Troy Rodent Control: Keeping Mice Out Through a Michigan Winter

What to look for

Norway rats burrow along foundations, under decks and beside sheds, and forage 100 to 500 feet from the nest. Deer mice and white-footed mice are native species that usually live outdoors at wooded edges but readily move into garages, sheds and attics once it turns cold. The humid continental climate drives the pattern. Summers average about 83F, a long and comfortable breeding season, and then winter lows drop to around 18F. That is cold enough that rodents outside actively hunt for heated space each fall, and once they're in, they don't leave until spring. So Michigan homes tend to have mice in walls and garages all winter, not just during a short fall surge. Deer mice add a health angle, because their droppings are the usual route of exposure to Sin Nombre hantavirus, the strain in Michigan's 2021 case. Four rodents matter here. House mice are the main indoor pest, nesting in wall voids, behind appliances and in garage storage, and they breed 5 to 10 times a year.

• 1Droppings in the garage near stored bird seed, grass seed or pet food.
• 2Shredded insulation, paper or fabric tucked into a drawer, box or the back of a cabinet.
• 3Scratching inside walls or ceilings, most often from late fall through winter.
• 4Seed husks or small food stashes in attics or storage boxes, a habit of native mice.
• 5Burrow openings beside the foundation, under a deck or along a shed, which point to Norway rats.
• 6Gnawed garage door weatherstripping or wood trim near the floor.
• 7A musty smell in a closed cabinet or a storage room that has sat untouched.

Treatment options and typical costs

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Deer mice and white-footed mice: who is living in your garage?

In fall they move into garages, sheds, attics and anything left closed up. In a Troy garage, that means stored boxes, lawn equipment and cars that sit for a while. House mice look different: a more uniform gray-brown coat, smaller eyes and a scaly tail. They are the ones that move into kitchens and wall voids. The difference matters most for cleanup. The CDC identifies deer mouse droppings in sheds, cabins and garages as the main hantavirus exposure route, and Michigan's first confirmed case, in 2021, involved Sin Nombre hantavirus. Every pile of droppings deserves the wet bleach method, but if you suspect deer mice, be especially careful and consider having a provider handle heavy contamination. If the mouse in your garage has a white belly, white feet and big dark eyes, it is probably a deer mouse or a white-footed mouse rather than a house mouse. Both are native to Michigan, and both normally live outdoors at wooded edges and in tall grass.

Is it safe to clean out a closed-up shed or garage in spring?

Spray droppings and nests with 1.5 cups of bleach per gallon of water, let it soak 5 minutes, then wipe up with paper towels and bag everything. Never sweep or vacuum dry material, because that sends particles into the air you're breathing. Keep an eye on your health afterward. MDHHS says illness begins one to five weeks after exposure to fresh urine, droppings or saliva, and hantavirus pulmonary syndrome kills about 40 percent of the people who develop it. If you feel sick in the weeks after a cleanout, tell your doctor about the rodent exposure. For a shed with heavy nesting, hiring the cleanup out is a reasonable call. It can be, if you follow the right steps. The Michigan Department of Health and Human Services names entering or cleaning rodent-infested structures as the highest-risk activity for hantavirus, and notes that most U.S. cases cluster in spring and summer. That timing lines up with when Troy residents open sheds and storage spaces that sat closed all winter. Before you start, prop open doors and windows and let the space air out for 30 minutes. Wear rubber gloves.

Troy's rodent year, from first frost to spring cleanup.

Upper Midwest homes often have mice in walls and garages all winter, so keep checking traps and watching for fresh droppings rather than assuming the problem ended with fall. March through May is cleanup season and the riskiest stretch for hantavirus. Clear nests from garages, sheds and attics with the wet bleach method, repair chewed weatherstripping, and look for new burrows along the foundation as the ground thaws. June through August, with highs near 83F, is when outdoor populations grow. Trim limbs back from the roof, cap the chimney if it isn't already, and protect garden beds with 1/2-inch mesh so the next fall push finds fewer ways in. September and October are entry months. Nights cool quickly in a continental climate, and mice, rats and native deer mice start testing garage doors, vents and utility gaps. Sealing should be done by now, and a few snap traps in the garage give early warning. November through February is the long middle. With Troy's lows averaging about 18F, nothing that made it inside is going back out.

How should you seal a house the way Michigan DNR recommends?

Use metal, not foam. Michigan DNR tells homeowners to seal holes with durable materials such as metal flashing or hardware cloth, because rodents chew through softer fillers. The CDC's target is any opening down to 1/4 inch, roughly the width of a pencil. Work from the roof down. DNR advises capping and screening chimneys and cutting tree limbs back so none are within a few feet of the roof, which removes the bridge rodents use to reach the attic. Check roof vents and soffit gaps while the ladder is up. At ground level, focus on the garage. Worn bottom seals and gaps at the door corners are a common weak point, and an attached garage connects to everything else. Seal around utility lines, dryer vents and AC line sets with hardware cloth or flashing, then caulk the edges. Don't forget the yard. DNR's guidance for homeowners and HOAs calls for solid sheeting or fencing with holes 1/2 inch or smaller to keep rodents out of gardens. Fewer food sources outside means less pressure on the house when cold weather arrives.

What should a provider check on the first visit?

Inside, they should look at the garage, the attic access and anywhere you've found droppings. Ask them to name the species. House mice, deer mice and Norway rats call for different approaches, and deer mice change how cleanup should be handled. Get the findings in writing: a list of entry points, the material proposed for each one, how many trap checks are included through the winter, and whether cleanup is part of the price. Ask whether they install chimney caps and screens, since Michigan DNR recommends both. With a median home value around $370,000 in Troy, many owners are protecting insulation, wiring and stored belongings worth far more than the sealing. A plan that leans on trapping without exclusion costs less now and more later, because each fall brings a new wave. A good first visit is mostly inspection, and you should plan to walk the property with the provider. On a Troy house, that means garage door seals and corners, the roofline, chimney and vents, the spots where utility lines enter, and the foundation for burrows.

Simple ways to keep rodents away

• Cut tree limbs back so none sit within a few feet of the roof, as Michigan DNR advises.
• Cap and screen the chimney.
• Replace worn garage door bottom seals and add sweeps to side doors.
• Seal gaps at utility lines, dryer vents and AC lines with metal flashing or hardware cloth.
• Keep bird seed, grass seed and pet food in metal containers with lids.
• Protect garden beds with fencing or sheeting that has holes of 1/2 inch or smaller.
• Stack firewood off the ground and away from the house.
• Set a few snap traps in the garage each September as an early warning.

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