In Illinois, fall is the most important season for pest prevention. As temperatures drop, dozens of pest species actively seek warm shelter — and your home is the most appealing option for miles around. The good news is that most of what makes a home vulnerable to winter pests is fixable before the season starts.
Which pests move indoors in winter?
- Mice and rats — The most damaging winter pest. Mice can squeeze through a gap the size of a dime; rats through a quarter-sized opening. They nest in walls, attics, and behind appliances, chewing through wiring and insulation.
- Stink bugs (brown marmorated) — Non-damaging but intensely annoying. They congregate in warm walls in fall and emerge throughout winter when temperatures fluctuate.
- Spiders — Many species move indoors in fall seeking warmth. Most are harmless; the occasional brown recluse is not.
- Overwintering cockroaches — German cockroaches especially prefer the warmth of kitchen and bathroom walls year-round.
- Boxelder bugs — Congregate on south-facing walls in fall and infiltrate through tiny gaps around windows and doors.
The most important thing you can do: seal entry points
No pest can get in without a way in. A thorough exterior inspection in September or October — before temperatures drop below 50°F — is the single highest-impact thing you can do to reduce winter pests.
Walk the entire perimeter of your home and look for:
- Gaps around utility pipes and wires where they enter the foundation
- Cracks in the foundation, especially where it meets the sill plate
- Spaces under exterior doors (a gap you can see light through is too large)
- Vents that lack screens or have damaged screens
- Gaps around window frames and door frames
- Openings in the soffit and roofline where squirrels can enter
Use copper mesh, steel wool, or hardware cloth to fill gaps before sealing with caulk or expandable foam. These materials are non-compressible and non-chewable — unlike foam alone, which rodents can bite through.
Reduce attractants before winter
Even a perfectly sealed house is more attractive to pests if it offers food and water. Before winter:
- Move firewood stacks at least 20 feet from the house (they're a prime rodent habitat)
- Clean up leaf litter and debris from your foundation — these create harborage for pests looking to overwinter
- Bring pet food and bird seed inside overnight, or use sealed metal containers
- Fix any dripping faucets or leaking pipes — moisture attracts cockroaches and silverfish
- Clean your gutters so water drains away from the foundation
When to call a professional
If you've already found evidence of rodents — droppings, gnaw marks, or sounds in the walls — DIY prevention isn't enough. At that point, you need a professional to locate the entry points, eliminate the existing population, and seal against re-entry. The longer you wait after finding evidence, the larger the population grows.
A single mouse can have up to 10 litters per year, with 6 pups each. One pair of mice in October can become dozens by January if left untreated.
