Larvae of the black soldier fly are increasingly viewed as a sustainable alternative protein source, but reliable data on their greenhouse gas emissions during production has been lacking. A new study from Germany’s Research Institute for Farm Animal Biology, published in Bioresource Technology, provides some of the first systematic measurements of carbon dioxide and ammonia emissions during black soldier fly larval rearing, and shows that the climate impact depends heavily on what the insects are fed.
Key Findings
- Lower quality feed reduces larval growth and protein accumulation while increasing CO2 output per unit of protein produced.
- Gas emissions from black soldier fly larvae vary significantly depending on the nutrient quality of their feed substrate.
- In an initial comparison, CO2 emissions per unit of protein from the larvae were lower than published values for cattle and poultry.
Black soldier fly larvae (Hermetia illucens) produce protein comparable in quality to soy, and they can do so from a wide range of organic inputs, including agricultural byproducts and food processing residues. That versatility makes them attractive for circular bioeconomy models. Yet despite growing interest, there has been little quantitative data on the greenhouse gases released during the insect rearing process itself.
The researchers addressed this gap by feeding larvae different biomass substrates that varied in nutrient composition and digestibility. They then continuously measured carbon dioxide and ammonia emissions during a critical developmental window, from the 9th to the 16th day after hatching, using respiration chambers.
Their results revealed a clear pattern. Larvae fed lower quality substrates with poor digestibility grew more slowly, accumulated less protein, and produced higher CO2 emissions relative to their body mass. Larvae that received more nutrient-rich feed grew substantially better. However, those better-fed larvae also showed elevated ammonia emissions toward the end of the growth phase, likely caused by an imbalance between protein and available energy in the feed as the growth period progressed.
Growth, emissions and the question of the correct reference value
“Emissions can only be meaningfully classified if they are related to the actual output – for example, the protein yield or the dry matter of the larvae,” explained PD Dr Manfred Mielenz from the Nutritional Physiology working group at the institute. “Higher absolute emissions do not necessarily mean a worse carbon footprint if the emissions per unit of high-quality protein produced are lower.”
That distinction matters because raw emission numbers without context can be misleading. A substrate that produces more total gas but also yields far more protein per cycle may actually be the more climate-efficient option. The study emphasizes that choosing the right reference metric is essential when evaluating insect production systems against conventional livestock.
The researchers also note that a complete environmental assessment would need to account for the full production life cycle. This includes not just the larval rearing phase but also the production and transport of feed substrates and the handling of residual organic material left after the larvae are harvested.
In a preliminary comparison, the CO2 emissions associated with protein production from black soldier fly larvae fell below values reported in existing literature for both cattle and chickens. The authors caution, however, that this is an initial estimate and that comprehensive life cycle analyses are still needed before firm conclusions can be drawn.
Initial guidance for the assessment of insect protein
Beyond the emission data, the study offers practical guidance. By adjusting the nutrient content and energy balance of feed substrates, producers could potentially reduce emissions while improving the efficiency of protein output. This kind of feed optimization could become an important lever as insect farming scales up commercially.
The research arrives at a time when both German national climate targets and European farm-to-fork strategies are pushing for more sustainable protein production systems. The authors stress that these new production pathways need robust, standardized metrics so that their environmental performance can be fairly compared with established livestock systems. While the current results provide a useful scientific starting point, they are not a substitute for full life cycle assessments.
The institute plans to continue expanding its insect research program to build a more complete picture of the environmental tradeoffs involved in insect-based protein production.
Source: Research Institute for Farm Animal Biology (FBN)