Horseflies can give painful bites and if not treated can result in even more ache. The perfect method on how to treat a horsefly bite is using soap and water to clean the bitten area. After that drying the area with a clean towel is also recommended. There are also other things that can be done to treat horsefly bites. Using topical hydrocortisone cream or a Benadryl cream on the bitten area can be effective. Other solutions could be to helping the injured victim is to place a soaked in salty water hot towel on to the wound. Vinegar has also been known to help with relieving pain. Aloe vera juice can also help as well as an ice cube or any other cooling substance to reduce itching.
Obviously the best thing to do is to prevent the horsefly from biting you in the first place. Start with using insecticide spray.