When do mice come inside on Long Island?

The trigger is cold nights, not the calendar. A mouse living in the mulch beds and under the deck all summer has no reason to come inside until the first run of nights in the 40s, which on Long Island usually lands in the first half of October. Then every gap at the foundation, garage door seal, and utility entry becomes a front door. By November the ones that found a way in have settled into the basement, the garage wall, or behind the kitchen cabinets, and that's when people hear them.

Mice can fit through a hole about 1/4 inch across, the width of a pencil (CDC). The usual entries are where pipes, cables, and gas lines pass through the wall, the gap under a garage door, cracks at the sill plate, dryer and crawl space vents, and gaps at the roofline where tree limbs touch the house. Plastic, foam, rubber, and wood all get chewed through; only steel wool with caulk, or metal, holds (CDC, UC IPM).

A female house mouse can produce 5 to 10 litters a year of 5 or 6 pups, and the young can breed at 5 to 6 weeks (UC IPM). Two mice in October is a population by January. They don't leave in spring either; a house is a better home than a mulch bed.

The homes that get hit first are 1950s and 1960s splits, ranches, and capes with attached garages and original foundations, which describes most of Nassau County, and older wood-frame houses near the North Shore harbors with fieldstone basements. Sealing before October is the whole game; trapping after is cleanup.