How are mice getting in my basement?

I put out traps and get them and then a couple months later they are back. I want to stop them from getting in at all. I don’t see any obvious holes or gaps so how do they get in?

The gaps don’t have to be “obvious.” I believe mice have been alleged to fit through cracks as small as 1/4"

Sent from my SM-T350 using Tapatalk

I’ve greatly reduced mine by “inviting” feral cats to move into the back of my yard under my shed.

Yep. Get a cat.
Mice always find a way in. I’ve heard horror stories about deer camp mice. And there’s that old tale about rats swimming up through plumbing and getting in.

I had bats in my house once, with bodies about the size of the average mouse. An exterminator told me "You are talking about creatures that can squeeze through holes the size of a dime. Mice can get through the tiniest of spaces, maybe even up dry pipes. Once inside I haven’t had an issue because my cat is an excellent mouser. Atilla even got one of the bats.

This is the straight dope, not Fox news. Smallest hole for a mouse experiments

They can get through some pretty small holes but don’t exaggerate.

I took a computer in for repairs. It had a dead mouse in it.* The mouse had to have got in through the place where I put in a 5-1/4 floppy drive, and it was not very big. I’m gonna say between 1/4 inch and 1/2 inch.

This, by the way, was really embarrassing. It also should have really embarrassed the cat I had at the time, but he gave no fucks.

*I did not know there was a dead mouse in there, obviously. Also, the mouse probably didn’t cause the problem I took the computer in for. Oddly enough.

If the hole isn’t big enough, mice are also pretty good at chewing through things. Like your dryer vent, and then the tube thing attached to the dryer, and then they’re in your house.

I hate rodents.

We live in an old farmhouse with quite a few add-ons in terms of rooms and porches, and most of those improvements were not done by professionals. Many were also done long ago when they did not have the better materials and methods that are available today. In other words, they weren’t necessarily “tight” and they didn’t exactly conform to standardized practices.

The basement and/or crawlspaces tend to be ground zero for entry. From there the critters can pretty much get just about anywhere in the house by running along plumbing and wiring, finding a tiny opening along the way, and entering into a room.

Mice can jump about a foot high and they tend to run along the foundation of the house to find an opening. One night I was coming from work and pulled into my driveway only to have my headlights hit just right and see a mouse jump up and disappear under the siding where it meets the foundation. That’s something you only need to see once. It makes an impression.

Oy. Mice will exploit any opening. They are not a big problem during the summer but, when the weather turns cold, they come in and bring their friends. Or, they make new mice.

We finally hired a pest control service and they just finished installing an exclusion system along the foundation where the siding meets the foundation. They also baited outdoors along the foundation and set a lot of traps in the basement and on the first floor where walls have been taken down and floors have been dug up. We’re slowly remodeling.

Of course, it’s summer now, so they only caught one mouse over the course of a week of trapping. The real test will start over the next few months as mice look for a place to shelter when the weather gets cold. We rarely see signs of mice during the summer.

The thing about the exclusion system is not just having the hardware installed, but it allows you the opportunity to find the vulnerable places that you never would have looked for previously. For example, under a small porch there was a sizable hole in the old masonry that provided a wonderful opportunity for entry. We fixed up quite a few vulnerabilities that we normally would not have seen.

In addition to the other suggestions, once the mice are in, look for any openings in the walls near electrical outlets. Is there a spot where maybe molding was taken down, thus providing a point where mice can enter the room once they make their way up the wiring? Did someone make some repairs on a wall and leave an opening?

Check the plumbing that is behind the cabinets where pipes come in and out. Sometimes people replace or fix a pipe and don’t seal the hole around the pipe. Mice love that.

Also, don’t neglect to check the plumbing lines that lead to dishwashers and washer/dryers and other appliances. Just make sure that there are no openings around the pipes where they go into the walls or floors.

Another thing you might want to consider is keeping your foundation plants to a minimum. They provide an excellent hiding place for mice and other critters. They also provide climbing opportunities. Mice will climb for a certain amount of distance. No need to give them additional boosters. If you use a wood mulch, mice tend to like that too.

Don’t neglect attached garages. It’s easy for mice to enter through garages since the doors are frequently opened and closed and garages aren’t as closely monitored as the rest of the house.

About that cat thing - some cats help and others are useless hunters. It’s a crapshoot. I’ve had both types of cats, but even cats will only catch the low-hanging fruit. It’s the ones they don’t catch that you have to worry about.

Ultimately, though, mice are a fact of life. They’re going to be around no matter what. Even the most fastidious people have mice at some point. I still hate them and don’t want to deal with them, let alone see them. I share your revulsion to the accursed nuisances.

Australian mouse plague

I used to have a problem with mice in my basement. There is a farmer’s field right behind by house. One day I was outside and noticed that there was a slight gap in my wall, at the hole where the air conditioner cables ran. I filled this gap with that expanding foam in a can stuff, and in the dozen or so years since, have seen no mice in my basement. It really is amazing how small a gap a mouse can squeeze through.

I put out traps and check them periodically. If I haven’t caught anything after six months, I collect the traps, clean them up and rebait them. If you wait until you “have mice” to set your traps, you’re doing it wrong (at least if you live in the country, like me).

I use the same approach for flea control on our dogs. I apply a product periodically; not because they have fleas, but to maintain their flea-free state.

Sure, stuff any crevices with steel wool, etc, but stillassume you haven’t totally sealed off your living space.

My cat brings them in from outside. Alive. She thinks she’s helping.

How did they do the exclusion system ?

If you burn wood, mice like woodpiles. So…in turn snakes like woodpiles. :eek: I set all wood on the deck for half a day before I bring it in. If it’s looking like rain I bring it in the garage. And set mouse traps. I’ve caught many mices, like that. We have a barn cat. But she/he is overworked, no time for the woodpile.

According to your link, the experiment showed a mouse going through a 17.5mm hole, and shrew fitting through a 17mm hole.

A dime has a diameter of 17.91 mm - why would you say Baker was exaggerating?