Mouse control in Michigan

Mice live outdoors in fields, woodlots and garden edges all summer. When Michigan nights start dropping into the 40s in September, they look for warm, protected spots with food nearby. Your basement, attached garage and wall voids fit the bill. Homes next to farm fields, vacant lots or wooded ravines usually see the first wave, often right after crops are harvested.

Once inside, mice breed year round. A pair that slips in during October can turn into a real problem by January, because a female can have a new litter every few weeks. That is why the fall push matters so much. Sealing gaps in September and October does more good than any amount of trapping in February, after the population has had all winter to grow.

In Michigan you are mostly dealing with two kinds. The house mouse is gray-brown, with a nearly hairless tail, and lives close to people in cities and suburbs. Deer mice and white-footed mice are tan to reddish with white bellies and white feet. They are more common in rural homes, cottages, pole barns and cabins that sit empty part of the year.

A mouse can squeeze through a gap about the width of a pencil, roughly a quarter inch. On older Metro Detroit and Grand Rapids homes, the usual spots are gaps where the foundation meets the wood sill, old dryer vents, and holes around gas, water and air conditioning lines. Garage door seals that have cracked from years of freeze and thaw are another common entry point.

Newer homes have their own weak points: gaps behind vinyl siding at the corners, unsealed utility penetrations, and the space where a garage slab meets the house. Up north, crawl spaces and seasonal cottages with stone foundations are almost impossible to seal completely, so trapping becomes an ongoing job every fall and again when you open the place in spring.

Walk the outside of the house at ground level with a flashlight. Look for smudge marks, droppings and chewed edges near any opening. Then check inside under sinks, behind the stove, behind the dishwasher kick plate, and at the back of the furnace room where pipes and ducts enter. Those spots tell you where to put traps and what to seal first.

Deer mice can carry hantavirus. Human cases are rare in Michigan but have been reported, and the illness can be serious. The risk comes from breathing dust from dried droppings, urine and nesting material, which is why the way you clean up matters more than most people realize. House mice are not the main hantavirus carrier, but their droppings still contaminate food and surfaces.

Do not sweep or vacuum droppings dry. Open the space to air it out for a half hour, wear rubber gloves, and wet the droppings and nesting material with a bleach solution or a household disinfectant. Let it soak for several minutes, then wipe it up with paper towels and bag it. This matters most in cabins, sheds and cottages that have been closed up all winter.