Fly Cage Black Soldier Fly Breeding UK.




Introduction: Fly Cage Black Soldier Fly Breeding UK.

Hello my fellow builders.

This is a big project BUT it can turn all of your household food waste or even dead fish from your Aquaponic or aquaculture system into high protein feed for your animals. Black Soldier Fly larvae are the best, balanced feed for chickens, lizards, fish and anything else that benefits from high protein feed.

The box is a self contained environment that will allow you to breed BSFlies all year round. It is insulated, heated and provides everything you need to raise maggots all year round.

The list of what you will need for this build will vary. You lucky sods who live in hot and sunny places will only need to build the frame and cover it with mosquito net.

For those of you who live in the UK, you need to insulate the box, provide heating, lighting, a lecking place (Usually leaves, where the female sits and waits for her mate) and airflow.

So here is the list.

-Sheets of thin ply wood. 6-8mm
-Sheets of thicker plywood. 12-16mm
-Sheets of Celutex insulation board25mm thick.
-Lengths of 50mm batton.
-Wood glue.
- Decking screws.
-4" Extractor fan.
-4" Ducting
-4" Carbon air filter
-Mosquito nets
-Door draft excluder sticky strips
-Oil heater
-50Watt LED floodlight. (MUST BE 50w or more or flies won't mate. They require BRIGHT sunlight.)
-Circulation Fan.
-Bottles of liquid. (They store heat and help prevent wide fluctuations in temperatures.
-Thermostat controlled Plug. (One for hear and one for cool. )
-Inline on/off timer.
-5m of 3 core cable and a plug.
-Maggot bin. (This box has space for 2 bins like the wooden one I posted a while ago. Without this you have nowhere for the maggots to eat. You have nowhere to feed them.)

-Cut off /Mitre saw

Step 1: First the Insulated Base.

Size matters. Now what some of you will like to hear but it is true.

Black Soldier Flies require a decent area to fly around because the first part of their mating ritual is aerial.

I chose to build a box 1.2×1.2×2m tall..

For step one we will be using 50mm baton.

Cut 4x2m Lengths and 9x1.2m lengths. (The extra length is for the door which hangs off the cross piece.

Next cut corner supports for each corner. Out of 50mm Baton about 20cm long with two 45°angles.


For your corners you could also use
Building restraint straps, cut into 20cm lengths and hammered to 90°.

Now put together the frame.

Step 2: The Floor.

Now that you have a frame, you need to make an insulated floor.

So, cut a piece of +-16mm ply to the exact outside dimensions of the floor.

Now tip your frame over, apply wood glue to the bottom of the batons that were previously touching the floor.

Now screw the plywood bottom onto your box.

Now that you have the bottom attached, lift the frame back up. Your 16mm plywood bottom should now be all that touches the floor.

Next, cut 25mm celutex to fill in the floor, inside the square made by the bottom batons. Once in place the celutex should completely hide the 16mm ply. Like in picture 3.

Lastly, cut thin ply wood to cover the celutex over. It too should fit inside the square made by the bottom batons.

Once in place, varnish the thin layer of ply and then silicone around the edges to prevent any future spilled water from seeping into the celutex which insulates the floor.

Once done, your floor should look like picture 5.

Step 3: Putting on the Sides of Your Box.

The sides of the box are simple.
A layer of 25mm celutex covered on the outside with a thin layer of ply wood 6-8mm ply is perfect and cheap but provides protection for the celutex.

Start with the back of the box.

What I did was run a bead of silicone around the baton frame then stick the celutex to the frame.

Next I would place the thin ply over the celutex before screwing through both the ply and the celutex into the baton.

Once the back of the box is on, you should cut the celutex and ply wood for the Left and Right sides but don't stick them in place just yet.

You are going to put a mosquito net across the front of the box, above the cross piece. The sides will hold this in place. You can see this in picture 4 above. I will explain how I did it in the next step.

Step 4: Your Mosquito Net for the Summer Time.

Run a bead of silicone along the left and right rear upright.

Now put the left and right side sheets of celutex and thin ply wood in place but only screw them in along the rear upright on both sides.

This will leave space for you to put the mosquito net in place.

Once you have cut your mosquito net to leave you with a double layer, run a bead of silicone around the front upright and both cross pieces on each side.

Now put the mosquito net in place on one side. Get it laid smoothly over the silicone then push the celutex+thin ply onto the silicone on that side before screwing it in place. It should now look like picture 1and 2.

(Be careful not to let the screw grab hold of the net as it will pull it all into a bunch.)

Now stretch the mosquito net over to the other side. It needs to be smooth and quite tight but don't stress the little bumps, they will go when you stretch the top and bottom later in the build.

