How to keep mice out of your house with steel wool and traps
Seal gaps larger than 1/4 inch with steel wool and caulk, clean up food, and trap the mice already inside.
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Seal every opening larger than 1/4 inch in your home's outside walls, and cut off the food that draws mice inside. Pack steel wool into small holes and cover them with caulk (UC IPM).
Why fall is the time to do it
Outdoor house mice frequently come indoors in autumn as nights get colder, so sealing before the weather turns pays off (UC IPM). A house mouse is only 5 to 7 inches long including its tail. That small size lets it squeeze through openings you might never notice.
Check low spots along your foundation, around pipes, and where cables enter. Mice can enter through holes the size of a dime, and rats need only a quarter-sized hole (San Diego County).
Mice are excellent climbers, and they can run up rough vertical walls and jump up to 12 inches from the floor (UC IPM). Look higher than you expect.
How to seal the holes
For small holes, pack in steel wool and seal it with caulk or spray foam. Mice cannot chew through the metal (CDC). For larger holes, cover the opening with hardware cloth before sealing (San Diego County).
Skip the wrong materials. Plastic screening, rubber, vinyl, expanding foam alone, and wood are all ineffective for plugging mouse holes, because mice gnaw through them (UC IPM). Steel wool pads work as temporary plugs but may rust over time, so plan to redo them with caulk.
Clean up what invites them
Store dried grain and meat products in airtight containers such as glass jars or metal canisters. Mice usually feed on cereal grains, but they will eat many kinds of food (Illinois Dept. of Public Health). Rodents will also feed straight from pet dishes, so pick bowls up between feedings.
Trim trees and bushes so branches sit at least 4 feet from the roof (San Diego County).
Dealing with the mice already inside
After you seal the holes, deal with the mice already inside. A mouse carries a musky odor around its nest, so follow your nose to find where it has been living (Illinois Dept. of Public Health).
Trapping is the preferred method when only a few mice are present. It also avoids the dead-mouse odor that poisoning inside a building can leave behind (UC IPM). Snap traps are the least expensive option.
Set traps behind objects and in dark corners where you see evidence of mice, close to walls. Space them no more than about 10 feet apart, since mice seldom travel more than 30 feet from their nest (UC IPM).
Bait with the food the mice are already eating. Set pairs of traps 1 to 2 inches apart, which catches more than a single trap (UC IPM).
Never use poison baits indoors or under the house, because rodenticide baits generally take several days to work. Poisoned mice often stay near their nests, so they die inside the structure and leave you with an odor problem.
If you find droppings, do not sweep or vacuum them, because that stirs up virus particles (San Diego County). Air out the room for 30 minutes. Spray the area with a disinfectant made of 9 parts water to 1 part bleach. Let it sit for 15 to 20 minutes before you clean it up with gloves on.
Skip what does not work
Ultrasonic sound does not keep mice out. There is little evidence that sound, magnetic, or vibrational devices drive mice from buildings, and mice quickly become accustomed to repeated sounds (UC IPM). Cats and dogs do not give effective mouse control either, so do not count on a pet as your plan (Illinois Dept. of Public Health).
This week, walk your foundation with a flashlight. Mark every crack, pipe gap, and door sweep that a dime could fit through. Seal those openings with steel wool and caulk before cold weather sends mice looking for a warm wall (CDC).
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