Cluster Flies – The Facts
What do cluster flies look like?
Cluster flies look much like large house flies, measuring between 3 to 4 mm in length, with black torsos and clear wings. When indoors, the flies hover near the ceiling in large groups. Cluster flies are attracted to the light and will often fly towards windows and lamps in a clumsy fashion, bumping into things along the way. They are also noisy and can be heard buzzing especially if they get caught between curtains and window panes or if they fall to the ground and land on their backs.
How quickly do cluster flies multiply?
A cluster fly will lay approximately 130 eggs in one go and will produce an average of two generations during her lifetime. They lay their eggs under rotting leaves or in damp soil near earthworm homes. Cluster fly larvae burrow into the earthworms and mature in their decomposing bodies. If the weather is warm it will only take the larvae seven days to mature. In colder climates it can take as long as 35 days.
Where do cluster flies live?
Cluster flies are sun worshippers and seekers of warmth. In the summer months they dwell in the garden, drinking flower nectar. However, as soon as the winter months threaten to appear, cluster flies cosy up indoors. They gather in large groups and hover near ceilings and in attics. It is not clear why they choose certain buildings over others, but once they have designated a warm site, they revisit the same place year after year. Homes, schools and commercial buildings are all common cluster fly haunts.
Once the winter chill has set in, the cluster flies hibernate. They settle into nooks and crannies all over their approved building and do not venture out till spring.
What are the signs of a cluster fly infestation?
- Large groups of slow-moving, seemingly clumsy flies hovering near the ceiling or in your attic from September onwards.
- Loud buzzing as individual flies bump into windows or fall on the floor onto their backs.
- A strong sickly smell that the flies give off to let their friends know they’ve found a warm spot for the winter.
Does a cluster fly infestation need controlling?
If a cluster fly infestation is ignored, it will grow and become worse every year. Cluster flies revisit the same places every winter and multiply quickly.
- If ignored the ‘clusters’ can be enormous with several thousand flies gathering under the same roof emitting a foul odour.
- They are very hard to get rid of once they hibernate as a hibernating fly will not respond to pesticide. In the summer they emigrate outside, only to return again in the autumn with all their extended family.
- A cluster fly infestation is unsightly and flies are associated with dirt. An infestation in a commercial premises will ruin its reputation.