How to rid my compost bin of its flying insects? Or are they okay?

February 13, 2025 10:56 AM

So we have a covered compost bin in the corner of the yard. We're careful not to put any bones or greasy food remnants into it (and now the city wants that stuff in their green, yard waste bin anyway). Yet like every composting experiment I've undertaken, removing the lid means a face-full of flying insects escaping. Nothing I see in the compost literature ever addresses this. Not to worry, their larvae are processing the compost? Or does this mean something's amiss with my composting mixture?

My wife's solution is to just cover it up with a layer of soil, which reduces the insect population, for a while.

posted by Rash to Home & Garden (8 answers total)

Best answer: It's probably black soldier flies, which are beneficial to compost! But you could also add more brown materials like wood chips, shredded cardboard, etc. to heat up the pile and kill the larvae.
posted by chaiminda at 11:02 AM on February 13 [8 favorites]

+1 to black soldier flies. There's a method of harvesting the larvae from active compost piles in a sort of automatic-snack-machine for home chicken flocks.

The flies are harmless though sorta scary lookin'.
posted by jquinby at 11:13 AM on February 13 [3 favorites]

Keep in mind that those flying insects you are breeding will feed a lot of songbirds! And bats! I get lots of them in my bin too, I just make sure not to lean over the bin when I'm opening the lid, it's fine.
posted by Rhedyn at 11:27 AM on February 13 [9 favorites]

Thirding black soldier flies. Also if you’re on fb there’s a group called “composting just composting” or something like that and it’s about, well, you know. Pmuch every third post is about black soldier flies, I’m guessing for the reason you mentioned
posted by toodleydoodley at 11:45 AM on February 13

If you don't have bugs in your compost, that's a sign something is wrong!*

(Ok some e.g. commercial composting for mushroom growth media is purposely kept insect-free but generally healthy home compost bins have plenty of bugs. I have a pair of wrens that nest near mine so they can feast and feed their babies every summer :)

Also you can just leave the lid off or ajar, that will allow for less of a flurry of bugs when you open it.
posted by SaltySalticid at 11:56 AM on February 13 [2 favorites]

Best answer: I have an outdoor compost bin without a lid, and while there are some flies not that many. When the weather gets hot i put either hay or grass over the latest addition to keep the flies out. Easiest is the kind of coconut mat used to wrap potted plants in winter from freezing, kept damp. When you add something just flip it open and cover again.
If the top is covered with damp organic blanket like the coconut mat the compost worms will come right up to eat the organic matter and you can see them when you open the mat.
Also, when it is very dry i water the bin which keeps ants from building a nest in the compost bin and discourages flies laying eggs there.
My urban garden is very small and so the bin is right by my seating, and also close to neighbours so i try to minimize flies and rather keep the very efficient compost worms happy 😊
posted by 15L06 at 12:14 PM on February 13 [3 favorites]

20+ year composter here - insect life is highly desirable, and yes, they are breaking down the organic matter. As noted above, very likely Black Soldier Fly, which are so useful that their larvae are sold specifically for this purpose.
posted by reedbird_hill at 8:13 AM on February 14 [1 favorite]

If it's BSFL there's a whole subreddit dedicated to those bad boys.
posted by deludingmyself at 11:07 AM on February 14 [1 favorite]