Size: Flies come in many sizes, from one-millimeter-long biting midges to horse flies over an inch in length.Color: Black, brown, yellow, and iridescent green are common colors for nuisance fly species and those often associated with dead animals.Shape: Body shape can range from compact gnats to the gangly, mosquito -like look of crane flies.Hair: Some varieties, like shiny bottle flies, appear to have little hair, while fuzzy drain flies have a moth -like look.Eyes: Forward-facing, goggle-shaped eyes are a hallmark of house flies. The eye placement of other types of flies can help experts identify them.