If you want to reduce the insect pests in your garden or simply enjoy a more insect-free evening in your yard, consider gardening techniques that attract bats. Each Minnesota bat consumes about 1500 mosquito-sized insects each night, a meal equal to between 25% and 100% of the bats’ body weight. [1] Reduction in the mosquito population by bats has led to the reduction of mosquito-borne diseases, including the West Nile virus. Bats also come with the added benefit of natural, organic fertilizer – i.e. bat guano – that automatically helps fertilize your lawn and can be captured to help fertilize your garden.

Beyond the gardening benefits of bats, bats devour enough insects every night to reduce agricultural pesticide use in the U.S., saving farmers about $3.7 billion dollars a year. In a similar fashion, bats eat forest insects that help preserve trees planted by the lumber industry [2]. In addition, bat research has led to advancements in navigational aids for the blind, use of sonar technologies and new medications (e.g. vampire bat saliva helps manage blood clots). [3]

Read on to learn more about bats, gardening to attract bats and bat houses.

Minnesota Bats (primary citation [1])

There are eight different bat species found in Minnesota, 42 species in the U.S. and over 1400 species around the world [4]. If you see a bat in Dakota County, you are likely observing a Big Brown Bat which is the most common bat species in Minnesota.  Big Brown Bats are 4 to 6 inches in length and like most bats are very light, weighing 12 to 15 grams (less than 0.06 pounds).  Their wingspan ranges from 12 to 14 inches in flight and they can often be seen flying 20-30 feet above ground near treetops. Big Brown Bats will swoop through the air and to the ground to capture their preferred meal of flying and ground beetles. However, Big Brown Bats are feeding generalists and will devour many insects including mosquitoes, flies, stink bugs, wasps, moths and leafhoppers. [5]

Big Brown Bats have long golden-brown fur on their backs with lighter fur on their bellies.  They also have large pointy snouts, bright eyes and large rounded ears (see image A).  Big Brown Bats are prevalent in Dakota County because they have adapted to urban living and can often be found roosting in buildings and other man-made structures. 

Each pregnant Big Brown Bat has a baby (called a “pup”) in June or July and will nurse their pups for 4-5 weeks. Big Brown Bats hibernate from November through April and generally will not travel more than 50 miles from their summer roosts to their winter hibernation site. Big Brown Bats are the only known Minnesota species that can hibernate in buildings to survive the winter.  Other Minnesota bat species must find a cave or other underground habitat or must migrate over winter. 

The other species of bat that you may encounter in Dakota County is the Little Brown Myotis, also known as the Little Brown Bat. Little Brown Bats have also adapted to urban areas and may be found in buildings and other man-made structures.  Little Brown Bats are 3 to 4 inches in length and weigh 7 to 12 grams (less than 0.03 pounds).  Their wingspan ranges from 8 to 11 inches in flight and they are often seen flying a few feet above water or near the top of bushes.  Their preferred food is water insects like mayflies and midges.  In addition, Little Brown Bats will eat mosquitoes, little flies, moths and beetles. [6]

Little Brown Bats have short brown fur on their backs with lighter fur on their bellies.  They also have small snouts, small eyes and pointed ears (see image B).  Little Brown Bats hibernate in caves or mines and mate just prior to hibernation or during hibernation.  Sperm is stored over the winter with female ovulation occurring just as the bats awake in the spring. Pups are born in May or June and are nursed for 3-4 weeks. Little Brown Bats will skim over the surface of water to drink or catch water insects.  Therefore, proximity to water is important for Little Brown Bats. Little Brown Bats were the most prevalent bat in Minnesota but the species has been decimated by disease in recent years with a 90% population loss.

The remaining species of Minnesota bats include the Eastern Red Bat, the Evening Bat, the Hoary Bat (Minnesota’s largest bat), the Northern Long-Eared Bat, the Silver-Haired Bat and the Tri-Colored Bat. It would be uncommon in Dakota County to observe any of these six species of Minnesota bats since they mostly live in forested areas and have not readily adapted to urban areas.

