Cluster flies in lofts are a common problem across London and Essex during autumn and winter. As temperatures drop, these slow-moving flies enter roof spaces through small gaps and hibernate in large numbers until spring.
People across Romford to Ilford, Barking and Dagenham often first notice them around windows or lights, especially on warmer winter days when they become active again.
Unlike house flies, cluster flies are not breeding indoors. They are overwintering in loft insulation, wall voids and roof timbers, which is why infestations can suddenly appear in large numbers.
In this guide, our fully trained and accredited pest control team at Bugwise explains exactly why cluster flies choose lofts, how long they stay, and the most effective way to get rid of them before they spread further into your home.
Table of Contents
What Are Cluster Flies?
Cluster flies (Pollenia rudis) are slightly larger and darker than common house flies, with distinctive golden hairs on their thorax that can appear almost dusty or shimmering in sunlight. They move slowly compared to house flies and often gather in large groups.
They are commonly referred to as attic flies or loft flies because of their habit of clustering together inside roof spaces, wall voids and upper floors during colder months.
Unlike house flies, cluster flies do not breed indoors or feed on rubbish. Their larvae develop in soil, where they parasitise earthworms before emerging as adult flies in late summer.
As temperatures begin to drop, adult cluster flies search for sheltered areas to hibernate. Loft insulation, roof timbers and wall cavities provide the ideal environment, which is why infestations often go unnoticed until large numbers appear inside the property.
If you are unsure whether the flies in your loft are cluster flies or another species, see our full identification guide:
What Are Cluster Flies and How Do You Get Rid of a Cluster Fly Infestation?
Why Your Loft Is the Perfect Hibernation Spot
Cluster flies are instinctively drawn to quiet, sheltered spaces where they can overwinter undisturbed. In UK homes, lofts provide the ideal conditions, which is why they are one of the most common hiding places.
Warmth
Heat rising from the rooms below keeps loft spaces slightly warmer than outside temperatures, allowing cluster flies to survive through winter.
Shelter
Lofts are dark, dry and rarely accessed, giving cluster flies a safe place to remain inactive for months.
Entry points
Small gaps around soffits, roof tiles, vents and window frames allow cluster flies to enter unnoticed. Once inside, they move deeper into insulation and roof timbers.
Pheromone trails
After settling in, cluster flies release chemical signals that attract more flies to the same location. This is why the same property can experience repeat infestations year after year.
Because of this behaviour, cluster fly infestations often return each autumn, even if the loft has been cleaned or treated with off the shelf sprays.
Did you know?
Cluster flies are not a hygiene issue. They enter clean and tidy homes just as readily as older properties.
When Do Cluster Flies Appear in the UK?
Cluster flies in the UK typically appear from late August through to October, when adult flies begin searching for sheltered places to hibernate.
During this period, they often gather on sun-facing walls, especially those warmed by afternoon sunlight. As temperatures drop in the evening, they move through small gaps around rooflines, vents and tiles, eventually settling inside loft spaces.
Once inside, cluster flies remain largely dormant throughout winter. However, they can become active on milder days or when heat from central heating and loft insulation raises the temperature inside the roof space.
By early spring, they begin to re-emerge, often appearing around loft windows, skylights and upper floors as they are drawn towards light. This behaviour is common across many flying insects, as explained in our guide on why insects are attracted to light.
Are Cluster Flies Dangerous?
NCluster flies are not considered dangerous. They do not bite, sting or spread disease like some other fly species.
However, large infestations can still cause problems inside a property.
Staining and mess
When disturbed or crushed, cluster flies can leave dark marks on walls, ceilings and window frames.
Odour and secondary pests
Dead flies inside wall cavities or loft insulation can produce an unpleasant smell and attract other pests such as beetles.
Nuisance and complaints
In rental or commercial properties, visible fly activity can lead to complaints and concerns around cleanliness.
While cluster flies are not a health risk, infestations can quickly become a nuisance if left untreated, especially when large numbers begin appearing indoors.
How to Get Rid of Cluster Flies in Lofts
Getting rid of cluster flies in a loft requires more than a quick spray. Because they hide deep in insulation and roof voids, a combination of treatments is needed to deal with both visible and hidden flies.
1. Fogging or smoke treatment
Fogging is one of the most effective methods for loft infestations. The insecticide spreads throughout the space, reaching areas that cannot be treated directly and killing both exposed and hidden flies.
