Using Flies to Manufacture Fertilizer

Yield Gaps

Agricultural production in many Sub-Saharan African nations is severely lacking compared to the rest of the world. According to the 2025 Global Agricultural Productivity (GAP) Report, most increases in output on the continent are derived from farmland expansion (Agnew and Nakelse, 2025). Given that most of Africa’s arable land is already under cultivation, the limited potential for expansion indicates possible future plateaus in production. The origins of this structural crisis are rooted in post-colonial neglect, leaving many nations with infrastructure designed for mineral extraction, political systems vulnerable to corruption, and borders riddled with conflict, which was further stressed by a post-independence population boom (Quitkin, 2011). On an agronomic level, the result of these socio-political challenges has been exhausted soils that require infusions of nutrients to regain fertility and support higher yields (Fugile, 2025). Accordingly, the GAP Report recommends significant increases in input use to drive future production growth, with fertilizer being singled out as especially critical.

Unfortunately, a variety of financial and infrastructural conditions hinder the use of fertilizer on the continent. Synthetic fertilizer markets have been famously volatile in the past few years, with price spikes making fertilizer utilization among many smallholders a non-starter. Additionally, there is often a lack of infrastructure to deliver fertilizer to agricultural regions. Regarding organic fertilizers, existing byproducts that could be used, such as field waste or manure, are often dedicated to feeding livestock or burned for fuel. Plainly, there isn’t much nitrogen to go around.

To remedy these issues, scientists at the International Centre of Insect Physiology and Ecology, based in Kenya, have turned to the black soldier fly (BSF) (Hermetia illucens). Or, more specifically, their poop (which in insects is called frass). By constructing composting systems that involve feeding BSF larvae agricultural byproducts, food waste from cities, or various manures, a high quality fertilizer can be produced (below is a video detailing the production process). Additionally, the speed and ease of management of these systems make them amenable to widespread yet scalable distribution, making this technology particularly amenable to constructing circular and distributed systems of fertilizer production (more on this later).

Agronomic Performance

The frass of the BSF is rich in nitrogen, phosphorus, and potassium1 along with a host of plant micronutrients, though these can vary quite a bit. The findings of one trial reported that, compared to other organic fertilizers available in Kenya (namely a commercial product produced by a company called Safi), BSF fertilizers are mobilized, mineralized, and transformed into plant-available forms more quickly (Beesigamukama et al., 2021a).2 Total concentration of nitrogen, phosphorus, and magnesium in soils was quite high, with BSF frass providing far higher volumes of nitrogen and phosphorus compared to the commercial organic fertilizer. The commercial organic fertilizer did provide more potassium and calcium, however. Soil biologic activity was also spurred by the BSF fertilizer, though the functional role of these populations in crop performance is still in question.

A number of field trials have documented how these soil improvements translate to field performance. In maize, grain yields under BSF frass were equivalent to those achieved under a synthetic fertilizer and higher than other organic fertilizers studied (spent brewers’ grain and a commercial product made from food and sewage waste) (Tanga et al., 2022). A combination treatment of synthetic and BSF led to the highest yields, but they were statistically the same as BSF alone. This boost is because BSF fertilizers are immobilized during the early stages of application, and the addition of supplemental, immediately available nitrogen helps to complement this initial shortfall. When economics are considered, net incomes were highest with the combined treatment, the next highest being synthetic, and finally the BSF frass treatment. However, prices in this evaluation were based on the 2019 fertilizer markets; today, I expect the financial calculus would advantage BSF or BSF + synthetic fertilizer. Plus, these evaluations don’t take supply shortages into account.

Similarly, another trial documented the total nitrogen economy and effect on plant physiological development furthers the benefits of BSF frass. Frass application was associated with taller plants, greater chlorophyll concentrations, and improved nitrogen and phosphorus uptake compared to both commercial synthetic and organic fertilizers (Beesigamukama et al., 2020a). Plants also showed greater nitrogen use efficiency and recovery rates when treated with BSF fertilizer. The authors attribute this to BSF frass’ high rates of mineralization and the availability of endogenous nitrogen in the soil to fill gaps during immobilization.

