Suddenly Lots Of Dead Flies In House? They Are Cluster flies

The dead flies in the house are dead cluster flies you come across during winter and spring.

These flies enter the house in winter, looking for warm hibernating areas. The sunny days in the winter cause them to come out of hiding by tricking them into believing that spring has arrived.

But they can’t survive the cold.

You can also suddenly come across dead cluster flies in the house during the spring when these flies fail to move out of the house.

This guide reveals the easiest ways to prevent cluster flies from entering the house and how to solve the dead fly problem in your home for good.

Keep reading.

Cluster Fly – Identification

Cluster flies are outdoor flies that feed on the flower nectar, fruits, and plants sap. These flies are 8-10 mm in size and dark gray with yellowish or golden hair on their thorax.

Dead Cluster Fly

Cluster flies have a pair of wings with visible veins that rest in a V-shape pattern while they’re stationary.

They look like ordinary house flies. But they’re slightly larger than the house flies.

Cluster flies will lay eggs in the earthworm burrows because their larvae are parasitic on the earthworms.

After feeding on the earthworms, the cluster fly larvae enter the pupae stage in the soil and emerge as adult flies ready to breed and repeat the life cycle.

Cluster flies are active starting from the spring till the end of fall.

When the temperatures start to drop, cluster flies enter homes to hibernate. And they hide in places like the cracks in the walls and attic.

Many people encounter these flies flying inside the attic, so they’re also known as attic flies.

How Cluster Flies Enter Homes?

Gaps or cracks on the window sills, open doors and windows are the primary entry points for cluster flies.

These flies can also enter homes through vents, openings, and chimneys.

Invasion occurs in the late fall when these flies look for a warm place to hibernate or overwinter.

During the peak of winter, these flies are mostly unnoticeable despite being present in the house because they remain hidden.

When spring arrives or during the sunny days of the winter months, these flies come out, and you see cluster flies flying inside the house, trying to make their way out.

But like other small household flies such as house flies and fungus gnats, cluster flies in your home won’t lay eggs.

House flies can lay eggs in any dead animal or insect in the house and cause an infestation. Where as, fungus gnats can lay eggs in the drains and in the wet soil beds of potted plants.

In contrast, cluster flies won’t breed inside the house because they primarily lay eggs in the earthworms’ burrows.

It’s not only the cluster flies that can enter homes to overwinter. Many other bugs, such as wasps, stink bugs, and kissing bugs, invade homes to hide and spend their winter in the warm areas of your home.

Sudden Appearance Of Dead Cluster Flies Inside The House

Dead Flies In House

A large number of cluster flies enter homes to overwinter. These cluster flies in your home come out from hiding places during early spring, trying to make their way outside the house.

Many try to exit the home through the windows. But if the windows are closed, these weak and starving repeatedly bang themselves on the window screens.

They can’t survive this effort for long, which leads to their death.

Many homeowners notice dead cluster flies in a closed house, and in places like basement, when they return from a vacation.

Another reason I mentioned earlier is that the sunny winter days trick these flies into thinking that winter has arrived.

And they come out of hiding to get outside of the house. But the cold winter months decimate these flies, and you notice dead flies in your home.

How To Eliminate Cluster Flies

Cluster flies are not household pests like house flies. The trick to getting rid of cluster flies is to prevent them from entering your home.

And it’s pretty straightforward to do that without using any toxic pesticides to kill them.

Seal The Cracks On The Window Sills, Door Frames, And Walls

The crevices and gaps on the window sills, doors, and walls are the easy entry points for cluster flies to invade homes during the late fall.

Seal those cracks with a quality sealant.

You should also install window screens with fine mesh to prevent cluster flies from entering the house while windows are open.

Sealing the gaps starting from late summer will be best to prevent flies from entering your home.

Install Window Screens With Fine Mesh

You can also use meshed screens on the vents and openings in places like the bathroom, attic, and basement to stop cluster flies from entering your home.

These areas are all overwintering sites of cluster flies, and shutting down the entry points is a wise way to prevent these flies in your house.

Remove The Dead Flies In Your Home

Use your vacuum cleaner to get rid of cluster flies in your house. These flies in your home turn a bit sluggish, so it’s easy to scoop them off the surface with the help of a vacuum cleaner.

Do the same if you see any dead flies on the window sill.

Dead flies in the house, especially in the summer, will also attract pests like ants that feed on their carcasses. So, it’s essential to remove the dead flies.

Use Scents That Cluster Flies Hate

Cluster flies hate the smell of lavender, peppermint, and eucalyptus.

To repel these flies, you can spray these fragrances on the overwintering sites of cluster flies, such as the attic, basement, and storage rooms.

Spiders, rodents, mosquitoes, stink bugs, and kissing bugs hide in those areas too. And these scents keep them away as well.

You can also spray the repellent on your garden and on the windows to keep cluster flies away from your property.

Hang Sticky Fly Traps

Sticky fly traps near the windows, doorways, and vents are also a great way to stop not just cluster flies but also many other flying bugs and pests.

If you want to make a DIY trap, keep sweetened water in a bowl and cover it with a perforated lid.

The lid holes should be big enough to allow the flies to sneak inside the bowl.

The sweet water will attract any flies hidden inside your home. Once they sneak inside the bowl through the holes, they’ll fail to get out. 

Dispose of the water with flies in it. 

This trick also works in trapping tiny flying bugs, like gnats and drain flies, in your home.

Keep A Bug Zapper Outdoors

Bug zappers help reduce the flies and, to an extent, eliminate the chances of flies and mosquitoes in your home.

Keep one of them on your patio deck or the terrace. The bug zappers draw the flies, and when the flies land on it, it electrocutes them. 

We do not recommend using any insecticide sprays indoors to eliminate cluster flies. You don’t need it.

Grow Plants That Keep Cluster Flies Away

Plants such as lavender, basil, marigold, and catnip repel flies and insects. And they work on cluster flies, too.

Growing these plants outdoors and indoors helps a lot in reducing or eliminating the chances of cluster flies in your house.

Hire Professional Pest Control

A big house can have many hiding spots or overwintering sites for cluster flies. And despite your best efforts, you may notice the dead flies in the house often.

You might not have treated all the hiding areas, leaving it open for the flies to remain inside the house.

In that case, you’ll need to hire a professional pest controller to solve the cluster fly problem in the house.

Do Cluster Flies Spread Any Disease?

A cluster fly looks like a house fly, so many think cluster flies carry diseases. But they don’t.

Unlike horse flies, cluster flies don’t bite. And they don’t lay eggs in rotting food, dead animals, and wastes like the house flies.

So, there’s no way cluster flies can cause an infestation in the house.


The presence of a dead fly in the house can have many reasons. But if you’re suddenly noticing a lot of dead flies in the house, then those flies are cluster flies that were trying to make their way out of your home.

These dead flies don’t signify a cluster fly infestation because cluster flies don’t lay their eggs inside the house.

Cluster flies sneak inside homes during late fall or early winter, looking to hibernate or overwinter in the warmth of your home.

When they come out of hibernation during the spring or the sunny days of cold winter, these flies die while struggling to go out.

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