Those pesky flies that congregate on your windows, in the winter and early spring, are called cluster flies. How did they get inside my house? Well, in late summer and early fall cluster flies begin looking for a warm place to survive winter. They fly until they hit a sunny side of a structure (your house) then crawl around until they find a crack that gives them access to your wall voids or attic. The flies feel heat radiated on warmer sunny winter and early spring days thus confusing them into thinking it’s time to go back outside. This is when you start to see them in your windows and flying around the inside of your house. At this point they are a little lethargic and are easy to control with a fly swatter. That tho can be monotonous when your dealing with hundreds of those buggers.  If there’s any good news it’s the fact that cluster flies do no damage to your house.  They do leave small black spots on your windows.  Those black spots are secretion fluid from salivary glands, gross huh!


So, what can be done to control cluster flies? You can seal any cracks you find on the outside of your house but usually you can’t seal everything and they end up breaching your barrier anyways. To get the best results you should call a professional pest control company to take care of the problem for you. The goal of the company is to lay a chemical barrier, using spot and crack and crevice applications, in strategic areas on the outside of your house. Using the correct chemical is also important. Less expensive chemicals won’t have the longevity needed to hold up to UV pressures. Your company needs to use a product that’s active ingredient is held in a micro-encapsulation or a crystal. This will help the product last longer on the surface your trying to protect. The more expensive formulations do not use emulsifiers to carry the active ingredient. Emulsifiers can stain siding, wood and other surfaces.

If your tired of seeing pesky cluster flies in your windows and flying around your house call a reputable pest control company. If you live in the Pikes Peak region of Colorado please reach out to my company, Chaney Pest Elimination, Ph. (719) 650-0246, email or visit my website