Tips for dealing with fly larvae in your compost bucket

As the weather warms, we’re starting to get questions about small larvae crawling around inside your Little Green Buckets. Based on last summer, we estimate that 5-10% of buckets will have this “problem” during the warm summer months.

Jump to the tips.

What are they? More often than not, they are Black Soldier Fly (BSF) larvae, though they sometimes might be housefly larvae (aka “maggots”). Both types of larvae are typically white and will grow to be at most about half an inch long.

Why are they appearing all of the sudden? BSF require warm temperatures (around 82°) to mate. It’s that simple. Here in Albuquerque, the problem may be exacerbated by the fact that so many of us switch to evaporative cooling right when outdoor temperatures enter the BSF breeding range, which means our indoor temperatures jump up 5° to 10° and our doors and windows are more likely to be left open, allowing them into our kitchens.

Are they bad? From a composting perspective, no, they aren’t bad. BSFs actually play an important role in the early decomposition of food waste, and are increasingly being farmed both as beneficial insects for the compost pile and garden and as a protein source for animals feed… and even for human consumption. There’s also some evidence that BSFs help control housefly and fruit fly populations by eating their eggs. The only problem with BSF larvae in your compost bucket is that they might give you the heebie jeebies. We understand completely, and we don’t like them squirming around in our office, either, so the rest of this post will focus on how to prevent their appearance in the first place, and how to manage them when they do appear.

Will they fill my house with flies? No. The first three phases of the BSF lifecycle (egg, larva, pupa) take 36 days, so even if you are on our biweekly pickup plan AND miss a week, your food waste will be at the compost facility before adult flies emerge.

Preventing & reducing fly larvae in your compost bucket

So what can you do to avoid fly larvae in your bucket, or control them once they start appearing? Here are a few tips that might help, either individually or in combination.

  1. Empty it weekly. Biweekly pickups members might want to upgrade to weekly memberships for the summer, and drop-off members might make a point of swapping buckets every week, even if the bucket isn’t quite full. BSF eggs take 4 days to hatch. So while they might emerge by the end of the first week, if you got unlucky and had eggs introduced right away, it’s really the second week that is problematic.
  2. Freeze or refrigerate your food scraps, or at least the stinky ones. You probably can’t fit your whole bucket in your freezer, but you can freeze (or even just refrigerate) smaller quantities in tupperware or plastic bags, then dump them into your Little Green Bucket when you put it out for collection. If you have air conditioning, keeping your bucket directly in front of the fan (with the lid on, of course) might do the trick.
  3. Snap the lid on, limit openings, and avoid leaving food out. While BSF might sneak in and lay eggs right there on your dinner table, it’s more likely that they are being introduced when you leave your leftovers on your counter for a few hours or leave your compost bucket open. Keeping your food scraps in the fridge and then emptying them into the bucket once a day is a good way to combine a few preventative measures.
  4. Spray them with vinegar. Once you see one larvae, expect more than you can squish by hand to appear in a hurry — a single fly can lay as many as 500 eggs at once. The easiest way to kill them is boiling water, but we obviously don’t want you dumping boiling water into your compost bucket. We’ve had some success spraying them with standard household white vinegar (5%). We’ll be testing garden vinegar (20%) and cleaning vinegar (30%) in the coming weeks and will update this post when we see the results.
  5. Keep the bucket outside. While keeping your bucket outside will increase the likelihood of larvae appearing, and increase their numbers, it will also limit your exposure to them and keep them out of your kitchen. Alternatively, just put it outside if you see larvae, to keep them out of site until your next pickup or dropoff day.

Do you have other ideas for how to address this problem? Please leave a comment — we’re all in this together!

5 thoughts on “Tips for dealing with fly larvae in your compost bucket

  1. I’m wondering if it’s possible to purchase smaller versions of the biodegradable green bags that come with the Little Green Buckets. If so, would it be possible to use those bags for scrap collection in the fridge or freezer, and then put them directly into the larger bag. It might reduce water use, as well as the handling of food waste.

    1. That would be fine — some of our members already do exactly what you describe. We don’t stock other sizes of bags, but they are widely available online. The key is to get bags that are “BPI certified compostable”. Don’t be misled by the word “biodegradable” — that is most likely a petroleum-based plastic with just a little potato-based plastic mixed in. If you’re unsure whether a particular bag is ok, send us a link or a photo and we’ll let you know.

  2. We had a bad outbreak of these in our backyard compost a few years ago. They seemed harmless, we didn’t know what they were or if they would bite, but the lizards and spiders loved hanging out and eating them as they would hatch and fly away. Now, we still have a few of the casings left in the compost. I kinda wonder why they don’t return every year – they were very beneficial to breaking-down the compost.

    1. In our experience, they are a bit picky about the conditions they reproduce in, at least in large numbers. It needs to be hot but not scorching, humid, moist, stable temp, and with the right feedstock. Our buckets create those conditions comparatively easily (especially since there are so many buckets out at a time, all in slightly different conditions), but outdoor open-air conditions in Albuquerque aren’t so hospitable, especially in terms of moisture.

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