Why bats are a specialized job, not a simple removal
Bats are not a pest you exterminate, and in Wisconsin you legally cannot. They are protected animals, several of our species are threatened, and the correct — and only lawful — way to deal with a colony in a building is humane exclusion done on a strict seasonal timeline. That makes bat work fundamentally different from a wasp nest or a mouse problem. Get it wrong, and you have not just failed to solve the problem; you have broken the law and created a far worse mess of decomposing animals in your walls. This is why BugBoss treats bats as specialized wildlife work, and why it is worth understanding what is actually involved before anyone touches your roofline.
The bats you find in Northeast Wisconsin buildings are almost always little brown bats or big brown bats, the two species most likely to form colonies in attics, soffits, and barns. They are small — a big brown bat is only a few inches long — insect-eating, and genuinely beneficial, each one consuming large numbers of mosquitoes and agricultural insect pests every night. That benefit, combined with how badly their populations have been hit in the last decade, is the backdrop for the legal protections. You are not dealing with vermin; you are dealing with a threatened, protected animal that happens to have moved into your building, and the job is to get it out humanely and keep it out.
Wisconsin biology, the maternity season, and the law
The single most important thing to understand about bats in Wisconsin is the maternity season, because it is written into how and when you are legally allowed to act. In late spring, female bats gather into maternity colonies to give birth and raise their young, and they often choose warm, protected building spaces — attics and soffits — to do it. The pups are born in early summer and, for several weeks, cannot fly. They depend entirely on the roost and on their mothers returning each night.
Because of those flightless pups, the Wisconsin DNR prohibits completing bat exclusions from June 1 through July 31. During that window, one-way doors and sealing cannot be used to shut bats out, because doing so would trap the pups inside to starve and die. That is not a guideline; it is the rule. Humane exclusion is therefore done outside that window — in spring up through May 31, and from August onward once the pups are flying and the colony can leave together — and continuing through fall until the bats depart for their hibernation sites. There is one narrow exception: if bats are getting into your actual living space during the closed window, the DNR allows a health-based exemption, which requires filing the proper form within five days of starting the work. Absent that, if you find bats in July, the right move is to plan the exclusion for August, not to seal the building.
The protections exist because Wisconsin’s bat populations are in trouble. White-nose syndrome, a fungal disease of hibernating bats, was first confirmed in Wisconsin in 2014 and has since killed cave bats across the state in staggering numbers. In response, Wisconsin’s four cave-hibernating species — the little brown bat, big brown bat, northern long-eared bat, and tricolored bat — are listed as state-threatened, and the northern long-eared bat is also federally endangered. When you understand that the little brown bat colony in your attic belongs to a species whose numbers have collapsed, the logic of humane exclusion over extermination stops being a legal technicality and starts being obvious. These populations cannot absorb careless losses, and the law reflects that.
The bat season in Northeast Wisconsin
The bat calendar runs in a clear annual loop, and it drives everything about the right timing for a job.
In spring, as the weather warms and insects return, bats emerge from hibernation and return to their roosts, and females begin gathering into maternity colonies. This is a legal window for exclusion — through May 31 — and doing the work in spring, before pups are born, is often the cleanest option when a homeowner already knows they have a colony from the previous year.
Through summer, from June into July, the maternity colony is raising flightless young, and exclusion is legally off the table. This is also, frustratingly, when many homeowners first notice the problem, because a full summer colony is active, noisy, and producing guano. The right response in this window is to inspect, confirm, and schedule the exclusion for August — not to act prematurely.
In late summer and fall, from August on, the pups are flying, the colony can leave as a group, and exclusion resumes. August through the fall is prime time for bat work, and much of our bat exclusion happens in this stretch, before the bats leave on their own for hibernation.
In winter, the building colony has dispersed to hibernation sites and the attic is quiet — but the entry points are still open, and unless they have been sealed, the same colony, loyal to its traditional roost, will return the following spring. Winter is a good time to plan and inspect so the exclusion is ready to execute the moment the legal window opens.
Where bats roost around Clintonville: barns, farmhouses, and cabins
The buildings that get bat colonies in Northeast Wisconsin are the ones with warm, protected, undisturbed upper spaces and plenty of half-inch gaps in the roofline — which describes a great deal of the rural building stock here.
