Recycling Food Scrap in Temperate Zones | Peculiarities of the Black Soldier Fly : The Life and Times of BSF (Black Soldier Flies)
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Recycling Food Scrap in Temperate Zones | Peculiarities of the Black Soldier Fly

by Terry Green on 12/29/12

Black Soldier flies (BSF) efficiently recycle food scrap in backyard gardens. But if you live in a temperate zone where temperatures in the late fall and winter drop precipitously down to freezing levels, are even well below freezing, you might be wondering how it is that BSF survive through this period of the year to emerge the following spring. In warmer sections of the world BSF persist and are active year round. They tend however to wind down their activity in Norther sections of the world when temperatures drop below about 60 F (~15 C), and do not survive if exposed for any lengthy period to freezing temperatures. So how is it that they survive in more Northern sections of the world during the bitter freezing winter months to resume activity as spring returns and temperatures again rise?

To use BSF, one of Nature's truly efficient recyclers, in your backyard garden in helping recycle your food scrap waste, it is helpful to have an appreciation of their peculiarities regarding how they go about processing organic wastes. Regarding their distribution around the world, they are ubiquitous and can be found on most land masses within tropical, subtropical and temperate zones North and South of the equator up to about the 49th parallel.

Unlike pesky houseflies, BSF do not spread diseases. They are not regarded as pests. They silently consume organic waste left in static piles outdoors. While efficiently incorporating the nutrient value present in waste into insect biomass, their larvae mineralize the waste, producing liquid and solid residue byproducts which are highly beneficial mixed with soil in enhancing the growth of healthy plants.

BSF larvae spontaneously self-harvest from the waste at the time they reach their prepupa stage. At this stage in their life-cycle, they can be used as a highly nutritious high-quality protein and lipid-rich feedstock sought out by many fish, birds, amphibians and reptiles.  Their exoskeleton is particularly rich in calcium and chitin akin to that of shrimp which also provides for increased dietary intake of calcium in feedstock used in feeding egg-laying domesticated chickens.

Adult BSF emerge from their chrysalis lacking mouth parts for feeding, and for this reason do not feed on waste piles, but instead seek out a mate before dying on average four to five days from the time of emergence from their chrysalis. Female adults lay egg clutches in upwards of 200 t0 400 eggs per clutch near decaying organic matter, leaving their newly hatched larvae offspring to find their own way to the nearby waste in starting over the same cycle their parents did before them.

Larvae process food scrap waste and move about freely within the waste at temperatures spanning from about 68 – 113° F ( 20 – 45° C). Below ~60° F (15° C) they become immobile. At lower temperatures, for example, under refrigeration temperatures in the range of ~40° F (~4° C) they cease all activity but remain alive for many weeks under these colder temperatures, resuming activity once the temperature rises again to ~ 60° F, or higher.  All of these latter characteristics, and additionally their ability to suspend growth and maturation in the absence of food intake, shows how remarkably well they are adapted in surviving the harshest extremes to live on for another day! They do not however tolerate freezing temperatures and die off rapidly if frozen.

Since indigenous populations of BSF have been observed North and South of the equator to about the 49th parallel, the cooler seasonal outdoor late fall and much colder winter temperatures common to these parts of the world explains why BSF in these regions are not observed actively flying about or processing waste outdoors in the late fall and winter months. The freezing temperatures commonly experienced in mid-winter temperate zones nevertheless raises the question as to how are BSF able to winter over into the next year in these regions of the world. The answer appears to be because of their propensity to burrow deep into waste materials as winter sets in. By residing deep inside the waste they feed on, they appear to insulate themselves from direct exposure to freezing temperatures.

Fig. 1 shows an example of how this likely occurs in the wild. In this example, BSF larvae were found burrowed deep inside a rotting tomato left in the garden. Larvae recovered from the interior of the tomato, warmed up to room temperature, came back to full activity and resumed feeding and carrying on in normal fashion. Outdoor temperatures where they were found burrowed inside the tomato in an inactive state had hovered from day to day over a period of several weeks between 35 to 45° F. The core of the partially degraded tomato would almost certainly have given them added insulation and shelter from the elements, including predators, as winter temperatures were setting up in the coming months.

image of Black Soldier fly larvae wintering over burrowed inside tomato
Fig. 1 BSF larvae found burrowed inside and motionless in the interior core of a rotting tomato plant left outdoors in the garden through late fall. Outdoor temperatures had been hovering between about 35 and 40° F for several weeks before discovering the larvae inside the core of the partially degraded tomato. Larvae resumed normal feeding activity on warming them up to room temperature (Copyright (c), 2012, Terry Green, All rights reserved).

In a future blog we will be discussing more about how BSF processing of food scrap can be integrated in temperate zones with fermentation technologies such as that commonly known as Bokashi fermentation in recycling food scrap year round where year round processing by BSF alone is not practical during late fall and on through the winter months.  Comments on this blog, or any of our other blogs, are always welcome. Follow us through our RSS feed. For additional information or follow-up questions, visit our Forums page, or Contact Us (

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