Where wasps actually get into a Michigan house
Every wall or attic colony started with a queen finding one opening in April or May, and the list of openings she checks is short. Soffit and fascia gaps come first. Where the soffit board meets the wall, or where two lengths of aluminum trim butt together, a quarter-inch gap is plenty. Gable and ridge vents come next, especially older louvered vents whose screening has rusted out or was never there. Then the utility penetrations: where the dryer vent, the hose bib, the electrical service, or the air conditioning line set enters the wall. Contractors seal these loosely and weather opens them further. Hollow structures are their own category. Rail ends, fence post tops, downspout openings, and gas grill frames are prebuilt cavities, and the European paper wasp treats them exactly that way. Finally, the ground. Abandoned rodent burrows along foundations, garage slabs, and fence lines are what a yellowjacket queen is looking for, and Michigan yards produce plenty of them. Walk the perimeter once in spring with this list. Closing five openings in an afternoon prevents more wasp problems than any spray does.
Yard work is how people find ground nests
The most common serious sting incident in Michigan does not involve someone poking a nest on purpose. It involves a mower. A ground colony announces itself with a hole the width of a pencil and nothing else. There is no paper structure to see and no way to judge from the surface whether the cavity below holds two hundred wasps or several thousand. University of Minnesota Extension reports that a mature yellowjacket nest can hold around 5,000 wasps at peak. What triggers the response is vibration, which is exactly what mowers, string trimmers, wheelbarrows, and shovels produce. Because the exit is at ground level and the whole colony reacts at once, stings land on ankles and legs in numbers rather than singly. The demographics follow directly from that. CDC records show 84 percent of sting deaths in the United States from 2011 through 2021 were male, matching who is typically doing the mowing, roofing, and brush clearing. The protocol is simple. If you hit one, walk briskly away rather than swatting. Then flag the hole, keep pets and children off that part of the yard, and have it treated after dark.
A season that starts late and stops hard
Michigan's wasp year has a shape worth knowing, because it tells you how much urgency a given nest deserves. April and May are the queen's solo stretch. She emerges from wherever she overwintered, chooses a site, builds a small comb, and raises the first workers alone. A nest at this stage is fragile in a way it never will be again. June and July are compounding growth. Workers take over foraging and construction, the queen switches to laying full-time, and cavity nests start filling the space available. With 34 inches of annual rain and humid summer air, insect prey is plentiful enough to fuel it. August through early October is the peak, and it is when nearly every complaint arrives. The colony holds its maximum number of workers, larval production winds down, and foragers turn to sugar and protein around trash cans and grills. Hard frost ends it decisively. Workers and the old queen die, and only newly mated queens survive, tucked under bark or in a woodpile. Nothing overwinters as a functioning nest, which is why Michigan never sees the multi-year colonies that turn up along the Gulf Coast.
Killing a nest is not the same as solving the problem
Plenty of Michigan homeowners pay for wasp treatment twice at the same address, one summer after another, and the reason is always the same. The colony was killed and the opening was left open. A queen choosing a nest site in spring is looking for a protected cavity with a small entrance. A soffit gap that suited last year's colony suits this year's just as well, and there is no residual effect from an old treatment months later. So the finished job has four parts, not one. Locate every entrance, not just the one you noticed. Treat after dark so the colony is inside. Wait several days for returning foragers to pick up the product, then confirm no traffic. Only then remove comb where you can reach it and close the opening with screen, caulk, cap, or wood repair. On the older, moderately priced housing that makes up much of the state, that last step is where the money is actually saved. A vent screen lasts years. A treatment lasts one season. When you get a quote, ask which of the four parts it covers.
Rentals, shops, and shared buildings in Michigan
wasps get complicated fast when more than one party is involved, and the split usually follows access rather than blame. Anything inside the building envelope, meaning a wall void, an attic, a soffit, or a shared exterior wall, requires access and repairs a tenant does not control. That is the owner's responsibility in nearly every lease. Ground nests in shared lawns and hornet nests over shared entries fall the same way. What a tenant usually does own is their own equipment: the grill, the patio umbrella, the storage bin on the balcony. For commercial property, the pressure point is the trash enclosure. From August onward, foraging wasps concentrate wherever sugar and protein waste sits, so a dumpster area near a service door or a patio becomes the site of most stings. Latched lids and frequent pickup do more than any spray. In every case, report it in writing with a photo and a date, and say plainly if anyone in the unit carries an epinephrine injector. That detail moves a nest from a maintenance item to a safety issue, and it should change how quickly it gets scheduled.