The call that comes in every June
Someone hears scratching over the bedroom ceiling on a warm May evening. A few nights later a bat is fluttering around the living room. They look up, realize there’s a colony in the attic, and they want it gone — today. Then they call around and get an answer that sounds like bureaucratic nonsense: we can’t seal them out until August.
It isn’t nonsense, and it isn’t your contractor stalling. Wisconsin protects bats during their maternity season, and from June 1 through July 31 you legally cannot restrict a colony’s exits from a building. This post explains what that rule actually says, why it exists, and — the part people really need — how to plan a legal, humane eviction around it so you’re not living with bats a day longer than you have to. For the full legal and procedural detail, our Wisconsin bat exclusion law guide is the deep reference; this is the seasonal, plain-English version.
What the maternity-season rule actually says
Here’s the mechanism in one sentence: in summer, female bats gather in maternity colonies to give birth and nurse pups that cannot yet fly, so sealing the building’s exits during that window traps the flightless young inside, where they die.
That’s the whole reason for the restriction. Per Wisconsin DNR guidance, from June 1 to July 31 you must not restrict a colony’s exit points. If one-way exclusion doors are already installed on an active roost, they have to stay open through that window — you cannot close them off and cut the colony’s return, because the mothers going out to feed at dusk would be locked away from pups still stuck inside. Do that and you’ve killed a colony of protected animals, and you’ve bought yourself dozens of decomposing bats in your wall voids and the smell that comes with it.
Outside those two months, humane exclusion is on the table:
- Spring, before June 1 — bats are active and out of hibernation, but pups haven’t arrived yet, so the whole colony can be evicted.
- August onward — the young are flying, so the entire colony can leave through one-way doors.
Fall, before the bats leave for hibernation, is a common and effective time to do the work. The point is that there are clear windows on either side of the protected season, and a good plan uses them.
Why Wisconsin takes this seriously: white-nose syndrome
The maternity rule isn’t just about individual pups. It’s tied to a genuine ecological emergency. White-nose syndrome, a fungal disease that kills hibernating bats, reached Wisconsin in 2014 and devastated the state’s cave bat populations. In the aftermath, four cave bat species were listed as state-threatened: the little brown bat, big brown bat, northern long-eared bat (which is also federally endangered), and tricolored bat.
Those are precisely the species most likely to be roosting in your attic. So a building colony isn’t a disposable nuisance the way a wasp nest is — it’s a remnant of populations that took a hard hit and are slow to recover. That’s the backdrop for why the state protects the maternity season, and why doing bat work correctly matters beyond just following a rule.
It’s also worth saying plainly: bats are on your side most of the year. A single little brown bat eats huge numbers of insects a night, including the mosquitoes that make a summer evening on the porch miserable. Nobody’s trying to eradicate bats. The goal is to get the colony out of your house and keep it out — humanely, legally, permanently.
How humane bat exclusion actually works
Done right, evicting a colony is a patient, mechanical process, not a spray-and-done job. It runs in four steps:
1. Find the exits. Bats can use gaps as small as a finger’s width, and they favor the high, hidden junctions of a roof — gable vents, ridge and soffit gaps, chimney flashing, the seams where a dormer or an addition meets the main roof. We inspect the structure and, when needed, watch the building at dusk to see where the colony streams out. You cannot exclude a colony you haven’t fully mapped, because a missed exit becomes the door they keep using.
2. Install one-way devices. At the confirmed exits we fit one-way doors or valves that let bats crawl and fly out at dusk to feed but block them from crawling back in. The colony empties itself over several nights.
3. Wait — at least a week. The devices stay in place long enough to be sure every bat has cleared, including stragglers. Rushing this step is how you accidentally seal a bat inside.
4. Seal permanently. Only once the building is confirmed empty do we permanently close the openings with materials and methods that hold, so the colony can’t re-establish next year. Then comes cleanup of the guano and any contaminated insulation, and the repairs that make the attic bat-proof going forward.
You never, ever seal a live colony in. And during June and July, if a colony is active, the one-way doors stay open and step four waits until the season ends. Our attic wildlife removal guide walks through this alongside the squirrels and raccoons that get into the same spaces.
The health side you shouldn’t ignore
Two real concerns come with a building colony, and both argue for handling it properly rather than living with it.
Guano and histoplasmosis. A colony’s droppings accumulate in the attic and can harbor Histoplasma, a fungus whose spores cause a respiratory illness when disturbed and inhaled. That’s why guano cleanup is part of the job and shouldn’t be done casually by dry-sweeping an attic.
Rabies. The risk is low but not zero, and it’s taken seriously any time a bat turns up in living space — especially a bedroom where someone was sleeping, or a room with a child or a pet, since a bat bite can be tiny and go unnoticed. If you find a bat in living quarters, don’t release it; contain it if you safely can and contact your local public health department for guidance on testing. This is separate from the exclusion work, but it’s the reason a bat in the house (as opposed to in the attic) gets urgent, careful handling.
So what do you do right now, in May?
Timing is everything with bats, and May is a genuinely useful month — because it’s still before June 1. Here’s the practical playbook:
If you have bats now and it’s still spring: call for an inspection immediately. Spring, before the maternity window opens, is one of the two legal exclusion periods. If we can map the exits and get one-way doors installed before pups arrive, there’s a real chance to clear the colony this season instead of waiting until August. Every week counts as June approaches.
If we’re too close to June 1 to finish safely: we set up the full plan now — exits mapped, materials and schedule ready — and do the exclusion the moment the window reopens after July 31. You’re not waiting on a waitlist in August; you’re first in line with the work already scoped.
If a colony is active and one-way doors are already up when June 1 hits: they stay open through July 31. That’s the law, and it’s also the humane call.
What you should not do is grab a ladder and start caulking gable vents in June because you’re fed up. Sealing an active summer colony in is illegal, it kills protected animals, and it leaves you with dead bats decomposing in your walls — a far worse problem than the one you started with.
Why this is a job for a local wildlife pro
Bat exclusion sits at the intersection of building science, animal biology, and state law, and it’s unforgiving of shortcuts. A missed exit means the colony’s still coming in. A rushed timeline means sealed-in bats. Work done in the wrong month means a violation of DNR rules and dead protected animals. And it’s genuinely rare among rural pest companies to do wildlife exclusion at all — most of the national brands dispatched out of the Fox Valley do pests only and will hand you off.
BugBoss does both. We’re based right in Clintonville at 600 S. Main St., we handle bats and the rest of the attic wildlife under one roof through our wildlife removal service, and we run every bat job on the DNR’s calendar — inspection and planning anytime, exclusion in the legal windows, one-way doors that stay open June 1 through July 31 when a colony’s active. There’s no contract, and you deal directly with the owner, Brian.
If you’re hearing scratching in the attic or seeing bats at dusk streaming from the eaves, the smart move in May is to call now, while spring exclusion is still legal. Reach BugBoss at 866-BUGBOSS, or request a quote. And read the full Wisconsin bat exclusion law guide so you know exactly what the rules require before anyone puts a ladder on your house.