Why mice come in every October, and the gaps they use

Every fall the same phone calls start. Something is scratching in the wall at night, there are droppings in the back of a kitchen drawer, and the house was perfectly quiet in August. Nothing changed inside. What changed was outside.

It is about temperature, not housekeeping

Once nights drop into the 40s and 30s, stone walls, brush piles, and woodpiles stop being comfortable. Mice are small and lose body heat fast, so they go looking for a spot that is warm, dry, and close to food. A house offers all three. A spotless house gets visitors too. Tidiness changes how many stay and how long, not whether they check.

The timing is also why the problem feels sudden. Mice have usually been living in the leaves and mulch around the foundation all summer. The first real cold simply moves them from the edge of your property to the inside of it.

The gap is smaller than you think

A house mouse can get through an opening roughly the diameter of a pencil. Their skeletons compress, and they will chew at an edge that is almost big enough until it is. If you can slide a pencil into a gap, assume a mouse can follow it. That standard turns up a surprising number of openings in an ordinary New England house.

Where they get in

• Where gas, electric, cable, and phone lines enter the house, especially if the hole was cut larger than the line
• The bottom corners of the garage door, where the rubber weatherseal wears thin or curls
• Bulkhead cellar doors that no longer sit tight against the frame
• The joint where clapboard or trim meets the top of the foundation
• Dryer and bath fan vents with broken flaps or missing covers
• Gaps around pipes under the kitchen sink and behind the washer
• Loose mortar in fieldstone foundations, which can leave gaps big enough to walk through
• Soffit and roofline openings reached by tree branches or porch roofs

Walk the outside of the house slowly with a flashlight, even in daylight. Look low, near the foundation, and then high, where the eaves meet the walls. Mice climb brick, stone, and rough siding with no trouble, so a high gap counts as much as a low one.

Signs you already have a guest

Droppings are the most reliable sign: dark, about the size of a grain of rice, often found along baseboards, behind appliances, and in the back of cabinets. Other signs include chewed cereal boxes or bags of pet food, nests of shredded paper or insulation tucked in a quiet corner, greasy rub marks along walls where they run the same path each night, and a stale, musky smell in closed spaces.

Noise is the other giveaway. Scratching or light scurrying in a ceiling or wall, usually at dusk or in the middle of the night, is typical. Mice are most active when the house is quiet.

What you can do this weekend

• Pack coarse steel wool tightly into small gaps and seal over it with caulk, since mice chew through foam and soft sealants on their own
• Replace worn garage door seals and install a sweep on any exterior door where you can see daylight at the bottom
• Move firewood and brush at least a few feet from the house
• Store pet food, birdseed, and grass seed in lidded metal or heavy plastic containers
• Trim branches that touch the roof or siding
• Rake leaf piles away from the foundation and the bulkhead

Why sealing alone can leave a problem behind

Here is the catch with a weekend of caulking. If a mouse is already inside, sealing the outside traps it in with you. Mice breed fast, so a pair that moves in during October can be a crowd by midwinter. Seal as you go, but if you are already seeing droppings or hearing noise, the right order is to deal with what is inside first and close the entrances after.

It also helps to keep a running note of where you find signs. Droppings clustered in one corner of a cellar usually point toward the entry, since mice tend to travel the same routes along walls.

Mice and rats are both on the list of pests Integrity Pest Control handles around Johnston, and the family's own motto is "If you wish it, we will squish it." If you have found signs or you would simply like someone to look over the gaps before winter sets in, call (401) 467-3344 and ask about an inspection.