Little Brown Myotis bats (sometimes called "little brown bats") congregate during winter hibernation. This species, once common and widespread in Minnesota, has suffered serious population declines due to their susceptibility to the fungus that causes White-nose Syndrome. Photo by Christine Salomon, University of Minnesota.
Bats are intriguing and important animals. They are the only mammal capable of true flight. They have become amazingly diverse, with more than 1400 species documented across six continents. Around the globe, bats benefit ecosystems in many ways. In warmer parts of the world, bats play a critical role in plant pollination and seed dispersal. Minnesota’s bats are strictly insectivores—with voracious appetites! Though a small mammal, bats can consume their body weight in insects each night. That’s up to 1,500 mosquito-sized insects! Although Minnesota’s bats do not aid directly in plant pollination, they do feed on a host of agricultural pests that damage crops and forests, providing an estimated $3 billion in ecosystem benefits annually in the U.S. alone.
- MN's bat species
Big Brown Bat (Eptesicus fuscus)
Minnesota’s most common species, the Big Brown Bat may be found throughout the state. This hardy species is capable of hibernating in places other than caves during the winter months. Hibernation sites may include buildings, where these bats may be encountered by people as the animals transition from their summer foraging areas. The Big Brown Bat is distinguished from the very similar Little Brown Myotis (aka "Little Brown Bat") by its larger snout and eyes. The two species names can cause confusion, though the Big Brown Bat is nearly double the size of Little Brown Myotis. Many people are surprised at the small size of bats in Minnesota, as they may appear larger in flight…and in the movies!
Silver-haired Bat (Lasionycteris noctivagans)
Rarely encountered, this species is named for its fur coloration. These bats are very dark with black pigmented fur and skin. The hairs on their backs are silver tipped, giving them a frosted appearance. This coloration may help blend in with preferred roosting sites: loose bark, cavities, and crevices in trees. Little is known about this species’ migratory journey, but they are known to relocate to milder climates where they might experience a light hibernation. Usually solitary, Silver-haired Bats may be found in groups during this time.
Eastern Red Bat (Lasiurus borealis )
A visually-striking bat, this species is named for its bright red fur. Rarely encountered by people, Eastern Red Bats are mostly solitary and prefer to roost in the tree canopy, where they cling to branches camouflaged among dead leaves. On occasion, they have been encountered in shrubs during fall migration at sites like Shooting Star Prairie SNA.
Hoary Bat (Lasiurus cinereus)
The largest bat species in Minnesota, the Hoary Bat is a distinctly colored and handsome species. Its fur is multicolored with warm-yellow areas near the face and white frosted tips over all of the body. Hoary Bats are solitary, typically roosting high in the tree canopy. Like other migratory “tree bats” they are rarely seen. During the fall, this species migrates in groups to the tropics or sub-tropics…although it is unknown exactly where Minnesota’s Hoary Bats spend the winter. Although a different species than our Hoary Bat, the Hawaiian Hoary Bat (Aeorestes semotus) is the only mammal species native to Hawaii!
Little Brown Myotis (Myotis lucifugus)
A beloved and once-common species in the state, Little Brown Myotis (commonly called "Little Brown Bat) populations have been heavily affected by White-nose Syndrome (WNS), a disease decimating bat populations across North America. This species is attracted to buildings and structures as roosting habitat and was once the most-likely species to be encountered by people. Little Brown Myotis typically use attics for maternity colonies, where a group of females raise their pups. But this species is an obligatory cave hibernator, meaning it can only overwinter only in caves (as well as mines and mineshafts) and typically does not hibernate in homes. As a result of WNS, it has become more common in Minnesota to see big brown bats in buildings. If you believe you have a colony of either species, please report them to the Bat Observation Report.
Northern Long-eared Bat (Myotis septentrionalis)
The Northern Long-eared Bat closely resembles the Little Brown Myotis but has longer ears, as the name indicates. This increasingly rare bat is highly impacted by WNS and was listed as Federally Threatened in 2014. This species is an obligatory cave hibernator and tends to roost solitarily within the hibernacula. A summer habitat study conducted statewide found females using large diameter trees with loose bark, cavities and crevices. Since preferred roost trees may be temporary, females had a network of trees, switching roosts nightly. Northern Long-eared Bat is rarely encountered and is not known to use buildings in Minnesota.
