Crawl spaces, garages and wall voids give pests shelter through the cold months. Iowa State University names deer mice, white-footed mice and the fall invaders as the species that move indoors in autumn. Sealing the openings and clearing the stored materials before cold weather is the most useful preparation.
Key takeaways
- Deer mice and white-footed mice move into buildings in autumn, according to Iowa State University.
- Fall invaders such as boxelder bugs and lady beetles seek shelter on sunny walls and gaps.
- Exclusion is the preferred method, with openings about a quarter inch or larger sealed.
- Stored boxes, firewood and damp materials give pests cover in garages and crawl spaces.
- Moisture in a crawl space draws insects and can support other problems, so ventilation and ground cover matter.
- This guide gives no temperature, snowfall or freeze date, since climate figures are not sourced here.
Which pests use crawl spaces and garages in winter?
The seasonal mice use crawl spaces and garages as they move indoors. The fall invaders gather in the gaps and voids where they can overwinter, and stored food pests may find the garage storage area.
Iowa State University Extension describes the deer mouse and the white-footed mouse as seasonal visitors to buildings, and the house mouse as a year-round resident. The first two look for shelter as the weather cools, and a garage or crawl space with an open gap is an easy route.
Boxelder bugs and multicolored Asian lady beetles are the fall invaders that ISU names. They gather on sunny walls in autumn and wander into buildings through small openings, where they can spend the winter in wall voids and ceilings.
Why are crawl spaces and garages attractive to pests?
They offer shelter, a stable place out of the wind, and often stored materials or food. A garage door that does not seal and a crawl space vent that is open give pests a direct route, and the stored boxes give them cover.
The garage is a common meeting point between the outside and the house. Its door, its window frames and the gap where the garage meets the rest of the building all give access. Stored bird seed, pet food, firewood and cardboard give pests food and nesting material.
A crawl space has a different set of attractions. It is shaded and often damp, and its vents, the gaps at the sill plate and the openings around pipes give pests access into the structure above.
What should I seal before winter?
Seal the gaps around the garage door, the window frames, the foundation joints and the places where pipes and wires enter. Repair or replace door sweeps and check the vents. Exclusion is the first step, and it is the step Iowa State University recommends.
A garage door seal and a door sweep that meets the threshold reduce the most usual entry point for garage pests. The gap where the garage meets the house, and any opening in the wall between them, should be closed as well. Screens on vents and windows should be checked for holes.
In a crawl space, the sill plate and the rim joist are the key points, along with the vents and any pipe penetration. A technician checks those points and explains which sealing is most useful for the building.
How should I clear a garage or storage area before the cold?
Move stored items off the floor and away from the walls, store food in sealed containers, and clear firewood and debris from the foundation. A tidy storage area is easier to inspect and gives pests less cover.
Cardboard boxes are a favourite nesting material for mice, and they hold moisture if stored on a damp floor. Replace them with plastic containers with lids that seal, and keep bird seed and pet food in sealed containers away from the walls.
Firewood should be stacked away from the house and off the ground, since it can hold insects and gives mice a route to the foundation. Leave a clear space around the foundation so the outside can be inspected.
Does moisture in a crawl space matter for pests?
Moisture draws insects and can support other problems in the structure, so a damp crawl space deserves attention. Ventilation, ground cover and drainage are the usual matters to check, and the technician can point out the conditions present.
A damp crawl space can attract insects that feed on moisture-loving material and can make the wood more attractive to pests that feed on it. The source of the water, such as a gutter that overflows near the foundation or a drainage problem, should be found and corrected.
Ground cover and vents affect how the space holds moisture. A technician will explain the conditions found and say when a contractor should look at drainage or ventilation.
What signs show pests have already moved in for the winter?
Droppings in a corner of the garage, rub marks along a pipe, chewed packaging, insects gathering in a warm room and noise inside the wall all point to pests that have settled for the season.
Mice leave droppings that are dark and small, and their rub marks are greasy and repeated along the same route. Chewed packaging and a nest of shredded material in a storage corner show that the animals have been there for some time.
