Wisconsin Bat Exclusion Law: When You Can (and Can't) Remove Bats

Wisconsin protects its bats, and that changes how you get rid of them

If you have bats in your attic in the Clintonville area, the single most important thing to understand is this: you cannot legally kill them, and you cannot legally seal them in. Wisconsin lists all four of its cave-hibernating bat species as state-threatened, and that status carries real weight. The only lawful way to get bats out of a building in this state is humane exclusion — evicting the colony through one-way devices and then sealing the structure so they can’t return — and it has to be done on a timeline the Department of Natural Resources sets.

This is not a technicality. A homeowner who grabs a can of spray, stuffs the soffit gap with foam on a July afternoon, or hires someone who does the same has almost certainly broken the law and, just as often, made the problem dramatically worse. Bats sealed inside a wall don’t vanish. They die there, or they crawl down into the living space looking for a way out, and a July “quick fix” can trap dozens of flightless pups behind your drywall.

BugBoss The X-Terminator does bat work the legal way, out of our shop at 600 S. Main St. in Clintonville, and we do it across the older farmhouses, village homes, and lake cabins that make up so much of Waupaca, Shawano, and the surrounding counties. This guide lays out exactly what the law says, why bats are protected, when you can and can’t act, and what a correct exclusion actually looks like — the same process we run on every wildlife removal job in the area.

The four protected species, and why they matter here

Wisconsin is home to several bat species, and the four that hibernate in caves and mines — and that most often end up in attics — are all listed as state-threatened:

• Little brown bat (Myotis lucifugus) — historically the most common attic bat in Wisconsin and the one most likely to form a large maternity colony in a house.
• Big brown bat (Eptesicus fuscus) — the hardiest of the group, often overwintering in buildings rather than caves, which is why you may find one active in a warm spell in January.
• Northern long-eared bat (Myotis septentrionalis) — not only state-threatened but federally endangered. It was reclassified from threatened to endangered after white-nose syndrome cut its population by more than 97 percent.
• Tricolored bat (Perimyotis subflavus) — one of the smallest bats in the state and among the hardest hit by disease.

The little brown and big brown bats are the two you’re most likely to find in a Clintonville-area attic. But because the northern long-eared bat carries federal Endangered Species Act protection on top of the state listing, and because a mixed roost can contain more than one species, the safe and legal assumption on any job is that you’re dealing with a protected animal. That’s the whole reason lethal control is off the table.

The two bats you’ll actually find in your attic

Of the four protected species, two account for nearly every building colony in this region, and they behave differently enough that it’s worth knowing which you have.

The little brown bat is the classic house bat. It’s small — a wingspan of eight or nine inches, a body no bigger than your thumb — with glossy brown fur. Little browns form maternity colonies, sometimes of dozens or even hundreds of females, that return to the same warm attic year after year to raise pups through June and July. When people describe bats streaming out of a soffit at dusk in a steady ribbon, it’s almost always little browns. They migrate to caves and mines to hibernate, so a little brown colony is a summer problem that empties out for winter.

The big brown bat is noticeably larger and hardier, and it’s the species most likely to overwinter inside a building rather than in a cave. That’s why a big brown is the bat you find flying around the living room on a mild January afternoon — it never left, it just woke up in a warm wall void and blundered into the house. Big browns tolerate cold better than any of the others, which is part of why they’ve weathered white-nose syndrome somewhat better and are now the bat you’re statistically most likely to encounter in a home. Their winter presence also means a big brown situation isn’t strictly seasonal the way a little brown colony is.

Knowing the difference shapes the job. A little brown maternity colony is worked around the June–July restriction and the fall dispersal; a big brown that overwinters in the structure may be present and torpid in the walls even in the dead of winter, when it won’t respond to exclusion and the work has to wait for a warm-season eviction.

White-nose syndrome: why the rules got stricter

None of these species used to be threatened. The reason they are now is a disease. White-nose syndrome is caused by a cold-loving fungus (Pseudogymnoascus destructans) that grows on the muzzles and wings of hibernating bats, rouses them repeatedly through the winter, and burns through the fat reserves they need to survive until spring. It reached Wisconsin in 2014, and at infected hibernation sites it has killed up to 99 percent of the bats present. Nationally the disease has killed millions of bats since it first appeared in the Northeast in 2006.

