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Cluster flies:  How to Fix Them Once and for All ?

Is your home being attacked by cluster flies? They are annoying and disgusting insects and this is the season when it all begins.

Cluster flies make their debut in the autumn when they fly to the sunny sides of homes in search of protected over-wintering sites and may be found flying about inside, often in great numbers, throughout the winter. The immature stages, egg and larva, are

seldom seen as the eggs are deposited on the soil and the larva or maggots burrow into earthworms on which they feed. The adults leave their protected over-wintering sites in the spring and will lay eggs on the soil, which contains earthworms

With the onset of autumn, the current crop of adults will seek protected over-wintering sites in such locations as hedge rows; under the bark of dead and dying trees; and voids in sheds, garages, barns, houses and other man-made structures. Cluster flies will not damage your home.

Occasionally, the flies may leave small dark-colored spots of excrement on windows and walls, but they are not known to carry any diseases of medical importance to humans. In addition to the ‘clustering’ on the sunny exterior of buildings in the fall, the flies will gather in large numbers at windows within the home on warm winter days. The flies are typically sluggish in flight and can be easily swatted or captured.


Before cluster flies enter the structure - Mechanical exclusion is the best method to keep cluster flies from entering homes and buildings. Cracks around windows, doors, siding, utility pipes, behind chimneys, and underneath the fascia and other openings should be sealed with good quality silicone or silicone-latex caulk. Damaged screens on doors and windows should be repaired or replaced.

If numerous flies are entering the living areas of the home, attempt to locate the openings where the insects gain access. Typically, flies will emerge from cracks under or behind baseboards, around window and door trim, and around exhaust fans or lights in ceilings. Seal these openings with caulk or other suitable materials to prevent the insects from crawling out.

New products coming into Canada could also help with this problem and also add value to your home. Cork spray, which has a stucco look would seal the exterior of your home preventing cluster flies from entering through any cracks and settling in your walls. You would still have to manage the cracks in your windows but that would be more manageable. Cork spray would also aid in heat loss and keep your house cooler in summer saving you money and possibly increase the value of your home.

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