So, you want to get rid of cluster flies. And you want to get rid of them fast.
Cluster flies can be extremely annoying just like regular house flies. And they can spread germs just like them as well.
That’s why you need to get rid of them ASAP.
This handy DIY pest control guide will teach you how to get rid of and kill cluster flies quickly so you can live once again without buzzing flies spreading bacteria all over your house.
Let’s get started. We have no time to waste!
Last updated: 8/29/19.
What’s a cluster fly?
The first thing we need to do is arm ourselves with knowledge about these annoying flies. With knowledge comes power. Don’t underestimate the power of knowing about the fly!
The cluster fly is about ¼ to ⅜ of an inch long. They look like dark gray ovals with wide wingspans. They don’t have any metallic coloration like the Bluebottle fly, so you’ll never see any metallic luster off their skin.
Cluster flies are very similar in looks to house flies, but they have a longer body and a yellow sheen on the thorax.
The cluster fly is often considered a parasite of earthworms and breeds outdoors in fields and lawns during spring and summer. They don’t lay eggs in human food, unlike house flies.
So they’re not as much of a health concern in food, but that doesn’t mean they can’t spread disease (we’ll discuss this in detail later in the tutorial).
The cluster fly life cycle (and why they breed so fast)
Female cluster flies lay their eggs in the soil where cracks are found.
The eggs hatch in 72 hours. The larvae eat earthworms as food for 22 days, to which then they go into the pupae stage for about 12 days before emerging as adults. Adult cluster flies eat flowers during the summer, as reported by Wikipedia.
When killed, their body gives off an odor of buckwheat honey
You’ll find them all over the US and Canada except for southern states.
What’s the difference between a cluster fly and a housefly?
The easiest way to tell is the coloration.
Cluster flies have no metallic green or blue on their ovular body and have a wider wingspan that forms a triangular shape rather than a semi-straight line like a housefly.
They also won’t lay their eggs in your garbage or food as the house fly does. Cluster flies only lay their eggs outside in the soil with cracks.
Houseflies fly and are quick to react. Cluster flies are slow-moving and easily killed.
A cluster fly vs. a house fly makes a marginal difference if you really think about. They’re both just pests that you want to get rid of from your house!
Cluster flies and seasons (summer and winter)
When fall comes, the flies begin to become a nuisance.
They enter houses in large numbers but will become worse using the winter as they move to a house for over-winter. They want war sites with cracks to live in and hide from any threat. This is where they become a problem.
Cluster flies will burrow deep into cracks and edges of windows that are weather=proofed. They’ll huddle within wall voids, attics, false ceilings, cracks, and every other nook and cranny.
Usually, they take over the upper regions of buildings, such as the second story or attic. They’re found on the upper two or three floors on the south and west sides.
They’ll come out when the weather warms up because they usually stop their “hibernation” during the spring. If there’s an unusually warm day in the winter or fall, they’ll come out. When they first emerge, they move very slowly towards any light source.
This is why they’re often found near windows or lamps.
Why do I have cluster flies?
Warner shelter. That’s about the only reason why they’ll come into your home. As fall and winter approaches, they seek warmer places to live.
Your house is much better than the freezing outdoors, so they’ll find any way in and then cozy up in a crack or crevice, usually around the weatherproofing of your windows or attic.
They’ll stay here until it warms up when spring approaches. It’s rarely a hygiene or cleanliness issue of why you have a cluster fly infestation dominating your property. They just want to migrate to seek warmth, and your house makes the perfect nesting site.
They’re also in search of food. But mainly they’re just there to winter-over until spring is here. So they take shelter in the many crevices in your home until it warms up outside.
But we want to get rid of them. So let’s kick them out!
How do cluster flies get in the house?
They get in through cracks, crevices, and other small entry points around your property- especially through window frames, doorways, and wall voids.
They take shelter in the attic or higher up floors rather than basements and floors closer to the foundation if you have a multiple-story house.
Part of this guide will cover how to seal up your house so you can prevent cluster flies from returning.
