Black soldier fly larvae outpace earthworms at turning food waste into biomass

Black soldier fly larvae and red Californian earthworms are two of the most widely used biological agents for processing organic waste, but direct comparisons under conditions relevant to tropical cities have been scarce. A new study from Veracruz, Mexico, now provides that head-to-head evidence, and the result is clear: under the conditions evaluated, Hermetia illucens larvae reduced waste faster, gained biomass faster, and finished processing in fewer days than Eisenia fetida earthworms in both laboratory and field experiments. The findings, published in Cleaner Engineering and Technology, come with important caveats about what the study did and did not measure, but they offer practical guidance for municipalities deciding how to treat their food waste.

The research team, led by Itzel Lucero Mondragón de la Peña, set out to compare the bioconversion performance of the two species by evaluating waste reduction rate, processing time, and net biomass gain rate. They hypothesized that the black soldier fly would outperform the earthworm, particularly during the warm season, and the experiments largely bore this out. The work was motivated by a growing global problem: an estimated 2.56 billion tonnes of municipal solid waste were generated worldwide in 2022, with annual generation projected to reach 3.86 billion tonnes by 2050 under a business-as-usual scenario. Food and green waste accounted for roughly 44 percent of global municipal solid waste in an earlier assessment, making the biodegradable fraction both a management challenge and an opportunity for resource recovery.

The laboratory experiment used a completely randomized design with three treatments: containers with black soldier fly larvae, containers with adult earthworms, and a control with no organisms. Each experimental unit was a 1-liter plastic container holding 200 grams of pre-composted organic waste and 10 grams of commercial humus, with 10 grams of larvae or earthworms added to the corresponding treatments. Each treatment had 30 replicates, giving 90 experimental units per season. The experiment was repeated during three seasons: rainy (September 2024), dry (November 2024), and warm (May 2025), for a total of 270 laboratory units. The substrate was a homogeneous mixture of banana, papaya, mango, tomato, lettuce, onion, carrot, and broccoli residues collected from the Central de Abastos market in Xalapa, chopped into roughly 1-centimeter pieces and pre-composted for seven days to reduce acidity and fermentation that pilot trials showed could kill earthworms.

Environmental conditions varied across the seasons as intended. Average laboratory conditions were 24 degrees Celsius and 95 percent relative humidity in September, 22 degrees Celsius and 94 percent humidity in November, and 27 degrees Celsius (range 11 to 28) with 93 percent humidity in May. Substrate pH remained at 7 throughout all seasons. The researchers covered containers with mosquito mesh for ventilation, inspected them daily, and added no water, allowing moisture to fluctuate naturally. The field experiment took place at the Municipal Composting Facility in the Banderilla–Xalapa–Emiliano Zapata metropolitan area, using larger plastic boxes with 1000 grams of substrate and 50 grams of humus per unit, again with 10 grams of organisms per treatment and 30 replicates per treatment. Because the organism-to-waste loading ratio differed between settings—0.05 grams per gram in the laboratory versus 0.01 in the field—the two experiments were analyzed independently and were not designed for direct quantitative comparison.

The statistical results were decisive. In the laboratory, waste reduction rate was significantly affected by treatment, season, and their interaction, with black soldier fly larvae consistently achieving higher reduction rates than earthworms across all three seasons, while the control showed the lowest values. Bioconversion time told the same story: treatment, season, and their interaction all had significant effects, and the larvae consistently completed bioconversion in fewer days than the earthworms, with the control requiring the longest processing time. Biomass gain rate differed significantly between the two species, with larvae showing higher rates, although no overall effect of season was detected on this variable; a significant treatment-by-season interaction indicated that the two species responded differently to seasonal conditions.

