Mice are most likely to enter houses during late fall and early winter. As the weather gets colder, mice start looking for warm places with easy access to food and shelter. Houses, garages, and sheds become very attractive during this time. While mice can enter homes at any time of year, the risk is highest as temperatures drop — typically from October through February.

New Hampshire: Month-by-Month Timeline

In New Hampshire, mice begin entering homes in September–October as nighttime temperatures drop below 45°F. Activity peaks December through February. By April, some mice move back outdoors — but those that have nested inside through winter rarely leave on their own.

NH Seasonal Prevention Calendar

• October: Seal all exterior entry points before the first frost — this is the highest-impact window
• November–February: Check traps weekly; inspect for new droppings or gnaw marks after each major cold snap
• March–April: Inspect for new entry points created by freeze-thaw damage — gaps in foundations and siding often open up in spring
• May–September: Outdoor prevention — manage woodpiles (stack away from walls), seal garbage, clear compost

For a full seasonal approach to pest prevention in NH, see our NH seasonal pest control guide.

Why Mice Enter When the Weather Changes

In the wild, mice live in fields, under rocks, and in woodpiles. When temperatures drop and outdoor food becomes scarce, they seek human homes for warmth, food, and nesting. A house in October is a far more attractive option than a frozen field.

How Mice Get In

An adult mouse can squeeze through a gap as small as a dime (about 6mm). During fall, they actively follow warmth coming from doors, windows, foundation cracks, and gaps around utility lines.

Key Signs Mice Are Trying to Get Inside

• Small droppings near walls, in cabinets, or in drawers
• Gnaw marks on food packaging, baseboards, or wiring
• Scratching or scampering sounds at night
• Nests of shredded paper or insulation in hidden corners

Prevention During High-Risk Months

• Seal all cracks and gaps 6mm or larger with steel wool, caulk, or metal sheeting before October
• Install door sweeps and check weatherstripping
• Store all food and pet food in sealed containers
• Trim shrubs and branches that touch the house
• Clear leaves, woodpiles, and compost away from the foundation

Call Anchor Pest Services at (603) 785-0118 for a pre-winter inspection across Manchester, Nashua, and Concord.

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