Outdoor pest pressure drops in winter, but indoor pest activity continues — and some pests actually increase in winter because they've moved inside for warmth. Mice that entered in fall are now breeding in your walls. German cockroaches don't care about the season — they're indoor specialists year-round. And the overwintering pests that entered in September start emerging on warm winter days.
Mice: Peak indoor activity in winter. They entered seeking warmth in fall, and by December they've established nesting sites and are reproducing (6–10 pups per litter, 5–10 litters per year). If you hear scratching in walls at night, they've been there for weeks. Trap aggressively and seal entry points.
German cockroaches: Fully active year-round in heated homes. Winter is actually a good time to treat — with windows closed, gel bait and IGR treatments work in contained conditions. No new cockroaches enter from outside in winter, so treatment results are more permanent.
Bed bugs: No seasonal variation — they feed year-round in climate-controlled bedrooms. Winter travel (holiday visits, ski trips) actually increases bed bug introduction risk.
Spiders: Indoor spiders remain active all winter, hunting prey insects in basements and corners. You may see more wolf spiders as they wander seeking water during dry winter heating.
Stink bugs, Asian lady beetles, cluster flies, and western conifer seed bugs entered your walls in September. On sunny winter days when wall voids warm above 60°F, individuals emerge into living spaces — sluggish, disoriented, and buzzing toward windows and lights.
What to do: Vacuum them up (don't crush stink bugs — the pheromone attracts more). There's no effective treatment for pests already inside wall voids. The prevention window was September — seal exterior gaps this coming fall to prevent next year's invasion.