First question: What the heck are Black Soldier Fly Larva (BSFL)?
If you asked me that question before this summer, I would’ve been just as oblivious as you. It was only after I went outside to dump my kitchen scraps in my backyard compost did I notice a bunch of fat, juicy looking larva devouring the food waste in the pile. Every time I came back to the pile it had shrunk in size, demonstrating how veracious of eaters these little guys were.
Now, after having done some research and built my own bin to harvest them, in my opinion there is no better solution for organics recycling on the planet. They naturally appear in any warm climate, can turn a diverse organic waste stream into close-to-nothing in mere days, and are extremely rich in protein, calcium, and other nutrients as animal feed. It’s a perfect closed loop system that nature has provided us. I see it as my responsibility to take advantage.
Another awesome thing about BSFL is they are self-harvesting, which means once they grow to their prepupae stage (the point when they’re mature and ready to morph into a fly) they crawl out of the substrate. You can see from my bin design below, I built them a ramp, railings to keep them from climbing away, and a hole at the top of the ramp for them to drop through into an awaiting tupperware. Each day I check the catch-container to see how many were harvested, and bring them over to my neighbors who have a small flock of chickens. On my arrival, the chickens go crazy, like I’m a member of The Beatles or something. Clearly the larva are tasty along with the other dietary benefits they possess.
Building my bin was fairly simple. I’m by no means a handyman or carpenter, but I used The Foxy Chicken’s step by step instructions to assemble the bin for less than $50. The bin doesn’t include any grand engineering feats or advanced technology, but there are some key points to consider when designing your bin:
- Include holes at the bottom for water drainage in case the food waste you add is heavy in moisture (i.e. vegetative/fruit scraps)
- Paint the outside of the bin, and inside the food waste area to protect against wood rot
- Build a lid, because the BSFL like the dark environment. Also, make sure to place bin in a shady place for the same reason
- Construct a ramp at a 30-40 degree angle. If any steeper, the BSFL have difficultly crawling up, if any flatter, the BSFL will likely spill over the railings. Also, DON’T paint your ramp, as it makes it slippery for them!
- Place a catch-container under the drop hole, and make it lizard-proof. The first day I started my bin, I opened up my side-hatch to find a open-mouthed lizard laying in my tubberware like it was his personal hot-tub, waiting for the larva to drop into his mouth. As a result, I created a down-shoot that connects the hole that the BSFL drop through to the container, eliminating outside interference
- Cut out a side latch that you can open up to take out the harvested BSFL in their catch-container beneath the ramp
- Mount corrugated cardboard or one of those plastic yard signs with ridges to attract egg-laying flies. (Also, use OSB for the bin’s walls. This engineered wood has enough ridges and bumps for the flies to lay eggs in.) This is essential to keep the bin going throughout the season. See my picture below
Since BSFL are only active during the warmer months, and go dormant in the Florida dry season, the bin is seasonal. The temperature range of 75 – 104 degrees are ideal of BSFL. Seventy percent humidity is considered optimal for their lifecycle, but Florida’s 100% humidity doesn’t deter them. I’m lucky because soldier flies were naturally attracted to my bin, and I didn’t need to buy eggs to jump start it. They came by themselves, and flies continued to lay eggs in the corrugated area as long as I have aromatic food nearby.
I’ve been asked about how much work goes into maintaining a BSFL bin. Managing the bin IS NOT passive! It’s difficult to automate all the challenges that may arise, and it takes a basic set of human problem solving skills. Although, there are some customizations that can save time. For example, I have seen some people who use PVC piping to connect the harvesting hole to their chicken coop, so that the BSFL are funneled straight into the coop for instant feeding.
Still, the biggest issue to avoid with any compost pile or BSFL bin is letting the waste turn anaerobic. You can instantly tell when this has happened due to the distinct smell. I’d recommend turning the pile of waste with a trowel or hand rake daily. All in all, the bin maintenance takes 5-10 minutes per day, and up to a combined hour of my time each week. To me, it’s totally worth witnessing a perfect closed loop system function, and I hope to one day scale it to a commercial level. Not to mention it’s awesome to see how quick they devour the waste! Watch this time-lapse video if you want to be blown away!