These gaps in nitrogen supply and demand were formally documented by another study, which showed that BSF fertilizers release nitrogen slowly over a long period of time. Since corn’s nitrogen needs follow an S-curve, with a surge of critical nitrogen withdrawn in the lead-up to reproductive development, it can be difficult to synchronize nitrogen release and uptake with this form of fertilizer (Beesigamukama et al., 2020b). Still, this study reported that the BSF fertilizer resulted in higher N uptake than a commercial organic fertilizer, showcasing that while frass releases nitrogen slowly, it is faster than some alternatives.

Aside from maize, BSF frass fertilizer was also associated with greater yields in other crop classes. In bush beans, the fertilizer raised yields by 18% compared to the control treatment and outperformed or matched other synthetic and organic treatments (Chepkorir et al., 2024). The beans themselves also showcased enhanced rates of nitrogen fixation, further driving fertility. In broccoli, the BSF fertilizer similarly outperformed a commercial organic fertilizer in terms of both yield and profitability (Kagehi et al., 2025). Finally, in tomato, kale, and French beans, a combined BSF and synthetic fertilizer treatment resulted in the highest yields, while the sole BSF treatment outperformed commercial organic fertilizers (Anyega et al., 2021). The nutritional quality of these vegetables was also enhanced.

BSF fertilizers also has plant protection effects. While maize grain production is improved, the use of frass also compels plant investments in various defensive traits, including the creation of proteins that impede digestion in caterpillars, driving away the destructive fall armyworm (Mutyambai et al., 2025). Similarly, in potatoes, frass fortified with chitin from the fly larvae was found to suppress nematode populations by stimulating the growth of microbes that feed on nematode eggs (Anedo et al., 2025).

The BSF composting process also shows some promise in removing contaminants from agricultural, food, and manure wastes, which can be a problem for traditional composting methods. BSF larvae reduce the presence of pathogens like Salmonella due to antimicrobial peptides residing in the frass (Basri et al., 2022). Pharmaceutical and pesticide residues from manure or agricultural wastes are also processed by the larvae, reducing the amounts of said compounds reaching the soil (Shelomi, 2024).

BSF frass is also effective in removing heavy metal contaminants from compost inputs. Some metals, like arsenic and lead, are hyperaccumulated in larval tissue, preventing said contaminants from passing into the frass and subsequent soils (Basri et al., 2022). One study has even identified the Black Soldier Fly as a possible candidate for bioremediation efforts (Bulak et al., 2018). Unfortunately, these same qualities potentially limit the usefulness of larvae as an animal feed (Shelomi, 2024). At the very least, the testing and control of inputs is necessary to ensure any larvae-derived feed is safe.

Finally, this method of compost can, under certain conditions, have modest greenhouse gas emissions, namely nitrous oxide, under certain conditions (depending on system design and choice in inputs) (Boakye-Yiadom et al., 2022). While it seems that these systems can be fine-tuned to minimize total warming potential, this risk makes ensuring the sustainable implementation of this technology more difficult. Playing around with humidity, temperature, and carbon/nitrogen ratios using bulking agents like sawdust can help mitigate nitrogen loss with the added benefit of lowering production time (Beesigamukama et al., 2021b). There are also odor issues that could cause conflict between producers and surrounding residents and complicate facility placement.

To summarize, BSF frass fertilizer seems to outperform other available organic fertilizers and is often equivalent to synthetic mineral fertilizers in effectiveness. Of course, this is under ideal experimental conditions, with success rates possibly changing as the practice is scaled up and disseminated. Additionally, a combined treatment of frass and synthetic fertilizers seems to maximize productivity in many systems (my pet theory being that the former acts to handle nutrient base loads and build healthier soils while the latter handles surges of nitrogen withdrawal during bursts of plant growth). Given price swings and shortages in global fertilizer markets, building out nutrient supply chains based on black soldier fly mediated composting seems like a strong solution to balance immediate production demands with long term food sovereignty and local economic development concerns.3

Economic Potential

While these agronomic qualities are impressive, the pace and flexibility of production make BSF compost uniquely amenable to circular supply chains and distributed economic models.

