Even though its winter, you may be experiencing fly problems in your home. Cluster flies look for warmer quarters in the fall and begin entering buildings, tending to cluster, many times in attics. They'll often spend the winter here, only becoming active and flying to other parts of the house on warm days.

Cluster flies resemble houseflies, but are larger and can be distinguished by the numerous fine yellow hairs on top of the back where the wings are attached. The eggs of cluster flies are deposited on the soil, the larvae of which feed on earthworms. Therefore, cluster flies cannot be controlled by the sanitary measures used to control houseflies.

The first thing you should do is locate their entranceways and block as many of these as possible to cut down on the number of flies you will have in the building. Once they are in the house you can pick them up with a vacuum cleaner. Dead flies should be removed because accumulations of these insects attract larder and carpet beetles.

Steve Jacobs, Pennsylvania IPM
From PA IPM News, Winter 1999 Vol.1, Number 4

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