This video from the USA says about itself:
Black Scavenger Fly (Sepsidae) Wing-waving
Photographed at Grand Forks, North Dakota (31 May 2010).
Translated from Dutch Vroege Vogels radio:
New insects discovered on dead animals
Sunday, September 4, 2016
Deliberately leaving dead animals in the wild in the Kuinderbos forest (Flevoland province) has resulted in three insect species new for the Netherlands. In the framework of the project “Death gives life” the Forestry Commission gathered in a special place corpses of deer, beech martens and a heron. That attracted various scavengers, including many insect species. Entomologist Elias de Bree of EIS Insects Research Netherlands therefore placed an insect trap there.
After analyzing the trapped animals he was able to identify three new species for the Netherlands: two species of ensign flies (Sepsidae) and a species of the family Piophilidae … . Small flies from 4 to 5 mm. They live as larvae in manure and carcasses of vertebrates. The Forestry Commission is pleased with the new discoveries: it says something about the biodiversity in the Kuinderbos.