Mouse and Rat Removal in Michigan Attics and Walls

How can you tell mice are in the house?

Often you never see one: EPA says a mouse or rat may stay out of sight unless the infestation is severe, so the signs do the work. The National Park Service’s rodent-proofing manual lists sounds of gnawing or movement in walls and ceiling voids, droppings and urine stains, odors, and shredded nesting material. Rodents are mostly nocturnal, the manual adds, so the noise tends to come at night, and they burrow into and rearrange wall and attic insulation. EPA adds holes chewed through walls and floors, and trails with greasy rub marks.

Photograph any droppings for the call rather than sweeping them up; the CDC’s cleanup advice below explains why. For more on house mouse biology, see the Internet Center for Wildlife Damage Management’s house mouse biology page.

For telling mice from squirrels, bats or birds by other clues, see the guide to identifying attic animals.

When do mice and rats breed in Michigan?

House mice can breed year-round once they are indoors. The National Park Service says house mice can reproduce year-round indoors and will keep nesting and breeding inside all winter. Mice breed much faster than rats, EPA notes. Even so, the Park Service says non-native female rats are mature at about 3 months old and can produce an average of up to 40 young a year.

Fall is when they start moving in. Competition for food and nest sites rises with the onset of cold weather, the Park Service explains, and that is when rodents begin looking for a way into buildings. It recommends checking the outside of a building at least twice a year: in spring, for winter damage and signs of activity, and in fall, before rodents try to move in.

What about rats?

Rats get in the same way mice do, through gaps in the outside of the house, and need only a little more room. The National Park Service says a rat can squeeze through a hole ½ inch across, smaller than a quarter, where a mouse needs ¼ inch, and Wayne County’s health department gives the same two sizes. Rats are harder on the repair, too: the Park Service says they can gnaw through concrete block, aluminum siding, wallboard, plaster and wood, which is why the sealing step below uses metal and mesh. The CDC’s cleanup method below covers rat urine and droppings as well as mouse.

In Detroit, the city runs its own rodent control line, (313) 876-0974, according to Detroit Animal Control.

What does mouse and rat removal involve?

1. Find the gaps. The National Park Service’s rodent-proofing manual says to check the siding, eaves, soffits, gables, chimney and furnace clean-out ports and utility line entry points for any crack or hole ¼ inch or larger, and to check around every pipe and electrical line that passes through a wall, foundation or roof.
2. Get the rodents out. The manual calls snap traps effective for removing rodents already inside, used together with sealing, and says that where rodents burrowing under a foundation have no other way out, they must be removed by trapping or other means before exclusion devices go in. EPA’s training for child care buildings puts trapping after the building is sealed. Ask the operator which order they plan for your house, and why.
3. Seal with the durable materials the Park Service recommends. The Park Service recommends galvanized sheet metal, 24-gauge or heavier, for most rodent proofing, ¼-inch hardware cloth for vents, and concrete or mortar for foundation cracks. It warns that mice, rats and squirrels can gnaw through aluminum. EPA suggests steel wool for small holes, but the Park Service’s manual warns that it is flammable, rusts and lets rodents work their way around it, and it prohibits its use.
4. Clean up safely once the activity stops.

Sealing is the part that lasts. The Park Service’s manual cites a study in which repairing a building’s rodent entry points once cut infestations by more than 90% compared with buildings left unrepaired. It also says exclusion is never permanent, so the seals need checking again each spring and fall.

Who handles mice and rats in Michigan?

Usually the homeowner or a company they hire; EPA notes that anyone can use a mouse or rat trap, with no license needed. EPA says that if you have mice or rats and are uncomfortable dealing with them yourself, you may wish to hire a rodent control professional.

If the plan includes rodent bait or another pesticide, ask which product, where it will go and how children and pets will be kept away from it. EPA says misused rodent bait can harm people and pets, that traps and baits always go where children and pets cannot reach them, and that dead rodents should be picked up promptly so pets and wildlife do not eat them. The federal rule is that the label is the law: every pesticide label states that using the product in a way its labeling does not allow violates federal law. For a company applying pesticides, EPA also suggests asking to see its license and calling your state pesticide regulatory agency with any concerns.

For Michigan’s own rules on small rodents, see the DNR’s small rodents page.

How should mouse droppings in the attic be cleaned up?

Wet, and never by sweeping or vacuuming. The CDC explains that diseases spread from rodents to people mainly through breathing contaminated air, and that sweeping or vacuuming urine, droppings or nesting material can put droplets containing viruses into the air. Hantavirus is one: the CDC says people get it from contact with rats and mice, especially their urine, droppings and saliva, and that the virus can get into the air when fresh droppings or nesting material are stirred up. Its method:

• Open doors and windows for 30 minutes before cleaning, and leave the area while it airs out.
• Spray urine and droppings with a bleach solution or an EPA-registered disinfectant until very wet, and let it soak for 5 minutes or as the label directs. The CDC’s bleach solution is 1.5 cups of household bleach in 1 gallon of water, mixed fresh.
• Bag insulation contaminated with urine and droppings in plastic for removal.
• The CDC lists a half-mask air-purifying (or negative-pressure) respirator with a HEPA filter as appropriate respiratory protection.

How much insulation comes out is covered on attic cleanup and repair.