Gardening to Attract Bats (primary citations [7]-[9])

Attracting bats to your yard starts by attracting the insects that bats eat, especially nocturnal insects.  Moths may be the most well-known nocturnal insects and will be more prevalent in gardens that contain native plants with open blooms at night. Bee Balm, Evening Primrose, Goldenrod, Phlox, Purple Coneflower and Yarrow are good examples of native Minnesota flowers that have open blooms at night. A more comprehensive list of plants that attract moths has been supplied by the Xerces Society for Invertebrate Conservation. [10] 

Gardeners may be leery about attracting moths because of the perceived damage that moths inflict on plants.  Moths do not eat plants; moth larvae eat plants. You can reduce the damage that moth larvae cause to garden plants by planting milkweed and native grasses in a remote location where the grasses can provide food and shelter to the moth larvae. The University of Minnesota has created a list of native grasses and the insects that the grasses attract. [11]

Many insects create their homes in dead tree branches and dead trees.  Therefore, you can increase the insect population and attract bats by allowing dead tree wood to remain in your yard. To attract beneficial beetles that are the favorite of Big Brown Bats, maintain a compost pile, keep piles of leaves, plant taller grasses, stop mowing part of your lawn and plant clover which attracts beetles. A couple of simple things that all gardeners can do to attract beetles is to maintain a container of rotting sticks and dead leaves and/or a mound of dirt without plants where beetles can make their homes. [12]

In addition to attracting insects, additional tips that can help attract bats to your yard include:

• Plant native, flowering vines at the base of walls or fences.  The vining spaces serve as temporary protective bat roosts when bats are flying at night.

• Minimize use of pesticides which can poison the insects that bats eat.

• Avoid using treated lumber in your yard because the chemicals may be absorbed by bats that come in contact with the lumber. 

• Keep cats out of your yard since they will hunt bats.

• Provide a large-surface water source for the bats if a natural water source is not available.

• Install a bat house.

Access to bat guano is an extra benefit to having bats in your yard. Always wear gloves and a mask when handling bat guano and wash your hands and clothes after working with bat guano. Bat guano has an NPK of about 10-3-1 and is a longer lasting fertilizer that is not easily washed away with the rain. Using bat guano that you collect rather than buying bat guano fertilizer helps conserve bat populations since store-bought fertilizers generally require people to disrupt bat caves. You can differentiate between bat guano and droppings from other animals by squishing the poop and holding it up to a light.  Bat guano will glitter due to the remains of hard insect shells that cannot be digested by bats. If the poop you find is dull, it is not bat guano. Moderate amounts of bat guano may be added to your compost pile and may accelerate the decomposition process. In addition, gardeners may sprinkle bat guano in the garden or make bat guano tea to spray on leaves to protect the plants from fungal diseases. You can make bat guano tea by wrapping ½ cup of bat guano in cheese cloth and letting the guano stew for three days in a gallon of water. Excess bat guano may be disposed of at The Recycling Zone in Eagan and should not be added to any curbside pickup bins. [13][14]

Interesting Bat Facts and Myths

• Bats are the only mammal capable of true flight. [19]

• Bats can live to be over 30 years old in the wild but the average life expectancy is between 6 and 7 years. About 50% of bats die during their first winter. (a)

• Female bats typically have one baby per year with little reproductive decline as they age. Gestation time varies based on bat species, temperature and precipitation.  Minnesota bat gestation times range from 40 to 70 days. (a)

• Some bats in warmer climates eat nectar, helping to pollinate plants such as agave which is critical in the production of tequila. There are also bat species that eat fruit, fish, frogs and lizards. [4][19]

• Bats do not drink the blood of humans. However, there are three species of vampire bats primarily found south of the U.S. that will bite animals such as livestock and lick their blood. [20]

• Brown bats use echolocation to detect objects up to 30 to 66 feet away. Bats are not blind and may use vision to see beyond their echolocation boundaries. [15]

• Bats do not sweat but will drink water, lick themselves, or sometimes urinate on themselves to cool off. [15]

• Bats may enter a state of “torpor” to conserve energy during cooler hours. Bats take 40 minutes on average to emerge from torpor and be able to fly, which puts bats at risk from predators or other negative disturbances during the torpor period. Torpor is different from hibernation in that torpor can last a few minutes to a few hours whereas hibernation can last the entire winter season. [21]

