"A long time ago, as glaciers retreated from North America, some arctic butterflies stayed behind. The Earth was warming and so they fluttered up mountain slopes, to where it was still cold. As the climate continued to change, the arctic butterflies continued to climb, toward the summits — and then, where?

At the other end of the continent, a tropical butterfly began to pursue milkweed northward, making the journey generation by short-lived generation, branching out toward opportunity, flying and breeding and dying. At the end of summer a “super generation” would make the entire return journey south, to an ancestral home it had never seen before.

Human beings eventually reached this territory and settled into tribes that lived in communion with the Earth. They had no practical use for the butterflies but saw the mysterious insects as symbols. They signaled a warning, or the harvest of corn. They carried dreams, or the souls of the dead."

Dan Zak reports for the Washington Post March 8, 2019. [2]