 Cluster
Flies are a very common pest throughout
North America. They are a medium sized fly
(1\4 to 3\8 inch long) which are usually dark gray
in color with golden hairs located on the thorax.
The
female lays eggs in the soil near the burrows of earthworms.
The tiny maggots that hatch from the eggs seek out
earthworms to feed upon. The maggots of cluster flies
have never been reared on any other food but living
earthworms. When full grown, the parasitic maggot leaves
the body of the host and enters the soil. There are
about four generations a year.
Cluster Fly ¼ to 3/8th of an inch
During most of the year, cluster flies are not a problem
in structures. In
August and September however, as evening temperatures begin to drop they seek
protected places in great numbers to over-winter.
In many cases, this is within walls, attics and storage rooms of houses.
Cluster Flies “clustered” around attic gable vent
They are attracted to warm walls (usually South
and West facing) where the sun shines the longest. They then squeeze
through amazingly small cracks and crevices to access the warmer interior of
the structure. They can even
get around the weather stripping of expensive windows Screens offer
little protection since these flies prefer to crawl in through small openings
elsewhere around the building or force their way around the edges of where
the screen fits the window. For this reason they are extremely difficult
to keep out of houses. Isolated houses in the country are especially
prone to invasion, since they offer the only warm shelter for miles around.
If they have not invaded the living space directly they eventually make their
way down from false ceilings, attics and wall voids into living and working
spaces. They can number anywhere from a few dozen to many thousands of
flies creating a very uncomfortable living or working environment.
Control is best achieved by preventing the flies from entering the structure
in the first place. This is accomplished by treating all areas at risk
to cluster fly infiltration in the early fall. This treatment must be
timed in anticipation of the flies seeking over-wintering sites. With
specialized equipment, an application of a residual insecticide, targeted to
critical areas will kill the vast majority of the flies as they attempt to
infiltrate the structure.
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