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)
About: Minnesota’s most common species of bat, the Big Brown Bat is found throughout the state. Big Brown Bats are often found in urban areas as they are attracted to buildings as summer maternity habitat where they will return every year to raise young. Outside of known maternity roost sites, these bats are most likely to be encountered in the spring and fall during their migration between winter hibernation sites and summer habitat. During migration, bats may rest on building exteriors or exposed walls for multiple days to conserve energy for the journey. Despite vulnerability to White-nose Syndrome (WNS), Big Brown Bat populations appear to be stable likely because of their ability to hibernate in buildings.
Summer Habitat: Common in urban areas, often found roosting in artificial habitat such as buildings, barns, bridges, and bat boxes. Also uses cavities of trees.
Winter Habitat: Only species in Minnesota capable of hibernating in buildings, also uses caves and mines.
Identification: Glossy, golden-brown fur on the back and lighter belly fur, large muzzle with rounded ears and bright eyes. The Big Brown Bat is distinguished from the very similar Little Brown Myotis (AKA "Little Brown Bat") by its larger snout and eyes. Weight: 12.5 – 28.8 grams, Length: 10.3 – 14.5 cm.Click to enlarge
Little Brown Myotis (Myotis lucifugus)
About: Little Brown Myotis (commonly called "Little Brown Bat) are long-lived, with a record 32- year-old bat documented in Wisconsin. Once the most common bat species observed in Minnesota, populations have been heavily affected by White-nose Syndrome (WNS), a disease decimating bat populations across North America. Hibernaculum in Minnesota have seen declines >90% of overwintering Little Brown Bats. This species is attracted to building roosts during the summer, similar to Big Brown Bats. As a result of WNS devastating impacts to Little Brown Bat populations, bats encountered in buildings are now much more likely to be Big Brown Bats.
Summer Habitat: Often found roosting in artificial habitat such as buildings, barns, bridges, and bat boxes. Also uses cavities of trees.
Winter Habitat: Exclusively hibernates in caves and mines.
Identification: Short brown fur on the back with lighter belly fur, small brown muzzle with pointed ears and small eyes. Weight: 7.3 – 11.9 grams, Length: 8.3 – 9.9 cm.Click to enlarge
Northern Long-eared Bat (Myotis septentrionalis)
About: 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 White-nose Syndrome and was listed as federally endangered in 2022 under the Endangered Species Act. This species exclusively hibernates underground in caves or mines 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 used a network of trees, switching roosts nightly. Northern Long-eared Bats are found in the forested regions throughout the state but are rarely encountered as they are not known to use buildings in Minnesota.
Summer Habitat: Tree cavities and crevices, generally large diameter declining trees in the forested regions of the state.
Winter Habitat: Exclusively hibernates in caves and mines.
Identification: Short brown fur on the back with lighter belly fur, small muzzle with long ears and small eyes. Pointed tragus key feature of identification. Weight: 4.9 – 6.4 grams, Length: 8.2 – 9.4 cm.Click to enlarge
Tri-colored Bat (Perimyotis subflavus)
About: Minnesota’s smallest bat, the Tricolored Bat weighs only about as much as a nickel. This species can be distinguished by its coloration: the forearms, nose, and ears tend to be pink rather than brown like other bats. Their name comes from the three distinct bands of color from gray to brown present on their hair shafts. Little is known about habitat preferences in Minnesota during the summer months and locations of summer colonies are unknown. Tricolored Bats have primarily been found in the southeastern portion of the state. 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 White-nose Syndrome along with Little Brown Myotis and Northern Long-eared Bats. This species is proposed to be listed as federally endangered under the Endangered Species Act as of 2023.
Summer Habitat: Known to frequent riparian areas, observed roosting under bridges and in tree foliage. Occasionally seen on building exteriors.
Winter Habitat: Exclusively hibernates in caves and mines.
