good aromas

(Virtual Scratch n’ Sniff v6.2)

It’s more accurate to say that a black soldier fly composter has a subtle, earthy aroma, plus the smell of whatever waste you’re processing. Some people compare the basic odor of a BSF colony to wet straw, but the main point is that it is not an offensive odor. If you’re smelling something foul in your BSF composter it’s not the larvae or their castings, it’s something else such as anaerobic bacteria and you need to change how you’re managing the system.

If you added the food shown above to a properly functioning BSF composter it would smell like those foods more than anything else. I realize you won’t be processing fresh food like that pictured above, but the point is that if you did then the aroma would be very similar to the fresh product. For example, once I added an entire loaf of stale cinnamon bread to my 5 gallon DIY bucket composter which I keep by the back door of our house. I walked by the composter a few hours after adding the bread and I was surprised by the delicious aroma of cinnamon. It’s not that the odor was just tolerable, it was appealing. Most of the time you probably won’t be adding something as aromatic as cinnamon in large quantities, so for the most part you shouldn’t notice anything but the subtle odors of the food scraps you’re processing. If you add bad smelling waste to your BSF unit it will smell similarly bad until the waste has been consumed.

Chronic bad odors can occur in a BSF unit, but it is a sign of imbalance which can usually be remedied fairly quickly. I know that some people reading this will be skeptical, especially those who have tried working with BSF with limited success, but I assure you I’m not exaggerating. I’ll be working on this post more in the near future and I will list several references to back up my assertions. I will also cover the causes of bad odors in detail as well as the remedies. For now I’ll add a quick quote from Kelly Slocum, a lady who has worked extensively with earthworms and also has considerable experience with black soldier fly larvae:

“I’ve worked on a few BSF waste processing systems, two of which were designed so that raw waste (usually hog manure) was processed initially by the BSF larvae, the poop from which (pretty liquid-y stuff) was stabilized by earthworms. These are remarkably efficient systems that process massive volumes of material each day and render the smelliest waste materials essentially odorless in just a few hours. I cannot emphasize enough the benefit of these flies or their suitability for working in conjunction with earthworms!” – Kelly S (SOURCE)

If you have experience working with BSF and can confirm my claim that foul odors are not a necessary aspect of it I hope you will post a comment below describing your experience.



10 thoughts on “Black soldier fly composting smells good…

  • June 11, 2010 at 5:23 am

    I am using Black Soldier Flies to compost at my house. They seem more suited to Florida than worms. How do I harvest the compost?

    Right now I am only using the tea which filters through the bottom of my system. Any help would be appreciated.

    • June 11, 2010 at 7:46 am

      Hi Tim,

      I still haven’t found a simple method for separating larvae from compost. You can remove most of them but getting the last 5-10% is a challenge. The juvenile larvae can be attracted with food so you can direct them the way you might do with worms, with desirable food scraps in one corner. You can also use this technique:

      The dark mature larvae don’t eat so you can’t use food to attract them, but if your unit has a self harvesting system the majority of those larvae should remove themselves.

      If you plan on using the compost outdoors you really don’t need to worry about getting every last larvae; any left in the compost will simply crawl away. The larvae aren’t able to consume fresh vegetables so releasing them in a garden isn’t an issue.

  • June 11, 2010 at 7:31 am

    We had record rainfall here yesterday, something like 10″ in less than 12 hours. My compost bin that was teeming with soldier fly larvae is now still. Can they drown? The bin is mesh wire so it does not hold water, but I know the rain must have soaked it for an extended period of time.

    • June 11, 2010 at 8:07 am

      Hi Barbara,

      I’m sure it’s possible to eventually drown a BSF larva but it would be difficult. I’ve found larvae thriving in containers of seed corn that have been flooded for several days. As long as the larvae can reach the surface they’ll be fine indefinitely.

      If your weather turned cool it might be that the larvae are buried, waiting to warm up so they can become more active again. Also, in an open system like yours there will be times when large numbers of larvae migrate away. I assume this happens because conditions in the pile become less than optimal, e.g., too hot, too little food for the size of the colony, etc. There is also an ebb and flow to a BSF larval colony and I assume an open system would experience greater fluctuations than one which contains the larvae.

      If most of your BSF have moved on don’t worry, just keep adding waste and they’ll be back to lay more eggs soon.

