A compost pile is fantastic and makes turning kitchen waste into soil a breeze. When a compost bucket in the kitchen is full, and you take it out to dump it in the compost heap, it feels good to know that you are reducing waste going to the landfill and working to build soil for the planet.
Nothing can diminish that good mood unless, of course, a hoard of pests flies out of your compost bin to greet you.
What pests would do something so diabolical, you might ask? Flies, of course, and many, many types of them. Where ever organic matter is left to decompose, flies will show up. Even in our fruit bowl, we can experience a fruit fly invasion before we are aware that any of the fruit has gone bad.
If you have organic material that is in the composting process, then chances are you have adult flies around your compost, so is that a problem?
Should Compost Have Flies?
Unless the only organic material in your compost is brown materials, you will end up with some flies outside and maggots in compost the bins.
While this isn’t always pleasant, even in a worm farm, you can expect the occasional fly or two. Just because one or two flies are normal doesn’t mean that the presence of insects can’t also indicate a problem. If you see a swarm, for example, you may have a fly problem.
When large areas of your garden and lawn near a composting site is full of flies, and your soil has maggots in it, then you have a fly problem. This will usually only happen in unhealthy compost, but if it happens, it can be a headache to fix. You will know if the situation is getting worse when successive generations of maggots are able to hatch and grow into adults inside your compost bin.
Why Are Flies in my Compost Bin?
Flies are the most active when temperatures are high as they have more energy, odors carry further, and fly meals are actively composting in the heat. In winter, flies may only be active during the days high and will usually not reproduce and spread as quickly.
If you are having unseasonably warm weather or coming into high spring temperatures, you may start to see more and more flies zipping around your compost.
Different odors and food sources attract flies in greater or lesser numbers. I had a relatively fly-free compost pile until I added some old aquarium rocks; the next day, my pit was swarmed. After adding plenty of newspaper and brown materials, the flies left, but initially, it was quite a big swarm out of seemingly nowhere. If you recently added something new and see flies, chances are that that material is attracting them in mass.
The great thing about having a compost pile in the yard is you have some helpers you might not even be aware of.
While we tend to associate most wild animals with causing problems to our compost and thus being pests, some predators like birds and lizards can eliminate huge amounts of flies without you having to do anything. If you recently pruned and removed some of these habitats, you might have inadvertently removed your flycatchers.
The type of composter you have can influence how easily flies can get into your bin and multiply. If you can allow airflow but block access, you can keep out house flies but may not be able to stop adult fruit flies which are too small even for window screens.
Green material and other compost material can be made harder to access if it is buried several inches deep under soil or brown material like pieces of newspaper and soil.
What Compostable Materials Attract Flies?
Common kitchen scraps that we toss in our compost will attract house flies. The food scraps often have bits of animal meats and dairy products that attract these foul odor-loving pests. Kitchen scraps also tend to have lots of condiments and other sauces that will bring even more bugs. Wrapping this kind of kitchen waste in scraps of newspaper before composting can help keep flies out.
Veggies and fruit are less likely to attract house flies who have no interest in that kind of decomposition. However, there are plenty of other types of flies that are happy to move in and eat them. Using banana peels and other fruit waste to make fruit fly traps can keep these flies away from your bin, where they will likely swarm around your face.
Aquarium water was not something I considered would draw a lot of flies, but apparently, it is a favorite. After placing rocks and gunk from an old fish tank in the compost, I was immediately visited by giant flies. A had to sprinkle lime and bury it all to avoid being completely overrun. Next time I will bury it much deeper to prevent fly infestations.
Pet food is another waste that can attract flies once it gets wet. Dry food can sit outside, and while it will attract some pests, they are few, considering how much animal product is packed into the kibble. Once it gets wet, flies will flock to it and will count it as a good place to lay their eggs to give the maggots a lasting supply of food. Bury kibble to make sure flies cannot access it.