• Bats reduce their energy expenditure by 98% during hibernation, lowering their heart rate from 200-300 beats per minute to 20 beats per minute. [21]

• Bats prefer to fly where there is protective cover within 30 to 90 feet. Bats will rarely cross more than 300 feet of open space since it makes them vulnerable to night-flying predators such as owls. [15]

• Seeding a bat house with bat guano to attract bats is a myth and has not been proven to help attract bats to a new bat house. [16]

• Some bats will somersault in the air when approaching a roost in order to land up-side-down which is their normal position while roosting. [15]

• An estimated 200,000 to 500,000 bats are killed each year by wind turbines. This number is expected to grow as use of wind energy grows.  Scientists do not fully understand why bats do not naturally avoid wind turbines. [4]

• Less than 0.5% of bats contract rabies each year, making rabies a rare disease among bats. [15] Rabies is even more rare in humans with fewer than 10 cases a year reported in the U.S. Humans may contract rabies if bitten or scratched by a rabid animal or directly exposed to fluids of a rabid animal. [22] Humans should avoid approaching bats and should never touch a bat without wearing gloves and possibly other protective clothing. As a precaution, pets should be vaccinated for rabies if bats live nearby. 

• Bats are more closely related to humans than to mice. [19]

Guidelines For Bat Houses (primary citation [15])

If this article has convinced you about the benefits of bats in your area, you may want to consider a bat house. A bat house may be beneficial if some natural habitat features exist and: 

• the natural habitat is not sufficient to support the local bat population, or

• you are trying to increase the local bat population, or 

• you plan to move bats out of a local building (never disturb bat roosts during March through August, the gestation and lactation months).

Not all bat species will utilize bat houses but Minnesota’s Big Brown Bats and Little Brown Bats have been observed in bat houses. Generally, if a bat species is willing to live in a building, the species will also be willing to live in a bat house.  Bats may occupy bat houses from early spring through early autumn. Bats do not overwinter in bat houses but instead find more suitable hibernation habitats (e.g. caves, mines, buildings) to protect themselves in winter.

When considering a bat house, first assess the area for natural habitat that my attract bats. Natural bat habitats include a nearby body of water, large tree canopy cover for bat protection, sufficient sunlight to warm the roost and an abundance of flying insects. Bats naturally roost in tree crevices and cavities where tree rot, birds (e.g. woodpeckers) or other animals have created holes in the wood. Bats prefer roosting in live trees but will also roost in dead trees. Little Brown Bats will sometimes roost under peeling or loose tree bark.  Bats may also roost in caves, mines and rock crevices.  Bats require multiple roosting sites in an area because mothers and their pups roost separately from males and non-maternity females. In additions, multiple roosting sites are needed to accommodate microclimate changes – e.g. bats may move to a cooler site on hot days.  Bats usually adopt a primary roost along with several secondary roosts and have been observed to switch roosts as often as every 2 to 3 days.  However, mothers and babies will remain in a roost longer during the maternity and lactation periods and typically return to the same maternity roost year after year.

If you install a bat house, will the bats come? Bats identify new roosts while foraging at night.  Attracting bats to new bat houses will be more successful if bats are observed close to the planned bat house site before a house is installed. About 50% of urban bat houses and 60% of all bat houses are inhabited by bats. These figures rise to 80% for bat houses that are at least 25 inches tall with the highest inhabitant rates observed for multi-chamber maternity houses and rocket houses. Of the inhabited houses, 50% were inhabited in the first year with 90% inhabited within the first two years. A small percentage of houses were inhabited in the three-to-five-year range but you may want to consider relocating and/or upgrading your bat house if the house has been empty more than two years. [16] Note that bats may treat your bat house as a temporary migration site or a short-term secondary roost site.  Both of these uses are important for bats but may make it challenging to verify that bats occupy the house. Install a bat guano catch container beneath your house or install a camera near the bat house to better determine if bats are using your house. Follow the guidelines noted below regarding bat house placement and design to maximize your chances of having bats move into your bat house.

