Link to a Scientific American article about how horses deter biting insects with their tails.

6628728 Cool. Like they said, it's kind of intuitive to think that the tail evolved as a successful (enough) method of taking vengeance on insects to remain as part of them, but the research about the mechanics of it is pretty interesting.

6628728

In just one day, a horse can lose a cup of blood to biting insects such as mosquitoes.

Well that's horrifying.

Also canon.

6628814

the research about the mechanics of it is pretty interesting.

Yeah, it is--I wouldn’t have thought they were used for more than fly swatting, but it makes sense that shooing off the insects before they land and start feeding is better.

I seem to recall coming across another thing about wild horses that were white somewhere in Europe, and scientists wondered why since the white ones were more prone to skin cancer (IIRC) and it turned out that the white ones were also less attractive to biting insects.

6628942

Well that's horrifying.

The good news is that real horses have lots of blood in them. If you’re feeling brave, google a horse nosebleed.

Also canon.

Interestingly, we normally don’t see flies and the like in Equestria, which does make me wonder how they manage them. Also, I’m surprised that Twilight doesn’t know a spell to zap them. (Or else that comes later in the episode)

6631050 I couldn't find anything on that (sounds interesting) but I did find this:
White horses are less attractive to horseflies.

And I should have known there would be such a thing as horse tail extensions, because of course there is.

Also, the Mongolian wild horse (or Przewalski’s Horse) has been released in the Chernobyl Exclusion Zone for a long while now, and last I knew was doing surprisingly well. Sadly right now it looks like people are still its greatest threat.

6631435

White horses are less attractive to horseflies.

I feel like that’s similar to the article I came across.

And I should have known there would be such a thing as horse tail extensions, because of course there is.

Oh, I totally knew that. I think I looked them up not long after that episode where we found out that Fluttershy wears tail extensions. They’re even specifically mentioned in at least one of my stories (The Trek to Ice Cream Rock)

Also, the Przewalski’s Horse has been released in the Chernobyl Exclusion Zone for a long while now, and last I knew was doing surprisingly well. Sadly right now it looks like people are still its greatest threat.

I didn’t know that. I did know that animals are doing all right around the Chernobyl Exclusion Zone these days, probably better than some places since in general they don’t have humans there messing with them.