Cluster
flies are found throughout North America
and Europe, and probably originated in
North America during the colonial days.
They are large dark gray to black flies
that resemble houseflies in appearance;
however, they are larger and, in
reality, are not related to houseflies
at all. In fact, they are in the same
family as blowflies and flesh flies. To
differentiate between houseflies and
cluster flies, look at the wings of the
fly at rest. Cluster flies' wings
overlap like a pair of scissors, while
houseflies' wings do not. Additionally,
cluster flies have golden hairs on their
thoraxes. When crushed, cluster flies
emit a smell that resembles that of
buckwheat honey.
Cluster flies become a nuisance when
they enter homes seeking shelter from
cold weather. They do not complete any
of their lifecycle indoors, since they
are dependent on earthworms and soil to
evolve.
In the spring, cluster flies lay their
eggs in soil near earthworms. After they
hatch into larvae, or maggots, the flies
find earthworms to crawl into, feed on,
and complete the larva part of their
lifecycle. After this, they enter the
soil to pupate, after which they have
completed the transition to adulthood.
During the summer months, adults feed on
fruit juices and flower nectar.
As summer wears on and daylight hours
shorten, cluster flies seek protection
from the impending cold weather. Colder
temperatures cause the flies to crawl
upwards, and in this way they enter
cracks and openings in buildings. Gaps
under eaves and siding are common places
for cluster flies to enter. Generally,
buildings located next to large lawns or
meadows are attractive to these flies,
while buildings next to large trees
hardly ever have infestations.
Once inside buildings, cluster flies
congregate in partitions and then move
to heated rooms with the onset of winter
temperatures. When inside heated rooms,
they fly erratically and aimlessly
around lights. When the air is chilly,
they gather together in clusters, which
is how they were given their name.
During the winter, many flies die inside
partitions; because of this, they become
food for secondary pests including
larder beetles and mice.
The best way to control cluster flies is
to deny them access to a building. To
prevent entry, do the following:
-Use yellow, non-attractive insect
lights outside at night
-All cracks in siding and eaves should
be sealed
-Windows, chimneys, and trim should be
tightly caulked
-Windows, Louvers, air vents, etc.
should be tightly screened
-When doing the above, pay particular
attention to the sunny side and upper
areas of a building
If cluster flies have already
established themselves in your home,
there are pest control methods that can
be undertaken to knock down their
population. Sprays and fogs can be used,
although complete eradication can be
impossible because cluster flies hide in
walls. A regularly scheduled pest
control maintenance plan, such as a
four-time per year (quarterly) service
is a good option to consider; this
allows the cluster fly population to be
continually treated, as well as any
other pest problems that might arise.
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