Monarch butterflies migrate from Canada to Mexico. It takes one generation to go South but 3 or 4 to return home. They must travel 50 miles per day to get to Mexico. No one butterfly makes the entire trip but they know instinctively where to go. Cycles within cycles - no single one completing the trip alone.

Also, the clusters when they rest at end. http://en.wikipedia.org/wiki/File:Monarch-butterflies-pacific-grove.jpg