Black soldier flies consume compostable material far faster than conventional composting methods, with turnaround times being as low as 5 weeks from waste material to high-quality fertilizer (Beesigamukama et al., 2021b). Since all it takes to spin up a fertilizer production facility is compostable material, a batch of eggs, some containers, and some basic tools, it’s a fairly simple to process to establish. This high throughput and ease of establishment make BSF compost systems easy to scale to the needs of different contexts and to time outputs with different growing seasons. A farmer could set up a side business with a couple of bins to serve themselves and their neighbors, a small-town entrepreneur could set up a dedicated facility producing fertilizer for a couple of villages, or a larger network of composting cooperatives could be established servicing a large region. Contrast this with conventional synthetic fertilizer production, which is only feasible at large industrial scales.

France 24’s Eyes on Africa program featured the Marula Proteen Hub in Uganda, which raises the eggs and sends them off to farmers in their network who use available scraps to create compost over a 14-day period. By localizing nutrient supply chains, they have been able to employ over 100 people and help over 1,200 farmers access affordable, soil-restoring fertilizers. Compared to existing fertilizer supply chains, BSF frass production can be structured to fit a range of niches in developing agricultural economies and keep wealth, nutrients, and energy localized.

BSF compost production also presents some unique opportunities to establish truly circular economies. The highly customizable metabolism of these systems means they can handle a variable level of waste from a variety of sources. Thus, circular systems that feed waste back into fertilizer production could handle inconsistent volumes of inputs resulting from the natural fluctuations in waste streams.

This quality presents an interesting opportunity for many African countries. As the continent is undergoing rapid urban growth and building out its cities, especially in nations like Burundi, Tanzania, and the Gambia, now is a fruitful time to establish urban-to-rural nutrient flows and build a modern circular economy from the ground up. Constructing collection, aggregation, and reverse logistics systems as housing, sanitation, and transportation infrastructure is being built out allows for systems to be paired together in a cohesive manner. If nascent rural composting industries can be co-developed alongside urban food waste and refuse recycling systems, enterprising African nations could establish themselves as a robust model for modern circular economies and leaders in sustainable food systems.

Whether these ambitious visions pan out or not, the core technology being developed and deployed will have a positive impact on the continent. Already, many farmers are using BSF fertilizer to close the yield gap while evading dependence on global fertilizer markets. Entrepreneurs and cooperative organizers are building local enterprises, driving employment and development, using a technology that is constructive, not extractive. The Black Soldier Fly is facilitating a nutrient revolution in Sub-Saharan Africa, making a more circular, distributed, and regenerative economy possible.

What I’m Reading, Watching, and Listening too

What Makes Judy Faulkner Run?: A fascinating interview with the founder and CEO of Epic Systems, the health records technology company. She discusses how she structured the enterprise to never go public, never be acquired, and to always prioritize functional products over profits. This should be the model every business is built from.

The economic outlook of the great outdoors: Explores how different recreation sectors are doing these days, with some intriguing changes in the ski industry to diversify into summer activities.

References

Agnew, and Nakelse. 2025. The TFP Growth Frontier: Plateaus and Progress in Agricultural Productivity Growth (Thompson, editor). College of Agriculture and Life Sciences, Virginia Tech.

Anedo, E.O., D. Beesigamukama, B. Mochoge, N.K. Korir, S. Haukeland, et al. 2025. Unpacking the benefits of black soldier fly frass fertilizer towards nematode suppression and potato production. Front. Plant Sci. 16: 1509643. doi: 10.3389/fpls.2025.1509643.

Anyega, A.O., N.K. Korir, D. Beesigamukama, G.J. Changeh, K. Nkoba, et al. 2021. Black Soldier Fly-Composted Organic Fertilizer Enhances Growth, Yield, and Nutrient Quality of Three Key Vegetable Crops in Sub-Saharan Africa. Front. Plant Sci. 12: 680312. doi: 10.3389/fpls.2021.680312.