Insects in a warm room on a sunny day can mean they have been overwintering in the wall. Those signs call for a visit before the spring, when the activity tends to increase.
When should I call a technician for winter pests?
Call before the cold sets in if you can, since sealing is most effective before the animals move in. If the pests are already inside, a visit can still remove them and close the routes, and the technician will explain the timing.
A visit in late summer or early autumn lets the sealing be done before the seasonal mice arrive. A visit later in the cold months can still remove the animals inside, and it can close the routes so the spring does not bring new ones.
Calls to Des Moines Pest Control are answered 24/7 in Des Moines, and a same-day visit is offered when a technician is free. The price is confirmed on site before any work starts.
What does a crawl space inspection look for?
A crawl space inspection looks at the sill plate, the rim joist, the vents, the pipe penetrations and the ground cover. It notes signs of pests, moisture and any opening that lets animals or insects in.
The sill plate and the rim joist are where the house sits on the foundation, and gaps there give access to the structure above. Pipes and wires that come through the foundation often leave openings. Vents admit air, and an unscreened vent admits animals as well.
Ground cover, such as a vapour barrier, reduces moisture rising from the soil. The technician notes whether the cover is present and in good condition, and explains what the findings suggest.
Why does a garage need the same attention as a house?
A garage is the outside edge of the living space and often holds stored food, firewood and cardboard. Its door seal and the wall it shares with the house give pests a route in, so the garage belongs in the inspection.
A garage door that does not seal at the bottom or a gap at the top of the frame is an open route. Stored bird seed and pet food draw pests in, and stacked cardboard gives mice a nest. Clearing the garage is part of the winter plan.
The wall between the garage and the house should be checked for gaps, particularly around the pipes and wires that pass through it.
What is the homeowner's part before the cold?
Clear the crawl space access, keep the vents clear, store food in sealed containers and clear firewood from the foundation. Note any damp spot or drip for the technician, and fix any leak you can reach.
Keep the crawl space access clear so the technician can reach the sill plate and the vents. Make sure nothing is stored against the foundation, where it blocks the outside inspection and gives pests cover.
Fix a drip or a leaking pipe where you can. Water in a crawl space draws insects and can support other problems, so a dry space is easier to keep clear.
How do I know the crawl space is clear for the winter?
A clear crawl space has sealed openings, screened vents, dry ground cover and no stored items against the foundation. A technician checks each of those points and records what remains open.
A check made in late summer lets any open gap be closed before the cold. The vents should be screened, the access hatch should close tightly, and the ground cover should be intact. Items stored against the foundation should be moved.
Ask the technician to note any point that cannot be sealed from the inside and to explain the options. The record of the check gives you a baseline for next year.
Frequently asked questions
Do mice really move into garages in the fall?
Iowa State University says the deer mouse and white-footed mouse move from outdoor cover into buildings in autumn. A garage with an open door seal or gaps in the walls can be a route in.
Should I put poison in the garage?
Poison bait is not a substitute for sealing and removal. Place any product out of reach of children and pets, and ask the technician what is appropriate for the garage and the household.
What is the best way to stop boxelder bugs in winter?
Exclusion comes first. Iowa State University recommends tight windows and doors, screens and sealed gaps. A barrier treatment on the sunny walls is timed for September to mid-October, before the insects enter.
Does a crawl space need a pest visit every year?
Not necessarily. A visit once a year or after a change in the house, such as a new vent or repair, can check the sealing and the conditions. The technician sets the schedule based on what is found.
Can I seal the crawl space myself?
You can seal small gaps at the foundation if they are easy to reach. The sill plate, the rim joist and any damp area need a careful look, and a technician can check them safely.
Is a cold garage free of pests?
Not necessarily. Garages can hold stored food and shelter that pests use through the cold months. The technician will check the garage along with the house and the crawl space.
Sources
- Iowa State University Extension, Crops: fall nuisance invaders
- Iowa State University Extension, Natural Resources: mice damage management
This guide is general information for Polk County homeowners, not a substitute for an on-site inspection. Prices are estimates. See our disclaimer.