Life cycle assessment (LCA) was applied to evaluate black soldier fly production using different diets, including typical Belgian agro-residues (Brussels sprout stems, endive roots and solid fraction pig manure). The LCA compared insect-based feed with soybean meal and fishmeal, and composting through insects versus conventional treatments. Underlying LCA data were derived through feeding experiments. To determine the sensitivity of the results, we tested the effect of alternative energy sources and dietary components. Non-residue insect feed and energy use contributed greatly to overall environmental impacts. Insect protein had greater impacts than protein from soybean meal or fishmeal due to the high energy consumption and, in some cases, agro-product demands. These should be areas of focus to make European insect production more sustainable. In the case of Brussels sprout stems and endive roots, conventional treatments outperformed composting by insects. Between industrial versus insect pig manure composting, the results varied greatly by energy source and impact category.