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Adult cluster flies are medium-sized, robust, somewhat bristly flies about 7 mm (0.3 inches) long. They are brownish-gray with numerous short yellow hairs on the thorax, a checkered pattern on the abdomen, and large, reddish-brown eyes. Adults are typically slow fliers. In the fall they begin to cluster in the sun on the warm sides of buildings, outcroppings, fences, and other prominent structures as they seek protected places to overwinter. They may enter houses and other buildings in large numbers. Homes built on the top of a hill or otherwise stand out in the landscape may attract many cluster flies. While cluster flies are a nuisance in the home, they do not bite, are not associated with the transmission of disease, and do not reproduce inside buildings. Cluster fly larvae (maggots) are parasites of earthworms and develop in the soil. They are not known to reduce earthworm populations to the extent that they disrupt soil ecology.
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Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Edwin J. Jones, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; M. Ray McKinnie, Administrator, 1890 Extension Program, Virginia State University, Petersburg.
May 19, 2015