Barns and older outbuildings are classic maternity-colony sites. They are big, warm under a metal or shingle roof in summer, quiet, and full of open gable ends, loose flashing, and gaps at the roofline where a colony can settle undisturbed for years. A hay-mow or the peak of an old dairy barn can host a substantial colony that most people never notice until the guano piles up or the smell arrives. Because these structures have so many potential entries across large, high rooflines, they are among the most demanding exclusion jobs — and among the ones most often botched by a quick patch of the one obvious hole.
Older farmhouses are the other heavy case. Decades of settlement open gaps at soffit and fascia junctions, around chimney flashing, at gable vents, and where the roof meets the walls, and a warm attic makes an ideal maternity roost. Bats will use the same farmhouse attic generation after generation if the entries stay open, which is why the loyalty to a traditional roost matters so much: seal it thoroughly once, and the colony has to relocate; seal it halfway, and they simply shift to the next gap.
Seasonal cabins around Iola, the Chain O’ Lakes, and the river corridors are frequent bat buildings precisely because they are quiet and unoccupied through the maternity season — nobody is there in June and July to notice a colony forming. Owners often discover the problem only on a spring or summer visit, finding guano in the loft and staining at the eaves. The seasonal schedule actually works in our favor here, since the legal August-onward exclusion window lines up with late-season cabin use.
The common thread is the roofline. Bats need only about a half-inch gap, they are patient, and the aging, high, complex rooflines of rural Wisconsin buildings offer plenty of them — which is why finding every entry, not just the first one, is the entire foundation of a bat job.
Signs you have a bat colony
A lone bat blundering around the living room is dramatic but does not by itself mean a colony — although it can be the first hint of one. The clearer signs of an established colony are outdoors and in the attic. The definitive test is to watch the roofline at dusk on a warm evening: a colony reveals itself as bats emerge one after another from a specific gap to go feed. Around entry points you will often see dark staining, where body oils and guano accumulate and discolor the siding or soffit. In the attic and on the ground below an entry, you will find guano — small, dark, pellet-like droppings that pile up, distinguishable from mouse droppings because they crumble to a powder and often glint with insect fragments. A strong ammonia odor from accumulated guano and urine is common with a well-established colony, and you may hear faint scratching or squeaking in the walls and attic around dusk and dawn as the bats settle and leave. BugBoss confirms the colony, gauges its size, and locates every exit as the first step of any job.
Are bats dangerous?
There are two health concerns with bats, and both are real but manageable. The first is rabies. Bats can carry rabies, and while the odds that any given bat is infected are low, the consequences are severe, so exposure is taken seriously. A bat found in a room where someone was sleeping, or where a child, pet, or impaired person could have been bitten unaware, should be safely contained without crushing its head, retained for testing, and reported to health authorities, with medical advice sought. Never handle a bat barehanded.
The second is histoplasmosis, a respiratory illness caused by a fungus that can grow in accumulated bat guano. People contract it by breathing in spores when dry droppings are disturbed — which is exactly why dry-sweeping a guano pile in an attic is the wrong approach, and why cleanup is done with proper protection, containment, and disinfection. On the structural side, a long-established colony does quiet damage: guano and urine soak into and ruin insulation, stain ceilings and drywall, corrode and foul the attic, and the ammonia odor can permeate the living space below. None of it is an emergency in the way a house fire is, but a colony left in place for years leaves a genuinely contaminated, damaged attic behind — which is why the guano cleanup is as much a part of the job as getting the bats out.
Why DIY usually fails — and why it is risky
Bat work is the wildlife job where do-it-yourself goes wrong most often and most expensively, for three reasons. First, the law: most homeowners do not know about the June 1 to July 31 maternity restriction, and sealing the building in that window — the instinctive thing to do when you find bats — traps flightless pups, which is illegal and turns a bat problem into a decomposing-animal problem with weeks of odor and a wave of flies. Second, the method: the fatal DIY mistake is sealing the entry points while bats are inside. Effective bat exclusion is the opposite of sealing them in — it uses one-way devices that let them out and block their return, and only then, after the colony is confirmed gone, does the sealing happen. Getting that sequence backward traps the whole colony.
Third, the thoroughness and safety. Bats need only about a half-inch gap, and a building — especially an older farmhouse or barn — may have several entry points scattered across a roofline that is genuinely dangerous to work on. Seal the one obvious gap and the bats simply use another, or claw at the netting until they find a way. Finding every exit, installing devices correctly, working safely at height, sealing with durable materials, and then cleaning up guano with the right precautions for rabies and histoplasmosis is a skill set, not a weekend project. This is the kind of specialized exclusion covered in our Wisconsin bat exclusion law guide and our attic wildlife removal guide, and it is exactly the work that goes badly when it is improvised.