Locate bat houses in sites that meet the natural habitat requirements as much as possible – i.e. multiple houses with diverse designs should be placed where there is water and trees nearby, with some houses in sun and other houses in part shade. Bats may overheat in bat houses on sunny, hot days so bats need nearby cooler houses to survive the heat. Ideally, three bat houses should be installed in the same general area (less than 300 feet apart), with one facing east (morning warmth), one facing south (all-day warmth) and one facing west (evening warmth). North-facing houses will likely be too cold to attract bats.  

Bat houses may be attached to buildings (retain the most heat at night), to poles or to trees that have tall, pole-like trunks that are clear of branches. When attaching a bat house to a building, use 2” to 4” spacers behind the house to reduce the amount of bat guano that may land on the building. Bat houses attached to trees will generally be used by bats as secondary houses due to shade and lack of clearance around the house.  Poles or trees should be wrapped with metal or another surface that discourages ground predators from climbing into the bat house.  Bat houses should be installed at least 10 to 16 feet above ground level with 10 feet of clear space below the bat house since bats usually drop from the house and then take flight.  Remove any thorny bushes or plants with burrs found underneath the bat house to protect the bats from potentially getting tangled in harmful plants. If water containers (e.g. bird baths, cattle troughs) are near bat houses, ensure that each container has rough sides or some device that would allow bats to crawl out of the water.

Do not install bat houses close to wires, poles or tree branches that could interfere with bat flight or where predators may wait to attack bats as the bats emerge from their houses. Avoid sites that are noisy, dusty (e.g. near dirt roads) or subject to industrial pollutants. Do not put bat houses where there is artificial light at night (e.g. near a streetlight). Find alternative sites if local insects are regularly subject to pesticides or other substances poisonous to bats. Avoid sites with high human traffic where bats may be vulnerable to human interference. Finally, steer clear of windy sites, especially around wind turbines that are known to be lethal to bats.

Once you have selected a bat house site, you may choose to purchase or build your bat houses. Good bat houses will be much larger than bird houses (typical size is 35” x 18” x 7”) and should contain multiple interior chambers that allow bats to move to the best microclimate within a house at different times of the day.  Bat houses should be taller than they are wide and contain a few vented chambers which also helps create multiple microclimates within the bat house.  Bat houses should not be built with chemically treated wood because bats may absorb or ingest the chemicals during grooming. However, the exterior of bat houses must be waterproofed, seams should be caulked and a roof should be installed to protect the bats from precipitation. Bats have shown a preference for dark-colored exteriors but secondary bat houses may be lighter colored to accommodate a cooler interior. Wooden bat houses should be constructed with screws rather than nails since nailed seams are more likely to gap open as wood ages. 

The interior chambers of bat houses should include grooved sides which aids bats when crawling around the bat house. Screening or other similar material is not recommended for the interior of bat houses since bat guano may become lodged in the screen.

Bat houses should be inspected monthly when inhabited and cleaned once-a-year during winter when bats are hibernating at a different site.  Spiders, spider webs, wasps and wasp nests should be removed from the bat houses during the annual cleaning.  Although some wasps may survive in concert with bats, wasp nests may grow large over the years and take over too much space in the bat house.  The bat house may be washed out with water or a 5%-10% bleach solution which can reduce parasites.

If you want to build a bat house, free bat house plans with detailed instructions are available from Bat Conservation International [17][18].  If you want to purchase a bat house, be cautious when exploring non-specialty retailers.  You may get a higher qualify bat house if you buy from organizations that have been certified by Bat Conservation International such as BatGoods.com (http://www.batgoods.com/category/Bat-Houses-by-BCM-58) or Fly By Night Inc. (http://www.flybynightinc.org/houses_files/bhbuy.html).

Bibliography

(a) “Bats of Minnesota”, Minnesota DNR, 2025 http://www.dnr.state.mn.us/mammals/bats.html

[2] USGS, FAQ: “Why are bats important?” http://www.usgs.gov/faqs/why-are-bats-important#:~:text=By%20eating%20insects%2C%20bats%20save,53%20billion%20dollars%20per%20year.

