Bats in barns, garages and outbuildings

Barns, shops, detached garages, sheds and cabins are some of the most common places Wyoming bats roost. Here is how to tell whether a colony is a problem, what Wyoming Game and Fish recommends, and how to get bats out of an outbuilding without trapping them or their pups.

The short version

Bats in an unused barn or shed are not always a problem. They eat insects and may do little harm where nobody works, sleeps or stores food.
Exclude them when they cause trouble: droppings on feed, hay, tack or equipment, bats in a heated shop or living quarters, or contact with people and animals.
Timing matters. Wyoming Game and Fish says one-way doors are best used in late summer or early fall, after pups can fly. Never seal a building with bats inside.
Treat heavy droppings with care. Wet them down and wear a respirator. Do not dry-sweep or blow them out.
Never handle a bat with bare hands. A bat on the ground may be sick, and bat bites can be hard to see.
Consider a bat house on a pole or wall nearby, put up a few weeks before the exclusion.

Why bats choose Wyoming outbuildings

Wyoming Game and Fish says the state is home to 18 bat species. All of them eat insects, and most roost in rock crevices, trees, caves and old mines. A few adapt well to buildings, and outbuildings suit them even better than houses. Barns, loafing sheds, shops, detached garages, pump houses and cabins often have open gable ends, gaps under metal roofing and ridge caps, loose board-and-batten siding, unscreened vents and doors that stand open all summer. They are quiet, warm under the roof in summer, and often close to water and livestock, which draw insects.

University of Wyoming Extension points out how much bats contribute on rural land: it notes that a single little brown bat can eat about 1,200 insects in an hour, and that big brown bats eat cucumber beetles and pallid bats eat crickets and grasshoppers. That is why many ranchers and acreage owners are happy to leave bats alone in a building they do not use. The species we see most often in Wyoming outbuildings are the big brown bat and the little brown bat; see our Wyoming bat species guide.

How to tell what is using the building

Look for droppings piled under one spot on the rafters, along a top plate or below a gap at the ridge. Bat droppings are dark, about the size of a grain of rice, and crumble into shiny insect bits when crushed (wear gloves). Mouse droppings are scattered and stay hard. Bird droppings are white and pasty. Dark, greasy rub marks around a gap show where bats squeeze in and out.

The surest check is an evening count. On a warm, calm evening, start about 20 minutes before sunset and watch the gable ends, ridge and eaves for an hour. Note where bats drop out and roughly how many. In an open barn you may instead see bats hanging from rafters or tucked behind beams during the day; leave them undisturbed and keep your distance. Our guide to signs of bats in your house covers the same signs in more detail.

When to leave bats alone, and when to exclude them

If bats are using the rafters of a building nobody works in, and the droppings are not landing on anything important, leaving them is a reasonable choice. Wyoming Game and Fish asks people to leave a sleeping bat alone and notes that bats seen in daylight on the outside of a building are often just looking for a place to roost.

Exclusion makes sense when the colony causes a real problem. Common reasons are droppings and urine on stored hay, grain, tack, vehicles or equipment; bats getting into a heated shop, bunkhouse, office or attached living space; a building where children, guests or workers spend time; or bats repeatedly found on the floor where dogs, cats or livestock can reach them. A barn that shares a wall or roof with a home also deserves a closer look, because bats in one can find their way into the other.

How exclusion works in a barn or shop

Wyoming Game and Fish describes the method plainly: if bats are inside unused parts of buildings, like the rafters of a shed, barn or attic, installing one-way doors for about a week lets the bats fly out but not back in. The doors go on the openings the bats actually use, every other gap is sealed first, and once the bats are gone the active openings are sealed permanently.

Outbuildings make this harder than it sounds. A barn may have dozens of possible gaps, from the ridge and gable vents to the spaces between corrugated metal and purlins, and doors that are left open undo the work. Successful exclusion usually means screening or closing large openings like gable vents and haylofts, sealing gaps under roofing with closure strips or foam designed for that profile, keeping doors shut at night for the exclusion week, and fitting one-way devices to the real exits. On a big or old building it is often better to exclude bats from the part that matters, such as an enclosed shop, tack room or loft, than to try to seal every board.

Timing in Wyoming

Do not exclude bats in early to mid summer. Wyoming Game and Fish warns that over the summer, one-way doors can separate mothers from their pups, which cannot fly and need to nurse several times each night, and says the doors are best used in late summer or early fall. Its Nongame Program advises excluding colonies outside the maternity season whenever possible. Spring, once bats are flying again, is the other option.

Wyoming nights cool fast in September, especially at higher elevations, and bats only leave through a one-way door on nights they are flying. Plan for the early part of the fall window and leave devices up for several warm nights. Some big brown bats hibernate in buildings over winter. If you see bats in an outbuilding between November and March, leave them alone, and report bats flying in winter to Game and Fish, since that can be a sign of white-nose syndrome. Our guides to when to exclude bats in Wyoming and bats in winter in Wyoming go into more detail.

