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  • Writer's picturePhilip Martin

Everything You Need to Know About Cluster Flies!

Updated: May 12, 2023

About Cluster Flies

Cluster flies, also known as blow flies, are a common pest problem for homeowners and businesses in Herefordshire and Worcestershire. These flies are not only a nuisance, but they can also cause damage to the structure of a building if left untreated.

In this blog post, we will be discussing everything you need to know about cluster flies, including their behaviour, life cycle, and how to prevent and control infestations in your home and business.

What are cluster flies?

Cluster flies, also known as blow flies, are a type of fly that typically enters homes and buildings in large numbers during the autumn, seeking a warm place to spend the winter.

PGM & SON Pest Control: Cluster Fly Image

What do cluster flies look like?

Cluster flies are typically larger and slower moving than other common house flies. They have a characteristic golden or yellowish-brown colour and are often mistaken for the common house fly.

However, cluster flies are typically found in numbers in lofts or upper levels of homes, whereas house flies are more commonly found in kitchens and living areas.

Seasonality of cluster flies

Cluster flies are more prevalent during certain times of the year, typically from late summer to early autumn and again in early Spring.

This is because the adult flies are looking for a warm place to spend the winter, and your home is the perfect place for them. They then re-emerge in the Spring to lay their eggs.

During these months, it's important to be extra vigilant about inspecting your home for signs of infestation and taking preventative measures to keep the flies out.

How do cluster flies differ from other types of flies?

Cluster flies are larger, around 8mm, and slower-moving than common house flies and have a distinct pattern of yellowish, golden hairs on their thorax.

They also have a tendency to congregate in large numbers, often entering homes and buildings in large numbers during the autumn.

Unlike house flies, they do not breed or feed indoors and are not considered a health hazard.

What are the identifying characteristics of cluster flies?

Cluster flies are larger than the common house fly, measuring about 8-10 mm in length.

They are typically dark grey in colour and have a distinct pattern of golden hairs on their thorax. Their wings are held flat over their backs and their bodies are slightly rounded.

They also tend to move in a slow, lazy manner.

How do cluster flies reproduce and spread?

Cluster flies have a life cycle that typically lasts for about a month. The adults lay their eggs in soil, the larvae then hatch and feed on earthworms.

After several weeks, the larvae pupate and emerge as adult flies. Once matured the adults will seek out warm, protected areas to spend the winter, often congregating in large numbers in lofts and wall voids of homes and buildings.

How do cluster flies impact humans and the environment?

Cluster flies are not considered a health hazard as they don't breed or feed indoors. However, they can be a nuisance when they gather in large numbers in homes and buildings.

They do not damage structures or property, but their presence can be a source of annoyance for homeowners. They don't transmit any diseases to human or animals, it is also not considered harmful to the environment.

Health concerns with cluster flies

While cluster flies do not pose a direct health risk to humans or pets, they can cause allergic reactions in some individuals. The flies tend to release a musty odor which can be a source of allergies, breathing problems, and headaches.

To minimise exposure, you should try to keep windows and doors closed, and use air purifiers or air fresheners to neutralise the smell.

Additionally, if you are experiencing any symptoms that you suspect may be related to a cluster fly infestation, you should consult with a doctor or an allergist.

How do Cluster Flies Infest Homes?

Cluster flies typically enter homes and buildings through small cracks or openings, such as around windows and doors.

They are attracted to warm, protected areas, such as lots, wall cavities and chimneys, which provide a safe place for them to spend the winter.

Once inside, they can become a major nuisance as they buzz around and can leave a strong musty smell.

Signs of a Cluster Fly Infestation

The most obvious sign of a cluster fly infestation is the presence of the flies themselves. They may be found in large numbers, especially in the upper levels of the home.

In addition, you may notice a musty smell in the affected areas. If you notice any of these signs, it's important to take immediate action to prevent further infestation escalating.

They can also leave stains on your property and when the die in numbers can be very unsightly and some people may find this distressing.

What are the common methods for controlling and preventing cluster fly infestations?

Preventing a cluster fly infestation in the first place is the best way to control them.

Preventing cluster flies from entering the home can be done by sealing entry points such as cracks and gaps around windows and doors and installing screens on vents and chimneys.

Once inside, the flies can be vacuumed or trapped, and pesticides can be used as a last resort. Keeping windows closed during the autumn when cluster flies are most active can also help prevent infestations.

How to get rid of Cluster Flies once they are in your home

Cluster flies can be removed from the home by vacuuming or trapping them. Chemical treatments can also be used as a last resort, but it's important to consult a professional, qualified pest controller such as PGM & Son Cluster Fly Control Hereford and Worcester for advice and assistance.

Professional Pest Control for Cluster Flies

While there are many DIY control methods available, it is more appropriate to consult a professional pest control service.

Everything you need to know about Cluster Flies!

For example; if an infestation is severe, or if you are unable to locate the point of entry, a professional pest control company can be helpful. Pest Control companies have the experience and specialised equipment needed to effectively identify and eliminate cluster fly infestations.

They may also be able to provide follow-up services to help you to minimise the risk of an infestation returning. It's important to note that there are also many companies that offer "green" or "organic" pest control options that are less harmful to the environment.

That said, cluster flies do usually return to the same location year on year so even if you eliminate your cluster fly problem one year you are likely to experience an issue in future years. One way to resolve this is to engage a professional pest control service in Hereford and Worcester to provide an annual cluster fly service for you.

Cluster fly conclusion

Cluster flies can be a major nuisance for homeowners across Herefordshire in particular, as this is a rural county and cluster flies are more prevalent in rural locations, but with the right knowledge and preventative measures they can be effectively controlled. Remember to seal cracks and openings around windows and doors and ensuring that screens are well maintained. With the right approach, you can keep your home free from cluster flies.


Engaging early with PGM & Son Pest Control can provide peace of mind that your cluster fly infestation will be handled quickly, efficiently, and safely. Integrated pest management is more than pesticides. You need to combine biological, cultural, physical and chemical tools to deal with an infestation.

Too often, we see botched DIY pest control attempts that result in even larger infestations. We’ve seen amateurs cause serious harm through the incorrect use of chemicals - not only to British wildlife and domestic pets but to themselves and their families.

About us

PGM & SON is an award winning company that provide pest control solutions to residential and commercial businesses across Herefordshire and Worcestershire. Our company is a well respected and experienced pest control service.

When people contact PGM & SON for pest advice or help, they can be assured they will receive reliable, friendly, professional, effective, value for money pest control services which put customers first and make animal welfare a priority. Check out our Common Household A-Z of Pests page.

When you're in need of a dependable local Pest Control Service in Herefordshire or Worcestershire, don’t hesitate, contact PGM & SON today, we are a family run business that is near you and open 7 days a week.

Why choose us?

PGM & SON are a member of the BPCA (British Pest Control Association) and have been assessed to ensure that we meet their strict criteria to obtain our membership to which we are very proud.

This also provides assurance to our customers that we are insured, trusted pest control company with a team of Level II and Level III professionally trained and qualified technicians who follow the BPCA Codes of Best Practice.

We are also members of the PROMPT Register, which ensures that pest control is carried out responsibly by people who are properly trained and competent in the field. The BASIS PROMPT Pest Controllers register is an industry initiative which provides independent proof that a pest controller has received proper training and continues to update their expertise.

PGM & SON; Everything you need to know about cluster flies

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