Why Pests Gather on the Sunny Side of Houses in Fall

Pests commonly gather and climb on the sunny (south or west facing) sides of houses in the fall mainly because they are seeking warmth and a safe place to survive the upcoming cold winter months. The sunny side of a house absorbs more daylight and retains heat longer, creating an ideal environment for pests such as stink bugs, boxelder bugs, ladybugs, and cluster flies. These creatures are trying to find shelter to overwinter—meaning they want to stay alive during the winter when it's too cold for them to be active outside.

When days start to get shorter and temperatures drop in the fall, these pests sense the change and begin moving toward places that will keep them from freezing. They aren’t interested in attacking your home or causing damage at first; they are simply trying to survive. The warmth that radiates from walls heated by the sun acts like a beacon for them. They gather in numbers, crawling up and clustering on exterior walls, especially the sunniest sides, because it’s the last place to lose its heat in the evening and can be significantly warmer than shaded spots.

Once they reach the sunny, warm walls, they start searching for cracks, gaps, or openings—like spaces around windows, doors, siding, vents, or beneath roof eaves. Even tiny openings can serve as entry points. If they find a way in, they hide in wall voids, attics, basements, or other quiet spots inside to wait out the winter. Some might inadvertently become active indoors if your home heats up during sunny winter days.

This behavior is called "overwintering," and it’s a natural part of their life cycle. Different pests may use slightly different strategies, but most of those you see clustering on fall afternoons are trying to protect themselves from the cold by finding the warmest place first, and then a way inside your home next.

How to Reduce Pest Clustering on Your Home in Fall

To limit or prevent this invasion, you can:

• Seal up cracks and gaps around windows, doors, siding, and where utilities enter the house using caulk, weatherstripping, or insulation foam.
• Repair or replace damaged screens on doors, windows, and vents.
• Install door sweeps or thresholds on exterior doors.
• Clear away debris (like leaf piles or woodpiles) from near the foundation, since these also hold heat and attract pests.
• Consider using outdoor pest barrier sprays around the exterior of your home—especially early in the fall before temperatures drop significantly.
• Keep exterior lights to a minimum at night, as these can attract some pests to the area.

By understanding that pests are simply seeking warmth and shelter on the sunny side of the house in fall, you can take steps early to prevent them from entering and overwintering inside your living spaces.