[3] “The Benefits of Bats”, Bureau of Land Management, http://www.blm.gov/sites/blm.gov/files/benefits_of_bats_brochure.pdf

[4] “State of the Bats, North America 2023”, Bat Conservation International http://digital.batcon.org/state-of-the-bats-report/2023-report/

[5] “Big Brown Bat”, National Park Service, http://home.nps.gov/shen/learn/nature/big-brown-bat.htm#:~:text=Numerous%20feeding%20studies%20of%20big,Whitaker%20and%20Hamilton%2C%201998

[6] “Little Brown Bat”, Virginia Department of Wildlife Resources, http://dwr.virginia.gov/wildlife/information/little-brown-bat/

[7] “Creating a Garden for Bats”, Bat Conservation International, March 2023, http://www.batcon.org/creating-a-garden-for-bats/

[8] “Night Shift Pollinators”, Minnesota State Horticultural Society, June 2021 http://northerngardener.org/night-shift-pollinators/

[9] “Bats & Blooms: Creating a Bat-Friendly Native Plant Garden”, National Wildlife Federation, http://gardenforwildlife.com/blogs/learning-center/bats-blooms-creating-a-bat-friendly-native-plant-garden?srsltid=AfmBOorPeLd4w409QCgIl-bdZG3ZqArTpV6i4aUkXEuN7LTurgZpfjy2

[10] “Native Plants for Pollinators and Beneficial Insects: Midwest Region”, Xerces Society for Invertebrate Conservation, http://xerces.org/sites/default/files/publications/22-025_01_NPPBI%E2%80%94Midwest_web.pdf

[11] “Native Grasses Benefit Butterflies and Moths”, University of Minnesota Extension, http://grasses.cfans.umn.edu/sites/grasses.umn.edu/files/files/native_grasses_benefit_butterflies_and_moths_0.pdf

[12] “Gardeners urged to help beetles”, The Wildlife Trusts, http://www.wildlifetrusts.org/news/gardeners-urged-help-beetles#:~:text=Build%20a%20beetle%20bank%20%E2%80%93%20Adding,Beetle%20%C2%A9northeastwildlife.co.uk

[13] “The Scoop on Bat Poop”, Bat Conservation International, http://www.batcon.org/the-scoop-on-bat-poop/

[14] “How to Use Bat Guano Fertilizer Safely in Your Garden”, Epic Gardener, http://www.epicgardening.com/bat-guano/

[15] “Best Management Practices for the Use of Bat Houses in U.S. and Canada”, Wildlife Conservation Society Canada produced in cooperation with US Fish and Wildlife Service and Canadian Wildlife Health Cooperative, September 2023, http://iris.fws.gov/APPS/ServCat/DownloadFile/241311

[16] “Attracting Bats”, Bat Conservation International and Colorado State University, http://sam.extension.colostate.edu/wp-content/uploads/sites/2/2016/05/attractingbats.pdf

[17] “Four-chamber Nursery Bat House”, Bat Conservation International, http://www.batcon.org/wp-content/uploads/2020/07/4-Chamber-Nursery-House-Plans.pdf

[18] “Two-chamber Rocket Box”, Bat Conservation International, http://batcon.org/wp-content/uploads/2020/04/RocketBoxPlans.pdf

[19] “Beneficial bats help control insects in the garden”, Oregon State University, May 2023, http://extension.oregonstate.edu/news/beneficial-bats-help-control-insects-garden

[20] USGS, FAQ: “Do vampire bats really exist?” http://www.usgs.gov/faqs/do-vampire-bats-really-exist

[21] “How Bats Survive Minnesota Winters”, Three Rivers Park District, http://www.threeriversparks.org/blog/how-bats-survive-minnesota-winters

[22] “Bats Lead in U.S. Rabies Risk”, Centers for Disease Control and Prevention, 2019 http://archive.cdc.gov/www_cdc_gov/media/releases/2019/p0611-bats-rabies.html

Photo credits: Minnesota DNR. http://images.dnr.state.mn.us/natural_resources/animals/mammals/bats/big-brown-bat.png (1), Minnesota DNR. http://images.dnr.state.mn.us/natural_resources/animals/mammals/bats/little-brown-myotis.png (2), Conservation Society Canada, produced in cooperation with US Fish and Wildlife Service and Canadian Wildlife Health Cooperative. http://iris.fws.gov/APPS/ServCat/DownloadFile/241311 (3)