UC Riverside scientists have created a small-scale system that transforms food waste into high-protein animal feed and fertilizer using black soldier flies, offering a sustainable solution to a major environmental problem.

Black soldier fly adults sunning themselves on the walls of a greenhouse at UCR. (Mauck Lab BSF Team)

Black soldier flies have long been used by cities and industry to break down food scraps and agricultural waste. Compared to industrial-scale operations, which require significant infrastructure and staffing, the DIY system is far more affordable and accessible.

“A commercial facility might process tons of food waste a day, but that comes with big capital and labor costs,” said Kerry Mauck, UCR entomologist who helped design and test the system. “Our system can be built with off-the-shelf materials, maintained by one person, and still produce useful products that can help grow more food.”

A paper co-authored by Mauck describing the bioreactor system and its effectiveness as a food transformation tool has been published in the journal Waste Management.

“This setup lets you recycle food waste right where it’s produced, either on a farm, in a greenhouse, or even at a large residence,” Mauck said. “We ran ours using food waste from a campus dining hall.”

Black soldier fly prepupae self-harvesting from the bioreactor system. The prepupae walk around the system until they reach the harvest point where they drop off into a bucket. (Mauck Lab BSF Team/UCR)

The research team found that with basic oversight, the system becomes remarkably stable, producing about a pound of larvae per square yard every day.

Black soldier fly larvae are sought after as protein-rich feed for poultry and fish. Their manure, called frass, is a valuable soil amendment. Unlike house flies, which transmit disease and are a nuisance, black soldier flies are harmless and uninterested in human environments.

The bioreactor’s primary output is frass, which is produced in even greater quantities than the larvae themselves. But frass offers more than nutrients. Insect body parts mixed in from molting stimulate natural plant defenses and improve soil microbial health.

“There’s a lot we’re still learning about how frass boosts plant immunity,” Mauck said. “We’re seeing that when insect fragments are part of the soil, it helps plants resist disease, almost like a vaccine.”

Climate control is key to keeping the bioreactor running smoothly. Researchers found that larvae need a shaded or greenhouse space that stays below 100 degrees Fahrenheit. During rearing, users occasionally add water and wood chips, and monitor basic metrics like temperature and pH, then adjust as needed.

Black soldier fly larvae. (Mauck Lab BSF Team/UCR)

“One of our big takeaways was that monitoring pH really matters,” Mauck said. “If the system gets too wet, anaerobic bacteria can take over, dropping the pH and harming the larvae. But small tweaks, like less water or more wood chips, can quickly bring things back into balance.”

By mimicking natural cycles where insects feed and die in soil, the bioreactor reconnects farming with the ecosystems it often disrupts. For farms seeking to reduce waste and input costs, the insect-powered solution offers both ecological and economic benefits.

“This isn’t just waste management, it’s resource creation,” Mauck said. “We’re taking what we don’t want and turning it into something we do.”

(Soldier fly cover image: Tomasz Klejdysz/iStock/Getty)