I think the first thing that strikes me is the composition. Great use of thirds!
The think the subject is great, lovely detail, it contrasts nicely with the soft background which works well bringing the focus to the butterfly.
The only bit that isn't working for me is the leaf(?) at the top. There isn't enough definition to make out what it is and it doesn't quiet flow with the feeling of the rest of the picture. In a way it doesn't look like it's suppose to be part of it.
Over all it's a beautiful calm piece relaxing colours. Great work!