Normally, the process of converting organic waste into organic matter (OM) is a slow and often unseen one. Organisms as large as earthworms and as tiny as bacteria break down dropped leaves, cornstalks and more at an almost glacial pace. However, one particular insect is really, really good at creating OM.

The black soldier fly (BSF) has an appropriate name. It performs a lot of duties that can actually be beneficial to farmers. Their larvae can serve as feed for poultry and pigs. They don’t fly around as much as houseflies, as they have less expendable energy due to their limited ability to consume food as adults. BSF are sanitary and they don’t bite or sting.

Milena Agila and Dr. Laura Ingwell in the Department of Entomology at Purdue University recently studied how BSF could convert organic waste into agricultural products. They noted, “Farmers confront several challenges, of which soil health, water quality and space limitations are due in part to agricultural intensification and increasing population. The addition of soil amendments is a strategy to improve soil health. One emerging source is the result of the digestion of organic wastes by black soldier fly larvae, which are farmed for protein production. This insect can contribute to circular agricultural economies, improving farm sustainability.”

(Note: The bit about protein production for human consumption is true. When the larvae are powdered, they can serve as a protein source to be added to shakes or porridge. Researchers at Cornell University are actively working on a project using BSF for protein.)

Black soldier fly larvae. Photo by David Cappaert, Bugwood.org

But back to OM production – Agila and Ingwell had two goals with their experiment. They wanted to estimate the amount of organic waste needed to breed one gram of BSF eggs; and to quantify and analyze BSF byproducts from the rearing process to use as agricultural sources.

Their BSF larvae were fed food waste from the dining court at Purdue and organic waste streams collected from the Meigs Horticultural Research Farm in Lafayette, IN. The larvae were harvested when they reached the prepupal stage and were no longer feeding. (After hatching from eggs, the insects grow through five instar stages before pupating to become flies.)

The BSF digestate (compost) and their shed skin was collected, weighed and analyzed. The two different collected materials were compared to Black Kow® compost, which served as a control.

The larvae performed their duties well. The researchers found that one gram of BSF eggs, before the insects reach the prepupal stage, can convert about 23.5 kilograms (51.8 lbs.) of organic waste into about 3.1 kg (6.8 lbs.) of soil amendment. (That one gram of eggs also results in about 2.4 kg (5.3 lbs.) of BSF larvae.)

The analysis also looked at the nitrogen, phosphorus and potassium (NPK) and OM values at the end of the experiment. It was discovered that:

  • The BSF digestate had similar levels of NPK (averaging 3.1% availability of each) and an enviable 81.2% available OM
  • The BSF’s shed skin only had about 1.7% available P and K, but almost 8% N and a whopping 82.4% OM
  • The Black Kow compost peaked with 1.6% available N, 0.1% K and .02% P and only 26.8% OM

In total, from November 2022 to August 2023, 62.2 kg (137.1 lbs.) of BSF digestate was produced.

For small farms looking to create more circular economic streams on their operations – to cut down on the amount of inputs purchased and waste products taking up valuable space – it may be worth it to call the black soldier flies up to serve.

by Courtney Llewellyn