After securing the other side it should look like picture 3 with the mosquito net covering the entire front.

Now you need to cut the left and right sides of the mosquito net covering the space under the middle cross piece.

Now fold the mosquito net around the back of the cross piece and stick it in place, try to stretch out all of the bumps in the process.

Step 5: The Roof and the LED Floodlight.

This is a few steps in one.

1. Cut a piece of thin ply to cover the entire roof but only screw down the back. Now cut celutex to fill the cavity below the roof inside the surrounding batons.

2. Now, cut a length of thick ply to hold the celutex in place. Screw this length to the underside of the batons between the front and rear top cross pieces.

3. Mount the LED flood light to a 30cm length of 50mm Barton then screw the bottom to the cross piece of plywood from #2 above.

4. Cut a hole in the side of the box at the top. The side you choose should be easily visible to you where you plan on running the box.

5. Mount the in line 24hour timer to run the floodlight while also mounting the thermostat controlled power plugs. This will control your heater to keep the box inside the optimum breeding temp range. Carve out a section of celutex to flush mount both the thermostat controlled plugs and a 4 plug extension lead which will be powered 24/7 from the power entering the inline timer.

6. Stretch out the mosquito net and screw down the rest of the roof to hold it in place. Now your mosquito net is stretched out smooth and your light and power is done.

Step 6: Covering the Mosquito Net in Winter.

Cut a piece of celutex and thin ply to cover the mosquito net in winter. Screw it in place above the cross piece.

I cut a circular port and put on a door with a seal. This allows me to check on the system without opening the big door, just the little one towards the top of the cover of the mosquito net.

Now for the door.

Cut a piece of celutex to cover the opening. Now cut two pieces of thin ply wood to cover the inside and the outside of the door. (I used offcuts for the inside of the door)

Now bolt the door together and bolt the hinges to the door before sxrewing them to the cross piece.

When the door opens it should sit up like in picture 5. I use a bunje cord to hold it up.

Step 7: Finishing Touches.

OK the last bits.

1. Cut a 4" hole in the back corner opposite to the power timer for the light. This will run as needed to clear any smell. (It should only smell if you put too much meat into the system)

2. Mount the carbon filter to the inside below the extractor. This eradicated the majority of smells while preventing flies from escaping.

3. Hang your small oil heater from the roof to hang just above the cross piece. This will plug into the heat plug of your thermostat controlled plugs. Set the heater to 80% if it has it's own thermostat. Alternatively if you prefer not to use the thermostat controlled plug, you can experiment with the heater and discover how high to set it to keep the temp between 26 and 30°C.

The only other heating option is to use a big bucket of water with a fish tank heater inside. This provides less heat but will have less fluctuation.

4. Hang as many cola bottles down the back corners. The liquid will hold heat and stop huge fluctuations.

5. Fit a fake branch of leaves about 30cm from the top to the box. The females will sit on the leaves and wait for the males they choose.

6. I set the extractor fan to run for half an hour 4 times a day. I also made it vent into a pipe that carried it's exhaust out through the wall.

Step 8: Now You Need a Maggot Bin.

Now that you have a happy breeding environment for your flies, you need a bin to raise the maggots in.

I recommend the wooden design I previously posted. 2 will fit in your fly box. This also has the benefit of auto harvesting into a bucket of flour. Just pass it through a seive and you are sorted.

You can put in anything that you can eat. Unlike worms, there is not much out there that maggots won't eat except egg shells, sticks and bones

I recommend adding some bokashi bran to the system to help break down the food you add and try not to add too much in the way of meat at one time.

I made a big mistake when I left my return pipe to one of my fish tanks turned off all weekend. I lost sixty trout and threw them all into my fly box. I took pic 5 and 6 just 18hrs apart. The problem is, they quickly began to stink because there was too much meat for a single bin to process fast.

My fly box provides an average of 2kg of maggots each week which feeds my 200 trout easily. This has made me self sufficient, free protein and less waste. The castings makes a great compost.

The last advice I can offer is this. While processed food does not smell bad, if you put too much food stuff in before the maggot population is high enough, the unprocessed food could start to smell. This is where the box comes in.

If constructed properly and vented regularly (by the extractor fan), your box will not smell. To be safe I recommend using draft excluded tape to seal any gaps that could let the smell out. This will mean that the only air leaving the box goes through the carbon filter.

The only other thing is humidity. 80% humidity is ideal for egg hatching. If you live in a dry region then you can set up a cheap humidifier to run a few times a day.

Anyway, I hope the build goes well for anybody who builds the fly breeding box. I am happy to answer any questions you have.

Happy building!

Step 9: Edits to the Build.

