“Yellow Soldier Flies” – Revisited

Last fall I reported on finding what looked to be soldier fly pupae in my compost tumbler (see “DIY Tumber – Revisited“). At the time I wasn’t able to track down any of the suspected adults (large, yellowish flies I’ve frequently found in close proximity to my outdoor composting systems over the years), and my attempts at getting the adults to emerge (from some of the pupae I collected) indoors didn’t end up panning out.

Well, I’m happy to report that I am now finally on the verge of putting the pieces of this puzzle together!

A short time ago I was lucky enough to find one of these adults sitting on a leaf outside on an overcast day (easier to get a nice, clear photo without the glare of the sun) – and it seemed to have no intention of moving, even as I got in super close for some macro shots!

As if this wasn’t cool enough, today when I walked by a bag of (compostable) used cat litter material – waiting to get added to my new litter vermicomposting system – I noticed a bunch of these large, yellow flies hovering around the bag. When I dug around in the material a bit I found some small larvae, so I’m hopeful that these are the young larvae of these flies.

Now that I seem to have this little (accidental) experimental system going, I will likely try to optimize it a bit by adding some moisure, and perhaps some food waste. I really want to see if these are at least semi-comparable to Black Soldier Flies in terms of their waste processing abilities.

I’m also thinking of tracking down a fly expert up here in Canada so I can get an actual ID on this species once and for all.

Stay tuned!

UPDATE: I e-mailed fly expert, Dr. Stephen Marshal, at the University of Guelph (my former stomping grounds) and received a very quick response, informing me that this is a very common Ptecticus soldier fly species. He suspects that it is Ptecticus trivittatus, but said it would be necessary to key it (i.e. ID it properly using a taxonomic identification key) in order to be sure. Another interesting tidbit Dr. Marshall shared with me was the fact that Black Soldier Flies (Hermetia illucens) ARE found in the southernmost regions of Ontario. So I guess I am not as far out of their range as I thought.

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  1. Very interesting and especially the info that the Black Soldier Fly can be found in southern Ontario.

    • Kim from Milwaukee
    • July 10, 2013

    Such pretty eyes! Bentley, is the litter getting moisture in it now, is that why the flies are breeding? They don’t proliferate unless there’s materials breaking down, right?

    • Bentley
    • July 10, 2013

    MIKE – I thought you might be interested in this one!
    KIM – This bag of scooped litter was sitting outside for at least a few days and we’ve been getting some rain so that likely added to its appeal. What I’ve noticed though, is that even when the stuff is stored indoors, fungal mycelium starts to grow all over it – pretty interesting! I guess it’s the chick starter itself that is providing fungal food once it gets wet from urine.

    I need to write an update on the compostable litter front! Thanks again for turning me on to this stuff – absolutely fantastic litter material!

  2. There is this paper (link) of a study done in Windsor

    “The Role of Black Soldier Fly, Hermetia illucens (L.) (Diptera: Stratiomyidae) in Sustainable Waste Management in Northern Climates” (2012)

    This research assessed the feasibility of using Black Soldier Fly, Hermetia illucens, in cold weather climates to manage organic wastes. The goal was to determine if the flies could be kept alive year round in a controlled facility when exterior conditions turned inhospitable. A proof-of-concept experiment was undertaken by constructing a small research facility in Windsor, Ontario, Canada at the Essex Windsor Solid Waste Authority’s Landfill Site inside two greenhouses. Although the data collected were highly variable, the experimental trials demonstrated that the design process was successful overall: Hermetia illucens can be propagated successfully in controlled environments in cold weather conditions. Key design parameters were investigated, including the waste consumption rate per maggot per day and the waste application rate. These parameters where then used as a basis for the design of a prototype waste processing facility utilizing BSF as the treatment method. A mass balance of the relevant flows and a life cycle inventory was conducted as precursors to future life cycle assessments of this process. A limited cost assessment was included to determine the economic feasibility of operating a BSF waste processing facility year-round in winter climates. The cost analysis revealed that the current design, under research conditions, could be economically viable and improvements to the process are necessary. These improvements include the more efficient use of electricity, water, natural gas and three dimensional waste processing via the use of aeration to the food pile.

  3. Yeah, not sure what all specie we have of soldiers. Do know ones that look like yours have been sitting on the front of my bin since I started it. Mines a lot smaller than a BSF. Knew it was a soldier fly of some sort though. Can almost touch the ones I have.

    • Kim from Milwaukee
    • July 13, 2013

    I crammed my brain with BSF info yesterday Bentley, and now I’m wondering if they’re not the perfect partner of the redworm. I’mI’m wondering if some fermented chicken starter would call out any female BSF in my neighborhood…

  4. Kim that might work. There are a few more ideas here.

  5. Kim store some wet S’bucks coffee grounds outdoors where they can find it in the bag they give it to you in. The coffee grounds start fermenting the BSF will be all over it! I tried doing it with corn and it smelled so bad I couldn’t sit on my front porch. Rotting corn smells bad! Coffee I had more BSFL than I wanted in 3 bags of S’Bucks!

    • Kim from Milwaukee
    • July 14, 2013

    Thanks Guru! I can do coffee grounds!

