Mice only need the tiniest of spaces to squeeze their way into your home. Zach Ciras, Quality Manager with Colonial Pest Control, talks about how to prevent a mouse infestation, as well as what to do once mice take over. Listen or read more to find out how to control mice in your home.

John Maher: Hi, I’m John Maher. I’m here today with Zach Ciras, Quality Manager with Colonial Pest Control. Today our topic is controlling mice in your home. Welcome, Zach.

Zach Ciras:  Good morning, John.

John: Morning. So, Zach, when you get called out to a house that has a mouse problem, what are some of the first things that you do?

Zach: Well, our job really starts before we even get to the house. We’re looking at the neighborhood, we’re looking at what kind of trees are around, what kind of garbage might be piled up. Is it suburban, is it urban? What kind of environment are we dealing with? And that already starts to influence what questions we’re going to go in with to talk to the homeowner. When we get to the house, obviously we want to say hi to the homeowner, see why they called. Sometimes they called because they heard a noise in the attic and they thought it was mice.

Well, we want to get an identification on is it mice, is it squirrels, is it bats, is it something else? Occasionally it’s an errant cable wire or a tree limb that’s brushing against the roof of the siding that they hear. But first thing we want to do is find out what we’re dealing with, get a proper identification. And as I said, as we’re pulling up to the house, we’re looking at the structure, we’re looking at the neighborhood. If we go to a house, I’m pretty sure it’s mice already. We knew when we spoke with them on the phone before we got there, and they described what they had been seeing or hearing and we go, “Okay, yeah, it’s probably mice.” Look at the structure and what kind of structure, how old is it? Have there been additions? I know if I . . . if I know it’s mice pulling into a driveway and there’s a nice house, but there’s a breezeway and a garage and an addition, I know where I’m going to look to find entry points where the mice are getting in.

Mouse Hiding Places

John: What are some of the typical places . . . when you’re looking at an addition like that, what is it that maybe didn’t happen to kind of seal it up properly?

Zach: Yeah, when you have two different concrete pours especially, the secondary concrete pour tends to sag a little bit as it cures. They don’t get quite as much in there to really level it off in all the corners. And for a contractor for structural purposes, it’s perfectly fine. But a contractor might see a quarter of an inch as a success, and a mouse sees a quarter of an inch gap between the new concrete pour and the old concrete pour as an opportunity.

John: So, what’s the next step after you . . . you get to the house, you assess the situation, maybe you see some of those immediate problem areas. And then what do you do after that?

Zach: Well, mice I like to say are bad criminals. They are . . . they’re always leaving evidence behind, and if you look at the evidence, they’ll show you exactly where they’re going. They always return to the scene of the crime.

So, we’re going to do a thorough inspection inside the house, especially the basement; up along the sills is the most popular place for mice to travel and run, because again, they’re coming in from the outside. Typically, it’s 80 to 90% of the time at the foundation level. So, they’re going to run along the foundation up on the sills, on the inside of the basement, and look for pipe chases, wire chases, other voids they can scurry up and see where that goes. And if they find something good, they’re happy. So up along the basement sills, look for rub marks. They have a coating of grease on their coat, on their fur, just like any animal, a cat or dog. I have three cats, and the cats always rub against the same part of the corner of the wall. And if we don’t keep up with it, there’s a little blackish stain that starts to happen from the grease.

Mice are covered in that grease too. They need to squeeze into small openings, and they have that grease on them partly to help lubricate them, partly to help protect them from the outside world. So that sebum or those grease marks that we see, they’re a key indicator of where the mice are running. Basement sills, like I said, is a common spot. Attic is another common spot, because the envelope of the house is kind of open as a void from the basement through the wall voids into the attic.

And then with talking to the customer, are they hearing something or are they actually seeing something? If they’re seeing something, it’s typically where a lot of conduits empty out, where you have pipes and wires that go into, say, the kitchen under the sink, under the dishwasher, behind the stove. So, we give a good inspection to those areas as well as inside the garage where there might be other openings, and see where they’re traveling, kind of see what the whole scheme is, what numbers we might be dealing with, and we can base that on are there food sources stocked up? Are we finding piles of acorns or dog feed or bird feed? Are we finding a lot of rub marks and sebum staining? Are we finding piles and piles of droppings, or could it be something new that’s going on?

So those are the signs we’re looking for, just to get an overall picture of the house and the mouse infestation inside the house.