Types of Compost Flies
Composts are known to be a beacon for a host of visits from animals and critters of all types. Sometimes one type of animal will send tons of species to your pile to feed on various types of waster, flies are one such creature. There are so many different types of flies that are attracted to compost bins that it pays to take a quick look at a few of them.
Some flies are no issue to have buzzing around your compost, others are a sign your pit needs help now.
| Fly | Attracted To | Effect |
| Vinegar Fly | Yeast-like bacteria on rotting food | Flock to fruits and decomposing kitchen scraps |
| Fruit Fly | Fruit peels and scraps | Stays on fruit in compost, especially banana peels |
| House Fly | Kitchen scraps and meat or animal products | Breed quickly and spread diseases in and around waste areas |
| Black Soldier Fly | Decaying plant matter and fermenting fruits and vegetables | Faster decomposition of plant matter in compost bins with soldier fly larva |
Vinegar Fly
Tiny flies are often mistaken for fruit flies; they do not eat the fruit or waste in the compost at all.
As food breaks down, it ferments and produces yeast which is used in bread and alcohol. These bacteria are what the vinegar flies eat and why the smell of vinegar and decomposition attracts them to your pile. They are small and harmless, so keeping them out is nearly impossible and not worth the effort.
Fruit Fly
These little flies are usually your first clue that some of the fruit in your centerpiece is really ripe. When these are zipping around, chances are you need to clean and throw away something that is starting to rot.
While these aren’t fun to have in the kitchen, they don’t follow you around like house flies and will disappear soon after the fruit has been removed. In your compost, they will be around, but you can keep them from buzzing into your face by using fruit fly traps.
House Fly
When talking about problem pests in the compost, these are the flies you are typically talking about. They are big, get inside your home, land on your food and face, and can spread diseases.
Their maggots can overwhelm a pile and cause many issues like reduced nutrient quality and bad smells. Keep these flies away by covering waste, reducing moisture, and hanging fly traps.
Black Soldier Fly
One of the best beneficial insects that can grace a pile, BSF is able to produce tons of larvae that quickly turn your compost materials into high-quality, nutrient-rich soil.
The adults resemble wasps and cannot bite as they have no mouthpiece. They will eventually stake claim to your pile by introducing pheromones that drive other species of flies away. Adding plant matter and starch to your pile will attract these flies quickly.
How To Keep Flies Away From Your Compost?
If you already have some flies darting around your pile or if you want to avoid the eventuality of it then there are a few things you can do. Flies need to access your compost to lay eggs and ensure a future generation. Being near compost isn’t enough for them, so any barrier, predators, or chemicals you can safely use to keep them away will pay off big time.
Barrier
Lids and screens are the most common compost barriers. Allowing airflow but blocking flies can ensure that your compost doesn’t develop anaerobic bacteria and stagnant smells while still excluding adult flies from laying eggs inside the scraps. Soil and dry material can also be used to bury green waste that is more likely to attract flies.
Covering compost during times of high activity, like right after adding waste, and opening when the flies are less lively, can help you deal with pests without changing your whole composting system.
Environment
There are lots of things in the environment that can make it difficult for flies to breed in your compost. Wind and other natural occurrences can be used to create constant airflow, which is harder for insects to navigate.
Allowing trees and other habitats of fly-eating birds and reptiles to grow close to the compost bin can give songbirds a snack and keep your pest problems to a minimum. Flies need to come from somewhere, so if the area around your bin is free of trash and other house fly-attracting smells, you will be less likely to see them in your compost pile.
Chemical
Different chemicals can be placed near the compost or sprayed to reduce fly populations. Composts are outdoors, and a lot of chemicals that are used for insecticides will not harm worms and soil microbes. These can be sprayed around composts outdoors to wipe out a large population of flies quickly while you correct the problem in the pit.
Traps and fly killers can be set around the pile to keep the population down. A dish of water with apple cider vinegar to attract the flies and dish soap to keep them under the surface can be implemented easily and is very effective at reducing house flies attracted to your compost bin.