Tabanus is a genus of biting horseflies of the family Tabanidae. Females have scissor-like mouthparts that aim to cut the skin. The horsefly can then lap up the blood. Horseflies of this genus are known to be potential vectors of anthrax, worms and trypanosomes.
The conical thing that you see in the middle of the photo is a trap for horseflies.
@koalagardens I know, if one bites me it becomes a very hard disk of about 10 centimeter and hurts very much. I’m glad the people do something to get them away from the horses.