I have battled flies in horse’s ears since I was a kid. Here in the Northeast the black flies are here from April until frost. If you don’t do anything, these nasty little blood suckers turn your horses ears into a crusty mass of dried blood. I’m thinking it doesn’t feel too good to your horse either.
One solution is a fly mask with ears, but our Pony Cadilac Man doesn’t care for them. I know people say that not clipping the hair in their ears helps, but ears couldn’t be any hairier than Caddy’s so I’m not sure it makes any difference. But here is what I have found that works great and I didn’t have to look too far; Alabu Tea Tree Body Butter.  I apply it every morning inside his ears and it heals any bites already there ( sometimes I forget to check for flies in his ears in the Spring) and keeps them from getting new ones. I also use it on the sheath area and the inside of our pony’s back legs where the horse flies like to bite. It heals and protects from them too. I have to say it works better than anything I have ever tried. I could probably apply less often, but Caddy really likes it, so usually he gets it every day. I think he likes the ear massage as much as keeping the flies away.