Cluster Fly Control

Most Effective Products

Supreme IT Insecticide
Suspended Concentrate
As low as $54.99
Pyrid Insecticide Aerosol
As low as $27.99
D-Fense Dust Insecticide
As low as $12.33
Keith's Pro Tips

"Focus your Supreme application on the southern and western exterior sides of your home since this is where the sun shines and where Cluster Flies often gather in clusters around windows and siding to rest or keep warm."

Cluster Fly Control: How To Get Rid of Cluster Flies

This page is a general Cluster Fly control guide. Using the products and methods suggested you will get control of Cluster Flies. Follow this guide and use the recommended products and we guarantee 100% control of Cluster Flies.

Cluster Flies are a common fly that invades homes, particularly when temperatures are cooler in the late portion of fall to early springtime. A Cluster Fly is often confused as a housefly or the horse fly because of their similar appearance. However, the Cluster Fly is larger than a housefly and can be distinguished by hairs on the thorax which appear to be yellow.

If it seems like you suddenly have cluster flies in your house, here's why:

During the fall and winter months, Cluster flies seeking warmth will make their way inside of buildings and structures, usually via a gap or hole which allows them entry. These flies often “cluster” together in large groups in dark secluded areas like spare rooms, wall voids or in attics.

Cluster Flies are then discovered when the weather becomes warmer and the flies, believing it to be Spring, begin to fly out and appear around windows, alarming homeowners.

If you have a Cluster Fly invasion in your home, this DIY guide will help you to eliminate the intruders using professional-grade DIY fly control products and expert techniques.


Cluster Flies on Screen Door

It is important to first identify the pest you are dealing with and get confirmation that it is a Cluster Fly before proceeding with a treatment approach. Misidentification can lead to using the wrong treatment methods and products, which will cost you time and money.

  • Cluster Flies are a smaller type of fly that ranges between 8 to 10 millimeters in length.
  • Cluster Flies are colored a dark, non-metallic gray with light and dark markings on their abdomens.
  • When resting, the wingtips of a Cluster Fly overlap over one another. When cluster flies land on a surface, they leave behind a greasy spot. 
  • What separates the cluster fly from a regular housefly is that cluster flies tend to fly much slower, making them somewhat easy to swat with a newspaper or fly swatter.
  • Much like their name indicates, Cluster Flies tend to hover around in large groups and can make for an unpleasant home infestation.

Use the image and description above to get confirmation that you are dealing with Cluster Flies. If you are not totally sure, contact us and one of our pros will assist you with proper identification.


Cluster Fly on an outdoor leaf

Once Cluster Flies have been properly identified, you can move forward with an inspection to find out where Cluster Flies are hiding or overwintering. During the inspection, you will focus on finding these hiding areas around your home, where you will apply the treatment.

Where To Inspect

Start your inspection indoors. Search in attics, storage rooms, or inside wall voids. When spring arrives they will emerge from their hiding spots and cluster around windows and doors. During the beginning of fall, they will be found in the walls outside of your structure. In the exterior of your building or home, inspect for any possible cracks, crevices, slits, or openings where they may enter the structure.

Homes that experience a Cluster Fly infestation should be forewarned that their presence will not be a one-off occurrence. Cluster flies tend to gather around the same home they have chosen year after year, essentially “marking” it as a prime area for hibernation by releasing a pheromone which lends a signal to other Cluster Flies telling them that this is a great area to nest and stay warm from the cold.

What To Look For 

You're looking for Cluster Flies and their hiding spots. Cluster Flies will make their presence known in warm days during winter or fall. If you already have a population overwintering in your home inspect the places mentioned above, paying attention to cracks and crevices inside the structure near windows or doors. 


Once you have confirmed Cluster Fly activity it is time to begin treatment. Remember to read all product labels and follow the application instructions on these labels and stay safe by wearing personal protective equipment (PPE).

To successfully eliminate Cluster Flies you will need to treat both outdoors and indoors with pesticides. Traditional fly control requires using thorough sanitation practices, but for getting rid of cluster flies, you will want to focus mostly on creating both physical and chemical barriers around the structure.

Indoors, use D-Fense Dust and Pyrid Aerosol. D-Fense Dust will be applied to cracks, crevices and voids while Pyrid will knockdown visible Cluster Flies as a space spray. Outdoors, use Supreme I/T insecticide to create a barrier around your structure.