  • June 19, 2010 at 9:29 am

    I have had homemade pod for a few months and my colony is swimming in this thick paste that has a strong, sweet, but offensive smell. The thick paste is not pleasant to work with, I don’t believe it is pleasant for the the bsf, and is too thick to drain out the bottom drain. I have been feeding them a lot of bread so I’m thinking the problem is I am feeding them too much bread and my bsf density is not high enough.
    Any suggestions?

    • June 19, 2010 at 11:33 am

      Hi Brian,

      BSF could do fine on nothing but bread, so it isn’t the type of waste that’s the issue, but you’re probably right about the quantity. Bad odors indicate a system that is out of balance and that will only get worse if you don’t correct the problems that caused it to become anaerobic in the first place. I believe the two main reasons for a BSF colony becoming anaerobic (sewer-like odor) are poor drainage and overfeeding.

      Drainage: I think the only way to have good drainage in a BSF unit is to have a filter medium that covers the entire bottom of the unit. I’ve described using coconut husk fiber (coir) in several places, but I’m also testing synthetic air conditioner filter material now. It’s possible to operate without drainage, but you must be careful not to add too much waste with high moisture content. Alternatively you can soak up excess liquids with dry waste items like cereals, or with wood shavings/sawdust. A proper drainage system provides the best results and the most convenience.

      Overfeeding: Besides causing anaerobicity, overfeeding can also result in undesirable fly species being attracted to the unit. BSF repel other species in a balanced system, but excess rotting food can nullify this effect. It takes a lot of larvae to process a lot of waste, and to operate a BSF unit near it’s maximum you need a population that equals 2-3 inches (5-8cm) of solid larvae. On average waste should be consumed in a day or two. Items like soft fruit, cooked vegetables/grains and fish should be gone in hours, and hard items like raw vegetables, and hard fruits might take several days. In a colony that is sufficiently dense any rotting food will be consumed very quickly because at that stage it becomes soft. This rapid consumption of any rotting waste is one reason that a BSF unit should not have a bad odor; bacteria doesn’t have time to multiply before the waste is eaten.

      An anaerobic system is in a downward spiral with regards to BSF because BSF females are not attracted to these conditions. You may get some eggs laid in the unit depending on the extent of the problem, but not as many as if it were in a aerobic state. If you live in an area with a good population of BSF you might consider starting over with an improved drainage system. You could collect some BSF from your current system and use them to seed the new one: You can also try salvaging what you have by drying the waste out and adjusting the amount of new waste added. It would probably be best to stop feeding at all until the anaerobic conditions begin to lessen. The problem with salvaging what you have now is that it doesn’t address the deficiencies of your BSF unit.

      Thanks for sharing your experience and please let us know what you try and how it works out.

  • June 19, 2010 at 3:18 pm

    Quick tip: if going on vacation always remove the liquid collection cup!
    I left for a month and asked one of my neighbors to add some food every now and then to my biopod. Unfortunately he added a lot of fruit and when I got back the colony had crashed pretty hard and was completely soaked and smelling bad. I was extremely grateful he took care of it but I’m not going to make the mistake of leaving the cup on again.

    • June 19, 2010 at 5:02 pm

      Hi Christian,

      That’s good advice; a lot can happen in a month. I don’t use the liquid so I modified my original BioPod with a straight drain. It’s worked like a charm and you can see how I did it on my “tips and tweaks” page: I highly recommend using a pre filter also, either coconut coir as I show on the same page, or a synthetic. With the straight drain and the pre filter I could pour a few gallons of water into the unit and it would drain in minutes.

  • September 10, 2014 at 9:35 am

    Dear Members,

    I am an student based in Germany and am really interested in aquaponics which is why I came across this blog times and again and finally designed and started my own BSFL composter. Here my issue:
    The larvae are developping quite well (its an indoor system) and are soon to reach maturity. but they are far to big for my fish to eat (i am waiting for tilapia fry and run my AQ currently with goldfish) my question is:
    is there a way to grind the larvae into smaller pieces? has anyone done something in that direction? if so I would appreciate your feedback
    thanks in advance

    • September 11, 2014 at 12:11 pm

      It is good to hear about your success Konrad. I would guess that your fish would eat ground up larvae, but I have no experience with this. I believe that the light colored juvenile larvae are more desired by fish, so you may want to try both the juvenile and the mature larvae.

      It’s possible that someone on our forum would have more information for you. You might consider registering and posting your question there.

      Good luck,

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