OK so after a question from FearAndLoathing, I spent half an hour and made a quick alteration.

So, the problem I was having was every time I opened the big door about 20 flies escaped. I tried installing a net curtain over the entrance but it just got in the way. So I decided to make a new, smaller door that would fit one of my 5L black buckets and would allow me to add food without loosing breeders.

If you look at the pictures.

1. I took a handheld circular saw and pulled the blade guard completely back before using it to cut the straight lines.

2. I used a reciprocal saw and cut the corners where the round blade didn't cut the whole way through.

3. I pulled out the square and used a 2 part epoxy to attach hinges...

4. After 10min, when the 5min epoxy was strong I did the same again, sticking the hinges to the front of the box, making the square fit into the hole it came from.

5. I used a rasp file to shave the bottom edge off the insulation to allow it to work.

6. I fashioned a handle that acts as a lock too.

10. I added food through the small hole quickly and easily..

Hope that helps.

Tip. To avoid smells, try not to add a huge quantity of fish all at once, the ammonia from the process of breaking down all that fish as well as the fish itself can get pretty nasty.

My last thing that I would do differently when building this box is that I would use a 6-8" extractor fan + carbon filter set rather than the 4" one I used

I hope this helps everyone.

This is an answer for Kingers.

Hi there.

Thanks for the questions.

Ok so for the carbon filter I would stick with a 6".

It will not run for long. I have actually found that air turnover is pretty low in general.

I use a temp controlled Heat and Cool plug system.

When the temp is under 15°c the heater turns on.
When it's over 27°C the extractor turns on for a few min.

The rest of the time the air just sits. I run a small 6" clip fan to move the air around inside the box. it keeps the air mixed and stops the hot air from pooling at the top.

Overall the box has been a massive success.

The only thing I will say is that you need an ozone generator to kill the smell.

I use a small system with a 4mm air hose. This runs for 15min per hour with the 4mm air hose dropping ozone into the top of the box. Without it, smell can become an issue but with it there is no smell.

I hope that helps.

Let me know if you have any more questions.

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    6 years ago

    Nice! I made a similar setup a few years ago but my flies never bred. I suspected it was the lighting. What kind of floodlight did you use?


    Reply 6 years ago

    Hi there.

    I hope this helps.

    There are a few things that influence mating.

    1.Light intensity: Throughout my research I discovered that the flies will not breed under a light source less than 3000 Lumen. Some believe that colour/light temp is also a factor so I went with 6000K which is close to summer light colour.

    2. Temperature: The flies require a temp above 25°C to mate regularly. Mating has been seen at lower temps but the for regular mating you need between 25-30°C hotter is not good. The same paper says 27°C gives best mating and strongest flies. Flies bread above 30°C were smaller and had shorter lives.

    Here is a link to the exact light I use.

    Check this out at
    50W Super Bright LED Floodlight, Outdoor Garden Waterproof Light, 3800lm,Cold White 6000k flood light, Security Light, light-weight Lamp


    Reply 1 year ago

    Did the 3800lmn at 6000k light work? I am putting up a lover cage and I have found a similar flood lights here.


    Reply 1 year ago

    Yes it worked for me. Hope it works for you too.


    Question 2 years ago

    Awesome build, so happy I found this. Based in Ireland and not much to be found in relation to breed these in colder climates so well done for this!
    Definitely trying this myself, thanks for sharing

    Was wondering what rough ambient temperatures did you have this unit running? (min max summer winter)
    I assume it was running "indoors" in a garage from the pics?
    So no direct sunlight etc?
    and not exposed to wind and rain etc?

    Was wondering to do this in a small garden shed but might get pricey to heat it out there in the winter. Then again if the BSF remain active and produce fish food over the winter it offsets the electricity bill big time.

    Sorry for all the questions, would highly appreciate some answers
    and again just need to say it one more time thanks so much for sharing this!!


    Answer 2 years ago

    I'd love to see your final product.
    I'm looking into designing a larger system that turns cattle and horse manure into good compost using chickens and BSF larvae. If you have space then it's well worth considering.

    I also design a lot of hydroponic and aquaponic systems which is my real focus. The BSF larvae are just a cheap fish food for my fish.


    Reply 2 years ago

    Thanks for the reply. Interested to see that bigger version. I am obsessed with those BSF now at this stage, such a WINWINWIN, for us the BSF and the animals we feed :-)
    Would love to get some info from you to my questions about what rough temps your unit was exposed to with the insulation? Just wondering if it would be at all possible to run this in our climate (Ireland) during the winter outdoors or in a poorly insulated shed if the unit itself is well insulated?