Be sure to read that part also or else it’s a waste to get rid of them because they’ll just come back next season. Cluster flies are a seasonal pest that only invades during the times when the weather gets cold.
They’ll stay hidden, breed, and thrive until it warms up. That’s when they resurface from the dark.
If there’s a random day in the wintertime where it warms up, you may see them come out. Or if there’s a bright light, because it looks like the sun and provides warmth.
What do cluster flies eat?
Cluster flies eat earthworms as they’re in the pupae stage. After they turn into adults, they’ll eat flowering plants.
They’re not interested in human food (or waste), so you shouldn’t worry about throwing foods out because they may be contaminated.
Though you should always check for signs of cluster fly activity in your food- just in case one may have found its way to your breakfast.
Are cluster flies dangerous?
Not really. They won’t bite, feed on, or prey upon humans.
But they can carry diseases on their body which may transmit to humans when they come into contact with food.
Regardless, they’re a real nuisance and should be ridden of quickly.
Where do cluster flies come from?
Cluster flies that are present in the home have been there for months already.
They’ve infiltrated your house and have been hiding in various cracks for months already. They came from the outdoors and sought shelter in your home due to the warmer temperatures.
Why are there cluster flies all of a sudden?
This is often due to a sudden change in temperature. If it gets cold, they’ll start moving into your house. It’ll take some time before the first batch of fly babies are born, but you’ll see them emerge when the temperatures pick up again.
There’s no real reason other than the temperature change.
Checking for cluster flies
The easiest place, and probably the area where you’ll find them first, is around windows.
You’ll find live and dead ones moving about slowly. Look for cracks and voids where they may be hiding for the winter.
Remember, cluster flies are small. You probably won’t expect to find them in a small crevice, but they’re there. You need to be meticulous to find the source of the flies.
You can also check around doors, patio doors, and even in your yard (don’t forget the outside of your house). Look for small moving flies that resemble miniature houseflies.
Carefully find crevices around the southern and western exterior walls to find ways cluster flies may be getting into your home.
Start with the walls, then move to windows and doors, and end with attics, crawl spaces, and false ceilings.
Don’t skip anything. Finding the source of the infestation is critical to preventing future cluster flies from getting into your property and beyond.
How to get rid of cluster flies naturally
Preventing the problem from happening in the first place is the best solution. If you already have them, trying out these prevention tips will help eradicate the current problem and prevent them from returning next fall or winter.
Get yourself a shop vac or mini vac.
Use this and suck up any and all cluster flies you see around your windows, doors, or other areas. This won’t eliminate the problem but will reduce the overall population. This is the first step and will wipe out a good chunk of the colony.
Don’t forget to stick the vacuum into the cracks and suck up any flies that are out of sight.
Vacuuming your house regularly should be an obvious plan of action during the time you’re trying to eliminate cluster flies. This will prevent them from settling in new areas and also keep your house clean from other pests.
Destroy their breeding areas
Cluster flies are slow, but will still attempt to migrate away from the areas you’re cleaning.
Be sure to vacuum them up if they get away. You can also use the vacuum to suck them up for easy eliminations whenever you see them. You can suck out cracks and crevices where they hide and you otherwise can’t reach with the hose extension.
If you don’t have a shop vac or mini vac, just use the proper attachment to your standard vacuum to get into the cracks and hard-to-reach areas where they may be hiding.
Keeping your house clean will get rid of cluster flies. Seriously. After they migrate and you eliminate the remaining population from the current season, keep your house clean and seal it up.
That’s pretty much all you need to prevent future cluster flies and kill the current generation of flies, not to mention all the other bugs and pest you’ll stop from infesting your house. Keep it up!
Vinegar has been known to be useful not in terms of killing cluster flies (though it can if they drown in it) but rather used as a cleaning agent around dirty trash cans or garbage dumpsters.
Cluster flies thrive off of food, waste, and especially liquids that have leaked from your trash bags and collected at the bottom and around the sides of your trash disposal.
Cleaning up clutter
One thing you can definitely do is clean up all the junk you’re hoarding.
This will not only take away a possible hiding place for cluster flies (plenty of cracks and crevices
Cluster flies will breed there like crazy.
