No Waste Left Behind: Insect Droppings Can Improve Soil Fertility

By Jessica Ryan

Insect droppings, commonly known as insect frass, may seem useless and downright disgusting, but scientists found that this waste can improve soil health when added as a fertilizer in farming.

Insect frass is a mixture of excreta, feed, and molted skins. These droppings are a by-product of farming insects like yellow mealworms, banded crickets, and black soldier flies. Farmers raise and breed insects, also known as "mini-livestock," to be an alternative protein source for animals and be a more sustainable practice in agriculture.

Insect frass may also be used as fertilizer. Previous studies by this team led by the United States Department of Agriculture (USDA)'s Agricultural Research Service (ARS) show insect frass can have higher carbon and nitrogen content than fossil fuel-based fertilizers and fewer pathogens than other animal manures.

These researchers, along with collaborators from the University of Arkansas System Division of Agriculture, also studied insect frass' potential as an organic fertilizer source when used as a soil amendment in farming. The study is published in the journal Scientific Reports.

In a two-year field study, researchers found that frass from yellow mealworm increased the amount of carbon by two times and nitrogen by three times in soils than other sources like poultry litter and ammonium nitrate. Furthermore, soils with frass addition produced crop yields and carbon dioxide emission rates similar to soils amended with poultry litter and ammonium nitrate.

"Insect frass substantially improved soil fertility which showed its ability to be used as an alternative to inorganic fertilizers," Amanda Ashworth, a soil scientist at the ARS Poultry Production and Product Safety Research Unit in Fayetteville, Arkansas, said.