Cluster flies, also known as Pollenia rudis, are a common household pest, especially in rural areas and homes located near open fields. Unlike other types of flies, they do not pose a significant health risk as they do not spread disease, but their presence can still be a nuisance. They are often mistaken for houseflies, but cluster flies are slightly larger, have a dull greyish-brown body with golden hairs on their thorax, and fly in a slower, more sluggish manner.
Unlike many other flies, cluster flies do not breed indoors, which means they won’t lay eggs in your food or bin. Instead, they are more closely associated with earthworms, which serve as their larvae’s food source.
Where Do Cluster Flies Come From?
Cluster flies typically make their presence known in the autumn and winter months. They are named for their behaviour of gathering, or ‘clustering’, in large numbers, particularly when seeking out warm, sheltered places to hibernate over the colder months. Their life cycle begins in the spring when adult cluster flies lay their eggs in soil. These eggs hatch into larvae, which parasitise earthworms. After feeding on earthworms for a couple of weeks, the larvae pupate and emerge as adult flies.
In the autumn, as temperatures drop, cluster flies seek warmth. Homes, sheds, and other buildings make ideal overwintering sites for them. They usually enter homes through cracks in walls, window frames, or attics, often gathering in large groups in unused spaces such as lofts, attics, or under roof tiles.
Once inside, they can be difficult to detect at first, as they tend to remain dormant during the winter. However, when warmer, sunny days return, even in winter, cluster flies may become active, flying sluggishly around windows or light sources as they are drawn to the light.
Please see an example of a cluster fly infestation below:
How to Rid of Cluster Flies
Dealing with cluster flies can be challenging due to their habit of hiding in wall cavities and roof spaces, where they are difficult to access. However, there are several steps you can take to control and prevent their presence.
1. Prevention: Seal Entry Points
Prevention is the most effective way to control cluster flies. As they typically enter homes in autumn, sealing up any potential entry points before this period is key. Check for any gaps or cracks around windows, doors, and rooflines, and seal them with caulk or weather-stripping. Pay particular attention to attic vents and chimneys, which may also provide entry points.
Fly screens on windows and doors can also be useful in preventing flies from entering your home. Make sure to inspect and repair any damaged screens, and consider installing them if you don’t already have them in place.
2. Vacuuming and Traps
If cluster flies have already made their way inside, vacuuming is one of the easiest ways to deal with them. You can vacuum up any live flies that are visible, particularly those that gather near windows. Dispose of the vacuum bag outside to prevent any flies from re-entering your home.
For larger infestations, fly traps or sticky flypaper can help catch flies. UV fly traps, which attract flies with light and then trap them, can also be effective. Position these traps near windows or in areas where flies tend to gather.
3. Insecticides
In severe cases of infestation, insecticides may be necessary. Aerosol sprays designed to kill flies can be effective if applied directly to the insects. However, insecticides have limited effectiveness when dealing with flies hidden in wall voids or other hard-to-reach places. For infestations in attics or loft spaces, a residual insecticide spray or fogger can be used to kill flies as they emerge.
Always follow the manufacturer’s instructions carefully when using insecticides, and ensure that you ventilate the area properly after treatment. If you are unsure about using chemicals or if the infestation is extensive, it may be worth consulting a pest control professional.
4. Professional Pest Control
If the infestation is particularly large or persistent, professional pest control services may be your best option. Professionals can use more powerful treatments that are not available to the public and can access areas that might be difficult for you to reach.
They will also be able to advise on long-term prevention strategies to ensure that the flies do not return in subsequent seasons.
Summary
Cluster flies are more of a nuisance than a threat, but their habit of clustering in large numbers can make them unwelcome guests. By understanding their life cycle and how they enter homes, you can take effective steps to prevent and manage their presence.
Sealing entry points, using traps, and considering professional pest control are all options that can help you rid your home of these unwelcome visitors.
