Domakihub How to Get Rid of Cluster Flies in Your Home
Stop cluster flies from taking over your walls and windows before they overwinter.
Reviewed by Domakihub home & decor pros · 2026-06-23 · 5 min read
Cluster flies are a familiar autumn nuisance in homes, holiday rentals, and hotels across Greece — particularly in rural or semi-rural areas where earthworms are plentiful nearby. Unlike house flies, they do not breed indoors or carry food-borne disease, but a single warm wall cavity can harbour thousands of them, and they will return to the same building year after year. The video above walks through the control products and methods that work; this article turns those into a clear, repeatable process you can follow yourself or hand off to a professional.
What are cluster flies and why do they invade?
Cluster flies (Pollenia rudis) are parasitic on earthworms during their larval stage. In late summer and early autumn, adult flies begin searching for a sheltered overwintering site — a cavity inside a south-facing wall, a loft space, or the gap behind a shutter. They release a subtle aggregation pheromone that draws more flies to the same spot, which is why numbers can build rapidly over a matter of weeks.
Because Greece's mild winters still see cold nights, even coastal holiday villas and hillside hotels experience cluster fly pressure from September through November. Properties that have been affected once almost always see the problem repeat the following year unless active prevention measures are in place.
How to tell cluster flies apart from common house flies
Cluster flies are slightly larger and noticeably slower than house flies. Their thorax has a distinctive golden or olive-yellow hair covering when viewed up close, and their wings overlap flat across their abdomen at rest — a useful identification point. They gather in large, slow-moving masses near windows on sunny days and produce a faint sweetish odour when disturbed or crushed.
Knowing you have cluster flies rather than blow flies or fruit flies matters because the treatment approach is different. Blow flies signal a dead animal nearby; cluster flies simply want warmth. No rotting food source needs to be found and removed — the focus is on exclusion and insecticide.
5 steps to eliminate and prevent cluster flies
- 1
Inspect entry points in late summer
Walk the perimeter of the building in August or early September, before flies begin moving indoors. Look for gaps around window frames, soffits, fascia boards, roof tiles, and where pipes or cables penetrate the wall. Mark every gap larger than 2 mm — cluster flies can squeeze through surprisingly small openings. Pay special attention to south-facing and west-facing elevations, which warm up fastest and attract flies first.
- 2
Seal and exclude before the season peaks
Fill structural gaps with exterior-grade silicone sealant, expanding foam for larger voids, or fine mesh fixed with staples for ventilation openings that need airflow. Fit brush-strip draught excluders to exterior doors. Sealing is the most permanent fix and reduces the need for insecticide year on year. If you manage a holiday rental or hotel, schedule this work for the August maintenance window so it is done before peak fly season.
- 3
Apply a residual insecticide to entry zones
Once entry points are sealed or where sealing is not possible (e.g. under roof tiles), treat the outer surface with a residual pyrethroid spray — products containing cypermethrin or permethrin are widely available and registered for this use. Spray all potential entry points, including the soffit line, window reveals, and the top of south-facing walls. The residual effect lasts four to eight weeks; re-apply in mid-October if the season is warm. Wear gloves and eye protection and keep people and pets away until the treated surface has dried completely.
- 4
Remove or trap flies already inside
For flies that have already entered a loft or void, use an insecticidal smoke generator (fumigation canister) in the affected space. Close all openings, ignite the canister, and leave for several hours, then ventilate thoroughly. For living areas, a UV fly trap or an electric fly killer (EFK) unit placed near a window will catch flies that become active on warm days. A standard vacuum cleaner is also effective for gathering sluggish clusters — seal the bag immediately and dispose of it outside.
- 5
Monitor and repeat annually
Set a calendar reminder for late July each year to repeat the inspection and seal any new gaps caused by seasonal movement in the building fabric. If the infestation was large, consider a professional treatment in the first year — pest controllers can apply residual insecticide deep into roof voids using ULV (ultra-low-volume) equipment that is not accessible with consumer products. After two consecutive seasons of proactive sealing and treatment, most properties see cluster fly numbers drop to near zero.
Rather have a pro handle it?
Get a vetted pest control pro in your city — one number, booked in EN/EL/DE.
FAQ
- Are cluster flies dangerous to people or food?
- No. Cluster flies do not bite, sting, or breed in food. They are not linked to disease transmission the way house flies or blow flies are. The main harm is the nuisance of large numbers, the faint odour they produce, and the staining they can leave on walls and window sills when they die. Properties used as food businesses should still remove them promptly to comply with hygiene regulations.
- Why do cluster flies keep coming back every year?
- Cluster flies are strongly site-faithful. Flies that successfully overwinter in a building release a pheromone that persists in the fabric, attracting new flies the following autumn even if the original occupants have been eliminated. This is why prevention — sealing gaps before September — is far more effective than simply killing flies after they have entered. A building that has had a large infestation may need two to three seasons of consistent exclusion work before numbers fall significantly.
- Can I deal with a cluster fly problem myself or do I need a pest controller?
- Small numbers entering through gaps you can identify and seal are straightforward to handle with DIY products — a residual cypermethrin spray and a smoke canister for the loft are widely available and effective. Large infestations in inaccessible roof voids, or repeat infestations in a property you rent to guests, are worth handing to a licensed pest controller who has ULV equipment and professional-grade products. For holiday rentals and hotels, a professional treatment also provides documentation useful for hygiene compliance.