Description
There are four main species of fly collectively know as cluster
flies. They are:
The Autumn Fly (Musca autumalis) - a small fly of about the same
size and colour as the housefly, but with a yellow abdomen.
The Common Cluster Fly (Pollenia rudis) - a larger fly of a
dull, dark, dusty brown/grey colour with a “tessellated”
abdomen.
The Green Cluster Fly (Dasyhora caynella) - about the same size
as a housefly, shiny green/blue in colour.
The Yellow Swarming Fly (Thaumatomya notata) a smaller species
of hibernating fly, yellowish body/black markings, sometimes
confused with the fruit fly.
Biology and Habitat
Cluster flies are very common, the adult flies hibernate during
the winter months in roof spaces of houses and/or farm
buildings. After this time the flies lay their eggs in the
earth and/or animal dung. As the soil temperature increases
in late spring, the eggs will hatch. The larval stage is
parasitic, entering earthworms and feeding upon them until emerging
as an adult fly. There may be two to four generations of
flies in a single year.
The common cluster fly prefers a warm wet summer, whereas the
autumn fly prefers dryer, hotter conditions.
Cluster flies migrate from the outside conditions into the lofts
of house and/or farm buildings during the winter months.
Obvious signs of an infestation include large quantities of
lethargic/dead flies around windows. Once in the roof spaces
the flies will stay in hibernation until the spring.
Importance
There is no risk to public health.
Cluster flies do not damage property, they will die and become
very unsightly if they do not successfully hibernate.
Water tanks in the loft spaces should be covered.
Cluster flies are not to be associated with dead animal bodies
or faeces and there are no maggots.
Control
Cluster flies emit a clustering pheromone that encourages them
to hibernate together and for subsequent generation to follow to
the same property.
For small infestations around windows and behind curtains, they
can be removed with the use of a vacuum cleaner. For large
infestation in loft spaces, treatment is best carried out after the
first frosts of winter, this usually ensures that all of the
hibernating flies are in the treatment area. The treatment
best designed at this time is to treat with an insecticide space
spray, Ultra Low Volume application through a Micro-Gen machine,
will quickly knock down any flies present.
Safety
All pesticides used by Bath & North East Somerset Council
are approved substances under the Control of Pesticides Regulations
1986 and are fully risk assessed.