That collapse is why the little brown bat — an animal that used to be so abundant that a colony of a few hundred in a barn was unremarkable — is now a threatened species the state actively works to protect. When you understand that a summer maternity colony in your attic may represent a meaningful fraction of the survivors in your county, the DNR’s insistence on non-lethal, well-timed removal makes a lot more sense. It also, frankly, works in the homeowner’s favor: a properly excluded colony often relocates to a nearby bat house, and everyone comes out ahead.

The rule that governs everything: the maternity-season window

Here is the single date range every property owner in central Wisconsin should memorize:

You may not restrict bat exits from June 1 through July 31.

During those two months, female bats gather in warm, protected spaces — attics, wall voids, behind fascia and ridge caps — to give birth and nurse their young. The pups are born flightless and stay that way for several weeks. If you install one-way doors during this window, the adult females fly out at dusk to feed, can’t get back in, and the pups are left inside to starve. It’s inhumane, it’s illegal for a protected species, and it produces exactly the outcome nobody wants: dead animals decomposing in the walls and, frequently, live bats crawling into the house.

So the legal calendar for bat exclusion in Wisconsin looks like this:

There is one narrow exception. If there’s a documented human health threat — for example, a bat in a bedroom where someone may have been bitten in their sleep — the DNR allows exclusion during the maternity window, but the property owner must file a health exemption form within five days of starting the work. That’s a real legal step, not a loophole to schedule routine attic work early, and it’s one of the reasons it pays to work with someone who knows which situations actually qualify.

If you find a colony in June or July, the right move is not to panic-seal the house. It’s to have the building inspected, get the exclusion planned and the entry points mapped, and then execute the eviction the moment August arrives. That’s how we handle every summer bat call in the Clintonville and Iola area.

The correct five-step exclusion process

Done right, bat exclusion is a methodical process, not a single visit. Here’s what each step actually involves and why it matters.

1. Find every exit — at dusk

Bats can squeeze through a gap as small as three-eighths of an inch, so a daytime look at the roofline rarely reveals every hole. The reliable way to map a colony’s access is an emergence watch: sit outside at sunset and watch where bats stream out to feed. On an older Clintonville farmhouse the exits are usually predictable — the soffit-and-fascia junction, gaps where the roof meets a dormer or gable, ridge-cap openings, chimney flashing, and the tops of walls in balloon-framed homes where the cavity runs straight up to the attic. Counting the bats as they leave also tells us roughly how big the colony is and, critically, whether the whole colony has cleared out later on.

2. Put up a bat house

Because these are protected, beneficial animals — a single little brown bat can eat its body weight in insects, including mosquitoes, in a night — the goal isn’t to destroy the colony, it’s to relocate it. Installing a bat house on or near the property before the eviction gives the colony an alternative roost. It won’t always take the first year, but it dramatically improves the odds that the bats settle nearby instead of trying to break back into the house, and it keeps their pest-eating benefit working for you.

3. Install one-way doors over the exits

Once the exits are mapped, we cover them with one-way exclusion devices — lightweight netting or specialized tubes that let a bat drop out and fly away but give it nothing to grab onto when it tries to crawl back in. The devices must not harm the bats, and they go over every active exit at once. Leave even one gap uncovered and the colony just re-routes through it, defeating the whole job.

4. Wait at least a week

This is the step impatient DIYers skip, and it’s the one that prevents disaster. The devices stay up for at least seven days, longer in cool weather when bats fly less. Bats don’t all leave on the same night; a maternity colony filters out over several evenings. Only after a full week with no more emergences — confirmed by another dusk watch — can we be confident the structure is empty. Sealing on day two is how you trap the half of the colony that hadn’t left yet.

5. Remove the devices and seal permanently

With the building confirmed empty, we take the one-way doors down and permanently seal every entry point — not just the ones the bats were using, but every gap that could become a future roost. That means proper materials: rustproof mesh, backer rod and sealant, and repairs to the soffit, fascia, ridge, and flashing rather than a smear of foam that a bat or a squirrel pops through by next spring. This sealing is what makes exclusion permanent, and it’s the part BugBoss guarantees.

