Lesser house fly
flies mate, adult males will form swarms in areas with still air out of direct sunlight where they remain in flight as they wait to be visited by an unmated [...] from the arctic to the temperate neotropics, and they typically reproduce in feces, compost and carrion. These flies are often a serious concern for commercial [...] abundant manure production create the ideal conditions for maggot development. In extreme cases, large fly populations can even represent a public health concern