I no longer recommend building this unit. I have released a new version which is far superior to this design. To see the BSF Bucket Bio-Composter version 2.0 please navigate to that page by clicking HERE. Please note that there are several very good and informative comments at the bottom of this post.

diy unit v1-1 lowered drain

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

diy unit-pilot holes diy unit-drilling vent holes diy unit-drilling vent holes closeup diy unit-finished 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.


diy unit v1-1 lowered drain diy unit-draining inside view diy unit-draining

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

diy unit-coir discs diy unit-coir discs installed diy unit-coir discs demo

(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

diy unit-lid with knob

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

diy unit-in water pan

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\


restarting the colony 2009

Starting my third year with the black soldier fly

I’m going into this season with a small colony made up of grubs that were laid last fall. Where I live the winters are mild so it was fairly easy to maintain the colony through the cool months. At the end of last summer my BioPod was full of compost and I should have harvested it.  As a result of that neglect my beautiful compost became anaerobic, dense and a bit smelly. What can I say? It’s been a hectic year. :) I think early fall may be a good time for removing the BSF compost because the grubs are likely to be less active on average in winter versus the warm months. I believe the churning action of a very active colony (summer) is an important factor in keeping the compost aerated and “fresh”. I said early fall for compost harvesting because I’m afraid that if you wait too long in the season you won’t have time to rebuild the colony to near maximum size in preparation for the winter when BSF breeding stops (unless you’re in the tropics).

Spring cleaning

first BSF of 2009

BSF don’t normally land on people,
but this one had just emerged from it’s pupa so I was able to handle it.

I removed all of the compost and washed my BioPod. I hand picked a few hundred of the light colored juvenile grubs from the old compost and added them to the unit along with some fresh food scraps. I didn’t clean the grubs themselves so a small amount of the old compost was transferred along with them. This old material will act as a great attractant to BSF adults who have now started the mating season. A healthy and balanced BSF colony doesn’t have a strong or bad odor, but the females will always be attracted to the faint scent of an established colony. As I mentioned previously, my compost is anaerobic now and therefore smelly, but the typical mild smelling compost from a balanced culture would work just as well.

BioPod-spring cleaning

A new drain

As you can see from the first photo in this post I have replaced the BioPod’s liquid collection jar with a straight drain into the ground. (I hope you won’t be too disappointed with me Dr. Olivier.) I haven’t been gardening and to date I haven’t done anything productive with the liquid (also called “tea”). For that reason I’m opting for the convenience of the straight drain for now. To see how I set up the drain you can go to my “Tips and Tweaks” page.

The pond

You can also see my pond in the photo. I moved the BioPod near the pond because I’ll be feeding fish scraps and culls to my BSF colony this year. I don’t enjoy killing fish, but to maintain the population in a healthy balance I will be removing some of them. I’ll have some help from birds, turtles, and snakes, but the pond is fairly close to the house and wild predators are limited. With the BioPod I’ll be able to convert the excess fish into nutritious black soldier fly grubs and return them to the pond as fish feed. I have a post about my philosophy regarding feeding BSF grubs to other animals here.

Black soldier fly grubs are also fantastic fish bait, so having the BioPod near the pond will be very convenient for fishing. I’ve created a page about BSF as bait which you can find here.

Winter BSF culturing

As I mentioned earlier I did keep the colony going through the winter, but I didn’t keep any records. The one thing I can confirm is that the BSF grubs will interrupt their usual development during the cold season. I had very few BSF laying eggs by October and the last one I observed laid her eggs late in that month. By November I stopped seeing any smaller grubs in my colony. I assume then, that the grubs that  currently make up my colony are at least five months old. During the summer this stage would only last 2-3 weeks. Next winter I want to be better prepared to test cold weather bio-composting and I hope that some of you will participate in it with me. At the end of this summer we should start a thread about this at the BioPod forum to share strategies and results.

Logging this year’s results

My goal this year is to keep a log of all the food I add to the colony and the weight of the grubs produced. I’ll be fairly general about recording the composition of the food scraps so this won’t be a controlled experiment. The fact that I’ll be adding a large amount of whole fish and fish scraps will certainly effect my results. My goal is to provide a general outline of what you might expect. You can find the log in the column on the right of this page under Black Soldier Fly Pages, or simply click here.


I recently collected a newly laid clutch of black soldier fly (Hermetia illucens)eggs for a photographic study of their development and I isolated three of them for the photos. I placed the three individuals and the remaining few hundred BSF from that clutch into identical containers. I didn’t keep detailed records, but there is an interesting comparison that I believe illustrates the flexibility of BSF development.


Temperature and humidity were approximately the same for both batches of larvae. The large larvae is one of the three that was separated for the photos and all three are similar in size. The small larvae is from the more crowded container which held the bulk of the larvae. The same type of food was available to both groups, but I can’t attest to the quality of the food in the more crowded environment that produced the smaller larvae. From casual observation it appeared that there was always food available to both groups. The most obvious difference between the two containers was the density of larvae. The small larvae where moved into a larger container six days after hatching and seem to be healthy and growing, but are still relatively small.