Identification: Short pale yellow or brown fur, small pink muzzle and ears with small eyes. Pink forearms identifying feature. Weight: 4.2-7.2 grams, Length: 7.9 – 8.8 cm.Click to enlarge
Eastern Red Bat (Lasiurus borealis )
About: A visually striking bat, this species is named for its bright red fur. Females are more frosted or gray in appearance while males are a brighter red hue. Both have distinct white patches of fur near the shoulder. This bat can be found throughout Minnesota. Eastern Red Bats are mostly solitary and prefer to roost in the tree canopy, where they cling to branches camouflaged among dead leaves. As a result, this species is rarely encountered. On occasion, they have been observed roosting in shrubs during fall migration at sites like Shooting Star Prairie SNA.
Summer Habitat: Forested areas, observed using tree foliage and shrubs as roosting habitat.
Winter Habitat: Migrates to areas with milder winters, may briefly hibernate in leaf debris.
Identification: Distinct red fur with frosted tips and white patches near the inner shoulder. Short rounded ears, light colored nose, and bright eyes. Pink forearms and black wing membrane. Furred tail patagium. Weight: 10.6 – 15.4 grams, Length: 9.4 – 11.6 cm.Click to enlarge
Hoary Bat (Lasiurus cinereus)
About: The largest bat species in Minnesota, the Hoary Bat has distinct coloration. Its fur is dense and multicolored, with warm-yellow areas near the face and white-frosted tips over the body. This bat appears large when flying with a wingspan of 14 inches. Hoary Bats are found statewide, they are solitary and typically roost 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.
Summer Habitat: Forested areas, observed using tree foliage and shrubs as roosting habitat.
Winter Habitat: Migrates to areas with mild winters.
Identification: Distinct yellow fur near the face with dark base and white- frosted tips through most of the body. Short, rounded ears, dark nose, and bright eyes. Light- blond fur on inner forearm and dark wing membrane. Furred tail patagium. Weight: 22.3 – 39.9 grams, Length: 13.0 – 14.7 cm.Click to enlarge
Silver-haired Bat (Lasionycteris noctivagans)
About: Encountered occasionally, Silver Haired Bats are named for their 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 their preferred roosting sites: loose bark, cavities, and crevices in trees. Silver Haired Bats have been documented statewide. Little is known about this species’ migratory journey, but they are known to relocate to milder climates during winter where they might experience a light hibernation. Silver Haired Bats may be encountered during spring and fall migration when they roost in exposed areas for multiple days to conserve energy for the long migration journey.
Summer Habitat: Known to use tree cavities, crevices, and loose bark. May occasionally roost on the exterior of buildings during migration in spring and fall. Observed using a bat box in central Minnesota.
Winter Habitat: Migrates to areas with mild winters.
Identification: Black to dark brown fur and skin. Dorsal fur has white silver tips and tail membrane is furred. Short rounded ears, dark nose, and bright eyes. Weight: 9.9 – 17.2 grams, Length: 9.3 – 10.5 cm.Click to enlarge
Evening Bat (Nycticeius humeralis)
About: This bat was thought to spend summers only as far north as Illinois, but recent surveys have found new evidence of the species in Michigan, Wisconsin, and now Minnesota! In 2016, a bat survey using mist nets captured a lactating female Evening Bat in Ramsey County. Additional records of this species’ presence in Minnesota have been observed, but it is unknown why this species may be shifting its range northward. Evening Bats share several traits with Big Brown Bats (e.g., largish snout, ears, and eyes), but are about half the size, and similar in weight to Little Brown Myotis.
Summer Habitat: Known to use tree cavities, crevices, and loose bark. May occasionally use buildings.
Winter Habitat: Migrates to areas with mild winters.
Identification: Brown fur on the back with lighter belly, large muzzle with rounded ears and bright eyes. Distinguished from Big Brown Bats by their smaller size. Weight: 7 – 14 grams, Length: 7.7 – 9.6 cm.Click to enlarge
Identification
General description: Bat species found in Minnesota are very small, weighing from two-tenths of an ounce to slightly over one ounce.
Food
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.
Fun facts
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.
- Bats in Buildings
Buildings are an important resource to two species in Minnesota: Little Brown Bats and Big Brown Bats. Historically, these species relied on large diameter trees with deep cracks and crevices that kept them warm and dry. Over time, the loss of many of these large trees led bats to recognize buildings as valuable structures for important life stages, such as pup (term used for baby bat) rearing in the summer, or hibernation in the winter. Single bats, or groups of bats called “colonies”, may use buildings. Read below to learn about the different ways bats use buildings, and bat-friendly methods to remove bats or prevent them from roosting in buildings.
