This is a notorious little pest (6 mm in length) of ranches and farms worldwide. It is blood sucking, you can see the tubular hard mouthparts in the pictures. It can reach large numbers and seriously weaken livestock. The economic costs of weight loss in cattle associated with stable flies and their control have been estimated to exceed $1 billion annually in the US alone. This fly will bite all warm blooded animals, but is especially drawn to livestock. They prefer to feed on the front legs which have short hair and are difficult to reach by the host. The bite hurts. The Stable Fly is also a vector of several parasites and diseases, including Trypanosoma evansi (the agent of Surra), Trypanosoma brucei (brucellosis), Equine infectious anemia, African horse sickness, and fowlpox. It is also reported to be a vector of Bacillus anthracis, the causative agent of anthrax. Family Muscidae.
I found this one on a lamp post at night, semi rural residential area, San Cristobal de Las Casas, Chiapas, Mexico 2,200 meters.