Abstract: A method for producing biogas includes: anaerobically digesting excrement with an additive, the additive including a pre-pupal stage of an insect from the scientific classification superfamily of Stratiomyoidea; and collecting the biogas. A method for producing an additive for anaerobic digestion of excrement includes: hatching eggs of an insect from the scientific classification superfamily of Stratiomyoidea in excrement; growing insect larvae by feeding with additional excrement; harvesting pre-pupal insect larvae; and grinding the pre-pupal larvae. An apparatus for producing an additive for anaerobic digestion of excrement includes: a tray having pivot along one lateral side and an upwardly sloping wall terminating with a lip along a lateral side opposite the pivot; a flume adjacent the lip; and a conveyor adjacent the pivot.