How does BugBoss handle bats?
Every bat job runs the same disciplined, DNR-compliant sequence. We start with a thorough inspection, watching the roofline at dusk to confirm the colony and its size and mapping every entry point across the whole structure — not just the one you noticed. That complete accounting of exits is what makes the difference between a lasting fix and bats simply switching to another gap.
Next, on the legal timeline, we install one-way exclusion devices over the active entries — plastic or netting configured so bats can fly out to feed but cannot get back in, and installed so they cause the bats no harm. We wait long enough, generally at least a week, to be confident the entire colony has left. Then, and only then, we seal every entry point permanently with durable materials, closing the building so this colony and any future one cannot get back in. Finally we handle the guano cleanup and decontamination — removing and disposing of contaminated material, cleaning and disinfecting the affected areas, and dealing with ruined insulation — with proper protection against histoplasmosis, so you are not left with a contaminated attic after the bats are gone.
Throughout, we work strictly within the June 1 to July 31 maternity restriction: if you call during that window, we inspect and confirm now and schedule the exclusion for the moment the legal window opens in August, unless a genuine living-space health situation qualifies for the DNR exemption. It is wildlife work done by the book, with no contract and the owner directly accountable.
How do you keep bats out?
Prevention for bats is exclusion done thoroughly and then maintained, because bats are loyal to their roosts and will keep testing a building they have used. Once a colony has been excluded and the entries sealed, the preventive work is keeping the building tight: periodically checking the roofline, soffits, fascia, gable and ridge vents, and chimney flashing for new gaps as the structure ages and settles, and closing anything that opens up before it becomes an invitation. Screening gable and ridge vents and maintaining chimney caps closes off the routes bats favor. On older farmhouses and barns, where the roofline offers many potential gaps, an annual look is worthwhile.
It is worth saying clearly that prevention does not mean driving bats off your property — they are beneficial, eating enormous numbers of mosquitoes and farm pests, and there is real value in keeping a healthy population nearby. The goal is simply to keep them out of your living structure. For homeowners who want to support bats after excluding them from the house, putting up a bat house well away from the building gives the colony an alternative roost and keeps the mosquito control going, which around here is no small thing.
One caution on timing your own prevention: the roofline inspection and any sealing of gaps that could become entries must still respect the maternity restriction if a colony is present. If you are only checking a building you know is bat-free, a summer look is fine. But if there is any chance bats are using the structure, do not seal anything between June 1 and July 31 — confirm first, and if a colony is active, wait for the legal window. When in doubt, that confirmation is exactly what an inspection is for, and it costs far less than the mistake of sealing pups inside.
When should you call BugBoss about bats?
Call as soon as you suspect a colony — bats emerging from the roofline at dusk, guano and staining at an entry point, an ammonia odor, or scratching in the walls at dusk and dawn. Call even during the June-to-July maternity window, because that is exactly when we inspect, confirm, and get you scheduled for a lawful August exclusion, so no time is lost. And call right away if a bat is found flying inside your home, especially if anyone was asleep in the room, so the rabies-exposure question can be handled correctly.
This is a service where the local, do-both-pest-and-wildlife company genuinely stands apart. The national pest brands that run this area from the Fox Valley do not do bat exclusion at all — it is not a spray, it is skilled, seasonal, regulated work at height with cleanup attached — so a homeowner with bats is usually left calling around anyway. Doing pest control and wildlife under one roof, from a base right in town, means the colony in your attic, the guano cleanup, and the mice or squirrels that found the same open roofline are all handled by one accountable company that knows the DNR rules and the local building stock, rather than farmed out across two or three vendors.
BugBoss is based right in Clintonville at 600 S. Main St., and bat and wildlife exclusion is a core specialty — a high-skill service most pest-only companies in this area do not offer at all. We know the DNR maternity rule, we do the full job from finding the exits through guano cleanup, and we handle the other attic wildlife that often comes with an aging roofline, from squirrels and raccoons to mice. Reach us at 866-BUGBOSS, or request a quote. Local, licensed, DNR-compliant, and humane — with the bats out and the attic sealed and cleaned.
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.