Step 1 - Outdoor Treatment with Supreme I/T

reclaim IT treatment cluster flies

If you want to prevent Cluster Flies from overwintering you must apply a repellent insecticide around the perimeter of your structure. To do this you will use Supreme IT. Supreme IT is a powerful insecticide that will both kill and repel Cluster Flies from coming close to your property. It also has a residual or long term effect that will last for up to 90 days.

Calculate the square footage of the area you want to treat to determine how much Supreme I/T you will need. You can do this by multiplying the length and width together (length x width = square footage). For general applications, 1 fluid ounce of Supreme mixed in one gallon of water will treat 1,000 square feet. If you had an area that measured 2,000 square feet, you would need 2 ounces of Supreme mixed in with 2 gallons of water. 

Mix the Supreme I/T with water in a sprayer by filling the sprayer halfway with water, adding the appropriate amount of Supreme I/T and then fill with the remaining half of water and agitate the sprayer. Once mixed, conduct a perimeter treatment or barrier treatment on the outside of your structure by spraying 3 feet up and 3 feet out from the foundation of your structure.

Apply in this manner all around your property, while also spraying windows, doors, eaves, soffits, rain gutters, fascias, garage doors, electrical/plumbing penetrations, and cracks and crevices. Pay close attention to also spraying the sunny sides of the home as well, as this is where they will congregate before going indoors.

Step 2 - Indoor Treatment with Pyrid Aerosol

pyrid treatment cluster flies

Indoors, you will use Pyrid as a contact spray to quickly knockdown Cluster Flies. Shake the can well, point, and spray in the direction where Cluster Flies have gathered. Use short bursts when spraying.

Pyrid Aerosol delivers a quick and powerful knockdown that will incapacitate and kill flies shortly after they come into contact with this product. 

Step 3 - Apply D-Fense Dust To Cracks and Crevices

Duster Fill for Cluster Fly Control

To use D-Fense Dust, you will need a handheld duster. Simply fill the duster halfway with D-Fense Dust and leave lots of room for air to circulate inside. Apply by squeezing the duster. Apply under baseboards, in electrical outlets (remember to turn off the breakers, and take the plastic lid off, and apply to the side of metal encasement if you have one, where the wall voids are found), in attics, and even outdoors in the structure where cracks and crevices are found.


prevention reclaim it treatment cluster flies

Once you have applied treatment products, Cluster Flies will no longer be a problem but you will want to make sure you don't experience a reinfestation. 

The best way to prevent cluster flies from seeking out your home is by implementing exclusion and preventative measures. One such way is by sealing up cracks and holes with caulk or by nailing pieces of wood around gaps and holes when clusters flies could use to gain entry into your home. This job starts in the summer or right before Fall in preparation for their potential arrival.

You should also be sure to have screens on your doors or windows and if you already do, make sure they are tightly secure and are not damaged in any way. If they are, replace or repair them.

Apply Supreme IT at the beginning of Fall as perimeter treatment or barrier treatment, when temperatures start to drop. This treatment will prevent Flies from coming close to your structure. For even better results, apply D-Fense Dust to cracks and crevices after treating them with Supreme IT.

Key Takeaways 

What Are Cluster Flies

  • Cluster Flies are an overwintering pest known to invade homes in large numbers to stay warm.
  • You can easily distinguish a Cluster Fly from a common household fly as it is slightly darker and larger, and moves sluggishly. 

How To Get Rid of Cluster Flies In Your Home

  • To control Cluster Fly invasions, apply Supreme I/T outdoors. Mix the product in a gallon sprayer and apply outdoors to all window frames, door frames, soffits, eaves and the sunny side of the home as well as any other areas that are vulnerable to entry.  
  • To control indoor infestation of Cluster Flies, use Pyrid Aerosol for a direct knockdown of lingering flies and apply D-Fense Dust to cracks and crevices where they like to hide.

Preventing Cluster Fly Reinfestation

  • Prevent Cluster Fly reinfestation by sealing up cracks and crevices with caulk and performing preventative treatments of Supreme I/T and D-Fense Dust in the fall when it starts getting cooler.
Questions and Answers
  1. Q:Is this product safe for use around animals?
    A:Yes, these products are safe to use around animals when applied properly according to label directions. Keep all people and pets away from the treatment area during application and after until product as completely dried.


  1. Size:
    Supreme IT Insecticide
    $54.99 - $179.99
  2. Size:
    Pyrid Insecticide Aerosol
    $27.99 - $27.99
  3. Size:
    D-Fense Dust Insecticide
    $12.33 - $12.33
  4. Size:
    Solutions Electric Sprayer 1.5 Gallon
    $84.99 - $84.99
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