Cluster Flies closely resemble House Flies, but they are usually larger (3/8”-1/2”) and have a yellowish sheen on the thorax. With a mostly black body, their thoracic hairs are short, curly, and yellow to golden. They have tufts of crinkly yellow-orange hairs where their wings attach to the thorax. Older specimens may have some of the yellow thoracic hairs rubbed off. The wings often overlap at their tips when the fly is resting.
Cluster Fly larvae are parasites of earthworms and breed outdoors in lawns and fields during the spring and summer. Earthworms are usually most abundant around places where manure has been piled or stored and are common in grassy areas where the soil is moist.
The large numbers of adults that emerge in late summer and early fall seek protected places to spend the winter. Often, as with Face Flies, this site is a structure. Inside a structure, the flies tend to “cluster” in large numbers at windows or on ceilings or other high places. They often occur within the walls, attics and basements of homes. Window screens alone offer no protection from these flies because they crawl into the home through small openings in the walls of the building. Both Face Flies and Cluster Flies may be attracted to the same structure year after year. Cluster Flies are also bothersome in the spring when they try to escape from the home. Vacuuming is the most effective means of removal from inside a home.
While no scientific studies have determined the effectiveness of Fly Predators for Cluster Flies, anecdotal reports from Fly Predator users indicate that one application of Fly Predators around the perimeter in spring provides control for the following year.
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