2. Residual insecticide application
After fogging, a residual spray is applied to rafters, joists and surrounding surfaces. This continues working for several weeks and helps control any flies that emerge later.
3. Removal of dead insects
Vacuuming dead flies reduces odour build up and prevents secondary pests such as beetles from being attracted to the area.
4. Sealing entry points
Gaps around soffits, vents, roof tiles and window frames should be sealed where possible. This helps reduce the chance of future infestations.
5. Professional pest control treatment
For ongoing or severe infestations, professional treatment is usually required. This typically involves targeted fogging combined with residual insecticide and advice on long term prevention.
Cluster fly infestations can persist because some flies remain hidden and emerge over time. In some cases, a follow up treatment may be required to fully resolve the problem.
For a detailed breakdown of treatment options, see our full guide: Can You Get Rid of a Cluster Fly Infestation?
Professional Cluster Fly Treatment in London & Essex
If you are seeing cluster flies inside your home, the infestation has already settled in your loft. Bugwise Pest Control provides targeted fogging and residual treatments to eliminate cluster flies and prevent them returning. Fast response across Romford, Barking, Ilford, Dagenham, Chigwell and surrounding areas.
Why Do Cluster Flies Keep Coming Back?
Cluster flies often return to the same property year after year, even after treatment. This is because they leave behind pheromone markers that attract other flies back to the same location.
Once a building has been used as a hibernation site, it becomes a repeated target each autumn unless preventative measures are taken.
The most effective way to break this cycle is with preventative treatment in early autumn, applying residual insecticide to external walls before the flies enter to hibernate.
Bugwise recommends scheduling this service between late August and mid September, especially if you have experienced cluster flies before. Preventative treatments are a key part of our wider fly control services across London and Essex.
How to Prevent Cluster Fly Infestations
You cannot stop cluster flies existing outdoors, but you can make your property far less attractive as a hibernation site.
Seal entry points
Close gaps around soffits, vents, roof tiles and window frames using sealant or fine mesh. Even very small openings can allow flies to enter.
Apply preventative treatment
Treating external walls, eaves and rooflines with a residual insecticide in late summer helps stop cluster flies before they settle inside.
Improve loft conditions
Cluster flies prefer warm, still environments. Increasing airflow and ventilation can make loft spaces less suitable for overwintering.
Remove debris and dead insects
Clearing out dead flies and organic debris helps reduce odours and prevents attracting other pests.
Reduce dark hiding areas
Cluster flies are drawn to dark, undisturbed spaces. Keeping loft areas accessible and occasionally disturbed can help discourage them.
These steps can significantly reduce the risk of infestation. For properties with recurring problems, combining prevention with professional treatment provides the most reliable long term control.
Professional Cluster Fly Removal in London & Essex
At Bugwise Pest Control, we carry out targeted cluster fly treatments using professional fogging equipment and residual insecticides designed for loft and roof void infestations.
Our technicians are fully trained, insured and experienced in working within loft spaces, providing safe and discreet treatments for residential homes, rental properties and commercial buildings.
Areas we cover
Romford, Barking, Ilford, Dagenham, Chigwell, Loughton, Woodford, Hornchurch, Upminster and across East London and Essex.
Our cluster fly service includes
- Targeted loft fogging to eliminate active flies
- Residual treatments to control emerging activity
- Preventative exterior treatments where required
- Follow up inspections if activity continues
- 30 day guarantee on residential treatments
Frequently Asked Questions About Cluster Flies in Lofts
What causes cluster flies in the loft?
Cluster flies enter lofts to hibernate as temperatures drop in late summer and autumn. They find their way inside through small gaps around roof tiles, soffits, vents and window frames, where they settle in insulation and wall voids for winter.
How long do cluster flies stay in the loft?
Cluster flies can remain in a loft for several months, typically from autumn through to early spring. They stay dormant during cold periods and may become active again on warmer days or when heat builds up inside the roof space.
Can pest control get rid of cluster flies?
Yes. Professional pest control treatments use fogging and residual insecticides to reach hidden areas within lofts and roof voids, eliminating both visible and concealed cluster flies.
Why do cluster flies keep coming back every year?
Cluster flies leave pheromone markers that attract other flies back to the same property each year. Without preventative treatment, the same loft can be used repeatedly as a hibernation site.
How do I stop cluster flies from coming back?
The most effective way to prevent cluster flies is to treat external walls and roof areas in late summer before they enter, combined with sealing entry points and improving loft conditions.
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