Basri, N.E.A., N.A. Azman, I.K. Ahmad, F. Suja, N.A.A. Jalil, et al. 2022. Potential Applications of Frass Derived from Black Soldier Fly Larvae Treatment of Food Waste: A Review. Foods 11(17): 2664. doi: 10.3390/foods11172664.

Beesigamukama, D., B. Mochoge, N.K. Korir, K.K.M. Fiaboe, D. Nakimbugwe, et al. 2020a. Exploring Black Soldier Fly Frass as Novel Fertilizer for Improved Growth, Yield, and Nitrogen Use Efficiency of Maize Under Field Conditions. Front. Plant Sci. 11: 574592. doi: 10.3389/fpls.2020.574592.

Beesigamukama, D., B. Mochoge, N. Korir, C.J. Ghemoh, S. Subramanian, et al. 2021a. In situ nitrogen mineralization and nutrient release by soil amended with black soldier fly frass fertilizer. Sci Rep 11(1): 14799. doi: 10.1038/s41598-021-94269-3.

Beesigamukama, D., B. Mochoge, N.K. Korir, K. K.M. Fiaboe, D. Nakimbugwe, et al. 2021b. Low-cost technology for recycling agro-industrial waste into nutrient-rich organic fertilizer using black soldier fly. Waste Management 119: 183–194. doi: 10.1016/j.wasman.2020.09.043.

Beesigamukama, D., B. Mochoge, N. Korir, M.W. Musyoka, K.K.M. Fiaboe, et al. 2020b. Nitrogen Fertilizer Equivalence of Black Soldier Fly Frass Fertilizer and Synchrony of Nitrogen Mineralization for Maize Production. Agronomy 10(9): 1395. doi: 10.3390/agronomy10091395.

Boakye-Yiadom, K.A., A. Ilari, and D. Duca. 2022. Greenhouse Gas Emissions and Life Cycle Assessment on the Black Soldier Fly (Hermetia illucens L.). Sustainability 14(16): 10456. doi: 10.3390/su141610456.

Bulak, P., C. Polakowski, K. Nowak, A. Waśko, D. Wiącek, et al. 2018. Hermetia illucens as a new and promising species for use in entomoremediation. Science of The Total Environment 633: 912–919. doi: 10.1016/j.scitotenv.2018.03.252.

Chepkorir, A., D. Beesigamukama, H.I. Gitari, S.Y. Chia, S. Subramanian, et al. 2024. Insect frass fertilizer as a regenerative input for improved biological nitrogen fixation and sustainable bush bean production. Front. Plant Sci. 15: 1460599. doi: 10.3389/fpls.2024.1460599.

Fugile, K. 2025. International Agricultural Productivity.

Gärttling, D., and H. Schulz. 2022. Compilation of Black Soldier Fly Frass Analyses. J Soil Sci Plant Nutr 22(1): 937–943. doi: 10.1007/s42729-021-00703-w.

Kagehi, N., D. Beesigamukama, C.M. Tanga, M.P. Ngugi, S. Subramanian, et al. 2025. Contribution of different frass fertilizer products on enhanced growth, yield and nutrient quality of Broccoli [Brassica oleracea]. Front. Plant Sci. 16. doi: 10.3389/fpls.2025.1613814.

Mutyambai, D.M., J.M. Mutua, A.A. Jalloh, D. Beesigamukama, A. Kessler, et al. 2025. Insect frass fertilizer upregulates maize defence genes and resistance against an invasive herbivore pest. Sci Rep 15(1): 29978. doi: 10.1038/s41598-025-14883-3.

Quitkin, M. 2011. The Hungry Continent. Howard G Buffet Foundation.

Shelomi, M. 2024. Mitigation Strategies against Food Safety Contaminant Transmission from Black Soldier Fly Larva Bioconversion. Animals 14(11): 1590. doi: 10.3390/ani14111590.

Tanga, C.M., D. Beesigamukama, M. Kassie, P.J. Egonyu, C.J. Ghemoh, et al. 2022. Performance of black soldier fly frass fertiliser on maize (Zea mays L.) growth, yield, nutritional quality, and economic returns. JIFF 8(2): 185–196. doi: 10.3920/JIFF2021.0012.