Cluster Flies are not a new pest but recent years have shown a marked rise in the numbers of cases that Target Pest are dealing with.
This is often due to weather conditions, a cooler, wetter spring and a warm humid summer allow for a greater number of the flies to breed, and once the weather cools down, all these insects look for a winter hibernation point.
And your house roof and walls are a prime place.
Cluster Flies are NOT a health hazard to humans as the larval stage (maggots) are parasitic on earthworms, and so the adult flies are not attracted to
human food or waste. The larval stage in earthworms is why cluster flies are usually a rural problem only.
;the females lay their eggs near earthworm burrows, and the larvae then infest the worms.
However, the flies are a nuisance because when the adults emerge in the late summer or autumn they enter houses to hibernate, often in large numbers; they are difficult to eradicate because they favour inaccessible spaces such as roof and wall cavities.
The adult flies leave pheremone markers that attract other fcluster flies to suitable hibernation points.
Please note that treatments will kill the flies and will prevent infestation overwinter, but may not stop the flies gathering in numbers and being
a problem in the short term as the pheremones will keep new flies coming in. The treatments do however reduce the population for the following season.
Please look at this link to TV3’s coverage of Cluster Flies by Target Pest
There are over 30 species of cluster fly, all belonging to the blowfly genus Pollenia. They are widespread throughout
Europe, Noth America, Australia and New Zealand
The most common cluster fly Pollenia rudis is about 7 mm long and can be recognised by distinct lines or stripes behind the head,
short golden-coloured hairs on the thorax,
and irregular light and dark gray areas on the abdomen.
Cluster fly mass in roof void