Indoor Black Soldier Fly Breeding
Black Soldier Fly (BSF) breeding in captivity is a relatively new development for the DIY crowd. There are a few commercial operations which raise them for pet food (link) and even for large scale waste disposal (link) but very few DIY small scale indoor systems (link). As an experiment I purchased a few Black Soldier Fly Larvae (BSFL) from a pet store this summer and after some trial and error was successful in having them complete a reproduction cycle indoors. ** December 2011 - Note that since this initial experiment concluded I've become aware of more small lighted indoor setups used by pet owners in Europe to raise BSF as feeder insects. Such systems show that mating can be achieved in a fairly small space (storage tote size) using bright artificial lighting. I will be using some of their design features in my next experiment. The details of my 'BSF - The Next Generation' will be found here. ** In researching raising BSF I found that having the larvae pupate and emerge as adults flies (eclosion) is the easy part. There are even a few reports on reptile related forums of this happening to larvae while stored in a fridge. The difficult part is having the adult flies mate, lay eggs and then for the eggs to hatch. The BioSystems Design blog has an excellent primer (link) with a summary of research on the best conditions for BSF reproduction. I live in Canada at 53°N latitude and 1000 metres elevation. Even indoors, the temperature and humidity are less than optimum for this subtropical species as I do not have a greenhouse. I'm not sure if the lower barometric pressure at my altitude causes any problems.
130 light and 13 dark (mature) BSF larvae in the original shipping medium. To start the experiment off on completely the wrong foot I accidentally overheated the original container and killed off 26 larvae. The remaining 117 larvae were raised in a 'tub' consisting of three nested plastic margarine type containers. The inner most contained the BSFL, has drain holes and sits suspended in the middle tub which captures any liquid that drains. The inner tub also has a screened top to contain the larvae. These nested tubs sit inside the largest tub which has a solid lid with pinholes for ventilation. This outer tub helps maintain the highest possible humidity for the larvae. The larvae were fed small amounts of kitchen scraps, mostly fruit and vegetables. I did feed them some fat trimmed from steaks but stopped after the tub developed a foul smell. Over feeding is reported to be a common problem when starting outdoor systems and I believe that was the problem here too.
The nested containers of the rearing tub. The outer tub
A 4 litre ice-cream pail with a screen lid was initially used for pupation. The pail contained:
I based my mating inclosure largely on Heather Twist's 'Honeymoon Hotel' described in her blog post of 2010-10-16 : Black Soldier Fly Babies! Basically this is an inclosure constructed from curtain sheers (used as netting) and a terrarium. My inclosure consisted of:
The transparent storage bin. From the top of the photo down are the sheers with the bottom of the zipper access, the bungee cord, twin lines of aluminum tape for the electric fence (link) and the access 'hatch'
Artificial Lighting:I opted to try using artificial lighting after reading a paper on the Journal of Insect Science website (www.insectscience.org) which details successful indoor breeding in China using an artificial light source. The study concluded that "... wavelengths from 450 to 700 nm were influencing mating behavior". That matches light from a Compact Fluorescent Light (CFL) according to this FDA (link) "Since CFLs are designed to provide general illumination, the majority of the light emitted by CFLs is localized to the visible region of the spectrum (approximately 400-700 nm in wavelength). In addition, typical CFLs emit a small amount of UVB (280-315 nm), UVA (315-400 nm) and infrared (> 700 nm) radiation." Initially only the one CFL in the reflector incorporated into the top of the inclosure was used. Later an additional CFL and small fluorescent tube light were added outside of the inclosure.
in the conical reflector.
I did not observe any mating or find any eggs clusters after 10 days with artificial lighting provided by compact fluorescent lights (CFLs). This may have been due to insufficient light intensity. At maximum I was using two 23 watt CFLs (one inside the netting) rated at 1600 lumens each plus another small 56cm(22") fluorescent tube light which I believe is rated at 725 lumens. The Chinese study mentions that mating peaked "at a light intensity of approximately 110 µmol·m-2·s-1". I had to look up that unit:µmol ?m² s¹
"µmol·m-2·s-1 unit refers to the number of photons (or particles) of light within the photosynthetic waveband that is received per second within 1 sq. meter of area"As I did not have a light meter it's impossible to know what intensity was actually achieved. The BSF were attracted to the light and bumped into it like other flying insects do. Although they didn't seem to be hurt by contact with the CFL I'd be worried about having any type of a hotter light inside the screen as the flies might fry themselves.
Hello Sunshine:Due to my lack of success using CFLs I decided to try natural sunlight which Heather Twist (link) and others had previously succeeded with. The large inclosure could not easily be moved to a window but something similar in size to a regular bird cage would be ideal. I constructed a small portable inclosure that could be hung by sunny windows and moved as required. Materials used:
The hanging inclosure was 56cm (22") high (between the rings of tube) x 46cm (18") in diameter. The rings of tube were suspended from four pieces of twine which were tied together at the top to form a loop for hanging the inclosure. A cardboard bottom was attached by looping twine around the tubing and through holes in the cardboard. The plastic screen was fashioned into a cylinder with a taped and stapled fold-over seam. At the top it was gathered together and tied while at the bottom it was taped to the cardboard. Clear plastic was added over the screen for the sun facing side and a green garbage bag for the other side in an attempt to maximize solar heating and maintain high humidity. As with the first inclosure, initially a removable 'hatch' was installed in the cardboard bottom for access and a zippered access in the screen was added later. I misted the inclosure several times daily and kept a wet piece of cotton in a shallow tray to maintain the humidity as high as possible and also provide water for the BSF. It was moved between sunny windows during the day and put in the storage closet overnight for warmth and humidity. I reduced the contents of the hanging inclosure to a minimum to keep the weight down. The contents of the pupation pail was separated into three smaller containers which could be put into the hanging inclosure only when transferring newly emerged flies. Otherwise they were kept in the storage closet and checked a couple of times daily. The grass plant was also replaced by a light weight plastic substitute. Small cups of moist used coffee grounds (UCG) and residue from the larvae rearing tub were still included.