Found a Bat in Your Living Space?
If you believe you or someone else was bitten or scratched by the bat, you have woken up to find a bat in the same room, or if the bat was found in a room with a child or someone who cannot reliably communicate whether or not there was physical contact with the bat, please call your county health authorities for instructions on submitting the bat for rabies testing. If the bat cannot be captured, contact your healthcare provider.
If the bat did not come in contact with a person and the bat is not njured, it is safe to release outdoors. Rabies is estimated to infect less than 1% of bat populations but caution should always be taken with any rabies vector species.
Further information: MN Health Department: Encountering a bat
Finding Injured, Distressed or Dead Bats
In most cases, it is best to leave bats alone when they are found outside, especially during the fall and spring. A healthy bat in a hibernation state may appear to be dying or non-responsive. If the bat is in a location where it is not safe to remain, such as an area where kids or pets may come in contact, you can move the bat to a nearby tree. Wearing leather gloves, collect the bat in a box or with a towel, and place high off the ground. A healthy bat will likely move on after sunset or remain for 2-3 days during the migration period. If you would like more information, you can take a photo of the bat and report to the Bat Observation Report.
If you find an obviously injured bat, such as one that is cat-caught or has a broken wing, reach out to a local wildlife rehabilitation for further instruction.
Found a dead bat? You can leave the bat in place if people or pets will not come in contact. Otherwise, you can dispose in a wooded area where contact with people will not occur, or double bag and place in a trash bin. Keep an eye out for more dead bats in the area, particularly during the summer months. If you find 5 or more dead bats within a week, please report to the Bat Observation Report or reach out to the DNR Info Desk. In this event, MNDNR is interested in tracking reports and collecting samples.
Releasing a Single Bat
Finding a single bat in a building does not always indicate a bat colony is present. Wayward bat encounters tend to increase in late summer when young bats start flying. More curious and less agile than adult bats, young bats may fly into open doors and windows.
Isolate the bat 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 screens, windows or doors that lead to the outside. Remain in the room so that you don't lose track of the bat and to confirm the bat was able to fly out. 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 does not leave on its own, you can try to capture it. When attempting to capture a bat, ALWAYS wear leather gloves to protect yourself. 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 1). Take the container outside and release the bat by placing it on a tree, out of reach from the ground.If you are unable to find the bat, search behind picture frames, shelves, in curtains, or other crevices in the room. Bats prefer to be off the ground, hanging somewhere that feels protected. Keep all interior doors closed until you locate the bat to narrow the search area.
If the bat appears injured, consider calling a wildlife rehabilitation facility. Take caution to secure the bat in a sealed box with air ventilation.
After the bat has been removed, you should attempt to determine how the bat entered your living space. Make sure doors to attics and basements are well sealed, and that dampers are kept closed when the chimney is not in use. If bats have shown up multiple times in the same location in the house, it could indicate pups can access the living space while exploring for exits from a building roost. Look for gaps that access the room such as vents, loose trim, outlets without covers, attic or basement access doors. Bats can fit through crevices as small as ½ inch. Identifying and sealing these interior entrances can help prevent entry from future wayward bats. See Summer Bat Colonies section for more information about bat colonies and removal process.
Single Bats Roosting on Buildings in Fall or Spring
During migration periods, bats may roost in exposed areas visible to broad daylight. These are likely bats that stopped to conserve energy, going into a hibernation mode known as “torpor” during a cold night. The bat may stay for 2-3 days before heading off. As long as the bat is not accessible to be grabbed by children or pets, you can leave the bat to rest. If you are concerned about the bat’s location, you can move the bat to a nearby tree where less traffic occurs. Wearing gloves, place the bat high enough that it is out of reach.
Common places to see these resting bats during spring and fall are close to the ground on trees, brick buildings, entry door shelters, windowsills, wood piles, folded patio umbrellas, and leaf piles.
