There are three species of clustering fly which are collectively known as ‘cluster flies’, by their scientific name they are Musca Autumalis (the autumn fly), Pollenia Rudis (The common cluster fly) and Dasyhora Caynella (the green cluster fly). The name ‘cluster fly’ is due to their habit of forming clustered groupings while in hibernation.

Species Identification

• Musca Autumalis (The Autumn Fly): the same size and colour as the housefly, with a yellow abdomen.
• Pollenia Rudis (The Common Cluster Fly): larger than a housefly, dull dusty brown/grey in colour with a tessellated abdomen.
• Dasyhora Caynella (The Green Cluster Fly): the same size as the house fly but shiny blue/green in colour.

Life Cycle and Habitat:

Clustering flies are field insects, often found in grassland or resting on southern facing surfaces on warm days. The life cycle begins when adult flies lay their eggs in damp soil generally located in areas of grassland, such as grazed pasture or parkland. Fields regularly used from crops are unlikely habitats for this type of insect due to the soil cultivation practices employed such as ploughing. As temperatures begin to increase the eggs hatch and transition to the larval stage of the lifecycle, being parasitic these larvae will bore through the body walls of earthworms feeding upon them until they pupate and emerge as adult flies. The adult clustering fly feeds on nectar from wild and garden flowers in addition to decaying vegetation. The life cycle is largely dependent upon prevailing weather conditions, as such two generations per year are most common, but with warmer summers up to four generations a year has been recorded.

The problem of Cluster Flies:

In late autumn when temperatures begin to drop cluster flies begin to seek out harbourages for protection against the elements as they hibernate over the winter. With the increased encroachment of human dwellings and buildings upon their natural habitat, cluster flies are increasingly using homes and farm buildings as hibernation sites. Cluster flies gain entry to properties through the smallest of gaps, typically under eaves, between roof tiles or air bricks and through cracks in window frames and ledges. As such cluster fly proofing is almost impossible and attempts are very costly.

Cluster flies cause no damage to properties, however can product a sickly smell and appear unsightly when in colonies of hundreds to several thousand; the bodies of flies which have failed to hibernate often cover insulation and fill light diffusers or sunken spot light lenses. Although activity largely drops off over the winter hibernation, if the local environment becomes warmer they can emerge during the winter to fly around, often making their way through light fittings into living areas. Developments in central heating often give the impression of the emergence of spring to hibernating cluster flies.

An important phrase to remember when treating cluster flies: “Population suppression”

When treating cluster flies population suppression should be your main aim in the lead up to hibernation, as preventing access is virtually impossible you will want to employ measures which keep the population levels suppressed before hibernation and thus reducing if not eliminating the risk of a nuisance both during the winter and in the spring. Fumigation is a vital component of this process, Pest Expert Formula ‘P’ Fumers and the Formula ‘P’ fogger are your reactive measures to kill the surface level population and give you a clean slate from which to employ residual insecticides. The Formula ‘C’ Cluster Fly Killer Spray when used after fumigation will form a residual film of insecticide which will last for up to 12 weeks; this cypermethrin film will  kill any new flies entering the property and coming into contact with the film, acting as an on-going pest control process and ensuring that the population remains suppressed. One last round of fumigation before the advent of winter will ensure that your property is free from the nuisance of clustering flies.