Signs of bats in your house

Bats can live in a Wyoming attic or wall for years before anyone notices. Here are the signs we look for on a home inspection, how to check for yourself from the yard, and what to do safely once you think you have bats.

The short version

Droppings piled in one spot below a vent, on a windowsill, along the foundation or on the attic floor are the most common sign.
Dark, greasy smudges around a small gap at the roofline show where bats squeeze in and out.
Scratching or squeaking at dusk in a wall or ceiling, followed by quiet, is typical of bats leaving to feed.
Bats leaving the roofline at sunset on a warm summer evening confirm a roost. Count them from the yard.
A bat in the living space, especially more than once or in winter, often means a roost inside the building.
Do not touch bats and do not seal holes yet. Handle health questions first, then plan exclusion for the right season.

Why Wyoming homes attract bats

Wyoming Game and Fish lists 18 bat species in the state, and all of them eat insects. Most roost in rock crevices, trees, caves and mines, but a few species readily move into buildings. The two we find most often in Wyoming attics and walls are the big brown bat and the little brown bat. In summer, females gather in maternity colonies to raise their pups, and a warm, dark attic or wall void near water and insects suits them well. See our Wyoming bat species guide for more on each species.

Older Wyoming homes, from brick downtown houses to early ranch homes, tend to have weathered trim, open roof returns and loose chimney flashing. Newer homes more often have gaps at ridge vents, at fascia and soffit joints, and where additions meet the original roof. A bat needs only a gap about a quarter inch wide, according to the CDC.

Sign 1: droppings (guano)

Bat droppings are the most reliable sign. They are dark, about the size of a grain of rice, and collect in piles under the spot where bats roost or enter: below a gable vent, on a deck or windowsill under the eaves, along the foundation, or on the attic insulation. Because bats eat insects, dry bat droppings crumble into a powder with shiny bits of insect wings and shells. Mouse droppings are similar in size but are scattered along travel routes and stay hard.

Do not crush or sweep droppings with bare hands or a dry broom. The CDC says the fungus that causes histoplasmosis can grow where bird or bat droppings build up, and people get sick by breathing in spores stirred into the air. Wear gloves and a well-fitting respirator if you must look closely, and see our guano cleanup page for how a heavy buildup is handled.

Sign 2: stains and rub marks at the entry

Bats use the same openings night after night. Oils from their fur leave dark, slightly greasy smudges around the gap, often with a few droppings stuck nearby. Look along the roofline, at the corners where fascia meets soffit, around chimney flashing, at the top of gable vents, behind loose shutters and where siding or trim has pulled away. Yellowish or brown staining on a ceiling or wall below the attic can mean urine and droppings have built up above it.

Sign 3: sounds and smell

Bats are quiet most of the night because they are out feeding. Homeowners usually hear them right around sunset and again before dawn: scratching, rustling or high-pitched squeaks in a wall, behind a chimney or above the ceiling. Sound that peaks at dusk and then fades is more typical of bats than of mice or squirrels. A large or long-used roost also gives off a strong, musty, ammonia-like smell, which can get worse on hot days.

Sign 4: the evening exit count

The easiest way to confirm a colony is to watch from the yard. On a warm, calm evening from late spring through summer, sit where you can see the roofline against the sky starting about 20 minutes before sunset and watch for about an hour. Bats leaving a roost drop out of a gap one at a time and fly off quickly. Note where they come out and roughly how many. That tells us which openings are active and how big the colony is. Wyoming nights cool fast, so the count works best on warm evenings from June through August, when bats are most active.

Sign 5: bats in the living space

One bat in the house can be a stray that flew through an open door. A bat that turns up inside more than once, or a bat found indoors in late fall or winter when there are no insects outside, usually came from inside the building. Bats roosting in an attic or wall can slip through gaps around attic hatches, recessed lights, ductwork, plumbing chases and fireplace dampers. If you find a bat in the house in winter, read bats in winter in Wyoming.

What to do if you think you have bats

Handle health questions first. The Wyoming Department of Health says bats and skunks are the most common rabies carriers in the state, and that bat bites are not always visible. Anyone who had direct contact with a bat or woke up with a bat in the room should call a doctor or public health provider right away. The department’s 24/7 public health emergency line is 1-888-996-9104. In 2026, Wyoming’s first confirmed rabies case was a bat found in May in the backyard of a home in a downtown Sheridan County neighborhood, a reminder that this is a town problem, not just a backcountry one. If you can do it without touching the bat, contain it so it can be tested. Our bats and rabies in Wyoming guide has the steps.

If no one had contact with the bat, Wyoming Game and Fish suggests closing off the room, opening a window with the screen removed, and letting the bat find its own way out. Do not try to keep or care for a bat. For a colony in the building, do not block the openings yet. Sealing a gap while bats are inside traps them, and in summer it can strand flightless pups. Wyoming Game and Fish says one-way doors are best used in late summer or early fall, and its Nongame Program advises excluding colonies outside the maternity season whenever possible. Our guide to when to exclude bats in Wyoming explains the timing.

Wyoming Wildlife Specialists inspects the whole building, puts one-way devices on every active opening at the right time of year, seals the rest permanently once the bats are gone, and backs the work with a written warranty. Call (307) 522-1433 for a free phone consultation.

Frequently asked questions

How do I know if I have bats or mice in my attic?

Look at the droppings and watch at dusk. Bat droppings pile up below where bats roost or enter, are dry and crumble into shiny insect bits when crushed (wear gloves and a mask). Mouse droppings are scattered along walls and travel routes and stay hard. Bats are most active right around sunset, when they leave to feed, so a short burst of scratching or squeaking at dusk points to bats.

I found one bat inside my house. Does that mean I have a colony?

Not always. A bat can come in through an open door or window. But a bat inside more than once, or a bat inside in late fall or winter when there are no insects outdoors, usually means bats are roosting in the attic, walls or around the chimney. If anyone may have been bitten or touched, or the bat was in a room with a sleeping person or a young child, call your doctor or county public health office first.

How small a gap can a bat get through?

The CDC says bats can get through openings as small as a quarter inch. That is why entry points are easy to miss at ridge vents, fascia and soffit joints, chimney flashing, loose siding and gaps around pipes and wires.

Can I seal the holes myself once I find them?

Not while bats are inside. Sealing an active roost traps bats in the building, where they die or find their way into the living space. Exclusion uses one-way devices so the bats leave first, and Wyoming Game and Fish says one-way doors are best used in late summer or early fall, after pups can fly.

Are bat droppings in the attic dangerous?

They can be. The CDC says the fungus that causes histoplasmosis can grow in soil containing bird or bat droppings, and people get sick by breathing in the spores. Do not sweep or dry-vacuum droppings. A heavy buildup should be cleaned up with proper respirators and containment.

Related Wyoming bat guides and cities

Sources

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