Black Soldier Fly Larvae: Pest or Partner?

As if the potential “ick factor” with worms wasn’t enough, some vermicomposters have moved beyond earthworms to eradicating organic waste with the Black Soldier Fly Larvae, a nice way of saying maggots.  I resisted learning more about BSFL because a man in the suburbs has his limits.

Many vermicomposters I speak to, especially those in warmer climates, encounter BSFL in their bins by accident.  At some point, the Black Soldier Flies themselves found themselves a nice worm bin, laid their eggs and left, only to die themselves no more than 8 days later.

People post pictures of the larvae on the extremely helpful Facebook groups, wondering what these “pests” are and how to get rid of them.  Hell, I’d probably want to get rid of them too.

But it wasn’t until my friends Larry Shier and Quoc-Huy Nguyen Dinh each separately began writing about BSFL with Larry taking a more academic angle by writing a highly enjoyable book about BSFL’s potential for waste mitigation while Quoc has documented his own experience with them, both on his site at The Little Worm Farmer , via his really cool online magazine, and his own how-to e-book aimed at getting people started with BSFL.

The BSFL Life Cycle

BSFL end up spending precious little time in the “fly” stage.  The adult Black Soldier Fly didn’t exactly win the Darwinian lottery as it lacks a mouth, believe it or not. Not being able to eat, it spends its last few days breeding and laying eggs before, predictably, starving to death.

Under ideal conditions, these eggs grow into larvae in about 4 days, spend at least two weeks in the larval stage before becoming pupae, then finally adults, where they spend their last few days in increasingly hungry copulation.

Black Soldier Fly Larvae’s Amazing Composting Chops

As it turns out, Black Soldier Fly Larvae are ridiculously effective composters!

For instance, here’s a side-by-side of Quoc’s bin.









A couple things to note here though.

Find the fish in the photo on the right. Gone. As you know, fish in a worm bin is a bad idea.

And the time between these two photos? 8-12 hours.

If you’re still not convinced, check out this video of BSFL destroying a couple fish.

It’s pretty gross, in an awesome sort of way.

BSFL Misconceptions

Newer vermicomposters – and I still consider myself in that category – need to overcome a couple common misconceptions about our vermicomposting bins to fully appreciate BSFL.

  • A vermicomposting bin should include only worms, worm castings, and decomposing organic matter. False.
  • A vermicomposting bin will be an ecologically diverse environment, attracting all sorts of critters.Some of these are actually pests, like mites and centipedes, but you should see various forms of life as a sign of success, not failure.

  • Worms are always the best composters. False.
  • BSFL are 75-100 times more efficient at processing waste than earthworms.If castings for your garden are your objective, stick with composting worms like the Red Wiggler, European Nightcrawler, or Indian Blue. But if eradicating waste is the point, then worms don’t hold a candle to BSFL.

BSFL is a Partner For Sure

Now if your objective is to harness the BSFL and possibly raise them, you’ll need a specialized bin like Quoc shows us here. But if they have found their way into your worm bin, there’s no reason to pull them out.

In fact, I’ve learned their frass (which is another fancy word for poop) makes an excellent food for your worms, so there is some serious recycling going on in a bin with both composting worms and BSFL, so much so that I can imagine you’d struggle to find enough feedstock in a worm bin with a lively BSFL community.

To boot, the BSFL themselves make an excellent source of protein for chickens, fish, and other animals while their oil content makes them a candidate for production of biodiesel if production can reach scale.

Learn More About BSFL

Exactly how to grow and use BSFL effectively is beyond the scope of both this article and my own knowledge.  But if you’re interested in how BSFL can process your own household waste (to include meats, which is pretty cool) or even how BSFL can be applied to larger-scale municipal waste mitigation, then I recommend Larry Shier’s book, Black Soldier Fly: Eco-Technology for a Sustainable Future and following Quoc’s progress at The Little Worm Farm and maybe even pickup his own book, A Guide to Composting with Black Soldier Fly Larvae.

24 thoughts on “Black Soldier Fly Larvae: Pest or Partner?

  1. While interesting, since my municipality forbids chickens, I think I’ll forgo the BSFL. Maybe if I get into aquaculture, I’ll reconsider, but for now, I’ll let others in zone 7 think about keeping them thru winter. 😉

  2. I had a biopod bin full of BSFL two summers ago; they are amazing! I’m in zone 7. But they were difficult to keep fed, and I didn’t harvest the castings until after they had frozen – couldn’t get over the maggot factor. So last summer I had a few in my worm bin, and that seemed to work out.

