Bats in the barn are usually working for you — until the guano piles up
Here’s something I tell farmers all the time: the bats in your barn are, on balance, on your side. A summer maternity colony eats a staggering volume of insects every night — mosquitoes, moths, beetles, the crop and livestock pests that cost you real money — and a barn full of bats is a barn with a free, tireless insect-control crew. So barn bat work is a little different from house bat work. In a house, you want them gone, period. In a barn, the honest question is often not “how do I get rid of the bats” but “how do I keep the benefit while getting the guano out of my feed, my stalls, and my work areas.”
That distinction shapes the whole job. Sometimes the right answer is full exclusion; sometimes it’s relocating the roost off the feed and out of the way while keeping the colony on the property. BugBoss The X-Terminator does both across the farms of Waupaca, Shawano, and the surrounding counties. This page pairs with the bats pest-library page, our Wisconsin bat exclusion law guide, and the bats in the attic page for the house version.
The guano is the real issue
An active colony drops a lot of guano, and in a barn it lands where it does damage. Over feed and water, it’s a contamination problem — droppings and urine make feed unfit for livestock, plain and simple. In stalls and work areas, it’s a mess you’re constantly cleaning and, more seriously, a health hazard: accumulated guano can grow Histoplasma, the fungus behind histoplasmosis, a respiratory illness caused by inhaling disturbed spores. Every time you muck a stall, move hay, or work under the roost, you risk stirring that dust into the air. So the case for acting isn’t about the bats being unwelcome — it’s about where their droppings end up.
The law doesn’t care that it’s a barn
One thing that trips people up: the Wisconsin maternity-season rule applies to a barn exactly as it does to a house. The DNR bars restricting bat exits from June 1 through July 31, wherever the colony is, because the same flightless pups are up in the peak whether that peak is over a bedroom or a hayloft. So barn exclusion happens before June 1 or from August onward, never in that window. If you call mid-summer, we inspect and plan and then hold the actual exclusion until the calendar allows — sealing a barn roost full of pups is both illegal and a guaranteed dead-animal mess in your loft.
The bats are the same two species you’d find in a house attic: big brown bats and little brown bats, both protected, both knocked back hard by white-nose syndrome since it reached Wisconsin in 2014. Little browns tend to form the larger maternity colonies you’ll find in a barn peak; big browns are common and more apt to overwinter in the structure.
Why barns host bigger colonies
Barns leak up top in a way houses don’t. Open gable ends, gaps at the ridge and peak, louvered vents, cupolas, open eaves, and spaces where the roofing meets the wall — a barn offers dozens of high entry points and acres of quiet, undisturbed space to roost. That’s precisely why colonies in barns tend to be larger than in houses: more ways in, more room to grow. The flip side is that exclusion on a barn is more work — more entry points to find on a bigger, taller structure, and more sealing to do once the colony’s out. The gaps themselves are the same tiny sizes — a big brown bat slips through around three-eighths of an inch — there are just more of them.
Exclude or relocate — deciding the goal
Before any devices go up, we settle what you actually want. If the colony roosts in a far corner of the loft and the guano isn’t touching feed, stalls, or work areas, plenty of farmers reasonably leave it — the insect control is worth keeping. Exclusion earns its keep when the guano is fouling feed, contaminating work or living areas, or building toward a real health concern.
Where the goal is to keep the bats’ benefit but get them out of the barn interior, relocation is the play: mount bat houses nearby ahead of the exclusion so the colony has somewhere to go, exclude them from the barn, and they’ll often adopt the new roost. You keep the insect control, you lose the guano indoors. It’s a good fit for the farm, and we’ll advise on bat-house placement as part of the plan.
How the work goes
The method mirrors house exclusion, scaled to the building. We start with a full inspection and a dusk watch to map every functional exit high on the barn — not just the obvious gable. We fit those exits with one-way devices that let bats drop out to feed and block their return, and we leave them up at least a week, longer in cool weather, to be certain the barn is empty. Then we seal the entry points comprehensively — the labor-intensive part on a big leaky structure — and finally we clean up the accumulated guano with containment and respiratory protection, which on a barn loft can be a substantial job.
The cardinal rule holds here as everywhere: let them out first, confirm they’re gone, then seal. Sealing an occupied roost traps the colony and creates exactly the dead-animal and odor problem you were trying to avoid.
What prevention looks like on a barn
You can’t make a barn as tight as a house, and you wouldn’t want to — barns need to breathe, and the ventilation that keeps hay and livestock healthy is the same ventilation bats slip through. So barn prevention is about being deliberate where it counts rather than sealing the whole envelope. Screen the gable vents and louvers with mesh sized to block bats while still passing air. Close the gaps at the ridge and peak and where roofing meets the wall, the high spots that make good roost entries, while leaving the intentional ventilation intact. And keep an eye on the peak and loft each spring, because that’s where a new colony starts and where you’ll catch it small.
The other half of prevention is deciding, ahead of time, where you’d rather the bats be. If you value the insect control — and on a farm you should — putting up bat houses on the property before you ever have a problem gives a scouting female an alternative to your loft. It’s cheaper and easier to steer a colony to a bat house than to evict an established one from the barn peak, and it keeps the benefit while keeping the guano off your feed.
The BugBoss approach
We handle barn bat work end to end — the assessment and the exclude-or-relocate decision, the legally-timed one-way exclusion, the patient wait, the sealing, and the guano cleanup and any bat-house setup. Because wildlife exclusion is our core trade and we know farm buildings, you get one crew for the whole project rather than a bat guy and a separate cleanup outfit. On a working dairy or livestock operation it fits into the broader rodent-and-wildlife picture in our dairy farm pest control guide. It’s no contracts, owner-direct with Brian.
When to call
Call when guano is landing where it shouldn’t — over feed, in stalls, in work or living space — or building up to where you’re worried about the dust, and call early enough that we can time the exclusion to the legal window rather than waiting out the summer. If you just want to know whether the colony in your loft is worth leaving, that’s a fair question and we’ll give you a straight answer. BugBoss serves the farm country around Clintonville, Marion, Shawano, and Waupaca. Reach out and we’ll come assess the barn.