Packed with calories: The larvae of the black soldier fly eat almost anything and thus produce lots of valuable protein

Packed with calories: The larvae of the black soldier fly eat almost anything and thus produce lots of valuable protein

Insects as animal feed

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Can maggots help to save the climate? A growing number of pioneering thinkers around the world are convinced that they can – and are working to develop sustainable products based on insects


TEXTTom Rademacher

Tom Rademacher is a freelance journalist based in Cologne. He writes about scientific and industrial topics, among others

Four million creatures, densely packed together in dark metal boxes. “Yes, we carry out factory farming,” says Heinrich Katz with pride. In fact, the conditions inside the box are heavenly for the larvae of the black soldier fly that grow here. “They only feel well if they swarm around each other. They need warmth, darkness, and plenty of food,” says Katz. His company, Hermetia Baruth, is based in Baruth south of Berlin. The firm is Germany’s largest breeder of black soldier flies.

These fingernail-size insects have elongated, slim-waisted bodies that make them look more like wasps than house flies. The creatures have become a beacon of hope for protecting the climate and the environment. From nutrition and cosmetics to mobility, the flies and the substances that are made from them are potential sources of benefits in innumerable areas. Another person who is enthusiastic about the black soldier fly is Thomas Häußner. “It turns residues that would otherwise be hardly usable into valuable protein that is ideal for use as animal feed,” he says. Häußner works at Evonik, where, among other things, he is responsible for strategic research and development projects related to animal feed. Since the summer of 2020, Evonik has been working together with the Bioresources division of the Fraunhofer IME in the INFeed research project, which receives funding from the German government and the state of Hesse.

Experts think that there is a bright future for animal feed made from insects fed on leftover food. “The black soldier fly larvae are very quickly growing omnivores,” says Dr. Martin Rühl at the Fraunhofer Institute’s branch facility in Gießen. This makes them interesting as feed for pigs and chickens – and for fish, where they could substitute for fish meal and soybeans.

Short and nutritious: The male flies are around 14 millimeters long, while the female ones measure 17 millimeters. BSFs are a non-invasive species and do not transmit any diseases

The use of insects for economic purposes is by no means a new idea. “The silkworm has been cultivated for the past 5,000 years,” says Professor Andreas Vilcinskas, Head of the LOEWE Center for Insect Biotechnology & Bioresources, to which Rühl’s Fraunhofer team belongs. Completely new possibilities are opening up as genomes become more and more decoded. Vilcinskas sees himself as an ambassador for “yellow” biotechnology, which employs insects. He coined the term himself. “There is red biotechnology in medicine, green in agriculture, and white in industry. ‘Yellow’ was still up for grabs.”

Insects have far more species than any other class within the animal kingdom. In fact, around 90 percent of all species on earth are insects. “They have an evolutionary head start of hundreds of millions of years and provide us with an unparalleled library of materials that we are now beginning to access,” says Vilcinskas. Among other things, he is investigating whether insect cells might be used to produce improved antibiotics. One of his studies is titled “Drugs from Bugs.”

Another big topic he is addressing is nutrition. The black soldier fly, or BSF for short, is an inconspicuous critter, which inhabits subtropical regions. It doesn’t sting, bite, pester, or transmit diseases. Moreover, it doesn’t even eat. The adult fly only exists to procreate; it doesn’t even have mandibles. Before the larvae pupate, they therefore store up enough energy for the fly’s two-week existence. That makes them real eating machines – packed with calories. Leftover food, biowaste, excrement, cadavers – they aren’t choosy in their tastes. The larvae can consume almost any organic material except for wood.


Maggots get fat especially quickly if their feed has an optimal composition. This is where the researchers from Evonik can contribute their expertise because the company has, for almost 70 years now, been producing amino acids for offsetting nutrient fluctuations in animal feed. These amino acids enable chickens, pigs, salmon, and prawns to optimally utilize their feed. “Within the INFeed project, we are responsible for analyzing and optimizing the feed,” says Häußner. These measures are improving not only the feed for the larvae, but also the feed that is produced from the larvae for the feeding of other animals.

The final act: The adult flies die after mating.

The final act: The adult flies die after mating.

To this end, samples and experts regularly commute between the laboratory in Gießen and the Hanau Industrial Park, where Evonik has pooled its animal feed expertise. “The right amino acid profile lets us exploit more of the leftover material for the larvae as well as reduce costs and thus produce a competitive protein,” says Häußner. This is the only way that the insect feed idea can make insect farming into a successful business.

