April is the beginning of Spring insect activity. One of the most common insects arriving in spring is the “Cluster Fly”. These flies land here, there and everywhere, carrying garbage, excrement, and germs with them.
Cluster flies cultivate their eggs in earthworms. The Larvae hatch, kill and eat the worms. When the weather starts to warm up in the spring, the flies are attracted from the grass to the heat on your siding and windows. From there, they find their way into your attic (where it is hottest), through the soffit or cracks and crevices, and make their way down into the house through the walls and “cluster” on the windows.
Control of cluster flies requires both interior and exterior treatments. An appropriate application is a fogging of the attic with an appropriately labelled insecticide, and the treatment of the interior window frames. An exterior treatment of the windows/soffits and the southern/western exposures of your siding is also required. A well done job would include treatment of the grass, 4-6 ft around the base of the house. Spring (late April or early May) is the best time to spray for cluster flies. Heavy infestations should be re-treated in the fall for long term control.