to reduce the number of insects attracted to the area.

Bats that are roosting behind downspouts and shutters on buildings occasionally find their way into the structure. A common entry point is where the foundation meets the house. Use expanding foam or copper wool to establish a barrier that fills the spaces between attached structures and the building.

An open chimney or furnace vent can be an entry point for bats, which may roost in the chimney or gain access to the interior of the structure. Install an approved stainless steel chimney cap with quarter-inch wire mesh to minimize access to bats.

If a colony of bats is residing in the attic or hidden area in the structure:

  1. Locate all exit/entry points by standing outside of the structure on a late-summer evening looking for bats that are exiting the building to go foraging at night;
  2. Create a one-way door by hanging 1-foot strips of flexible quarter-inch netting over the exit/entry points;
  3. Fasten the netting only by the top edge just above the entries (Figure 5), the bats will exit hit the netting, go to the bottom of the barrier, take flight, and upon returning, will be unable to go through the netting);
  4. Allow at least one week to pass, then seal and patch all entry points;
  5. Do not install one-way doors or seal exit/entry points during June through July when young bats are likely to be in the roost (June through July — let them fly!).

Young bats abandoned or sealed in a structure will move about the structure looking for a way out, will starve and ultimately may cause an odor problem.

Live Bat Trapping

Occasionally large colonies of bats roosting in structures need to be trapped when there are no natural roosting sites in the area. Several bats can be captured using one-way door devices that have a holding/collection bag attached or by building “roost traps.”

Secure a 10-inch long cloth sleeve/funnel around the bat’s exit point and hang it on the outside of the structure. Attach a 6-inch length of 2-inch diameter aluminum pipe to the bottom of the cloth sleeve. To the other end of the pipe secure, a cloth or plastic sack with a strong elastic band or duct tape; this device also can be used to capture a lone bat (Figure 6).

A cage trap consisting of pockets, slots and crevices can be attached to the underside of an attic or overhang. After leaving the structure, the bats are captured by the trap, unable to return to the den site. The trap is covered and the collected bats can be removed. Only professional wildlife control experts should handle, remove and transport live captured bats. Bat traps are commercially available for $100 to $200 each (Figure 7).

Individual Bat Removal

If a single bat has entered a home or structure, these steps may be followed:

  1. Open all exterior doors and windows in the room(s) in which the bat is observed;
  2. Shut all doors leading to adjacent rooms to confine the bat in the area where entries are opened;
  3. Leave the lights on and stand motionless next to a wall or in a hallway leading to the room;
  4. Patiently wait as the bat swoops around the room trying to find escape route (contrary to popular belief, bats are not attracted to people’s hair). It likely will fly out of the room on its own. Do not wave at or herd the bat!

If the bat is at rest on a wall (usually behind curtains or window blinds):

  1. Put on a pair of leather gloves;
  2. Get a large-mouthed glass, cup or plastic container;
  3. Approach the bat slowly from one side and place the container over the bat;
  4. Slide a piece of cardboard or stiff paper between the container and wall;
  5. Carry the bat in the container with the paper lid outdoors;
  6. Place the container with lid against the side of a tree 4 to 6 feet above ground or other elevated location outdoors;
  7. Carefully slide the paper out from between container and tree then slowly lift the container. The bat may not fly immediately, but it will be safe from predators until it flies away.

Repellents

Several commercial products are available to repel bats such BatScat™. The effectiveness of these products, however, is questionable and they have not been tested on bats in Nebraska. Mothballs and ultrasound devices have not been proven effective in deterring bats.

Toxicants

No toxicants are registered for bats in Nebraska or the United States. Since bats feed exclusively on live insects, it is unlikely that any toxic baits would be effective. In extreme cases, the Centers for Disease Control and the Environmental Protection Agency may provide special permits to use toxic tracking powder on bats.

Bat Houses

To take advantage of a bat’s search for insect foods, consider installing bat houses in the yard. While there are several bat house designs, all seem to have the same appeal to the common big brown bat. Bat houses can be purchased or easily built. Refer to the “Bat House” NebGuide http://www.ianrpubs.unl.edu/epublic/live/g1575/build/g1575.pdf.

Reference to commercial products or trade names is made with the understanding that no discrimination is intended of those not mentioned and no endorsement by University of Nebraska–Lincoln Extension is implied for those mentioned.

Visit the University of Nebraska–Lincoln Extension Publications Web site for more publications.
Index: Wildlife Management
Urban Wildlife
Issued February 2007

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© 2007, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension. All rights reserved.