Summer Bat Colonies
Bat groups are occasionally found roosting in buildings, which can offer safe, warm shelters for bats in Minnesota. During summer months, female bats group into colonies to raise young from May–August. Females will give birth to one pup per year and return to a known roost site year after year. Attics, eaves, and other tight, weather-proof spaces that receive sun exposure can provide a suitable environment for raising pups who depend on warm roosts. Bats cannot chew through building exteriors or create access points and instead rely on damaged or worn structures that are no longer weather tight.
- Typical signs of a bat colony:
- Guano (bat feces)/urine-stained entry points, typically towards the top of a building
- Hearing movement, high pitched animal vocalizations in the wall, scratching noises
- Seeing bats exiting from your house during sunset
- Bats entering living quarters frequently or every year in August
Bats also use building shelters for night roosting. These are locations bats come to rest and digest during the evening only while they are out foraging for insects. You might have a night roost if you find guano accumulations occurring overnight, particularly in sheltered porches or entry overhangs, but don’t see or hear bats during the daytime. Small accumulations of guano outdoors are not a cause for concern, but if you would prefer bats not to use the space as a night roost, you can hang streamers or smooth, shiny material difficult to grip to help deter bats from resting in that location.
Winter Bat Colonies
One species of bat in Minnesota, the Big Brown Bat (profile description above), will hibernate in buildings over the winter. Bats may be noticed during winter months when they end up in interior living spaces while looking for exits, chattering is heard in the walls on warmer winter days, or bats are found during renovation projects. It is likely that a summer colony also uses the building if bats are found hibernating during winter.
Winter months are not a suitable time to conduct exclusions or bat removals. Bats are in a dormant state until the weather becomes reliably warm again, typically in late March and early April. Exclusions (see Excluding Bat Colonies from Buildings below) rely on bats being active to leave the roost at night, and so winter exclusions are not effective. Waiting until spring months is the best solution to evict overwintering bats.
Excluding Bat Colonies from Buildings
An exclusion is the process of installing one-way exit devices that allow bats to leave, but not re-enter a building access point. After all bats leave a roost, typically after a week, the entrances can be permanently closed or repaired so bats can no longer access the building. Exclusions are the only successful and safe solution for bat colony removal as long as they are done either in the early spring or fall, avoiding the May–August pupping season.
Trapping or killing bats is never an acceptable solution for bat removal, as this does not solve the root problem of entry points in the building that are no longer weather tight and are thus available to bats. If the structural issues are not resolved, more bats will continue to use the building as a roost.
- Quick Reference – Exclusion Steps
- Confirm a bat colony is using your building by doing an emergence survey, looking for bat signs, or hiring a bat exclusion specialist.
- Conduct exclusions in April or September to avoid harming bat pups.
- Identify all entry points bats use to access roost, including non-primary exits.
- Place one-way exit devices on entry points so bats can leave but cannot get back inside.
- Leave devices up for at least one week and up to three weeks if the exclusion is conducted in early spring or late fall.
- Permanently seal or repair access points to prevent bats from re-entering.
- Note that you can complete the exclusion yourself or call a professional to conduct an exclusion. The DNR does not conduct bat removals. Ensure bat exclusion professionals are not using methods that harm bats (shop vacuums, pressure washers, sticky traps) or blocking exits without first installing exclusion devices while bats are present inside the building. Trapping and translocation of bats should never be offered as a solution, outside of situations where bats need to be removed from an interior living space where they may come into contact with people.
- Exclusion Tips
- The ideal exclusion period is generally during April or in September, when bats are consistently active with warmer weather. Exclusions can be conducted until November, when bat activity generally decreases. Avoid conducting exclusion from May–August to avoid adults abandoning flightless pups, who cannot leave the roost during exclusions.
- Killing or relocating bats is not an effective or ethical solution as other bats will continue to access the buildings through the same access points. Conducting an exclusion followed by repair of bat entry points solves the root problem of removing available entrances without harming bats.
- Sealing or removing bat entrances to a building without first completing an exclusion in any season can cause bats to enter living spaces as they look for a new exit out of the roost. In Minnesota, the Big Brown Bat can hibernate over the winter in buildings. Sealing or entrance closures in the winter or late fall may result in bats entering living spaces after hibernation as they look for a way out of the roost.
- Deterrents like ultrasound or bright lights are not known to be effective at repelling bats from roosting in buildings.
