"The monarch butterfly ... May be the most familiar North American butterfly, and is considered an iconic pollinator species. ... The Eastern North American monarch population is notable for its annual southward late-summer/autumn migration from the United States and southern Canada to Mexico. During the fall migration, monarchs cover thousand of miles, with a corresponding multi-generational return north." - Wikipedia
Just as we love the red admiral butterfly in Britain, monarch butterfly seems to be its counterpart in America. Since we don't have this species here (I am lucky if I could spot a red admiral even!), this was painted from a photograph.
I have seen monarchs' annual migration on wildlife programme on TV, but it would be really miraculous if I could see it in real life.