Tri-colored Bat (Perimyotis subflavus)
Minnesota’s smallest bat, Tri-colored Bat weighs about as much as a nickel. This species can be distinguished by its coloration: forearms tend to be pink rather than the brown of other bats. Their name comes from their hair: the hair shaft has three colors from the tip to base. The Tricolored Bat has rarely been found in Minnesota during the summer months, and location of its summer colonies is unknown. During winter this species has been observed hibernating as far north as Soudan Mine in St. Louis County. It is the longest hibernating bat in the state, usually being the first to enter caves and the last to leave. Unfortunately this species is also highly impacted by WNS along with Little Brown Myotis and Northern Long-eared Bats.
Evening Bat (Nycticeius humeralis)
This bat was thought to spend summers only as far north as Illinois, but recent surveys have found new evidence of the species in states such as Michigan and Wisconsin...and now Minnesota (press release?)! In 2016 a bat survey using mist nets captured a lactating female Evening Bat in Ramsey County. Additional evidence of this species’ presence in MN is yet to be found, and it is unknown why this species may be shifting its range northward. The Evening Bat shares several traits with Big Brown Bat (e.g., largish snout, ears, and eyes), but is about half its size, and similar in weight to Little Brown Myotis.
General description: Bat species found in Minnesota are very small, weighing from two-tenths of an ounce to slightly over one ounce.
Insectivorous, they feed mostly on flying insects, including beetles, moths, and mosquitoes which they catch in their cupped tail membranes as they dart and weave through the nighttime air. Once an insect is caught, the bat transfers its prey to its mouth while in flight.
Habitat and range
All of Minnesota's bat species occur throughout the state, with the exception of Evening Bat which is known from a single location.
Bats locate insects and dodge obstacles by using echolocation. As they fly, they constantly emit supersonic cries. Their ears pick up echoes bouncing off objects. These echoes either guide bats toward prey or away from obstacles. Discovery of this unique principle led to development of sonar and radar by which boats and planes navigate, and fishermen locate schools of fish.
- MN's bats and White-nose Syndrome (WNS)
White-nose Syndrome (WNS) is a disease that has killed millions of bats across North America, since first discovered in New York state in the winter of 2006/2007. Infected bats often have white fungus growing around their muzzle —the “white nose” that gives the disease its name— as well as on their wings, tail and ears. As of summer 2021, bats in 37 states and 7 provinces have been confirmed with the disease. There is evidence of the fungus that causes WNS, Pseudogymnoascus destructans, in an additional three states.
WNS was first confirmed in Minnesota's bats at Forestville/Mystery Cave State Park during the winter of 2016-2017. As of 2021, the number of bats hibernating at Soudan Underground Mine and Mystery Cave has declined by over 90%.
Learn more about WNS at the White-nose Syndrome and Minnesota's bats page.
- Living with bats
The following suggestions can be used to keep bats away before they become pests.
- Bright lights placed in attics may disturb bats enough for them to leave. On the other hand, it may also cause them to move to more concealed areas behind boards or between walls. The amount of light necessary to disturb the bats may create an electrical hazard. Fans have been used to create air drafts to disturb bats but again with very limited success. However, once bats have been physically excluded, permanently venting an area or adding a window may make a structure less attractive to bats in the future if new entry points develop.
- Ultrasonic devices are not effective in repelling bats. Be very wary of any pest control company that suggests the use of ultrasonic devices or toxic chemicals.
There are no chemicals registered in Minnesota for use on bats. At one time DDT and Rozol were used to poison bats. However, these chemicals could seep into humans living quarters posing a significant health hazard to people. Use of these chemicals also greatly increased the risk of humans and pets coming into contact with sick or dying bats. Their use has been discontinued and is now illegal.
The reason most methods of bat control fail is because they do not prevent bats from reentering the structure. Whether tackling the problem yourself, or hiring a pest control operator or carpenter, the goal should be the same - non-lethal, non-chemical, permanent, physical exclusion of the bats.
Removing a single bat
A bat that unexpectedly appears in your living quarters may have entered through an open door or window. Another possibility is that it entered from the attic, basement or chimney. In order to solve this problem, isolate the animal in one room of the house by closing the doors to adjoining areas. Next, as long as the bat has not bitten or scratched anyone, open any windows or doors that lead to the outside. Remain in the room so that you don't lose track of the bat. Stand or sit quietly to allow the bat a clear flight path and give it a chance to exit by following the air currents to the outside. Turn down any lights in the room so that the bat doesn't hide behind the curtains or furniture to avoid the light.
