3 min read · Updated 2026-09-05
Mice do not hibernate. As overnight temperatures fall and outdoor food becomes harder to find, they look for warmth, shelter and a reliable food source — and a heated house is the best option within reach.
What makes fall different
- Overnight lows drop into the 40s, and rodents shift from field and woodline habitat toward structures.
- Summer populations have grown all season, so more animals are competing for shelter.
- Harvest and leaf drop remove cover and food in fields and hedgerows.
- Homeowners start using fireplaces and closing up seasonal spaces, which is when noises get noticed.
Where they get in
A house mouse can fit through a gap roughly the width of a pencil. The usual openings are utility and pipe penetrations, gaps under garage and basement doors, damaged soffit and gable vents, dryer vents, and settled gaps at the sill plate where the framing meets the foundation.
On older Hudson Valley homes with fieldstone foundations, small mortar gaps can create a continuous path from grade into the basement.
Get ahead of it
Late summer is the best time to seal. Once activity starts inside, exclusion still matters — but it needs to be paired with removing the animals already in the structure.