Monday, 30 January 2017

Vermicomposting: Can Compost Worms and Black Soldier Flies Live In The Same Bin? Yes!


A while back I bought a Reln 3-tier worm farm from Bunnings, also sold as Tumbleweed Worm Cafe. The info provided was scant, but it seemed pretty straight forward.

Living in a hot climate (Brisbane, Australia), I began an ongoing battle with Black Soldier Fly Larvae (BSF or BSFL) almost the moment I bought my worm farm. I made the mistake of ignoring the advice not to overfeed the bin, and soon the whole thing was overrun. The worms of course hated the heat and acidic conditions, and began digging down and committing suicide into the water at the bottom of the bin. A grim death, but perhaps not as grim as being cooked and eaten by BSF larvae.

Searching the internet it seems most people's experiences are the same - once the BSF's move in, your worms move out, die off, or are never seen again. A lot of people say they just can't live together - and they're pretty well right, the conditions that BSF create are completely different to those required by the worms to thrive or even survive. But they're both so good at what they do - why can't we have both? We need the BSF for processing large amounts of food waste, and we need the worms to turn the mess the BSF leave behind into vermicastings, and we don't have room to run multiple bins!

Problems & Solutions:

P1: Worms don't eat enough. The reason I kept getting Black Soldier Fly in my worm bin was because there was too much uneaten scraps - this was a problem that wasn't going away.

S1: Black Soldier Fly eat everything you throw at them and they'll still want more.

P2: Worms don't eat the kind of scraps I have. I need something that will eat onions and citrus and scraps I can't feed my chickens or dog - worms don't fill this niche 100% of the time. 

S2: Black Soldier Fly eat basically every type of scrap besides paper & grass clippings.

P3: Black Soldier Fly keep infesting my worm bin and killing my worms. At first I fought back - fed them to my chickens, tried to add more soil and wait for the worms to catch up with the backlog - it didn't work, the BSF just kept coming back.

S3: Instead make an environment that supports and benefits both - the best of both worlds!

Final Solution - converting the worm cafe into a co-habitation destination with no extra parts required:

In my frantic google searching to find a solution to this co-existence problem, I stumbled upon a post on a forum by a person aptly named "Sludge Feeder". He had drawn the following diagram as an idea of how a system might look, but there was no follow up or pictures to say whether it had been built or whether it was successful. Well, it does work, so props to you SludgeFeeder!

On the face of it, his diagram looks kinda confusing, but you might notice there's clearly 4 sections - just like the 3 tier bins - just like the worm cafes and worm cans! We don't need the mesh grill because the trays already have fairly small holes between sections. He has in essence drawn exactly what we already have! Great! No extra parts required!

So basically we're using the same bin, but tweaking it from this:

to this:

Let's break it down:

Level 1: normally this would fill with watery leachate, which you would drain out occasionally and use on the garden. However, we want a bit of airflow, and we really don't want water building up, as the worms will sometimes come down to this level when its hot - don't want them drowning!

I tend to put a little bit of shredded newspaper in the bottom of this tray, at least across the side opposite the tap, just to help the worms find something cool and wet when they're hot. There is a raised hump in these 3 tier systems that allow the worms to move from this lowest level back up to the upper levels, and no, I've never had any crawl out the open tap!

Level 2: I used a tray which had previously had BSF through it here, but you could use soil, blended compost, leaves, newspaper etc in here - make it nice for worms. No big chunks of rotting food needed at this level as that will draw BSF into this tray, which we don't want, we want to keep them slightly segregated by level 3.

Level 3: a mostly empty tray - provides an air gap between the heat and acidity of the BSF. I put a layer of shredded newspaper along the bottom of this tray so that the water falling from the BSF tray directly above drops onto the paper here and the worms can feast upon its slimy goodness.

