Overwintering Pests in Western Wisconsin: Why They Invade Your Home in Spring

The answer is overwintering pests.

These pests spend the cold winter months hiding inside walls, attics, and other protected areas of homes and buildings. As temperatures warm up in late winter and early spring, they begin waking up and searching for a way back outside — which is why homeowners suddenly start seeing them.

Here are some of the most common overwintering pests in Western Wisconsin and why they choose your home.

Boxelder bugs are one of the most common overwintering pests in the Midwest. In the fall, they gather in large numbers and squeeze into tiny cracks around siding, windows, and soffits to escape freezing temperatures.

During warmer days in late winter or early spring, they become active again and often appear around:

• Windows
• Light fixtures
• Walls
• Ceilings

While they don’t cause structural damage, they can become a major nuisance when large numbers emerge indoors.

Often mistaken for regular ladybugs, Asian lady beetles are another pest that looks for warm shelter during the fall months.

They gather on sunny sides of buildings before entering through small openings in siding, vents, and window frames.

Once inside, they remain dormant until warmer temperatures wake them up. In spring, homeowners often notice them gathering around windows as they try to find their way outside.

Cluster flies are a common overwintering pest in rural areas throughout Wisconsin.

These flies enter homes during the fall and hide in:

• Attics
• Wall voids
• Crawlspaces

Unlike house flies, they move slowly and often appear in groups near windows once temperatures rise.

Cluster flies don’t reproduce inside homes, but they can become annoying when large numbers emerge all at once.

Many species of spiders also spend the winter inside homes.

Spiders enter buildings in the fall to escape cold temperatures and remain hidden in quiet areas such as:

• Basements
• Garages
• Storage areas
• Attics

They usually become more visible in early spring as they search for food and mates.

Homes and buildings provide the perfect winter shelter for insects because they offer:

• Warmth
• Protection from snow and freezing temperatures
• Small cracks and entry points
• Quiet, undisturbed spaces to hide

Even small gaps around windows, siding, and foundations can allow pests to enter.

The best time to prevent overwintering pests is actually late summer and fall, before they begin looking for shelter.

Helpful prevention steps include:

• Sealing cracks and gaps around siding and windows
• Repairing damaged screens
• Installing door sweeps
• Treating exterior walls where pests gather

Professional pest control treatments can also create a barrier that helps stop these pests before they move indoors.

If you're noticing pests appearing in your home this spring, there's a good chance they spent the winter hiding inside your walls.

Professional pest control can help identify entry points, eliminate pests, and prevent them from returning next season.