Also note the twine attaching the cardboard bottom to the plastic hoop.
Egg Laying and Incubation
Initially a cup of residue from the BSFL rearing tub and rolls and strips of cardboard were kept in the hanging inclosure. I was checking these almost daily but never found any eggs. Later I discovered that the flies had been laying their eggs between the layers in the rolls where they were hidden from view. I moved these egg clusters into ziplock bags with moistened pieces of bread to incubate but they had probably desiccated before I found them as none hatched. There may still be other clutches hidden in nooks and crannies of the inclosure that will not be found until it's cleaned out at the end of the experiment. This ziplock incubation system was based on the method developed by Brain Travis and shown in this video (link). I did not use a heated incubator but kept the bag on an upper shelf in the storage closet. I changed tactics and removed all the cardboard and the residue from the rearing tub leaving only small cups of UCG with lids added which had a small hole for the females to enter. These provided an attractant (the UCG) and a dark humid place to deposit their eggs. Several days later I found a clutch of eggs in one of the cups and put it in a ziplock bag to incubate. The next day the eggs had started to hatch and there were quite a few tiny larvae crawling around inside the bag. Unfortunately at this point I was away for 10 days. The hanging inclosure was left by the east facing window subjected to reduced humidity and lower temperatures. When I returned there were a few larvae in another cup of UCG so at least one more clutch of eggs was laid in this period. However no more were laid after my return which is not surprising as by then most of the flies had already died. During my absence a large number of the hatchlings died due to problems with humidity. Many of the larvae which had been left in the sealed bag were moldy and dead. Conversely the coffee grounds, which had been left in the hanging inclosure, dried out which probably killed many of those larvae.
So my experiment to see if the BSF could complete their life cycle and reproduce indoors was a limited success. Mating under artificial light did not occur but did succeed with natural sunlight. Successful reproduction only began after the majority of flies had already died limiting the number of larvae produced. Only about a half dozen clutches of eggs resulted from the original 143 larvae. The experiment did illustrate how little space is actually required for the adult flies to mate. The small hanging inclosure had a volume of only about 99 litres or 3.5 cubic feet. Large inclosures are not really necessary, at least for mating. It also shows that breeding could be separated from the composting bin if necessary allowing more flexibility for systems. A small scale system like this experiment could be used to provide feed for pet herptiles (amphibians and reptiles) or fish. A working bin for composting would require a much larger population of BSFL but a similar mating setup could be used. I will continue experimenting with this next generation and refine my methods. To start the next cycle I've put the larvae and coffee grounds from both cups into the rearing tub. I think I'll try raising them mainly on coffee grounds and experiment with different artificial lighting as sunlight will be in short supply over the winter. The details of my 'BSF - The Next Generation' will be found here.
grounds at about 3 weeks old and 1 cm in length.
Some Dates and Numbers
Some dates (yyyymmdd) in chronological order:
BSFL have a reputation as escape artists so for this experiment they were kept in closed containers. Ventilation was provided by screening or pinholes in lids. Even though these were large larvae still a surprising number went missing. Of the original 143 larvae 26 were presumed heat killed and removed leaving 117. Of these 111 were manually transferred to pupation containers so six are unaccounted for. These either escaped or died and were eaten. BSFL are reported to eat their dead so there would not be any corpses. A count of the pupal cases (puparia) from the three pupation containers showed 92 versus the 111 mature larvae that were transferred into these containers, a difference of 19. Assuming that some of the larvae transferred remained active these may have escaped and are pupating in the storage closet. These active larvae may also have eaten any that died in the pupation containers. Some of the pupa recovered from the pupation containers appeared to be intact but dried out. I assumed these were dead and disposed of them, along with the 26 heat killed larvae, in one of my worm bins on 2011/11/07. Surprisingly live adult flies appeared on one of my windows on 2011/11/15 and again on 2011/1125. These were almost certainly from the escapees or from those disposed of in the worm bin as none of the second generation should have pupated yet.
BSFL Electric Fence
BSFL have a reputation as escape artists which would be a big problem for indoor systems. This is a small scale test of an electric 'fence' to keep them corralled. Two thin parallel strips of aluminum tape are placed inside a bin just below the top. These are connected to a small 9 volt battery and any larva that touches both strips at once completes the circuit receiving a non-lethal shock. My use of metal tape was inspired by a worm fence developed by Brain Travis as shown in this video (link). It was not clear that the larvae would react to the fence like worms as they do not have a coating of mucus. As long as the larvae are not totally dry it appears to work and in dry conditions the larvae are not as able to climb vertical surfaces. The fence is only effective for larva large enough to span the gap between the strips and could be used to contain mature larvae in the crawl off collection bucket of larger systems.
Here are some links with information about raising Black Soldier Flies:
'Small Scale Indoor Breeding' topic at the Black Soldier Fly Blog Forum
Off the Food Grid - BSFL category posts
LEKKING BEHAVIOR OF THE BLACK SOLDIER FLY (PDF file)