Black Soldier Fly Larvae and Red Worms

The cow, the pig, and the chicken – in producing manure – create an ideal substrate for BSF larvae. I wholeheartedly agree that “No other insect comes close to closing so many material flow loops and creating nearly self-sustaining food production cycles as BSF larvae, effectively making BSF larvae rearing on wastes a self-financing form of pollution reduction” (Review of Black Soldier Fly as Animal Feed and Human Food). The larvae in the picture below were only fed pig manure, and they self-harvested by means of a biopod only when fully mature.

In the transformation of fecal matter, BSF larvae are incredibly fast and efficient. The speed at which they eat manure, when properly presented to them, is typically measured in hours, sometimes in minutes. Here you see what happened to horse manure within 40 minutes: Larvae Eating Fresh Horse Manure. One can stand back several meters from a larval bin and can clearly hear at times tens of thousands of larvae as they engage in frenzied feeding. “Black Soldier Fly larvae are voracious eaters, and can consume more than twice their own body weight of hog or poultry manure each day under favorable conditions” (A Comparison of the Greenhouse Gas Production of Black Soldier Fly Larvae versus Aerobic Microbial Decomposition of an Organic Feed Material). BSF larvae are reported to digest certain types of putrescent waste “more efficiently than any other known species of fly” (Biochemical characterization of digestive enzymes in the black soldier fly, Hermetia illucens).

BSF larvae are remarkably tough and robust. They can live for over an hour when submerged in rubbing alcohol. They can be centrifuged at a 1000 g’s without harming them. They can tolerate waste of a pH as low as 2.0, although they gain more weight at higher pH’s (Dynamic Effects of Initial pH of Substrate on Biological Growth and Metamorphosis of Black Soldier Fly (Diptera: Stratiomyidae). They grow quite well on crops contaminated with fungal mycotoxins, and they do not accumulate these poisons (Aflatoxin B1 Tolerance and Accumulation in Black Soldier Fly Larvae (Hermetia illucens) and Yellow Mealworms (Tenebrio molitor)). If manure contains tetracycline, for example, BSF larvae have no problem breaking it down (Systematic characterization and proposed pathway of tetracycline degradation in solid waste treatment by Hermetia illucens with intestinal microbiota). These larvae are superbly adapted to eating fresh manure, even fresh chicken manure. Note well that BSF adults are not filth-bearing flies, and they are not associated in any way with the transmission of disease.

For shorter larval development time and for increased bioconversion efficiencies, it is important that manure be fed to larvae while still fresh (Nutrient utilization by black soldier flies fed with chicken, pig or cow manure). Furthermore, fresh manure should be a firm solid so that larvae can access it efficiently under aerobic conditions. Fresh manure should not come into contact or be mixed with urine or water.

Larvae and Red Worms – an Outstanding Partnership

Larvae, in producing residue, create an ideal substrate for red worms or nightcrawlers. An extensive and prolonged conditioning of larval residue for worm cultivation is normally not required. Dr. Tran Tan Viet noted that when red worms ate larval residue, they grew 2 to 3 times faster than when fed conditioned waste.

Larvae eat fresh manure, something that worms cannot do, and worms breakdown and digest a fair portion of the fibrous material in manure, something that larvae cannot do. Together they form an outstanding partnership in nutrient extraction, waste valorisation and waste sanitization (High waste-to-biomass conversion and efficient Salmonella spp. reduction using black soldier fly for waste recycling and Reduction of E. coli O157:H7 and Salmonella enterica Serovar Enteritidis in Chicken Manure by Larvae of the Black Solider Fly and The Effectiveness of Vermiculture in Human Pathogen Reduction for USEPA Biosolids Stabilization)

The fact that fresh manure is not mixed with urine or water; the fact that manure substrates, when eaten, do not release water; and the fact that the sanitizing effect of larvae is followed by the sanitizing effect of red worms – should assure a very high degree of pathogen destruction. Finally, worms in producing vermicompost or vermichar, create an ideal substrate for microbes within mutualistic soil ecosystems where endless loops and cascades abound.

It is important to view the co-working of larvae and worms as a single process. Larvae and worms can be raised at the same time in two pods next to one another, with larvae in one pod and worms in the other. As larvae eat fresh manure added to the larval pod each day or perhaps twice daily, only mature prepupal larvae self-harvest into a bucket. Immature larvae stay in place where they belong and continue to eat. Mature prepupal larvae have higher protein, fat, dry matter and chitin contents than immature larvae.

When the larval pod fills up with larval residue, larvae in several stages of growth are removed from the surface of the pod and placed in an empty pod ready to receive more fresh manure. After the larvae are removed, worms are put in their place and begin eating larval residue from top to bottom. Each day vermicompost is removed from off the surface of the worm pod, so that the worms stay well aerated as they eat their way down. As worms continue to eat, and as vermicompost is continually removed, in the end only worms remain at the bottom of the pod. They are easily scooped up and used as feed.

Pod 1 with larvae and pod 2 with worms is followed by pod 2 with larvae and pod 1 with worms. Switching back and forth between the two pods goes on and on. Larval residue does not have to be scooped out of larval bins and transported to an off-site vermicomposting facility.

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