You can use vinegar to clean off any trash residue and also pour it to soak up the debris on the bottom of your trash can and let it sit for 24 hours. If you suspect there are cluster flies there at the bottom of your trash, pour more and let it sit even longer.
Then let it drain out and use sunlight to dry it. Be wary of mosquitos and frogs though.
Bleach is another excellent cleaning agent for trash cans.
This stuff will kill cluster flies on contact, so use bleach to kill them and clean your trash cans.
You can pour some to soak up all the mess collecting at the bottom of your trash cans and if you suspect a cluster fly colony at the bottom of your garbage receptacle.
If you have an area where you see a lot of cluster fly activity, consider using those sticky fly strips. They work extremely well because cluster flies aren’t too smart and are very slow-moving, so they’ll get stuck on them and perish.
You can buy this stuff in a roll that you unroll and stick to whatever surface in whatever position you want. Stick this fly tape around windows, doors, and even kitchen cabinets if you have them there.
This tape will reduce the population and also serve as a monitoring tool to see how the population is doing. You can use this to gauge your progress as you get rid of them.
DIY cluster fly traps
You can build a simple, yet effective cluster fly trap at home by using a canning jar and a lure.
Step 1: Get a mason/canning jar
Step 2: Fill it with sugar and water in a 1:1 ratio (half water, half sugar)
Step 3: Pour the solution into the jar and leave it alone
Step 4: Use the perforated lid and open it slightly so that flies can get in
Step 5: Put the jar wherever you see cluster fly activity
The flies will smell the sweet water and lure themselves into it. Once they go in, the usually can’t get out. Use the jar to catch cluster flies automatically and also use it to monitor your progress like the fly strips above.
You can use colored jars to hide the trap if you don’t want to look at disgusting flies in a jar.
Or you can use something to cover or wrap the outside of the jar. The flies don’t need to see the liquid, they’ll just smell it. So it doesn’t matter if it’s covered or hidden.
You can also just stash it somewhere that no one will see if you want to hide
Building your own DIY cluster fly trap with a 2-liter bottle
You can also just use a soda bottle and cut it in half and invert the top. Then follow the same process.
DIY cluster fly traps are cheap, effective, and serve as a monitoring tool to see how many more flies are in the area. At first, you’ll catch a lot.
Over time, you should be seeing less and less if the process you’re doing to get rid of them works properly. If not, reassess and try another method on this list. There are plenty of natural ways to get rid of cluster flies.
Cluster flies like warmth and are also attracted to light (when it’s warm) because it signals that spring is here.
Since light bulbs often offer both warmth and light, they’re known to gather around any light fixture indoors and outdoors.
You can easily spot them around lights and you can even use them as traps. When they gather around light sources, you can vacuum them up with a hand attachment.
Cleaning up clutter
One thing you can definitely do is clean up all the junk you’re hoarding.
This will not only take away a possible hiding place for cluster flies (plenty of cracks and crevices
You’ll also have less clutter which is always good, and you’ll have less dust every time you vacuum. Stuff that you want to keep can be organized into storage bins. The other stuff can all be thrown away or donated.
This is always a good opportunity to clean up your household of all the junk that’s piled up over time.
You’re cleaning up a cluster fly problem, so you should take the time to prevent further pest problems by cleaning up. Hygiene first!
The best type of sprays to kill and prevent cluster flies are residual sprays.
These are the sprays that linger and stay behind so future colonies can’t be established. Spray as directed.
The most popular places to spray are outdoor areas where cluster flies can enter the building.
Note the following locations:
- Beneath eaves
- Around windows
- Under doorways
- Cracks in the foundation or building
Apply in the late summer or early fall before they seek warmth. This will keep them out of your house for warmth.
There are also sprays that can be sprayed directly into the soil so they can’t lay eggs and will minimize cluster fly populations and future generations.
You can even make your own fly spray at home using natural elements:
Pets (dogs, cats, and livestock)
Dogs, cats, and other livestock or pets can be the source of cluster flies. Keeping food, waste, and other clutter around your house will help create a situation where cluster flies (and many other flies and pests) will thrive. Keep your area clean and maintained.