How to tell a colony from a one-off stray

Not every bat in the house means a colony. Knowing the difference tells you whether you have a five-minute problem or a three-week one.

A single bat flapping around a room at night is usually a stray. It came down an open chimney, slipped through a door left open on a summer evening, or got confused and wandered in from a wall gap. The move is to calm down, close the interior doors, open an exterior door or window, dim the lights, and let it find its own way out — or, if it lands and can be safely contained under a container without touching it, release it outside. If there’s any chance someone was bitten, especially a sleeping person or a child, don’t release it; contact your county health department, since the bat may need to be tested for rabies.

A colony announces itself differently. The signs to look for:

• A dusk emergence. Bats streaming out of the same spot — a soffit corner, a gable vent, a gap under the ridge cap — around sunset, evening after evening. This is the single clearest sign, and it’s why the dusk watch is step one of any real exclusion.
• Guano accumulation. Small dark droppings piling up below an entry point, on the siding, on a porch, on the ground, or in the attic. Bat guano crumbles to dust and often glistens faintly with insect fragments, which distinguishes it from mouse droppings.
• Staining and rub marks. A brown, greasy stain around an entry hole where the oils in the bats’ fur have darkened the surface over repeated use.
• Sound. Squeaking, scratching, and rustling in the walls or attic, usually strongest around dusk as the colony gets active, and loudest in June and July when pups are present.
• Odor. An established colony produces a distinctive ammonia-like smell from accumulated guano and urine, strongest in warm weather.

If you’re seeing these, you have a roost, not a visitor, and the legal timeline and the full exclusion process both come into play.

What a colony does to a building

Bats are beneficial animals outdoors, but a colony living in your structure causes real, cumulative damage that’s worth understanding — both because it justifies the cost of doing the job right and because it explains why cleanup is part of the work, not an add-on.

The most obvious is guano and urine accumulation. A colony of any size deposits droppings continuously in the same spot, and over several seasons that builds into a substantial pile on the attic floor and in the wall voids. The urine soaks into wood, drywall, and insulation, and the combination corrodes and stains building materials, saturates and ruins insulation, and produces the ammonia odor that eventually pushes down into the living space. Guano is also the source of the histoplasmosis risk covered below. Left long enough, a heavy accumulation can stain ceilings and even, in extreme cases, add real weight to a ceiling.

There’s also the entry damage — the gaps bats use tend to be at vulnerable spots like the soffit-fascia junction and roofline flashing, and a colony’s constant traffic keeps those weaknesses open and can widen them. And an active roost tends to attract secondary pests: guano supports certain beetles and mites, and the roost itself can draw other scavengers. None of this is catastrophic overnight, but a colony that’s been in an attic for several summers is a genuine cleanup and remediation job, not just an eviction.

Bats in barns, pole buildings, and cabins

Houses aren’t the only structures that host bats around here. Barns and pole buildings are classic bat roosts — high, open, undisturbed, and full of the gaps bats slip through — and a colony in a barn is common enough that many farmers just live with it. That’s a reasonable choice when the animals aren’t over a living or working space and the guano isn’t accumulating where it matters; bats in a barn are earning their keep on mosquitoes and crop pests. When a colony does need to move, though, the same protections and the same June–July restriction apply, and the exclusion is worked the same way.

Seasonal cabins are a special case, because a quiet attic on a lake or in the woods is nearly ideal bat habitat, and the owner is often away for the whole maternity season. A colony can establish and grow through the summers with no one noticing until the guano and odor become obvious. Cabin bat work has to be timed around both the legal window and the owner’s season — usually executed in fall after the property closes down. We cover the cabin angle in detail in our cabin and seasonal property guide.

Why DIY bat removal usually backfires

Homeowners understandably want to handle a bat problem themselves, and it’s the one wildlife job where doing it wrong causes the most trouble. The common DIY mistakes:

Sealing too soon. The impulse is to find the hole and close it. Do that with bats inside — or during maternity season — and you’ve trapped the colony, with the consequences described above. Sealing the wrong number of holes. Most colonies use more than one exit; close some and leave others, and the bats simply re-route. Only a proper dusk watch finds them all. Acting in June or July. Even a well-intentioned eviction is illegal and inhumane during the maternity window, and it produces the worst outcome — dead flightless pups in the walls. Using repellents and gadgets. Ultrasonic devices, mothballs, and sprays don’t move an established colony and some are illegal against a protected species. Underestimating the cleanup. Even if the eviction somehow goes right, disturbing the guano without protection is the histoplasmosis exposure scenario. Bat work rewards patience and method, which is exactly what a rushed weekend fix lacks.

