* Sweat and Moisture: Flies are attracted to the sweat and moisture produced by horses. This is especially true for stable flies, which feed on blood. Horses sweat a lot, especially when they're working or in hot weather, providing a perfect breeding ground for flies.
* Manure: Flies love manure, as it's a breeding ground for their eggs. Horses produce a lot of manure, providing a constant supply of resources for flies.
* Dark, Damp Places: Flies are also attracted to dark, damp places, which are common around stables and barns.
It's important to note: Flies don't actually enjoy being around horses. They are simply attracted to the resources available there.
Fun Fact: Flies can be a major nuisance and health risk for horses, spreading diseases like West Nile virus and Equine Infectious Anemia.