Ha-ha, no, no it's not suppose to be from a horse's perspective, that's interesting that you thought that though! It's a humorous piece, suppose to be a guy sitting on a bench, in serene surroundings and this fly continues to bug him, and he refuses to move b/c of the fly, so he just gives in a becomes the flies horse while he sits on the bench.
Okay, I have a suggestion. I do agree with thething912. It just seems like a rant from a horse. You say that it is supposed to be a man that is being bothered by a fly. Well, I'm sure that we are not the only ones who took it as a horse and a fly. I think if you want your poems to be more understandable, you should clarify what you want to be known. And as a good example, you should clarify in the poem that it is from a man and not a horse. That's a start to making this poem better. That will help people understand more as to what the poem is actually about and what's going on.