Tight Seals Prevent Mice from Entering

John: One thing that you just brought up was your appliances, like your dishwasher and even your sink and things like that, where you’ve got pipes that are coming up from underneath maybe a basement, and then they’re coming up through the floor. If I’m having something like a washing machine installed, is there anything that I can do to ask the installers, “Hey, I really want to make sure that I don’t have mice coming up from the basement. Can we please make sure that these holes are not very big or that they’re sealed up really properly before you get that washing machine pushed into the wall?”

Zach: Oh yeah, for sure. Yeah. Yeah. Everything needs to be tight. A mouse doesn’t need much room. They say quarter of an inch to get their nose in. And the mouse head is the widest bone in its body. They don’t have what we call a true collarbone, so our collarbones are connected to our shoulders, and we can only squeeze them in so far, which still sticks out wider than our head. They don’t have a true collarbone. So, a mouse, as long as they can get their head in there, their skull’s the widest part, everything else they can kind of wiggle in.

It’s funny when you see the ones who’ve been dining very well. There’s videos of these. They get halfway through the hole, then they hit their belly and they just kind of have to shimmy and shimmy. It’s almost like they’re looking for a stick of butter to help them through. But anyway, sealing up those holes as tight as possible. A quarter of an inch is what they need.

I think if you give them an eighth inch, and they can get their claw in there and start to scratch and then get their teeth in there and start to gnaw . . . I guess “rodent” means “to gnaw”, from the Latin, so they will gnaw. They’ll make any hole as large as they can. Making that as tight as possible, especially if they can make it so that there’s no air flow between the void and the living area, because the mice have very sensitive whiskers. Terrible vision, but excellent whiskers. So their whiskers do most of their sensing for them, even to the point where if there’s a mouse in one corner of the room, you enter the room, the mouse is not going to be able to see you, but the mouse will feel the air pressure change as you enter the room.

John: Wow.

Zach: So that’s how . . . their whiskers are so sensitive and so important for them, so if they feel there’s air flow between where they are and where the yummy stuff smells, they’ll sense that there’s something to work for. So, they’ll start scratching and gnawing and chewing and trying to get through. So, air tightness is very important. All those appliances, especially around electrical, because the worst thing that you could do is have a little bit of an airflow between the electrical and the void where the mouse wants to come out from, and then the mouse starts to chew and then doesn’t know if it’s chewing on the drywall or the electrical. And that could be a major issue going forward.

Mice Can Destroy Homes

John: Right. That can actually cause fires, right?

Zach: Exactly. A lot of home fires that . . . I don’t know how they come up with this statistic, but the large portion of unexplained home fires are suggested to be due to mice.

John: Wow, that’s really interesting. Can you ever really get rid of all of the mice in your house and keep them from coming back? Or if you have mice in your house and you’re in that type of a neighborhood where there’s mice around, they’re just always going to get back somehow.

Zach: Well, mice are always going to be there. Mice are always going to be, at least on the outside. And there’s natural means to control the population with the birds of prey. And the birds of prey are doing very well right now. All the foxes and coyotes that might eat small animals like that. Even shrews will eat mice. Other things will eat mice. So, they’re always going to be a population around the exterior of a home or a neighborhood. But the reason we build homes is to keep nature outside. We love nature. Everybody at Colonial, we’re like dog guys, cat guys. Everybody loves the animals. And we have a woman who works for us, she has frogs and lizards, and we really get into this stuff. I spent last weekend, a couple of hours, walking around my yard taking pictures of the different pollinators.

We love nature, but we love life inside the house as well. You know, families, wives and kids and all that kind of stuff. We like maybe even more than the life outside and the life inside, we liked that no-go zone in between. So, the outer envelope of the house separates us, so that . . . good neighbors are made by good fences. We can enjoy the life inside and outside as long as you have that good barrier in between. And to point with the dishwasher and the washer and dryer, even more important than sealing off those interior potential entry points into where you are from a void, they’re still inside the envelope of the house. So, the number one thing to do long term is to try to seal off as best possible the outer envelope of that house.

And at Colonial, we do have a full exclusion program. Our standard mouse program does a … We do some minor exclusion with that, and if the house qualifies, and by that I mean if it’s possible to seal off the outside of the house and I’ll get back to that in a second, we have a full program where we’ll spend some substantial amount of time with some really good long-lasting hard materials to fully seal off the outside of the house. And I mean ground to chimney. If there’s an exposed chimney, the whole roof might be opened up because the mice will crawl straight up the chimney like it’s flat earth and get onto the roof. Any weak points on the roof, they’ll also go into and start to exploit to get inside the house. So, our exclusion program really covers everything and makes it bulletproof for mice.