    • Bentley
    • July 17, 2013

    MIKE – thanks for sharing that abstract! Fascinating.
    KIM – I think they are a great option for certain kinds of wastes and/or for those who are really interested in producing a nutritious live food for birds, reptiles etc. I’m still not convinced that they can be good partners in the same systems as Red Worms, since their tolerances/requirements are a fair bit different.
    LARRY – I think you’ve got the right idea with the coffee grounds! That’s what I’m going to switch over to. My little bag ‘o’ litter got so foul (I could smell it from pretty far away in the yard) that I just ended up dumping the contents into my cat litter vermicomposting bed (and making sure to cover WELL! lol). Loads of maggots in it, but I think they were a variety of different fly species.

    I thought maybe wet coffee grounds with some bread in it might work.

  6. Bentley said “I’m still not convinced that they can be good partners in the same systems as Red Worms, since their tolerances/requirements are a fair bit different.” This is very true. BSFL process food waste rapidly releasing a lot of moisture from the waste in a hurry. Purpose built BSFL bins have drainage systems but worm bins may not. This can make conditions in the bin soupy and not attractive for worms. Also BSFL generate a lot of heat which can also create temperatures to high for the worms to tolerate.

    I’m seeing quite a few requests for methods of removing them from worms bins. AFAIK there is not a sure fire method to do this. Also BSF are likely to repopulate the bin anyways as the gravid female BSF find the conditions in worm bins ideal for laying their eggs as there is a ready supply of food for the larvae when they hatch.

    • Kim from Milwaukee
    • July 17, 2013

    When I said ‘partner’ I didn’t mean in the same bin….their pH requirements and temperature requirements differ greatly, but to convert the ‘waste’ product of the BSF into something nice and fluffy I think the worms would be great to process that since they love the BSF residuals.

    I can see having a worm bin indoors and a BSF bin outdoors so the female doesn’t repopulate the worm bin. Would that work??

  7. Yes the indoor outdoor setup should work. You’ll have to try not to transfer larvae along with any BSFL frass (castings) when putting it in the worm bin. It would probably only be a few but the larvae can pupate and emerge as flies in a worm bin. If that’s a problem you could freeze the frass first.

    • Kim from Milwaukee
    • July 17, 2013

    Great idea Mike! Thanks!

    • Jereme Tarr
    • July 21, 2014

    Did you ever find out if yellow soldier flies are any good for composting? That’s all I seem to be able to attract in the SouthEast US.

  8. Jereme if you do end up trying to compost with YSF I hope you’ll let us know how it goes.


    • Jereme Tarr
    • July 24, 2014

    I’ve got a 10 gallon tub full of rotting scraps out in a shed by my woods that I’m using to bait them into laying eggs. However, I’m only finding pupae (no larvae) in the food scraps. In any event, I’ve been transferring the larvae to a 50 gallon exo-terra tank filled with more rotting scraps to see if I can get the flies (so far I’ve hatched 6) to mate and lay a swarm of larvae.

    My initial impression is that they’re so much smaller than BSFL, that they couldn’t possibly be as good for composting. Also, they seem to go from larvae to pupae VERY quickly. So, I doubt they’ll eat anywhere near as much. However, I’m wondering if I can get enough numbers of them… maybe they can still do some damage to food scraps?

    I will certainly update you guys with anything I learn.

    P.S. Thanks to everybody for all the information I’ve gotten from this site sneaking around reading things like a creeper!

  9. Jereme that’s interesting about their short duration as larvae. If they’re like BSFL that can be directly related to temperature and abundance of food.

    There’s a bit of information on YSF here and here.

    • JTarr
    • August 2, 2014

    Thanks for the links BW. Interesting info.

    After working with both species for a couple weeks, I can tell you that there’s really comparison between the two. BSFL do EXPONENTIALLY more damage to rotting food than YSFL could ever hope to do. Also, it seems that YSF do not lay anywhere near as many eggs, and thus its much harder to get enough grubs at any one time to actually break down food in any meaningful way. Another interesting observation, the YSF totally ignore cardboard strips, so I’m assuming that they either lay their eggs on the side of the container or directly onto the food. Also, they are not afraid to land directly on the food, unlike BSF, and are thus probably more likely to spread germs. Also, YSFL do not self-harvest. They try to find a drier spot within the container and pupate there. Finally, BSF pupae are 4-6 times bigger than the biggest YSF pupae.

    I finally broke down and purchased BSFL larvae off the internet a little over a week ago. In that time, some of the mature larvae (pupae) have hatched, bred, mated, and laid thousands of eggs (which have not hatched yet).

    Conversely, my YSF have hatched, bred, and laid maybe 100 eggs which did hatch and have done nowhere near the damage that 10 BSFL can do in one night.

    Bottom Line: the only reason that I can think of that you would want to actively propagate YSF is if you need a high protein feeder for a very small pet, such as baby tilapia, baby geckos, etc.

    I haven’t checked my observations against any other sources or studies… just my observations. So to your point Mike, there could be some external factors that I’m not accounting for that are unfavorable to the YSFL. However, considering that they are the indigenous species, I would expect them to outperform the species that I had to fly in.

    Last observation: the YSFL REALLY like dog feces (probably why they exist in my area in the first place). They are not as enticed by coffee, bread, or meat. They do, however like corn and high sugar content foods such as rotting grapes. BSFL don’t seem to really care what you feed them. They annihilated about 10 gallons (sorry, container measurements) of coffee grounds in about 2 days.

    Conclusion: even if you have to purchase a few BSFL off the internet in order to jump start a local population [I live downtown, so that was very necessary for me], I would absolute do that over trying to compost with YSF. Just my $.02, hope that’s helpful.

  10. Jermey thanks for sharing your observations. The comparison of the two species under the same conditions was appreciated and I’m sure others will find it useful.

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