The market is promising, and insect startups are currently getting hundreds of millions in funding every year from investors. The global market for insect proteins is forecast to grow dramatically between now and 2030: by 5,000 percent to half a million tons of proteins per year. It will still have room for growth even then, because almost five million tons of fish meal and more than 380 million tons of soybeans are produced every year. Overfishing, deforestation, and huge climate-related effects are the result. “Just like our amino acids, insect proteins could help to feed the world’s growing population much more sustainably,” says Häußner.


The larvae begin their lives in net-covered “love cages,” where thousands upon thousands of flies mate if the conditions are right. The incidence of the light, the temperature, and the humidity all have to be the same as those in the flies’ home, the tropics. In Gießen, the love cages are located in a hothouse; they fill a well-heated hall at Heinrich Katz’s company in Baruth.

After mating, every female fly lays around 500 eggs, from which larvae hatch two days later and immediately begin to eat. If put on the right substrate, they will grow to 15,000 times their original size within two weeks. As a result, the larvae easily reach a “dressed weight” of 300 milligrams.

In the "love cages", each female lays around 500 eggs.

A small percentage of the larvae are allowed to pupate so that they turn into flies that can create the next generation. Most are used for production. In the laboratory, the larvae are flash-frozen, after which they are ground into a powder that can be dosed directly into animal feed or broken down into its constituent elements: protein, fat, and chitin. In addition to being used in feed, proteins are also in demand by the chemical and pharmaceutical industries. The same is true of the chitin from the carapace, which can be used to make biodegradable polymers. The fats, meanwhile, can be used by industry to make biodiesel or plastics.

Even the muck from the “maggot stable” is useful. Known as “frass” (a term derived from a German word for “feed”), this contains excrement, cast-off skin and the remains of feed. “Experiments in India have shown that this material can double rice yields when it is used as a fertilizer,” reports Vilcinskas.

Martin Rühl (left) from the Fraunhofer Institute in Gießen and Thomas Häußner (center) from Evonik check the feed’s nutrient profile

Martin Rühl (left) from the Fraunhofer Institute in Gießen and Thomas Häußner (center) from Evonik check the feed’s nutrient profile

So, is everything set for a big revolution in animal nutrition? Not quite, because the feeding of larvae to pigs and chickens has only been permitted in the EU since this summer and only to a limited extent. The ban was a relic from the BSE crisis of the 1980s and ’90s. The disease had been caused by the use of processed animal cadavers in cattle feed. After that incident, farmers were no longer permitted to use animal-based proteins in feed. The only exception was the use of fish meal in aquacultures. For decades, experts tried to get the ban lifted because pigs, chickens, and fish like to eat insects when they are outdoors. “Insect protein contains many essential amino acids,” says Häußner. “In addition, the soldier fly produces around 50 antimicrobial peptides, which strengthen the animals’ immune systems and might thus reduce the use of antibiotics.”


The researchers are correspondingly pleased that the ban has been partially lifted. However, there is still one obstacle in Europe: Livestock may not be fed waste and the black soldier fly is defined by law as livestock. The situation is different in other countries. The Kenyan startup Insectipro, for example, feeds larvae with 20 to 30 tons of waste per day from the capital city of Nairobi. It sells the larvae to pig and chicken farmers in the surrounding region. Similar projects are also under way in Asia. In some places, the BSFs also consume manure, slurry, and human feces.

The researchers in Gießen are striking out in new directions and trying to exploit food channels that might be approved by the EU. For example, the INFeed project also involves a sweets manufacturer that is looking for ways to use cocoa bean shells. The researchers have also garnered interest in Indonesia, where huge amounts of material from the fruiting heads is left over at palm oil mills. “To date, the fibrous plant material has been either used to generate energy for the mill or simply burned out on the fields,” says Rühl. The researchers in Gießen have developed a fermentation process that makes this material edible for the BSF larvae. These larvae would be an almost climate-neutral feedstuff for fish and prawn farmers in Southeast Asia. The frass would be spread on the fields. “The antimicrobial peptides in the feed might also make the shrimps more resistant to disease and reduce the need for antibiotics.”

The researchers in Gießen want to demonstrate this benefit, so a shrimp farm is to be built next to the Fraunhofer Institute this year. Located far from the sea, this farm will contain big tanks, where black tiger prawns will eat sustainably produced larvae – the insatiable waste consumers from the dark boxes.

“Insects provide us with an unparalleled library of materials that we are now beginning to access”


Photos: Robert Eikelpoth (5), Oliver Soulas / Fraunhofer

Illustration: Oriana Fenwick / Kombinatrotweiss on the basis of an original photograph by Stefan Eisenburger


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