Exclusion Program to Prevent Mice Infestations

John: That’s really interesting, so you just brought up an interesting point, which is you said that some houses will qualify for that full exclusion where you’re able to completely seal up the house, and then maybe some houses don’t qualify for that. What’s the difference?

Zach: Yeah, so a house that qualifies is typically going to have a poured concrete foundation, is going to be in pretty good shape. The siding, whether it’s wood or vinyl, is in good condition, doesn’t need to be replaced. The roof is in fair condition or good condition, especially if there’s a hard ridge vent rather than one of the newer, cheaper soft plastic ridge vents. That’s at the peak of the house. A lot of times you’ll see that little cap. It looks like it’s just a little cap of siding, but there’s actually a vent in there to help with air flow in the attic. If that’s a soft, weak plastic, some of the cheaper ones, the mice can actually still get in there by chewing through the plastic ridge vent. But typically, a more modern house, anything that has a poured concrete foundation and access to the entire exterior perimeter of the house, that’s a perfectly-qualified house for a rodent exclusion.

Something that might not qualify would be if the house has a fieldstone foundation that needs to be repointed. So, fieldstone foundations, if it’s been repointed, repointing would be making sure that in between the stones, the mortar is in good shape. Occasionally, every, I don’t know, 10, 15, 20 years, a house with a fieldstone foundation will need to have a mason come out, scratch away the mortar that’s falling apart, the concrete that’s falling off the stones, clean it off and then apply new mortar or concrete to really seal off the house. If that’s in good shape, we can still do a full exclusion.

A lot of the older homes especially . . . Manchester, Worcester or Boston/Framingham area, where you have the three-families that are all tenements, all rentals . . . a lot of those foundations, especially under the front porch, haven’t been repointed in a while, and at that point, I would say I think you want to take that money and put it towards a good mason to seal off the foundation, then let us come back and reassess how things are at that point. But without sealing off the foundation, a fieldstone foundation or even a crumbling brick foundation, our efforts might be in vain.

Traps, Baits, Poisons: Are They Effective?

John: Right, you’re just going to go in there, you can put some traps out, you can put some bait and poison out or something like that, maybe kill some of the mice that are in the house, but then you’re just going to get more coming back in.

Zach: Exactly, yeah. We should still be able to control the existing population and warranty it for between three and six months. Maybe have to make a couple of return visits if there’s a high population, a lot of pressure coming in. We should still be able to get control of the situation, but for long-term prevention and bulletproof the house, that’s when we need to maybe have assistance from a mason. Sometimes it’s even a carpenter or a handyman that needs to bore it off underneath the raised porch that has a lot of access points, or replace some lower siding that has some water damage on it.

I’m thinking of a house right now. It’s somewhere in north central Massachusetts. In the back of the house, it’s vinyl siding, but the back of the house, you can only see a few inches of the foundation and a lot of water from the gutters or from the roof splashes back on that, so the sheathing, which is basically particle board underneath that, was constantly getting wet. And we did a mouse treatment there and we had pretty good success initially. Then they came back, and then we had good success again. Then we had to come back. It was that the water damage to the sheathing underneath the siding was exposing weak points where the mice knew if I just scratch a little bit, that particle board is going to fall apart, and then we’ll be able to get inside again.

So, that was a situation where we had to really think outside the box, and we could shore that off as well as long as we could figure out what the issue was. And at that point, it was water. We were able to take care of that ourselves with some tin flashing. But a carpenter might’ve been good there too to pull off some of that siding and replace it with a good longer-lasting wood and really waterproof that as well.

John: Right. All right. Any other thoughts, Zach, on mouse control and maybe some of the issues that are involved in it?

Zach: Yeah, I would say for mouse control, it’s not hopeless. A lot of folks, especially who live outside of cities, they just . . . “We live in the country, we’re going to have mice. It’s a normal thing. My husband’s been putting out traps for 30 years.”

You know, I’m sure your husband’s getting sick of it, and it’s something that in most cases we can not only control, we can not only provide a short-term solution or recurring maintenance-based solution, in a lot of cases with our full exclusion program, we can solve the problem. And for my two cents, solving a problem for the long term is much better for so many reasons: the fire, the health, the disease and vectors that they might be carrying, the ticks that might be on . . . it’s all just the overall ickiness of having nice in the house. If we can solve a problem, I think that’s the best way moving forward to have the life outside, stay outside, and the life inside, happier.

John: All right, that’s great advice so Zach, thanks again for speaking with me today.

Zach: My pleasure.

John: And for more information, you can visit the Colonial Pest Control website at or call 1-800-525-8084. That’s 1-800-525-8084.