A no-frills approach
Introducing the Black Soldier Fly Bucket Bio-composter v1.1, a minimalistic approach to black soldier fly composting. Despite it’s limitations I hope this simple DIY composter will inspire people to try their hand at attracting and culturing BSF grubs.
Each bucket will vary but the basic concept is the same.
Vent Holes
I used a 1/2 inch flat drill bit for the vents, but a larger hole is acceptable. Smaller might work but the vent holes are the primary entrance for the adult BSF and they might have difficulty with less than that. The pilot holes were drilled level with the bottom of the raised band that is near the top of the bucket. I put the vents there for two reasons. 1) By placing them close to this “overhang” there is some protection from rain entering the bucket 2) The female BSF will be attracted to the scent coming from the vents and the protected spaces created by the reinforced rim will present them with a good egg laying site. I expect most of the eggs to be laid in these protected spaces.
Go slowly when drilling or you may tear up the overhang. I drilled very slowly and still chewed it up a little. 
On my particular bucket the reinforced rim was 3 to 4 inches below the top of the bucket, but it’s higher up on some buckets. Higher is better if you have a choice because as we all know, hot air rises. To exhaust the dead space above my vents I drilled the singe hole that you can see in the photo of the finished composter.
Drainage
This composter doesn’t utilize a continuous drain system. There is a drain hole on the side of the bucket and periodically you’ll need to tilt the bucket and let the accumulated liquids drain out. I plugged mine with a cork.
I picked a place about 3-4 inches from the bottom so that when tilted all but a small amount of liquid will drain out. The bucket biocomposter can be placed at an angle in the opening of another 5 gallon bucket for draining. Handle this liquid or “tea” carefully and sanitize your hands afterward. The tea can be used as fertilizer, but I don’t have experience with that so you’ll need to do your own research and testing.
Coconut Coir Liner
(The photos above are from version 1.0. In the newer version the drain hole is placed lower.)
Coir is made from the outer husks of coconuts and is commonly used for lining wire planters and hanging baskets. I bought a flat piece at a garden shop about 1 inch thick and cut 3 disc shapes to fit the bucket. Coir is also available in loose form. I don’t think it matters which type you use, and I’m guessing that about 3 inches of total material should work. Be careful if you cut it because it’s pretty tough. I set mine on a thick piece of Styrofoam and “sawed” through it with a utility knife. I feel fortunate to have completed the task with all ten digits still intact.
The purpose of the coir liner is to provide a space for liquid to accumulate without flooding the food scraps that you’re composting. The BSF grubs cannot process the scraps well if they’re submerged, and the liquid creates an anaerobic environment (no air) that encourages the growth of bad bacteria. BSF grubs create an aerobic environment (with air) through the churning action that happens when they feed. By maintaining aerobic conditions you will avoid imbalances that are easily recognized by offensive odors. A balanced BSF colony smells like wet straw plus whatever food you’ve added recently.
The Lid
You can snap the lid into place on your bucket composter but I don’t want to go through that process every time I open and close the unit. A simple solution is to just set the lid on top without pressing down and then secure it with small bungee cords as you can see in the photo. My dog keeps raccoons and other scavengers away so usually I don’t even use the bungees. Of course if you have a dog it might be the worst scavenger of all.
The knob serves a more important function than the obvious one. I’ve observed BSF females laying eggs on the top of the lid on several occasions and by using the knob you can avoid crushing the fragile eggs. It won’t be the primary area for egg laying but there’s no good reason to crush good BSF eggs and the knob is easier to handle anyway.
Avoiding Ants
In the photo above I’m using a barrier created by setting the composter in a pan of water to prevent ants from invading the contents. You can also set the bucket on a stand like a stool and treat the legs to repel ants. Similarly you could suspend the bucket on a chain or rope.
One issue I didn’t consider with the water pan is that the black soldier fly grubs that migrate out of the bucket may drown. A possible solution is to put the bucket in a dry pan that in turn sits in a larger pan with water.
The process of composting
I’ll go into detail about using the bucket composter on a separate page and I will add a link here when it’s ready. The basic concepts will be the same as using a BioPod, just on a smaller scale and with a few addtional steps. During hot weather keep the bucket in full shade, don’t overfeed, and if it begins to smell bad you’re doing something wrong. I expect I’ll be able to process about a half pound (.25kg) of food scraps with this unit each day, or maybe a little more. This composter isn’t designed for high effeciency or high volume, it’s designed as an introduction to bio-composting with black soldier fly grubs (Hermetia illucens). If you enjoy this you’ll probably want to graduate to a BioPod or a more elaborate DIY system. On the other hand you might find that this bucket design is all you need…
Harvesting Grubs
To harvest the mature BSF grubs you will need to periodically leave the bucket in a tilted position. Alternatively you could mist the inside walls of the bucket and set the unit in a larger container with a layer of sawdust (not pressure treated), peat, or some other dry bedding material. The moisture on the walls will allow the grubs to climb vertically, exit via the vent holes, and onto the bedding material. Assuming the bedding remains dry the grubs will not be able to escape the catch pan.
Coming soon: “how to” page for the BSF bucket biocomposter v1.0\
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