    Nice article; I’ll definitely look at these links.

  3. I’m not sure if they are BSFL or not but in my compost digester that I throw all kitchen waste in I welcome the maggots in the spring time. They reduce the volume enough that I only have to empty if 1x per year and help a lot with the stink.

  4. Yes, I have raised BSF. It is different and fun. I even purchased a special composter to raise them in.

    They work hand and hand with red wigglers but sometimes they can over power them. There is a little more care with them. If you haven’t watch the video 4500 larvae and a hamburger, DO. LOL
    There is a great forum

    I had to stop raising them for a while but would love to start back up when I get chickens. (don’t tell my husband LOL)
    The funny thing is that last summer because it was very hot I separated my Red Wigglers and BSF to bring the red wigglers in the house. So I thought. LOL every once and while a left over larvae will hatch and I have a BSF flying in the house.

    1. How did you separate your RW from the BSFL? I am trying to bring my vermiculture bin inside and the maggots immediately crawled out, even though I thought I had sealed off the container, so it was only tiny mesh at the top.

  5. That’s funny about your husband! I’m sure my wife would file divorce papers if I brought these things in the house! 🙂

    And thanks for that video. Simply amazing.

  6. I’m still not sure if the maggots that show up in my pit are BSF or not. They are about the size of a grain of rice, maybe a little bigger.

  7. I’m no BSFL expert, but I would check them in a week or so. They should have grown considerably in that short of a time.

  8. Last year they stayed the same size the whole time they were around. Being outside in a corner of the yard with a lid that allows air flow and bugs to enter/exit there is never a great amount of flies. Whatever they are I’m happy to have them because they get rid of the stink of rotting food and make it so I only have to empty my bin 1x per year.

  9. The same maggots are back and the bin is overrun by them. The stink from the food waste is gone and the level is dropping so I’m happy. I will still have to shovel it out in the fall but I will be able to fit kitchen waste into it for the rest of the summer.

  10. My maggots are black! Never white and it’s a seething mass! There is no smell but my bin is very close to the house, so I’m anxiously on the lookout for a fly plague! I’ve carefully not put citrus in and I eat my egg shells ? No animal waste or bread goes in either so must just be too much fruit and veg. I’ve had my bin for 5 years and never emptied it! Don’t even get enough compost for my garden!

  11. My compost is currently a seething mass of them.
    Rome wrote “… I’ve had my bin for 5 years and never emptied it! Don’t even get enough compost for my garden!…”
    My guess is the waste turns into flies and flies away, leaving no compost!

  12. I find they overtake the worm farm. I’ve tried fishing them out of my warm farm and depositing them into my tumbler compost bin. Even with regular tumbling and the addition of plenty of brown compost (dried leaves, cardboard, pea straw mulch) the BSFL maggotscause the compost to go to sludge 🙁

      1. I just bought a worm farm with $60 worth of various worms and it has been taken over by BSFL I am not sure if they will eat the worms? What do you think..the worms were a serious investment and I lost my last batch by giving lots away to friends!

        1. Hi Jacqui,
          The BSFL will not eat the worms but they will outcompete them for food, I’m afraid. They eat really fast.
          Urban Worm Company

  13. Hmmm. No wonder the compost goes down when those soldier fly larvae move in. They eat all the scraps, hatch into adult flies and fly away, taking those nutrients away in the form of their bodies.

  14. I’m so infested with these that they are swarming up the sides of my compost bin as if trying to escape, makes me afraid to open the lid! And the smell is really putrid. I get that that these guys can be beneficial, but how many is too many??

  15. was thrilled to see that they set up shop in my wormery as I have chickens! It’s been hot as an oven this summer and I kept getting 5 eggs a day on average from 6 laying hens! I attribute my newfound chicken rearing success to bsfl as I don’t do anything out of the ordinary.

  16. Two weeks ago I had a thriving worm population, although I started to see a lot of large fly larvae in the bag. From what I read. They are harmless, so I let them go
    Today I went to harvest some castings, and I found NO live or even dead worms or any signs of them anywhere in the bin. What I did find were hundreds of fly pupae. Is it possible they ate every last one of worms?

    1. Black soldier fly larvae are harmless to worms as in they are not predatorial. They do have the ability to outcompete worms for food if their population gets out of control. This is most likely what happened. It is probably due to adding too many food scraps without adding enough brown material. Or overfeeding in general, without allowing enough time for microbes and worms to break down the food.

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