House flies leave gray, orange, pale yellow, and brown specks of feces and regurgita.
Stable flies leave black specks which are the product of blood digestion.
Stable flies rest mostly on surfaces within 3 feet of the ground. House flies rest with their bodies parallel to the substrate. Adult house flies utilize garbage, manure, uncovered foodstuffs, and a wide array of other organic materials for food. Cyclic daily activity patterns of house flies probably vary greatly with the type and availability of food. However, you may see some stable flies on animals from shortly after daybreak until dusk.