If you live on a farm or have livestock, be sure to clean up any straw, manure, or bedding. Use fly masks on larger species and pyrethrin-based sprays can also help eliminate any pests around your animals.
Use a combination of traps, sprays, and screening to control cluster fly populations around livestock.
Stopping cluster flies from returning
The best way to prevent cluster flies from returning is prevention. This means sealing up your foundation, attic, cracks, crevices, and other ways for them to enter your home.
Again, check the most commonplace areas that flies will enter- eaves, windows, doors, and attics. If you can’t get to all the places you need to check, use residual sprays around the same places and also use sprays for the soil to prevent breeding.
Just doing basic upkeep will keep cluster flies out and never again will they return.
Stop them from getting into your property
The trick isn’t to kill them after they’ve laid eggs and started a colony in your house. It’s to stop them from breeding in the first place.
And they won’t breed without a warm and dark crevice to start. So stop them from getting into these nooks and crannies around your house (and the soil) and you’ll never have to deal with cluster flies again.
Use a cheap caulk gun and a good quality caulk to seal up gaps and cracks around your house. Even the smallest cracks or gaps around your home can provide a way for cluster flies to enter.
They’re likely to enter through the attic or second/third floors as there’s plenty of space to hide from predators and it’s dark and quiet. So be sure to seal up your attic from the inside and outside first.
Then get the rest of your house including your foundation.
Check upper floors
They’re likely to enter through the attic or second/third floors as there’s plenty of space to hide from predators and it’s dark and quiet.
So be sure to seal up your attic from the inside and outside first. Then get the rest of your house including your foundation.
Also be sure to seal cracks in walls, as wall voids are another favorite for cluster flies.
If you have larger gaps that can’t be sealed with caulk, you can use basic housing insulation. Use spray foam insulation and fill up those cracks.
This won’t only prevent cluster flies from entering your home, but keep your temperatures constant and even save your power bill as your house will keep temperatures stable.
How to protect your home against cluster flies
You can check if you’ve sealed up all cracks by doing this simple method:
Step 1: Wait until it turns nighttime.
Step 2: Get a flashlight and walk outside and point the light in all the possible cracks you’ve found and filled.
Step 3: have another person on the inside and look for light shining through. These are cracks that need to still be filled. If you’re alone, you can mount the flashlight anywhere and go indoors to observe the light that infiltrates the wall.
Repair all screening
Be sure to check your patio doors and window screening for small tears.
Cluster flies will easily find these gaps and get into your home. They’re easy and cheap to replace, so be sure to fix that problem.
Here’s a video that demonstrates the process of fixing a screen door:
Clean up drainage and gutter systems
Check around your house for backed-up drainage and gutters. Cluster flies need water to survive besides the occasional meal. Look for standing, stagnant water, as this will give them a source to drink from.
Also, look for spots on the lawn that are significantly softer than the surround areas. When this dries and forms cracks, cluster flies will lay their eggs in the soil cracks. Fill the cracks after it dries or
Check all around your property for cracks and entry points
If you have a basement that’s often humid, get a sump pump or drainage line that’ll help get rid of the excess moisture. Or consider just getting a cheap dehumidifier.
Also, check your gutters for backed up water or standing water. Remove all debris like leaves and garbage from them so water flows freely and drains properly.
Check the following locations around your house for drainage problems:
- Basement drains
- Soil soft spots
- Drain pipes
- Sewage/septic systems
- Ponds or bodies of water
- Any other source of water
Did you get rid of the cluster flies?
Well, I hope this guide has served you well and eliminated your cluster fly problem.
If you’ve dealt with them before and have any tips for others who are trying to deal with them, leave them in the comments section below. If you have a persistent problem, you may want to hire an exterminator for professional help.
Let me know if this guide has helped you!
Thanks for reading.
Currently an active researcher in the pest control industry for the past 8 years- with a focus on using natural and organic methods to eliminate pest problems.
I share handy DIY pest techniques I come across here to help out others (and possibly save them from a mental breakdown).
Fight nature with nature.