Published on January 13th, 2014 | by Henri


Cluster flies

Q.    It’s time for a short essay from you on cluster flies. Where do they come from? Where are they going? What do they want? What do they eat? When do they sleep? When is it all over? My carpet and ceiling look like a polka-dot pattern.

A.    Cluster flies, which congregate on sunny sides of buildings in late summer, are seeking shelter from the approaching cold weather. They enter buildings in the fall to find shelter from the cold. They do not breed in buildings; they lay their eggs on soil and, when they hatch, the maggots attack earthworms.

They are not “dirty” flies in the sense of being disease-carriers like other types of flies. The best control is to seal all cracks and crevices on the outside of the house. To discourage them from nesting in the walls, a residual spray can be applied on all exterior parts of the house, especially on the south, east and west sides. It should be applied thoroughly but not to the point where the spray runs off, as a light covering is sufficient.

The time to spray is late August or early September in the colder regions, later in warmer climates, before the first hard frosts when the flies are congregating on the walls. Repeat as needed. You should be able to get the appropriate spray for cluster flies in hardware stores. But if you can’t find it, call the extension service of your university or the agricultural department of your state for sources. Get the concentrate form and follow directions.

If you suspect that the flies are coming in around the windows, readers have told me that they have had success with placing orange peels between primary windows and storm windows. On warmer and sunny days, the flies come out of their hiding places within the house to buzz on windows and light fixtures.

Other readers have hung flypaper near windows to trap them. A vacuum cleaner is also useful to suck them all up when they cluster (as their name indicates) on windowpanes. Of course, you can have a local, independent pest management professional do the spraying for you; he or she can also deal with inside infestations.

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