If the bat doesn't leave on its own, you can try to capture it. Wait until the bat lands. Then, place a net, coffee can or other container over the bat. Slide a piece of stiff cardboard or other material under the container (see figure at right). Take the container outside and release the bat. When attempting to capture, ALWAYS wear leather gloves to protect yourself.
If the bat appears sick or does not fly well, use caution when capturing it. Use the methods described above or pick it up with a shovel or tongs and place it in a box or bag. DO NOT RELEASE A BAT THAT APPEARS TO BE SICK OR INJURED. Call the county health authorities for instructions on how to submit the bat for testing.
Persons who wake up with a bat in the room where they have been sleeping are advised to submit it for testing, especially if it is unable to fly or seems weak. The possibility of an unnoticed bite or scratch is a special concern in situations where a young child, a mentally disabled person, or an individual under the influence of alcohol or drugs is found alone in the same room with a bat. In these situations, post exposure treatment should be considered unless prompt testing of the bat can rule out rabies infection.
After the bat has been removed you should attempt to determine how the bat entered your house. Make sure doors to attics and basements are well sealed and that dampers are kept closed when the chimney is not in use. In spring or summer, noise coming from the chimney, attic or behind walls may indicate the presence of a bird, bat, mouse or other animal.
What if there's more than one?
Although caves and trees are bats' natural roost sites, some species will utilize attics, chimneys and other areas of homes and buildings for maternity roosts. These places provide a warm, dark, secluded environment for the females, which each raise one young a year. You may find bats roosting in exposed areas (ceiling joists and rafters) or in concealed areas (behind boards and between walls). In the winter, buildings provide a protected area for a bat to hibernate and some bats may even find their way into your basement, particularly during hibernation.
Often the first indication that bats inhabit a house is squeaking or scratching noises coming from the ceiling, walls or chimney. Or, you may notice stains on ceilings or walls from the accumulation of bat droppings. Bat droppings can be distinguished from those of other animals in that they easily break apart and contain many small shiny insect parts. Unlike bird droppings, bat droppings do not contain any white matter.
A number of methods have been tried to evict colonies of bats from buildings. Whether you do the work yourself, or call a pest control company, the ONLY CONSISTENTLY SUCCESSFUL METHOD IS PERMANENT PHYSICAL EXCLUSION.
Timing is critical for excluding bats. In the spring and summer, if a maternity colony has taken up residence, you will need to delay excluding the bats until August when the young are able to fly. If you exclude the adult bats while the young are flightless, the young bats will needlessly starve to death and may create an odor problem. Frantic mother bats, excluded from their young may mistakenly get into your living area when trying to find a way back to the roost to care for the pups.
First step: Bat-proofing
Whether or not you decide to delay excluding the bats for the above reasons, concentrate your efforts first on bat-proofing the living areas of your home. Make sure doors to attics and basements are sealed with draft guards and holes in any interior walls and ceilings are repaired so that a bat can't mistakenly enter the main parts of your house.
Second step: Locating entry points
The next step in excluding bats is to locate the exterior entry points. During the spring or summer, station several people around the outside of the house 1/2 hour before sunset to watch for bats leaving each evening to feed. The watch should continue for about 1 hour after the first bats emerge. Bats can enter through holes as small as 3/8" (the diameter of a dime) or spaces 3/8" by 7/8". Typical entry points include chimneys, louver fans, air intakes, exhaust vents, openings around plumbing, power or cable lines, spaces around doors and windows and where exterior siding has shrunk, warped or loosened. Close inspection during the day will help determine the exact location of the entry points.
If there are many entry points you can close the less frequently used holes. Hardware cloth (1/4"), can be used to cover chimneys and vents. Caulk, weatherstripping, insulation materials, screening, steel wool or even duct tape can be used to close these and other entry points. Efforts to bat proof your home will also often improve energy efficiency. Make sure to leave the most frequently used entry sites open until mid-August.