Droppings, dust and cleanup

Heavy guano under a long-used roost is the part that most often needs professional help. The CDC says the fungus that causes histoplasmosis can grow in material containing bird or bat droppings, and that people get sick by breathing in spores when it is disturbed. That makes dry sweeping, leaf blowers, compressed air and power washers a bad idea in a barn. Wait until the bats are out, wet the material down, wear a well-fitting respirator and disposable gloves, and bag it. For large accumulations, especially in an enclosed loft or shop, see our guano cleanup service.

Rabies, pets and livestock

Most bats are healthy. But bats and skunks are the most common rabies carriers in Wyoming, according to the Wyoming Department of Health, and a bat that is on the ground, active in daylight or unable to fly is more likely to be sick. Barn cats and dogs often find these bats first. Keep pet and horse rabies vaccinations current, and never pick up a bat with bare hands. If a person may have been bitten or scratched, call a doctor or your county public health office; the Wyoming Department of Health’s 24/7 public health emergency line is 1-888-996-9104. If an animal had contact, call your veterinarian. If you can do it without touching the bat, contain it so it can be tested. Our bats and rabies in Wyoming guide walks through the steps.

White-nose syndrome: keep gear clean

White-nose syndrome, a fungal disease that has killed millions of bats in North America, has reached Wyoming. It was confirmed at Devils Tower National Monument in 2021, and Wyoming Game and Fish later reported the fungus that causes it in caves in Carbon and Platte counties. The disease does not affect people or pets, but people can spread the fungus on clothing and gear. If you explore caves or old mines, Game and Fish asks you to clean your boots and gear before and after, and not to wear the same clothing between sites. Report sick or dead bats in winter or spring to the Nongame Program at (307) 332-2688.

Give them somewhere else to go: bat houses

University of Wyoming Extension suggests that rural landowners consider bat houses, which can suit a handful of common Wyoming species including the little brown bat, the big brown bat, the pallid bat and long-eared myotis. Bat Conservation International recommends mounting a bat house at least 10 feet above the ground, and 12 to 20 feet is better, in a spot with 6 to 8 hours of direct sun, away from bright lights, and not above a door or window where droppings will pile up. Nursery colonies usually choose roosts within a quarter mile of water. When a bat house goes with an exclusion, BCI suggests putting it up two to six weeks before the eviction. There is no guarantee bats will use it, but on a ranch or acreage it gives the colony a nearby alternative.

Who to call

Possible bite or contact with a person: your doctor or county public health office, or the Wyoming Department of Health 24/7 line, 1-888-996-9104.
A bat on the ground or loose in a building: your city or county animal control. In unincorporated areas this is usually the county sheriff’s office.
Bat questions, bats flying in winter, or sick or dead bats: the Wyoming Game and Fish Nongame Program, (307) 332-2688, or your Game and Fish regional office.
A colony in a barn, shop, garage, cabin or home: Wyoming Wildlife Specialists, (307) 522-1433. We inspect the building, fit one-way devices on the active openings at the right time of year, seal the rest permanently once the bats are out, and back the work with a written warranty. For bigger structures, see commercial bat removal.

Frequently asked questions

Should I get rid of bats in my barn?

Not always. Wyoming Game and Fish says one-way doors can be used when bats are in unused parts of buildings, like the rafters of a shed or barn, but bats in a building that nobody works in, stores food in or sleeps in may cause little harm, and they eat a lot of insects. Exclusion makes sense when droppings land on feed, hay, equipment or work areas, when bats get into living or work space, or when people or animals could come into contact with them.

When can bats be excluded from a barn or shed in Wyoming?

Wyoming Game and Fish says one-way doors are best used in late summer or early fall. In summer, mothers can be separated from pups that cannot fly yet and need to nurse several times a night. Spring, once bats are flying again, is the other window. Bats that hibernate in a building over winter should be left alone until they are active again.

Are bat droppings in a barn dangerous to people or livestock?

They can be for people. The CDC says the fungus that causes histoplasmosis can grow in soil or material containing bird or bat droppings, and people get sick by breathing in spores when that material is disturbed. Do not dry-sweep, blow out or power-wash heavy droppings. Wet them down, wear a well-fitting respirator, or have a heavy buildup cleaned professionally.

Can I put up a bat house after I get bats out of my outbuilding?

Yes. University of Wyoming Extension notes that bat houses can give a few common Wyoming species, including the little brown bat and the big brown bat, a place to roost on rural property. Bat Conservation International recommends mounting them at least 10 feet up, ideally 12 to 20 feet, in a sunny spot, and putting them up two to six weeks before an exclusion if possible.

What if I find a bat on the floor of my barn or shop?

Do not touch it with bare hands. A bat on the ground may be sick. Keep pets, children and livestock away, cover it with a box or bucket if you can do so without contact, and call your local animal control or county public health office. If a person or animal may have been bitten or scratched, call a doctor or veterinarian and public health right away so the bat can be tested.

Related Wyoming bat guides and cities

Sources

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