Level 4: BSF home town - throw everything you've got into this top tray, they'll gorge themselves silly. The water and leachate they release will drip down through the holes in the tray and filter through the shredded paper in level3, and then through the substrate of level2, providing more food for worms.

Benefits of this system:

  1. In level 4, you can process large amounts of kitchen waste - with BSF you can process large amounts over days that would take worms weeks or months
  2. You can feed them just about anything, even the stuff worms won't eat. 
  3. Your BSF problem is contained and doesn't hurt your poor wormies. 
  4. You can process worm only foods - newspaper, leaves etc straight into level 2 worm bin (or along the bottom of level 3 if level 2 is full). 
  5. The best of both worlds - in the one bin!


Q. Can I feed the worms also?

A. Yes! My wife does a lot of juicing - so I first freeze the less acidic, non-citrus fine particle waste and then put them into level 2 as an occasional worm treat. The acidic stuff like orange peels etc go in level 4. Freezing helps to break the cell walls of the plant material, which allows worms to eat it sooner.

Q. Well, does it really work?

Yes! Worms are big, and much happier now. The heat of Queensland causes them a lot of stress, even in the shade. With this system there is a lot less rotting going on in their main tray (level 2), which means less heat and less harsh conditions. They now no longer try and crawl out of the trays or spend a lot of time in the lowest tray. There will always be some that want to hang out in level 1, but level 2 will be much more popular. 

Q. I really want BSF - how do I get them?

Basically just wait - if you're adding all your table scraps and waste to the top level like this, and there's nothing else to eat all that waste - they will come. As long as you're in a warm area it won't take long. The adults will lay their eggs on the lid, and in the Reln/Tumbleweed 3 tier system, the top lid has holes in it for air flow, the tiny larvae will hatch on the outside and crawl through those holes. You don't really have to do anything - don't need to leave the lid off or put cardboard for them to lay their eggs in as others suggest. I have gone to absolutely no effort to attract them and they just keep coming. Maybe check if people are selling BSFlarvae on gumtree - that would indicate there is a wild population.

Q. Ok so what do I do when the BSF tray becomes full?

If you're looking to retire the top tray because it's mostly eaten down sludge now, and you can't fit more scraps - great! Make it the new tray 2 - the worms will love 'finishing' it. To get your worms out of their current tray 2, just take the top trays off and expose it to the sunlight, they'll dig down deeper - keep taking a few CM's of compost off the top and wait for them to keep digging down. Eventually they'll wind up in level 1 and you can do the swap of level 2 and level 4 trays and start the process over. At the point level 4 becomes mostly full of composted sludge, you simply stop adding more food scraps for a bit and the current generations of BSF will finish their life cycle and there'll be no new ones.

Q. BSF are getting into my worm tray - nooo!

Make sure there's hardly any food scraps in there. Add more leaves or newspaper - the stuff BSF can't eat and aren't interested in. They'll eventually clear out. Also add your compost conditioner to this tray - this makes it more worm friendly and less BSF friendly.

Q. What about harvesting the BSF - my chickens need to eat too you know!

I've got the legs of my wormfarm sitting in medium sized potplant trays/water dishes or old ice cream tubs. This is so I can top them up with water to keep ants away if they flare up. They also catch falling BSF larvae that are doing their crawl off and attempting to escape the compost to pupate. The BSF will actually climb up the side of your top tray and push their way out of the lid, and then fall helplessly into the trays at the bottom. You could improve the efficiency by creating a ramp in the top level - but it would have to be temporary as you want to be able to swap level 2 and 4 over as you progress. I find that a fair amount fall into the trays down the bottom and then because there's no more moisture they can't climb out vertically anymore and they're simply stuck. My chickens appreciate it. You could also try a tarp pegged to each of the ice cream buckets around the legs, so that when the BSF abandon ship, if they miss the buckets, then they're trapped inside the tarp. This will have the added benefit of not attracting cane toads who like to feast at night on the exiting BSF. 

No comments:

Post a Comment