Undergraduate student Chris Hornsby ('19) studies black soldier fly larvae as a possible means of closed-loop waste processing and livestock feeding at Sewanee's University Farm.
The maggots that make our meal
Her hand reaches into the black bin of composting food scraps and pulls out a speck of rotting something, careful not to disturb the inch-long vagrant clinging to it. The handler, Carolyn Hoagland, flicks the food off her palm and lets the female soldier fly crawl across her hand while quickly and skillfully shepherding the fly toward a bit of torn cardboard. Enticed, the female crawls onto the board and perches on its exposed internal grooves. Her black abdomen curves downward as she gingerly placed her egg depositor at the entrance to a thin column of paper, and leaves behind a small clutch of nearly 1,000 young.
This was late July of 2017: Exhausted from farm work and eager for a break in the shade, my coworkers and I were more than happy to indulge our manager in watching this menacing-looking fly lay her eggs.
The University Farm in Sewanee can afford these small breaks and experiments. Subsidized by the University of the South, the farm was reestablished in 2012 as a research and hands-on learning opportunity for undergraduate students, like Christopher Hornsby, who has been intentionally breeding these ‘Black Soldier Flies’ on the farm for over two years, harvesting their maggots.
These flies’ larvae are grown on a commercial scale across the United States for fish and chicken feed, but Chris’s project focuses on what the larvae can feed on: once hatched, these larvae fatten for two weeks before emerging as adults, eating twice their own weight every 20-24 hours. To Chris, and to many small farmers, this can be an invaluable service. Reducing whatever mass of food waste given to them by ninety percent, the flies would expedite the University’s composting process by weeks, if not months, and allow the farm to accept 400-500 pounds of food waste from Sewanee’s dining facilities every day.
An impressive metabolism hardly signifies the soldier fly as unique; most larvae can consume a large amount compared to their own mass. But many species’ adult flies can damage the local environment or become a nuisance to humans if their populations get out of hand, so it took a few weeks of research for Chris to find the right fit for Sewanee’s ecosystem.
“They’re very harmless,” Chris explained; “When it becomes an adult fly it sheds the inner lining of its gut, expelling any hazardous microorganisms. And it loses its mouth. So it’s got no mouth, meaning it’s not a disease vector, it’s not a crop pest, and they won’t swarm in houses, usually, unless you’ve got a mountain of food waste in there. And they die after two to three days.” He paused momentarily, and added almost as an afterthought, “They’re also native to the entire western hemisphere. ”
But even this fly isn’t perfect. According to a pair of UGA entomologists’ research from 1984, 99.6% of egg-laying takes place from 81.5° to 99.5°, and the University of Windsor released a study from 2010 suggesting that the larvae’s ideal developmental environment has about 70% relative humidity. Although a Tennessee July easily provides these conditions, only tropical climates can host them year-round. The seasonality of the larvae may not be a problem to small farmers hoping to establish their own backyard colony because most agricultural systems dwindle as winter encroaches, anyway. But at Sewanee, the converse is true: winter is when all 2,000 students are huddled together in the same dining hall, and it’s when the farm grows the most greens and accepts the most food waste. So Chris’s project comes down to controlling climate, which would allow the flies’ reproduction and developmental cycle to continue through the farm’s busiest season.
Chris and Carolyn have worked on multiple prototypes for smaller weather-controlled breeding boxes, but in the summer of 2017 the University’s Domain Management raised a pole barn for the farm to house tractors, large equipment, and gave them the space to accommodate a room full of soldier flies. So Chris’s project has shifted from research to construction, as he tries to plan and prepare an insulated and vermin-proof home for his maggots.
“I don’t know how to vermin-proof a building, but I’m learning. But it’s just me, and I can’t do that kind of construction on my own. If I had more time and more people and more skills… it would all be very helpful.”
Since he graduates in 2019, Chris’s project might not be completed soon enough for him to see it. With preliminary research finished and finding success in smaller-scale larvae breeding, now he needs to build the larvae a home. As a full-time student he can only work eight hours a week on the farm, which limits a project that is now so contingent on major construction work.
However close his graduation looms, he is confident that another student will bear the torch after him. Once it’s finished, he sees Sewanee’s waste management system as a model that can be used by other small farms across the country, like Bill Keener’s Sequatchie Cove Farm.
Keener, a dairy, poultry, and vegetable farmer outside of Sewanee, is intrigued by Chris’s work. Sold at first by the prospect of self-producing chicken feed, he’s now hoping to do research about a small-scale implementation of a soldier fly colony in his farmland.
“Maybe I could find an easy and big enough source of food waste to feed them with. Maybe I could talk to local public schools.”
Keener typically feeds his hogs excess whey from his dairy operation, and if the public school falls through as a food source, he may be able to use the whey as a substrate for soldier fly growth. The soldier flies would create an organic alternative to grain chicken feed, which would lower the price of his organic eggs and increase his competitivity in the local organic market.
“I think it’s a good project for me. For a homestead, it’d just make sense.”