Cluster Fly Guide

Your home may unknowingly serve as a winter retreat for cluster flies. These pests seek shelter in cracks and crevices to escape the cold, only to reemerge in spring when temperatures rise—a process known as overwintering.

Once cluster flies have entered, they are difficult to control, making prevention the best solution. The key is to block their entry points before cooler temperatures arrive to stop an infestation before it starts.

How to Keep Cluster Flies Out

• Seal cracks and gaps around windows, doors, vents, and siding.
• Inspect attics and crawl spaces, as these are common hiding spots.
• Install weather stripping to close gaps around doors and windows.
• Use fine-mesh screens on vents, chimneys, and other openings.
• Apply residual insecticides to exterior walls before fall to deter entry.

These preventative measures must be taken before temperatures drop—once inside, cluster flies are much harder to eliminate. Taking action before fall ensures your home stays pest-free through the winter.

For effective cluster fly prevention, select an insecticide labeled for cluster flies, such as Onslaught or Suspend Polyzone. The best option is a residual insecticide, as it remains effective for an extended period, allowing more cluster flies to come into contact with the treatment.

Why Use a Residual Insecticide?

• Long-lasting protection – Residual insecticides continue to kill pests long after application.
• Prevents reinfestation – Flies that land on treated surfaces will be eliminated over time.
• Ideal for barrier treatments – Helps stop cluster flies before they enter your home.

Before applying, always read the product label for proper dilution rates and safety precautions. Treat outdoor surfaces before temperatures drop to prevent cluster flies from overwintering inside your home.

Creating a protective insecticide barrier around your home is an effective way to keep cluster flies from entering. Using an outdoor insecticide labeled for cluster flies, you can treat key areas where these pests attempt to gain access.

How to Prepare and Apply Insecticide

1. Read the insecticide label to determine the correct mixing ratio of insecticide to water.
2. Wear protective gear, including gloves and long sleeves, before handling chemicals.
3. Mix the insecticide solution in a hand pump sprayer, securely replace the cap, and shake well.
4. Refer to our guide on how to properly mix and apply liquid insecticides if needed.

Where to Apply Insecticide

• Spray 3 feet up and 3 feet out around the foundation perimeter.
• Apply 3 feet up on the sunniest side of the home, where cluster flies tend to gather.
• Treat around outdoor light fixtures, as these areas attract flies.
• Spray around door and window frames to block common entry points.
• Apply where utility pipes enter the home to seal off hidden access spots.
• Treat any cracked caulking around windows and doors to prevent entry.

Applying insecticide before cooler temperatures arrive will help prevent cluster flies from overwintering inside your home.

In addition to exterior treatments, applying insecticide indoors serves as a second layer of protection against cluster flies. Using a residual insecticide-water mixture, target key indoor areas where these pests may enter or hide.

Where to Apply Insecticide Indoors

• Around door and window frames – Treat these common entry points to stop flies from moving further inside.
• In cracks and crevices – Apply insecticide in small gaps where cluster flies may hide.
• In crawlspaces and basements – Dark, undisturbed areas are prime hiding spots for overwintering flies.
• Where utility pipes enter the home – Seal off access points where flies may enter from outside.

Application Tips

• Use a residual insecticide to maintain long-term effectiveness.
• Follow the product label for proper mixing and safety instructions.
• Apply before temperatures drop to prevent cluster flies from settling indoors.

By treating both the interior and exterior of your home, you create a comprehensive barrier to stop cluster flies before they become a problem.

For additional protection, applying a residual aerosol insecticide, such as D-Force Insecticide, can help prevent cluster flies from entering your home. Aerosol treatments are particularly effective in hard-to-reach areas where flies may attempt to hide.

Where to Apply Aerosol Insecticide

• On window and door screens to deter flies from landing and entering.
• Around outdoor light fixtures, where cluster flies are often attracted.
• In the corners of garages and porches, where flies may seek shelter.
• Around window and door frames to block potential entry points.
• Around soffits and eaves, common resting areas for cluster flies.
• In cracks and crevices around the foundation to prevent fly access.

Application Guidelines

• Follow the aerosol insecticide label for recommended reapplication intervals.
• Do not apply aerosol spray in areas already treated with liquid insecticides, as this can reduce effectiveness.
• Use before temperatures drop to stop flies from overwintering inside your home.

By combining aerosol treatments with liquid insecticides, you can create a layered defense to keep cluster flies out all season long.

Practicing basic sanitation and exclusion techniques is the most effective way to prevent cluster flies from entering your home. By sealing entry points and maintaining cleanliness, you can reduce their access and eliminate attractants.

Steps to Keep Cluster Flies Out

• Seal cracks and crevices around doors, windows, soffits, vents, and utility entry points using caulk or sealant.
• Install door sweeps to block flies from sneaking in under exterior doors.
• Use Xcluder cloth to seal any gaps where pipes or utilities enter the home.
• Maintain indoor cleanliness by regularly vacuuming, sweeping up crumbs, and emptying trash cans to remove potential attractants.
• Fix drainage issues and eliminate moisture buildup around the home.
• Manage yard waste by removing grass clippings, wood mulch, and debris piles that attract earthworms—a key food source for cluster flies.

By following these exclusion and sanitation practices, you can significantly reduce the risk of a cluster fly infestation and maintain a pest-free home year-round.