I’ve lived in a well-built old house sheathed with cedar shingles for decades, throughout which I’ve often (but never intentionally) shared it with mice, flying squirrels, sometimes chipmunks, and, occasionally, Norway rats. What to do? Here's advice for identifying, controlling, and preventing rodents in the home.
How Do Rodents Get In?
Rodents are able to come in through impossibly tiny openings: A rat or flying squirrel can squeeze through an opening the size of a quarter; a mouse, the size of a dime. They come in through soffits, vents, and openings in chimney flashing.
The word "rodent" derives from the Latin root rodere, which means “to gnaw”—and gnaw they do. Their upper and lower incisors grow continuously throughout their lives, which means that the rodents must constantly gnaw. They will chew their way through wood, cinder block, brick, mortar, and even aluminum, not to mention all manner of plastics.
Why Do Rodents Invade the Home?
Rodents enter homes for the same reasons that people live in them: to meet their needs for shelter, water, food, and protection (in their case, from predators such as foxes, coyotes, cats and dogs, weasels, hawks, and owls).
Signs of a Rodent Problem
If you have rodent guests in your home, you might:
Find a stash of dog kibble or sunflower seeds tucked in behind the socks in your underwear drawer.
Discover that the plastic has been chewed off electrical cords or wires.
Encounter evidence of nesting materials: chewed-up toilet paper, newspaper, wrapping paper, or old term papers tucked away in a paper box in the attic.
Find chew marks or shreds of chewed materials with holes chewed or partially chewed through in sills in the corners of doors or cupboards or in mattresses, couch cushions, or rag piles.
See droppings, especially in areas where rodents have come into your living space to feast on left-out food and crumbs: Mouse droppings are the size and shape of a grain of rice; rat and squirrel droppings are sausage-shape and up to ¾ of an inch long. (Note: A rodent will pass 50 to 75 fecal pellets in a day. It’s rare to host a single rodent.)
Hear scratching, chewing, squealing, or rustling sounds inside the walls.
Hear them shrieking, squealing, and chasing each other through your walls after dark.
Find your cat or dog meowing, whining, or sitting for hours staring at a patch in the wall if they hear or sniff rodents inside.
Detect a rank, musky odor in areas where rodent droppings and urine have built up.
How to Remove Rodents
One you’ve detected a rodent problem and identified the invader(s), you’ll need a removal strategy.
Some people like having a cat or cats to deter and dispatch household rodents. This can work, but it can become a problem when cats bring live rodents in for your approval and the prey escapes, especially when the cat enters through a cat door while you’re not home. Cats may also leave half-dead prey or unmentionable rodent parts on the living room rug.
I prefer snap traps for mice. Properly set, they kill quickly and humanely.
Rats are hard to trap in any device. They’re very smart and wary. You’re more likely to catch one if you bait a trap but don’t set it for a few days, replacing the bait when it’s eaten. In my experience, rats lose interest if you’re meticulous about keeping all food and water unavailable.
We’ve found that live traps work pretty well to lure squirrels but don't work for mice or rats. We release the squirrels outdoors, even close to our home—and then check carefully to find where they came in and seal the opening. But after two or three are captured and released, they seem to take the message back to their group.
Research has shown that sonic repellent devices are not effective at keeping rodents from your home, although the same devices may disturb sensitive humans in the household.
I don’t use glue traps or poisons because they subject the animals to excruciating deaths and may have unintended effects. Poisons may also kill domestic cats, birds, and other wildlife that eat the rodents who die outside in their search for water.
How to Prevent Rodents
Exclusion is your first line of defense.
Twice a year, inspect your sills, siding, vents, soffits, and chimney flashing for openings that could serve as rodent entryways. Also check for holes where water lines, drains, and cables have entered the building. Stuff smaller openings with a plug of fine steel wool sealed with caulk. Fasten small-mesh hardware cloth or sheet metal to seal large openings.
Prune all tree branches that hang over or close to your roof to prevent squirrels from jumping or flying over.
Keep brush and leaves away from the sides of your house to provide less cover for rodents to burrow in from below or to detect burrow openings when they do.
Rodents have a terrific sense of smell. Don’t leave food items on counters or tables.This includes fruit bowls, ripening tomatoes, and anything enclosed in a plastic bag or fiberboard container (cereals, whole grains, bread).
Sweep up all food crumbs.
Don’t put meat scraps into your kitchen compost bucket or trash container.
Keep bags of pet food in covered metal containers. Store grains and seeds in glass jars.
Pet food and water dishes are especially attractive to rats. If you have an infestation, don’t keep the bowls out at night.
Seek Help From Professionals
If you live in a rodent-prone home or rural area, you’ll probably need much more technical/professional advice than this post can offer.