What to do about flies in your compost

Surprise: the answer might be "nothing."

Nine out of ten times, this happens because you’re adding too many food scraps at once or you’re not adding your food scraps properly. If you tend to throw food scraps on top of your compost and leave them, you’re more likely to get flies. If your compost is composed entirely of food scraps, you will definitely get flies.

Are flies really a problem?

Yes and no. Broadly speaking, flies and maggots are a normal and healthy part of the decomposition process, and managing a compost pile means adjusting your overall perception of their existence. Yes, they can be a nuisance—but their presence is often a strong positive signal that your compost is nutrient rich and high-functioning. Soldier fly larvae, for example, are actually extremely beneficial and should be left alone. They’ll break down green material and manure in your pile efficiently and extremely quickly, which reduces overall odors and the potential for your pile to attract other, larger animals.

However, if your pile is teeming with flies, you probably want to deal with that. (Fair.) There are four types of flies that tend to crop up in compost piles: fruit flies, vinegar flies, soldier flies, and house flies. The best way to deal with them is to figure out which kind you’ve got, and then adjust the conditions of your pile to make it a little less hospitable.

Soldier fly larvae in a compost pile (sorry!)

Fruit and vinegar flies look very similar and are attracted to similar conditions. Specifically, a lot of rotting fruit. If you’re finding these guys in your pile, throw in more browns and make sure to bury new food scraps deep into the pile each time you add them. Check the overall moisture of your pile, as well, and make sure you’re not keeping things too wet.

We all know what houseflies look like. If you find yourself with an infestation, make sure to add more carbon right away and then turn your pile. Bury new food scraps as you add them. You might also consider fiddling with your overall pH. You can do this with store bought garden lime (you only need a little), or you can do it by adding in a lot of high pH, naturally-sourced materials like pine leaves or citrus peels.

Soldier flies are most easily identified by their larvae, which are about a half-inch long, brown, and scaled. Finding them in your compost is a tremendous honor, even if they look objectively disgusting. Leave them alone.

Overalle best way to get rid of flies is to avoid attracting them in the first place. Make sure your pile stays balanced, and that your carbon and nitrogen are in roughly correct ratio to each other. A good rule to abide by: roughly two handfuls of carbon for every handful of nitrogen. Lastly, and I cannot emphasize this enough, integrate your food scraps into your pile when you add them. Cover them in leaf litter or make a small hole in your pile, add them there, and cover them up again.

Love,

Cass