About cluster flies
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Cluster flies resemble large house flies and may suddenly appear indoors around windows or lamps in the fall, spring or winter.
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They often become active on warm, sunny, winter days or when heat in the home arouses them.
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Cluster flies are 3/8" long, dark gray, and non-metallic.
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They are sluggish fliers.
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These flies are not associated with garbage or manure. The larvae are actually parasites of earthworms.
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Adult flies usually enter homes in late August to overwinter and occupy attics and/or wall voids that are warmed by winter sun exposure (most often southern-facing).
Management
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Prevention is the best control. In summer, seal up access openings. Place tight screens over vents. Caulk or seal cracks and holes.
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Inside the home, swat or vacuum any flies that appear.
Rev. 2020