By Dan Zarlenga, Missouri Department of Conservation
For generations, Indigenous people in parts of central Mexico have associated the arrival of monarch butterflies in early November with the return of departed souls during Día de los Muertos, the Day of the Dead. Some believe those spirits make this journey on the butterflies’ wings.
The monarch butterfly undertakes an amazing journey of its own, a voyage spanning multiple generations. The cycle of the eastern cohort of monarchs begins in the high mountains of Central Mexico, in the state of Michoacán. Dense forests of oyamel fir trees at elevations of 7,500 to 11,000 feet provide the ideal climate, humidity, and temperature to sustain them through winter.Laden with countless monarchs, the boughs of the trees bend under their weight. Skies are filled with clouds of fluttering darkness. And the gentle sound of countless butterfly wings, amplified a millionfold, rises like a sustained breeze.
The monarch butterfly exists in a cycle of four generations. Generations one through three focus on reproduction, each driven northward starting in spring, first to the southern states of the U.S., then through the Midwest, and finally up to southern Canada.
Along the way, these butterflies feed on nectar, mate, and lay their eggs exclusively on varieties of milkweed plants. Missouri provides vital opportunities for monarchs to hatch successive generations and carry on their reproductive cycle. These generations of butterflies live for only about a month each.
But it is the fourth generation that is truly amazing. It’s called the “Super Generation”. Using perception beyond our grasp, this generation can sense changes in temperature and shortening day length. This prompts them to enter a condition called diapause. Their reproductive hormones shut down, putting reproduction on hold and conserving energy for the incredible odyssey to come. Unlike the other three in the cycle, the lifespan of this particular generation stretches to nine months—many times that of their immediate ancestors. This longevity gives them the time necessary to complete their genetic mission.
In September, the monarchs pass southward through Missouri, beginning a 3,000-mile journey mapped out with instinct alone. Guided by the uncanny ability to use the sun as a compass, they flutter their way toward a destination they’ve never seen. On the multi-month trek to those special mountains in Mexico, Missouri becomes an essential stopover for rest and refueling.
This super generation of monarchs arrives in Mexico during late October and early November. They converge by the millions just as Mexican families are building beautiful altars adorned with candles, marigolds, and photos to welcome ancestral spirits. For the butterflies, though, Día de los Muertos marks a time to rest through winter and to mate, beginning the cycle anew. Come March, these monarchs will embark on the voyage northward. It will be a journey for their descendants to complete.
Perhaps Indigenous peoples in Mexico understood something that science has only recently begun to discover. The monarch butterfly truly does bear the spirits of generations past—in an inherited knowledge that will guide its future descendants.
Caption for photo above: A monarch butterfly takes to the sky. Photo by Noppadol Paothong, MO Department of Conservation.