I imagine any properly educated researcher would not be surprised by this difference in development, but to this layman it’s very interesting.


frigid north

Actually, this post applies to any region that has seasonal temperatures below that which support BSF mating. This encompasses the entire continental U.S. except for a few extreme southern areas.

Black soldier flies (Hermetia illucens) are common in tropical and subtropical regions, but their range extends into many northern states of the continental U.S. You can easily operate a BSF bio-composting unit in northern states during the warm months, but you can also maintain the colony through the colder months with a little extra effort.

A black soldier fly colony generates its own heat

Maintaining a BSF unit in cold weather without heating it is possible because the churning action and digestion of the black soldier fly grubs creates heat as a byproduct. Under cold conditions keeping the colony at the optimal temperature range of 85° – 100°F (30°-38°C) is as simple as consistently feeding them and placing an insulating material directly on top of the pile. Simply remove the insulating material, add the food scraps, and then replace it. It’s important to feed the colony consistently in cold weather because without food the temperature will drop and the colony will become dormant. You can think of it like a diesel engine, if it gets cold then it’s hard to get it started again.

If the larvae are exposed to freezing temperatures they will die. Also, any insulation on top of the colony needs to have an air gap between it and the BioPod.

Maintaining a BSF colony during extended periods of sub-freezing weather will probably be a challenge for a novice, but it’s worth tying because at worst you’ll learn more about this fascinating creature. If you aren’t up to the challenge just yet then you can enjoy BSF culturing up to the point where the weather in your area makes it difficult and then resume in the spring. If you can store some or all of the compost through the winter it should make attracting the BSF easier in the spring.

Process more food scraps, harvest less larvae

The time it takes BSF larvae to mature increases in cold weather from the usual few weeks to a period of up to several months. I’ve maintained BSF larvae in the juvenile stage (light color, actively feeding) for five months through winter keeping the unit outdoors with some insulation. The same individual larvae will eat all winter which enables you to continue bio-composting without the need to replenish the colony with visiting females. However, since reproduction doesn’t happen at this time you must stop harvesting larvae if you wish to continue processing waste through the cold season.

In warm weather the colony has a tendency to overheat, so in cool weather the larvae are able to consume food scraps even more efficiently.

How adventurous are you?

I don’t recommend bringing the BSF unit into your living room, but why not try keeping it in the garage or a shed when the temperature drops? Sure, a few larvae might get out, but so what? The adult fly will just emerge from it’s pupae in the spring and then you’ll have the pleasure of gently capturing it and releasing it outdoors. They are harmless creatures after all. I don’t think a heated space would be the best choice though, because it might trick the larvae into developing too quickly. I would guess that 40° – 60°F (5°-15°C) is a good range to try testing this theory, and of course you would need an insulating disc of some sort to keep the colony warm. The degree of insulation would depend on the ambient temperature in the space.

I’m cursed with living in an area that rarely gets cold so if you try this experiment please let me know how it goes. I would love to post photos of your set up (if it works :) ).

Mike made a comment below reminding me of a presentation by ESR about BSF culturing in winter. Here is a link to that article: http://www.esrla.com/winter/frame.htm


This method doesn’t involve the dark, prepupal larvae which are self-harvesting

The coffee colored black soldier fly grubs (prepupae) are the final stage before pupation into adult BSF (Hermetia illucens). To our advantage they are programmed by nature to crawl away from the food source in search of a suitable pupation site. In a properly designed BSF unit these larvae crawl up a ramp and drop into a collection bucket where they will live for weeks without any maintenance.

The method described below is for harvesting the earlier stages when the larvae are actively feeding and growing. It doesn’t work for the mature larvae because they don’t eat therefore aren’t attracted to the bait in the collection container. It works very well for the light colored immature larvae.

The Immature Larvae Collection Device or ILCD (old butter tub)

Take a cheap container and cut some small holes around the bottom edge.

immature larvae collector with fish pellets

(click on images to enlarge)

Add something delicious (any food scraps will do), and simply place it on the surface of the compost. I used moistened fish food because I’m training my fish to eat it and this is a good way to introduce them to the flavor (I feed the larvae to the fish). Just about anything will work, but fresher items will make handling the collected larvae more pleasant.

The photo below was taken 2 minutes after placing the tub on top of the compost.

immature larvae collector after 2 min

This is after 11 minutes.

immature larvae collector after 11 min

The photo below was taken 40 minutes after adding the container.

immature larvae collector after 40 min

This quick harvest totaled about 2 cups (.5 litre) of small to medium larvae. I don’t have many large larvae at this time due to the crash I caused in the colony a few weeks back. I do have a lot of larvae, just not large ones yet.

fishing, bait,