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 Question about using BSFL just for composting 
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Joined: Mon Jul 20, 2015 1:47 pm
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Location: SF Bay Area, CA
Post Question about using BSFL just for composting
First off, an introduction - I'm new to both composting and BSFL. We started composting in a plastic bin just to see what would happen and I think due to our large coffee consumption we ended up with BSFL. At first I was horrified (so gross looking!) but then I realized all the wonderful things they were doing for our compost and how quickly they can mow through a ton of food.

Now that we kinda know what we're doing we are building ourselves a new composter to take advantage of the BSFL. But I have a question. So many of the units I've seen let the BSFL crawl out of the bin and into a bucket. We don't have chickens or any other use for the BSFL, all I want them to do is stay in the bin and keep eating my food so I can use the compost for the veggie garden. It's my understanding that they crawl out when they are ready to mature, right? If I put a rubber tube in the compost bin so they can crawl out and into a bucket, then what? This is where I'm stuck.

I need to know two things - what do I do with the larvae that end up in the bucket (throw them back in the bin? Let them stay in the bucket?) and what's the best way to encourage them to lay their eggs back in the bin? Or should I put some corrugated cardboard in the bucket and throw that in the compost when there are eggs on it?

My idea for the compost bin is to have a large tray (2ft x 2ft x 7" high) made out of wood with 1/4" mesh on the bottom. When the food is done composting it will fall through the mesh and into another tray underneath. My hope is that the BSFL will stay in the upper tray where there's food and I can retrieve the compost out of the bottom tray when I need it without removing the BSFL from their food source. Is this a terrible idea?

Thanks for any advice!


Mon Jul 20, 2015 3:44 pm
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Post Re: Question about using BSFL just for composting
Welcome Kate. Lots of questions for your first post. I'll try to answer some and hopefully others will chip in.
craftykate wrote:
... It's my understanding that they crawl out when they are ready to mature, right?
That's generally correct. If your bin is wet the perpupal larvae (the dark ones) will crawl out to find a better place to pupate. However if the conditions in your bin allow (are dry enough among other things) the larvae may stay put, pupate and emerge as flies in the bin.

Regarding your other questions about what to do with the larvae, since you do not have a use for them and since they volunteered in your bin you may be able to just leave things as they are. The larvae will likely be able to find a way out of your bin to pupate somewhere in your yard. The flies will then find a way back into the bin to lay their eggs completing the cycle.

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... My idea for the compost bin is to have a large tray (2ft x 2ft x 7" high) made out of wood with 1/4" mesh on the bottom. When the food is done composting it will fall through the mesh and into another tray underneath. My hope is that the BSFL will stay in the upper tray where there's food and I can retrieve the compost out of the bottom tray when I need it without removing the BSFL from their food source. Is this a terrible idea?
You didn't give your location but most folks wait until the winter to harvest the frass (what's left after the BSFL eat material). This way the BSFL are gone.

Also if you have a wild population of BSF we would love to add your location to our Black Soldier Fly Mapping Project (link). See the Range and Identification section (link) for instructions.

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Mon Jul 20, 2015 4:12 pm
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Joined: Mon Jul 20, 2015 1:47 pm
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Location: SF Bay Area, CA
Post Re: Question about using BSFL just for composting
Thanks for your response! I'm in Benicia, CA, which is in the San Francisco Bay Area, but more inland so it's pretty warm/hot for a long time. It's 90 degrees here today and I'm melting. I'll look at the map link and add my location if I can figure it out.

I'm thinking now that I will not provide a way out for them since I don't need the larvae for anything. I wasn't sure if you were supposed to do that all the time or just if you wanted to feed them to something. Maybe what I will do is attach something spongy to the underneath of the lid of the unit and drill some holes in the lid to encourage the flies to come back and lay their eggs there. And they can get out if they want to and can find a way. Maybe I'll put a spacer between the tray and the lid. Anyone know if they can climb up a redwood box?

The conditions in my current bin are not good. It's a soggy mess. I have some drainage holes on the bottom but not enough since I wasn't preparing for the larvae when I set up the bin! My problem with waiting for winter to use the compost is that we do a LOT of gardening in our yard and waiting until winter (which takes a while considering our warm climate) means we can't use the compost for most of the year. And there's a lot of compost in the bin that's ready to go but we keep adding food to it since it's our only bin and removing the compost means removing the larvae. That's why I was thinking of having a secondary bin underneath to catch the finished compost.


Mon Jul 20, 2015 4:41 pm
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Post Re: Question about using BSFL just for composting
BSF are likely seasonal in your area so a colony of BSF would be inactive in the winter.

The female flies are attracted to the odor of an active colony and the frass so they would likely also lay eggs in your lower tray. If your using the compost outside then if it contains BSFL it shouldn't really be a problem? BSFL do not eat living plants or their roots. Using the compost indoors would likely result in larvae and flies in your house.

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Mon Jul 20, 2015 4:48 pm
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Post Re: Question about using BSFL just for composting
Drainage is a common problem with BSFL bins that are fed food waste. The larvae shred food quickly releasing any water it contains in a rush.
Have a look at some of the DIY bins in this section for ideas on how to handle drainage.

Adding some holes and somewhere for the females to lay eggs is a good idea. Cardboard or coroplast (plastic sign board) strips are often used.

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Mon Jul 20, 2015 4:54 pm
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Post Re: Question about using BSFL just for composting
Okay, you've convinced me. No lower bin. I'll just scoop out the compost when I need it throughout the summer and let the larvae come with. I'm not using compost inside, so it won't be a problem. We have plenty of birds hanging around, I'm sure they'd love the meal.

I'll have just one bin and put window screen on the bottom. The liquid can run out the bottom and into a bucket.

Do BSFL compost bins get overrun with houseflies over the winter? Or more likely the houseflies also die off in winter...


Last edited by craftykate on Mon Jul 20, 2015 5:08 pm, edited 1 time in total.



Mon Jul 20, 2015 5:00 pm
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Post Re: Question about using BSFL just for composting
craftykate wrote:
... Do BSFL compost bins get overrun with houseflies over the winter?
That I don't know. If it's warm enough that there are house flies then it's likely there will be BSF too. This thread (link) about another San Francisco sighting shows that adults were still active in Novemeber.

Image

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Mon Jul 20, 2015 5:08 pm
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Post Re: Question about using BSFL just for composting
Craftycate if you're more into the veggies than anything else, you can throw the BSF pre-pupae around your garden and when they hatch they'll become food for songbirds, dragonflies and other animals. There is an anecdotal story about a woman in a dense suburban neighborhood in California who has been composting for decades and now has a reliable population of songbirds that hang around her home because they know there's a meal on the wing!


Tue Jul 21, 2015 4:28 am
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