Homeowners in Aude, Pyrenees-Orientales, and Herault: are you dealing with a sudden fly infestation? If you see black flies buzzing around your windows, you likely have cluster flies (Pollenia rudis).

Unlike house flies, which are attracted to filth, these flies are parasitic. Adult flies lay their eggs in the soil, and the larvae that hatch will seek out an earthworm. The larva then feeds on the worm from the inside. While they are outdoors, you can't control the earthworm population, but you can block their entry into your house.

As temperatures drop, especially in the fall, adult cluster flies look for secluded areas to hibernate. Flies can enter through the tiniest cracks in your eaves, around window frames, or cracks and crevices in your masonry. Once cluster flies have found a crevice, they gather in large numbers in attic spaces or wall voids.

When temperatures rise during a sunny spell, flies become confused and become more active. These sluggish flies find their way into homes and swarm around windows and on window sills, often following the light. 

Identifying Cluster Flies

The trick to dealing with flies is to first know what kind of flies you have. 

At around 8mm long, cluster flies are slightly bigger than the common house fly in Occitanie. They are a dull gray or black colour, not shiny like bluebottles and other carrion flies. They are not attracted to human food, but they are attracted to light. If you look closely at the thorax (the middle section of the body between the head and the abdomen) you might notice some golden hairs. 

Keeping Them Out

To prevent cluster fly infestations, a homeowner should inspect and repair their property in the late summer.

Use caulk for sealing cracks around window and door frames. Pay attention to cracks around door and window areas on the west sides of the building. Sealing gaps around doors and checking potential entry points is also vital. Flies are often looking for warmth on south-facing walls.

If you have a fly problem, don't just use a fly swatter. While you can use a vacuum to manage minor infestations, you must remove dead flies to prevent secondary pests. You can use fly traps (sticky kind) or natural repellents, but for a long-term pest problem, you need extermination services. If you try to control them yourself, you might miss where the flies go in the attic.

To get rid of flies, a professional pest control service can apply a repellent or insecticide barrier. Cluster flies may return every year if you don't control cluster flies correctly with specialized control products. To effectively keep your home free of these types of flies, hiring a pest control expert is the best way to enjoy a fly-free life.