You might have mice in your home without knowing it. Here's how to outsmart them

Preventing mice from breaking in is a tall order, because they can squeeze through any small opening. Picture: REUTERS/Dennis Thiele/University of Michigan-Handout

Preventing mice from breaking in is a tall order, because they can squeeze through any small opening. Picture: REUTERS/Dennis Thiele/University of Michigan-Handout

Published Jul 18, 2023

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By Rachel Kurzius

Talk to almost anyone in pest control and you'll immediately detect their begrudging respect for mice.

They are "so adaptable," says Matthew Frye, an educator with the New York State Integrated Pest Management Program at Cornell University.

"They're great at living right alongside us, sharing the table with us and really just coexisting with us - but in a sort of klepto-parasitic way where we don't really want them there and they're stealing from us."

There's good reason to sever our ties with this unwanted guest - mice can carry diseases and cause damage to homes.

Their wire-chewing can lead to house fires. And if you ignore the signs of an infestation, they reproduce quickly enough that you can end up with generations of mice under your roof in less than a year.

But it's not easy to kick them to the curb.

Frye says you'll need a "detective mind-set to figure out where they are, where they're moving, what they're preferring to eat, and how [you can] collect as much information as possible to develop the best management strategy to eliminate them."

Why you might not realise you have mice

"Mice are secretive opportunists that can be in your house six or seven months and you don't even know it," says Gerard Brown, who runs the D.C. Health Department's rodent control programme.

"Sometimes you might be in a room looking at the TV or sitting down, and you notice something, you think, out of the corner of your eye - some movement. And a lot of times, that's mice."

As a means of survival, they stick to the shadows. "They will move along walls so that they're not as easily detected," says Frye.

The types of mice that live in homes

The most common is the house mouse, which can live its whole life as long as it has food and shelter.

"House mice are in the walls, established with their friends hanging out," says Leland Rudner, the SMART program lead at American Pest.

If you find one, there are probably more. The house mouse is typically all grey or brown.

How to keep mice out

Preventing mice from breaking in is a tall order, because they can squeeze through any small opening.

Find any openings such as that in your home, especially near ground level, and plug them.

For holes less than an inch in size, stainless steel, copper mesh or caulk will work.

Mice can also walk through your front door. "If you look at your exterior door and you see daylight underneath, then you need to weatherstrip that door," says Brown.

Mice probably won't stick around without something to eat, so clean up crumbs and put away food. If you have an active infestation, store food in airtight containers.

Otherwise, less extreme precautions - such as closing chip bags with clips - should suffice. Store pet food in sealed containers and remember to get leftovers out of pet bowls.

How to know if you have mice

Mice might be sneaky, but they leave behind some incontrovertible evidence.

The most obvious is their droppings, which resemble dark grains of rice.

Look for those in corners and underneath appliances such as your oven and fridge. Another surefire clue: a box or bag of food that has been chewed through.

Use your nose, too. A mysterious, ammonia-like scent could be rodent urine.

If you smell what Rudner describes as "old deli meat" meets "mould," you may have a dead mouse (or a few).

Frye says his experienced nose comes in handy: "I may go into a restaurant and get a whiff of something and I'll be like, 'Yeah, we're not eating here because there's a mouse problem.'"

You should also trust your ears - don't ignore phantom rustling or scratching in the walls or ceiling, especially at night.

And if your dog has been barking or otherwise focused on one part of the wall, she probably knows something you don't.

House cats often don't prevent a mouse problem, because they're well-fed.

They may kill a few mice for amusement, and there is some evidence that rodents are less likely to set up shop where they smell a predator, but mice are adaptable and can generally work around a cat's nap schedule.

The best way to get rid of mice

The gold standard for trapping mice remains the wooden snap trap, according to pest experts.

"The best thing is the old-fashioned way," says Brown. You'll want a snap that falls through a full 180 degrees of motion, which should quickly kill the mouse.

Never use glue traps - they are ineffective and cruel. Poison is another method to skip.

Animal advocates contend that it causes suffering and if it works, then you've got a dead mouse somewhere in your house that you have to find.

You might be tempted to live-trap and release the mouse, but there are a couple reasons not to.

For a house mouse - which has no experience living outdoors - depositing it outside "may just be death in a different way," says Frye.

There are many other products that promise to rid you of rodents, but be wary.

One prominent option, the sonic repellent, claims to keep mice away with sound, but there's no evidence that it works.

Inventors continue to strive for a better mouse trap - there are thousands of patents related to their design. Yet the snap trap, patented in 1894, endures.

Set and bait mouse traps like a pro

You can't just put mouse traps anywhere and expect results. To determine where to place them, start with the mouse droppings and follow their trail.

"You may find the entry point where [the mice] are coming in, for example, or you may find where they've set up their nest site or where they're finding food," says Frye.

Another thing to look for are marks from the oils in a mouse's fur. These greasy trails are often left behind on walls where mice are routinely squeezing through the same opening.

"The goal is to get the device as close to activity areas as possible," says Frye. Don't limit yourself to the floor, either, because mice surely don't.

You might place traps atop kitchen cabinets or attach them vertically to exposed pipes. "We also recommend using way more traps than you think you need," Frye adds.

The idea that mice prefer cheese is a myth. When it comes to bait, Frye suggests using whatever food you've found the mouse has been eating in your home.

Brown has had success with chicken. Rudner often uses almond or sunflower butter (hypoallergenic alternatives to peanut butter).

Just be careful not to over-bait your trap - that'll make it easier for the mouse to abscond with the food, and too much weight can distort the snap.

When to call a professional

You may have to wait more than a week to have success with your traps. But if it's taking longer than that, you might be out of your league.

Additionally, if you find significant amounts of droppings, you may have a serious infestation that requires expert help.