How To Get Rid Of Cluster Flies

September 21, 2021

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Though cluster flies (sometimes referred to as black eyed or lethargic flies) do not pose a significant health threat, they can be a nuisance. Named for their tendency to cluster together in groups while overwintering indoors, these insects can take over your home or business if not dealt with right away. Using over 65+ years of pest control experience, we’ve put together some of the most effective tips to get rid of cluster flies in your home or business.


What Do Cluster Flies Look Like?

Adult cluster flies are dark grey in colour, 8 to 10 mm long, and have numerous golden or yellowish hairs on thorax. Despite bearing a strong resemblance to house flies, cluster flies are larger in size and darker in colour, they lack the dark stripes found on thorax of house flies and the metallic coloured shining bodies of bottle flies.

They can be considered sluggish when moving (commonly identified as lethargic flies) compared to house flies and bottle flies. The wings of cluster flies overlap across the abdomen when the insect stands at rest.

How Did Cluster Flies Get Inside My Home/Business?

Cluster flies are most visible during fall (September) as the days shorten and weather becomes cool. Typically, these pests look to enter your home or business in order to hibernate as the temperatures drop and winter approaches.

These pests find their way in through openings in the wall, like cracks and crevices near window and doorframes, open and unscreened windows, and unscreened vents that provide access into the building.

Common Signs of Cluster Flies

Like their name suggests cluster flies, do in fact cluster together making it easier to recognize if these pesky flies have invited themselves into your home or business. The first sign of cluster flies is when they gather in numbers on exterior walls, particularly south facing walls that get much sun and warm. You may also notice that on warm sunny days, they emerge and cluster on windows attempting to get outdoors.

They can commonly be found in protected areas of your house or business, such as attics, lofts, sheds, garages and basement areas. You may also notice stains on windows and curtains in areas where there is high cluster fly activity, this is actually cluster fly droppings.

Risks Associated With Cluster Flies

Unlike house flies, these pests may not present a disease risk, but you’re not out of the woods yet. This is because cluster flies can attract carrion-feeding insects if they die inside wall voids and other hard to reach areas. These pests can also cause a nuisance when large numbers congregate in common areas of your home or business such as on windows, doors and in kitchen and pantry areas. This occurs on warm sunny winter days making them a major nuisance and contaminants. When they congregate, you can also expect your windows and walls stained with droppings.

How To Get Rid Of Cluster Flies

When trying to get rid of cluster flies in your home or business it is important to follow these tips:

  1. Prevent them from clustering on your exterior walls and eventually going inside. If home or business is in an area prone to cluster flies, an exterior perimeter treatment is the first prevent step, should be done by professional. it will create a barrier and get rid of any cluster flies as they gather on the wall surface hence prevent entry all together.
  2. During the early fall, it can be important to perform an exterior inspection of your property. Focusing on areas around your home or business that may be an entry point for cluster flies. You will want to be on the lookout for any cracks, gaps, areas around loose fitting electrical outlets or switches, loose baseboard and other potential entry points. Once you’ve located the openings, it is important to seal the cracks to keep vulnerable areas such as behind baseboards, around windowsills and near doorframes.
  3. Cluster flies also love the sunlight and warmth, which is often why they buzz against windows. Always make sure that any open windows have mesh screens to keep cluster flies, along with other insects from entering. It is also important to avoid keeping doors without screens open for long periods of time because this can create an easy unprotected opening for cluster flies to come inside your home or business.
  4. For any visible cluster flies, they can be vacuumed up. If there is a larger population of cluster flies indoors, using a fly light trap can be just as effective to control the population. When using the fly light trap, it is important to place the trap in areas where cluster flies are most active to see the most effective results.
  5. When possible seal any exterior gaps and cracks around windows, doors, eaves, siding and utility pipes.
  6. Repair or replace all damaged screens on doors or windows where possible.

We hope you find these tips helpful in your quest to rid your home or business of cluster flies.It is important to remember that you’re not alone. If your cluster fly issue seems too daunting for you to deal with on your own, your local Orkin Canada technician is happy to assist you. Contact Orkin Canada today for effective and reliable fly control you can trust.

Remove pests from your home, and stop them from coming back

We work hard to listen, understand and assess your unique situation. Request a free, no-obligation estimate today for a customized pest program that fits your needs.

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Reviewed by Alice Sinia, Ph.D., MSc on September 19 2021.

Master of Science Degree in Pest Management (MSc.) – Simon Fraser University; BSc. (Hons) Biological Sciences (Entomology & Parasitology) – Makerere University; Advanced Level Certificate of Education – Trinity College; Ph.D. – University of Guelph)

With more than 20 years of experience, Alice is responsible for the management of the Orkin Canada Quality Assurance Laboratory located at our GTA Training Centre. She performs analytical entomology (investigates product adulteration using biochemical and comparative tissue methods), and provides technical support in pest/insect identification to branch offices and clients nationwide. In addition, Alice also prepares scientific reports for Orkin Canada clients, updates Orkin management on any changes or updates to any government regulations pertaining to the pest control industry. Alice also performs quality assurance account compliance audits.

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