Guano, histoplasmosis, and rabies: the health side

Two health issues come with a bat colony, and both are manageable if you respect them.

Histoplasmosis is a lung infection caused by Histoplasma capsulatum, a fungus that grows in accumulated bird and bat droppings. A colony that’s been in an attic for a few seasons can leave a substantial pile of guano, and when that dries and gets disturbed — by a broom, a shop vac, or footsteps across the insulation — it releases spore-laden dust that you breathe in. For most healthy people a small exposure passes unnoticed, but a heavy exposure, or any exposure for someone immune-compromised, can cause real respiratory illness. That’s why guano cleanup is a respirator-and-containment job, not a weekend chore. On our exclusions we clean and decontaminate the affected area and replace insulation that’s too soiled to salvage, so the attic is actually safe again.

Rabies is the other concern. The large majority of bats do not carry rabies, but bats are nonetheless the leading source of human rabies exposure in the United States, largely because their bites can be tiny and go unnoticed — especially if a bat is found in a room where someone was sleeping, or with a child or someone who can’t reliably say whether contact occurred. The rules are simple: never handle a bat with bare hands; if a bat is found in a bedroom or there’s any chance of a bite, treat it as a possible exposure and contact your county health department; and if the bat can be safely captured without damaging its head, it may be testable. This is exactly the kind of situation that can justify the DNR’s health-exemption exclusion during maternity season.

Why you must never seal bats in — the practical version

We’ve said it’s illegal. Here’s why it’s also a genuinely bad idea even setting the law aside. When you close a colony’s exits with bats still inside, the animals don’t accept it. They spend days searching frantically for another way out, and in an older home there’s almost always an interior path: down a balloon-framed wall cavity, through the gap around a bathroom fan or recessed light, behind a wall register, or through the chase around plumbing. So the family that sealed the attic to “solve” the bat problem ends up with bats in the bedroom instead. The ones that don’t find a way out die in the wall, and a decomposing colony in July heat produces an odor and a staining problem that outlasts the summer. Every part of the correct process — the dusk watch, the week-long wait, the confirmation before sealing — exists to make sure this never happens.

How BugBoss handles bats in the Clintonville area

Bat work is a core part of what we do, not a sideline we refer out. The older housing stock across this region — pre-war farmhouses with balloon framing, village homes with aging soffits, and the seasonal cabins around the Waupaca Chain O’ Lakes — gives bats exactly the high, undisturbed roost sites they want, and we see colonies in all of them.

Every bat job runs the same disciplined way. We start with a full inspection and a dusk emergence watch to confirm we’re dealing with a colony, identify the species where we can, and map every exit. We plan the exclusion around the legal calendar — executing it in spring or, more often, from August into fall, and holding off on any sealing during the June 1–July 31 window. We install one-way devices over every entry, leave them up the full week-plus, and only seal once the building is confirmed empty. Then we decontaminate the guano, replace ruined insulation, and permanently seal the structure, and we guarantee that sealing work.

Because we’re a local company that does both pest control and wildlife, you get one accountable outfit for the whole problem — eviction, cleanup, and the exclusion that keeps them out — instead of a pest franchise that won’t touch bats and a separate wildlife trapper who won’t do the sealing. You also deal directly with the owner, Brian, on no contract.

If you’ve got bats in an attic, a barn, or a cabin anywhere around Clintonville, don’t seal anything yet. Call BugBoss at 866-BUGBOSS, or request an inspection. We’ll tell you exactly what the law allows, when we can act, and what it takes to get them out for good. For more on the animal itself, see our bats pest-library page, and for the other critters that share these attics, our guide to farmhouse and pole-barn rodent exclusion.

Source: Wisconsin Department of Natural Resources bat protection and exclusion-timing guidance. Reviewed by Brian Zahringer, WI Commercial Applicator #103689 — August 2026. Rules change; confirm current requirements before scheduling exclusion work.