Sunday, 10 June 2018

Our Frugal DIY Black Soldier Fly Larvae Setup

After I killed a couple of batches of earthworms and my bokashi bin just went soggy, I knew I had to find a better way of composting food waste - and I'm so glad we found out about black soldier fly larvae farming!

My elevator speech as to why I love my grubs:
  • In our climate, they pitch up on their own! No cash outlay required.
  • They don't spread disease like houseflies do - Adult black soldier flies don't land on food because they don't even have mouthparts and they prefer to lay their eggs in a dry spot above rotting food, not in it.
  • BSF larvae dramatically decrease the number of houseflies. The actual mechanism for this is unclear but it seems they consume the waste quicker than housefly larvae can hatch.
  • They eat pretty much everything that comes out of our kitchen so definitely not as fussy as earthworms, and less effort than a bokashi bin. Any and all food preparation waste and all our plate scrapings (except bones) go to the BSF larvae.
  • When the grubs are mature, they self-harvest, providing us with an excellent source of fish food, and one day, chicken food.
  • The leachate (liquid) harvested from the farm is an excellent fertilizer.

So, the moment you've been waiting for... Our Frugal DIY Black Soldier Fly Larvae setup!
I'll warn you it's quite rough and ready, we're still experimenting so we haven't made the fittings and supports permanent, but it works!

In all her creep crawly glory - Our Black Soldier Fly Larvae farm

So there you can see the setup in its entirety. It's an old bath - salvaged by my father-in-law who works as a builder, set up on some bricks. Underneath is a container to catch the leachate. The red bucket catches the grubs coming out of the ramps inside. The cover is a piece of aluminium that extends slightly longer than the length of the bath so it covers over the bucket also.

If you lift up the lid and look from the top near the bucket end, this is what you'll see. A discarded section of pool cleaner pipe, cut in half lengthways. When BSFL are ready to pupate, they climb upwards towards a dry spot - so ramps that drop off into buckets work well for harvesting! You can just see the edge of the bucket on the right-hand side of the picture below. One ramp along one side of the bath exits over the top edge, while the other pipe (currently too submerged for my liking) exits through the 'overflow' hole.

You can see citrus peels, egg shells, tea bags, avocado skins and various other bits of debris in this image. The dark marks you can see on the edge came about when it rained and we didn't have sufficient rain protection. BSFL can crawl up vertical surfaces if they are wet, thus bypassing our ramps (and our buckets!). I just haven't bothered to clean the previous trails since setting up the system with the new cover.

Above is a closer view of the pool pipe dropping off into the collection bucket, with a layer of grubs already in the bucket. Below is a close-up view of the grubs working their magic.

And this is what they look like in the bucket. Mature larvae have a dry velvety surface and are about 2cm long. They don't smell bad at all - unlike housefly larvae that stink! To start the system we left some old meat in a bucket, with sections of corrugated cardboard fixed above the meat. The Black Soldier Flies love laying their eggs in the crevices formed by the cut edge of corrugated cardboard. Obviously, the houseflies will come, but over the course of a few weeks, the Black Soldier Flies come to lay their eggs and voila! Black Soldier Fly Larvae! I'll try to get a pic of one of the flies so you know what they look like. They're quite sweet actually - longer than houseflies, with little bobbles on the ends of their antennae.

The reason we've lifted the whole setup slightly off the ground is so that the leachate that runs out via the plug hole can be easily reached. The runoff process is assisted by the natural drainage slope of a bath. To prevent the drainage hole from getting clogged with debris, we placed a broken swimming pool weir basket upside down over the plughole. Below is a closeup of the leachate collector. We need to find something a little larger but this is working well for now.

And below you can see some shots of our bigger koi feasting on the grubs. The smaller koi are there in the hope that we'll drop some smaller food in as well.

So that's the quick version! If you have any questions, ask them in the comments below.


  1. Thank you for your informative post! Do you use the leachate as-is on your plants, or do you dilute it with water? And does it smell?

    1. We do dilute it - I only dilute it a little (1:5) and use into the soil directly (i.e. not on the leaves) but some recommend diluting 1:100! So it really is best to see what works with your particualr setup. Usually it only has a very mild smell - like a forest floor - If it is smelling then we know there is something wrong i.e. grubs not coping with the volume of waste.

  2. My setup is an old discarded utility sink.
    I have read that the Black Soldier Fly larvae consume the housefly larvae. As an experiment, I tossed a chunk of meat (pork tenderloin) into the BSF bin and yes, tons of houseflies were attracted to the meat and went to work creating hundreds++ of housefly larvae; the BSF gobbled them up before the housefly larvae could pupate. Win-win!!

    I had actually considered scooping up some local roadkill to both clean the environment and to keep my BSF larvae fed. (Still thinking; haven't done it yet.)