Fall Pest Guide
Cluster Flies and Boxelder Bugs on Sunny Walls: What Colorado Springs Homeowners Should Know
Every fall, flies and red and black bugs gather on the warm sides of houses. They are trying to get inside for winter. Here is how to keep that number low.
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- Document signs and affected areas
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- Use qualified medical or veterinary care when needed
Fall Pest Guide
Fall Invaders in Colorado Springs
Written by Preventative Pest Control for Colorado Springs, Fountain, Monument and Pueblo homeowners.
Cluster flies and boxelder bugs are "overwintering" pests. They spend the summer outdoors, then in fall they gather on south and west facing walls and slip into attics, wall voids and window frames to wait out the cold. On warm winter days, some wake up and wander into living space.
How to tell which one you have
- Cluster flies look like slightly larger, slower house flies. They gather at upper windows, often in rooms that are not used much, and buzz against the glass.
- Boxelder bugs are about half an inch long, black with red or orange lines. They cluster on sunny siding, fences and window frames, especially near boxelder and maple trees.
Why they pick your house
These pests are drawn to warmth and to light colored, sun facing walls. A house is not "dirty" because cluster flies or boxelder bugs show up. Gaps around windows, siding, soffits and attic vents are what let them get inside.
What you can do now
- Check window screens, door sweeps and gaps around window frames on the sunny sides of the house.
- Vacuum bugs and flies that come inside instead of crushing them; boxelder bugs can stain surfaces.
- Rake up fallen boxelder seeds near the foundation.
- Notice which walls they gather on and when. That decides where treatment and sealing matter most.
Timing matters
The best time to reduce fall invaders is late summer and early fall, before they move into the walls. Once they are inside wall voids, the goal shifts to limiting how many reach living space during winter and planning earlier treatment for next season.
When to call
Call when large groups gather on the house every fall, or when flies and bugs keep appearing inside on warm winter days. Learn more on our boxelder bug control and fly control pages.
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