Third step: Deter entry
In August, the next step is to drape 1/2" X 1/2" structural grade (weight 1.3 oz. / yard), bird or bat netting over the remaining outside entry points (see figure at right). This netting should be available at most garden or hardware stores. Drape the netting over each entry point extending several inches above, 1 foot to the sides and 2 feet below the opening. Attach the top and sides of the netting to the structure with tape, staples or Velcro strips. The bottom should left open so the bats can crawl out when they exit. Don't stretch the netting too taut or the bats will not be able to get out. When the bats return from feeding they will land on the netting close to the hole but will not be able to enter.
Experiments indicate that bats quickly become frustrated and fly away. Unlike rodents, bats probably will not attempt to chew through the netting and they can't squeeze through because the netting is not stable enough. Not all bats leave the roost each night, therefore, the netting should be left in place for several days or up to a week if the weather is cool or wet. Removal of the nets and permanent screening or repair of these last entry points should be done simultaneously, once all bats have left.
Or just wait for them to leave
Provided you have secured the interior of your home, an even easier solution is to wait until late fall when the bats will have left on migration to their winter hibernating sites. Buildings are usually unsuitable as winter hibernacula as bats prefer mines, caves, and tunnels underground where humidity is high and temperatures consistently cool. Once the bats have left on their own accord, the hole closure is most easily accomplished using chalking, screening or other repairs discussed above.
Occasionally, an individual bat will attempt to hibernate in a building. See the section "removal of a single bat" for advice on how to evict such a creature.
What NOT to do!
Attempts to poison bats, or exclude them using inappropriate methods can actually increase human contact, as sick or homeless bats may disperse through the neighborhood thereby increasing chance encounters with people or pets.
Clean the area
Once the bats have been excluded from the roost area, it should be thoroughly cleaned. Bat droppings can create a strong odor. This odor may also attract new bats if openings develop in the structure.
Use caution cleaning the area to avoid contracting histoplasmosis. Histoplasmosis is a respiratory infection caused by inhaling fungal spores which may grow in bat droppings. This fungus is widespread in soils throughout the world. In this country it is most prevalent throughout the Mississippi and Ohio River valleys and primary sources of infection are the droppings of starlings, pigeons and poultry. Although most people contract histoplasmosis have few if any symptoms or problems, some people develop serious respiratory conditions.
When cleaning up bat droppings
- Wear a tight fitting respirator that will filter particles as small as 2 microns.
- Dampen the droppings before cleaning them up will. This will help decrease the spread of any spores.
- The droppings should be sealed in plastic bags for disposal.
Disinfect the area
After you pick up all the bat droppings, the area should then be cleaned and disinfected with a solution of 1 part household bleach to 20 parts water. Clothes worn while cleaning should be washed immediately.
Many people believe that bats are dirty creatures harboring parasites that readily transfer to humans. Actually, the fleas, ticks, mites and bed bugs that live on bats rarely bite humans. Once the bats have been excluded from the area, any remaining parasites will quickly die without the bats to feed on.
Using a pest control operator
If you decide to contact a pest control operator, look for one that uses non-lethal, non-chemical methods to permanently exclude bats. All pest control operators need a permit from the Department of Agriculture. Remember that ultra-sonic devices are not effective. Also be wary of any company suggesting the use of a pesticide or insecticide once the bats have been excluded. As stated above, insects associated with bats rarely pose a problem to humans whereas the chemicals used could be harmful to you and your family.
Build them their own house
Once the bats have been excluded from your home or other structures, you may want to provide an alternate roost site for the bats by putting up a bat house. The following tab contains more information.
- Bat houses
Bat houses (human-made structures to shelter bats) have been used in Europe for many years and are becoming increasingly popular in this country. Encouraging bats to stay around your yard will help control mosquitos and other insects. Detailed plans for two bat house designs are available from Bat Conservation International as well as the Alberta Community Bat Program.
What you can do to help Minnesota's bats
- Prevent the spread of WNS
- Do not disturb hibernating bats
- Do not enter hibernacula during the winter
- Do not exclude bats from buildings during winter
- Report sick or dead bats, and groups of bats
- Help bats survive
- Enhance bat habitat on your property by retaining large trees, protecting wetlands, and constructing homes for bats
- Use bat-friendly methods to exclude bats from your home. Never exclude bats when females are raising young (May—August). See Dealing with Unwanted Guests and Removing Unwanted Bats
- Learn about bats through participation in Bat Week and Bat Festivals!
- White-nose syndrome website
- Bat Conservation International white-nose syndrome webpage.
- Alberta Community Bat Program