The field trial, conducted only during the rainy season because access to the composting facility was limited during the 2022–2025 study period, mirrored these patterns. Waste reduction rate, biomass gain rate, and bioconversion time all differed significantly among treatments. Black soldier fly larvae showed the highest waste reduction rate and the shortest bioconversion time, earthworms fell in between, and the control showed the lowest reduction rate and the longest processing time. Larvae also posted higher net biomass gain rates than earthworms under field conditions. Notably, the field trial showed longer processing times than the laboratory, but the authors caution that this cannot be attributed solely to environmental conditions because experimental scale and loading ratios also differed between the settings.

One intriguing nuance emerged in the seasonal data. Although the larvae reduced larger quantities of waste during the warm season, this did not translate into a proportional increase in larval biomass. The authors suggest that as an ectothermic insect, the black soldier fly shows temperature-dependent metabolic and developmental rates, and elevated temperatures may enhance feeding and metabolic activity without necessarily increasing the proportion of assimilated resources directed toward somatic growth. Some consumed substrate may instead support maintenance metabolism, respiration, development, and other energetic processes. Because the study did not quantify respiration, nutrient partitioning, dry-matter losses, or carbon flows, the mechanisms underlying this pattern remain unclear, and the authors call for future research incorporating mass and energy balances. The earthworms, by contrast, showed comparatively consistent waste reduction across the laboratory seasons, a pattern the authors attribute to the environmental variation remaining within a range tolerated by the species rather than proof of general climatic tolerance.

The study is careful about its limits, and readers should be too. Mass loss in the control containers indicates that substrate reduction occurred without larvae or earthworms, likely from microbial activity in the non-sterilized substrate plus moisture loss and gaseous emissions; because measurements were based on fresh mass, these contributions could not be separated. The bioconversion endpoint was defined operationally—material that looked visually homogeneous and dark brown and smelled damp and earthy—rather than by physicochemical maturity indicators. Mortality was observed but not systematically quantified, so net biomass gain reflects the change between initial and final recovered biomass and cannot distinguish individual growth from survival-related changes. The study also did not measure final frass or vermicompost yields, nutrient composition, maturity, stability, phytotoxicity, or agronomic value, meaning that the earthworm treatment’s higher residual fraction does not demonstrate better fertilizer quality.

Despite these constraints, the authors argue the findings support a decision-oriented approach rather than a search for a universally superior species. When rapid processing and limited storage capacity are the main constraints, black soldier fly larvae are recommended for their shorter processing time and higher waste reduction rate. When vermicompost production is prioritized and longer residence times are acceptable, earthworms are suitable, provided acidic fresh waste is pre-composted and appropriate bedding and moisture conditions are maintained. The authors also recommend that municipalities start with pilot-scale units that systematically document waste input, organism loading, temperature, moisture, processing time, product yield, and operational costs before scaling up, and that fruit and vegetable waste be separated at the source to reduce feedstock variation. Future work should test both species across all seasons with standardized loading rates, conduct complete dry-mass and nutrient balances, characterize product quality with indicators such as carbon-to-nitrogen ratio and germination tests, and evaluate economic viability and environmental impacts before either treatment is recommended for municipal implementation.

Subject of Research: Comparative bioconversion performance of black soldier fly larvae and red Californian earthworms for treating organic waste under laboratory and field conditions

Article Title: Comparative performance of Hermetia illucens and Eisenia fetida for organic waste bioconversion under laboratory and field conditions

Article References: de la Peña, I. L. M., Baena, M. L., Piñar-Álvarez, M. Á., Pérez-Staples, D., & Morteo, E. (2026). Comparative performance of Hermetia illucens and Eisenia fetida for organic waste bioconversion under laboratory and field conditions. Cleaner Engineering and Technology, 35, Article 101349. https://doi.org/10.1016/j.clet.2026.101349

Image Credits: AI Generated

DOI: 10.1016/j.clet.2026.101349

Keywords: black soldier fly, Hermetia illucens, Eisenia fetida, vermicomposting, organic waste, bioconversion, municipal solid waste, circular economy, waste reduction, biomass production, Xalapa, seasonal variation