For in-depth information on bats in buildings and information on how to conduct an exclusion yourself, see these resources. These guides originate from outside of Minnesota, but the information is relevant with our regions sharing similar bat species.
Frequently Asked Questions
- When do I need to submit a bat for rabies testing?
- Bats should be submitted for testing if they have bitten or scratched a person, or they were found flying in a room with a non-verbal person, a child, or sleeping person. Bat bites or scratches are not always noticeable, therefore if contact with a bat is unknown it should be submitted for testing. Bats that were found inside a house that have not had contact with people can be released. See the Minnesota Department of Health for more information.
- Is my house “infested”?
- A bat colony occupying a building is not comparable to mice entering a building. Bats do not reproduce quickly (a female will have only 1 young per year), they do not chew or create openings, nor do they counter-surf for food in the kitchen! A bat colony often goes unnoticed for many years until a wayward bat is encountered in the living space or insulation remediation finds a few in the attic. Summer bat colonies are composed of a group of females and their pups, keeping safe in the weatherproof crevices that weathered buildings provide. Because the only resource the building provides is a warm roost, bats do not take over buildings and such colonies rarely grow large in Minnesota.
- Are the bats a danger to me and my family?
- As long as the bats are staying outside the interior living spaces, a bat colony does not pose an immediate threat to people. See Removing a Single Bat section for a description on typical interior access points. While rabies is a common concern for bats, the frequency of the disease in wild populations is estimated to be less than 1% suggesting that it is not common to encounter a bat with rabies. However, as bats are a rabies vector species, safety around bats is key by avoiding contact with bats, wearing leather gloves if you need to handle one, and submitting bats for testing when a bite or scratch occurs, or contact is undeterminable. If bats regularly enter living spaces during summer months, an exclusion and interior inspections should be conducted to prevent continued exposure to bats.
- What about bat guano, is that dangerous?
- Guano (bat feces) and bat urine has potential to accumulate where large colonies persist for many years. Histoplasmosis is a fungus that can grow in guano piles, which can pose a health hazard when dust containing the fungal spores is inhaled. Although histoplasmosis is not common in Minnesota, it is always important to take safety precautions when cleaning guano or any animal waste accumulations in interior spaces. Never sweep or vacuum guano piles or stir up dust where guano has persisted without wearing adequate respiratory protection, such as N95 masks. Guano found outdoors is generally not a concern for histoplasmosis.
- I like bats but don’t want them in my home, how can I help them?
- If you need to get bats out of your building, conduct bat-friendly exclusions during the right time of year (April OR September) to avoid harming bats. Consider placing bat boxes in your yard to provide an alternative roost site for the displaced bats before conducting the exclusion process. If you do not have a bat colony in your home and want to help bats, see What you can do to help Minnesota’s bats
- Why do I get bats in my living space in August?
- August is the most common time of year to encounter bats in interior living spaces. During this month, bat pups are active on the landscape, learning to fly and catch insects. Pups are also exploring more, both in the outdoors and within their building roosts. As a result, pups can end up in interior living spaces as they are likely to get lost in building roosts as they look for roost exits or fly through open doors and windows.
- Typical signs of a bat colony:
- Bat boxes
Bat boxes are artificial roosting structures used by bats during the summer months, when females gather in groups to raise their young. These boxes can support bat populations by providing important summer habitat, providing alternative roosts to buildings when used according to recommendations. For more information on using bat boxes in Minnesota, visit our Guide to Artificial Roosts for Bats.
Plans for Four-chambered bat house originate from Bat Conservation International. Plans for Two-chambered rocket box available from the Alberta Community Bat Program. For in-depth reading about bat boxes visit Holroyd S. et. al (2023) Best Management Practices for the Use of Bat Houses in the US and Canada.
What you can do to help Minnesota's bats
- Prevent the spread of WNS
- Honor cave closures and gated caves.
- Avoid caves and mines where bats hibernate. Be familiar with cave advisories (National Speleological Society).
- Decontaminate clothing and gear according to recommended decontamination protocols
- 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!
Further information
- White-nose syndrome website
- Bat Conservation International white-nose syndrome webpage.
- Alberta Community Bat Program
