Black soldier flies (BSF) are attracting attention in agricultural communities. These non-biting flies are about 3/4” long and black; they look more like a wasp than a fly, but they neither sting nor bite. The larvae consume various organic materials, including manure and larvae of more pesky flies. BSF larvae can also be food for animals and birds.
In 2019, BSF became the topic of a meaningful conversation between Purdue University entomology graduate student Caydee Terrell and entomologist Laura Ingwell. From Ingwell, Terrell learned about black soldier fly larvae’s (BSFL) ability to break down chemical contaminants in organic material and impact the bioavailability of heavy metals. Terrell noted that this combination of breaking down organic waste while remediating contaminants and generating nutritional feedstuff could benefit the urban farmers in her area. She was curious to know if the compost material left by BSFL would make a good growing substrate.
Composting with Black Soldier Flies
In 2020, Terrell applied for and received a $14,832 NCR-SARE Graduate Student grant to study BSF and work with urban farmers who could benefit from a BSF composting system that could recycle organic waste and generate nutrient-dense soil amendments.
“Traditional compost production strategies include aerobic, anaerobic, and vermicomposting,” explained Terrell. “Aerobic composting involves the regular turning of the pile, so it is well aerated and only slightly odorous if not kept unturned. Anaerobic is the opposite, with no interference (turning), and is very odorous, making it unsuitable for urban farmers. Almost 70 percent of urban farmers struggle with land access (Oberholtzer 2016) and operate on small, confined lots. Because of this, urban farmers often do not have the space or the authority, due to zoning regulations, to implement traditional composting methods.”
Rearing Black Soldier Flies
Terrell got to work developing a BSF-rearing system optimized for urban production using materials commonly available at a hardware store. She tested a variety of food waste streams, including table scraps, manure, and spent grains from a brewery. When the waste streams were pooled and fed to BSFL, the result was a soil conditioner/amendment comparable to traditional compost. She worked with the Purdue Horticulture Research Farm, community gardens in the greater Lafayette area, and three urban farmers to test rearing BSFL and explore using the compost they made. An urban chicken farmer involved with the project was especially impressed with BSFL’s ability to break down manure.
“We put our bin right behind the layer coop,” said the farmer. “Inside the coop, we have a poop board that gets a layer of pine shavings below the roosts, which collects just about any manure the hens leave in the coop. We usually clean the board twice a week, but if I do it only once a week, the manure is crawling with tiny to small BSFL. There is also much less chicken manure because the larvae actively break it down. That all goes right into my compost pile. Just a bonus and less mucking out the coop for us!”
A community gardener liked how easy it was to set up and use the rearing bin, but separating the compost from the larvae proved challenging. Terrell addressed this issue in her tests by keeping the larvae-rearing bins in mesh cages. She collected the adult flies from the mesh cages surrounding the rearing bins until no more adults emerged, and then she would remove the compost.
With so much left to explore, Terrell will continue with her Ph.D. and pursue a career in research and extension. She’s especially interested in agricultural waste issues.
“My project defined and highlighted agricultural loops we can take advantage of. Right now, most ag systems are linear, which requires a lot of inputs and generates a lot of outputs, also known as agroindustrial wastes,” explained Terrell. “But if you could repurpose that waste, it would no longer be considered ‘output only waste’ and go from having no value to having some. And although my research is one little piece when looking at a system this big, it would be noticeable if it were missing once we had the bigger picture.”
Terrell presented her BSF project at Indiana's Urban Soil Health's 2022 Get the Dirt conference training.
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