    3 years ago

    How do you make sure the new generation turns from pupae to the adult flies? Do you just leave a portion of them in the bucket, or do you move them to a new location within the box? Do the flies land directly on the outside of the maggot box to lay eggs? I've read through the fourms and they suggest placing cardboard on the outside of boxes to incourage egg laying.


    Reply 2 years ago

    Ok so pupating takes time so yes I put about 15% of the maggots into a bowl and they pupate then reproduce. The light brightness, wavelength and timing is a huge part of breeding.

    Temperature is also mega important.


    4 years ago

    Hi, thanks so much for this design.
    I've been wanting to build a BSF farm that would survive in the UK
    for a while. But, until I found this I hadn't come across anything

    I've got a few questions about

    1. You suggest using a 6” or 8”
    extractor fan. But those things shift around 75m3 per hour. The cage
    is 2mx1.2mx1.2m which is less 3m3. So in each of the 4 x 30 minute
    extractions you'd be changing the air 12 times, which would surely
    lead to a massive temperature fluctuation. Also, wouldn't the air
    currents be too much for the BSF?

    2. Before you suggested the addition
    of a 4” inlet fan at the bottom, the system was pretty much sealed,
    wasn't it? Therefore, rather than shifting so much air, didn't it
    just reduce the internal air pressure?

    3. However, with the 4” fan at the
    bottom, you have suggested wiring the air exchange up to the
    temperature controlled plug so its switches on when it gets too hot.
    But, what if it doesn't get too hot, especially in winter? And,
    again, when it was on, wouldn't the air currents and temperature
    fluctuations be a bit too wild? I'm wondering if a less powerful air
    exchange set up running for longer periods might not be better.

    4. Finally, you make reference to a
    circulation fan. Do you have any recommendations? I'm guessing
    something very gentle. I was thinking of a 5v brushless fan (for
    longevity) powered via a multi-plug with a couple of USB sockets. Or,
    if you're changing the internal air, can you do away with a
    circulation fan?


    Reply 2 years ago

    Hi Kingers.
    Ok now I'm going to confuse you and myself.

    I changed my extractor to run only when the temp broke 30°c. It was set lower before and it was over heating. When I changed it to kick in only at that temp, I no longer had the system over heating...

    I cannot for the life of me work out why the temp stayed lower when I didnt upgrade the 4" extractor. It just did and I'm happy.

    The only change I made at that time was the inclusion of a 30cm x 30cm muck doors maybe that allowed more air in, even though it closed and sealed pretty well.

    The system has served me extremely well and produced hundreds of Kg's of maggots. I hope that everybody else has the same success.

    The part I'm happiest with was the muck box. It was a massive improvement on my original bucket and I've even considered making my next one out of fibreglass. I've been messing around and experimenting with fibreglass and making moulds for aquaponic grow beds. I find it to be so versatile and easy.

    Any more questions, just ask, I'm here as often as my good days allow.


    5 years ago

    This design is excellent Sheldon, thanks for sharing, I'm starting to get the bits and pieces together so I can build it. I've just bought some larvae so I can start my own population but I have since read that imported larvae are sterile and so aren't fit for breeding. Where did you get yours from to start your breeding population?




    Reply 5 years ago

    actually, I just read on your other instructable they can be found on ebay - I changed my search from black soldier flies to Calci worms and found some.

    now your systems been working for a while are there any changes you would make to it?


    Reply 5 years ago

    Hi Fear.

    Firstly, the larvae are not sterile. So if you find some culci/bsf larvae then with time and the right conditions they should work perfectly.

    If the ones you receive are still white in colour and wriggle a lot then you will need to feed them up until they are ready to pupate.

    As for changes.

    Not many to be honest. I think the only real change I would make is to change my 4" extractor fan, that removes air through the carbon filter, into a 6 or even 8 inch extractor. This is because, during summer the super insulated box actually over heats without extra airflow.

    You could also install a 4' fan to force cool air into the box from the bottom. Power both fans using the thermostat controlled plug and when the box needs cooling they both kick in and cool it down.

    Now that I think of it, I might also make a muck schute so you don't have to open the main door to throw in your food waste. It could be as simple as a couple of smaller doors above each bin so flies don't escape each time you add food waste.

    I hope that helps.

    lastly, if you need more Larvae and you are not producing enough food waste then buy cheap raw oats and min some with a bit of water. They eat that happily and grow fast. Depends on how many maggots you need.


    Reply 5 years ago

    cheers for the quick reply and tips, I'll definitely incorporate those. I've actually got some blocks out of old storage heaters so maybe I'll locate a couple of those high up to see if they absorb some of the extra heat to dissipate back over night. I'm up in Scotland so the air temp fluctuates quite a lot.

    thanks again