The Monarch butterfly is known by scientists as Danaus plexippus, which in Greek literally means “sleepy transformation.” The name, which evokes the species’ ability to hibernate and metamorphize, is actually inspired by the Greek myth of Danaus, in which the daughters of Danaus, king of Libya, flee Libya for Greece in order to avoid marrying their cousins. The long, migratory journey of the Monarch butterflies is reminiscent of the daughters’ flight.
Each adult butterfly lives only about four to five weeks. But one of the many wonders of the Monarchs is the annual creation of a unique “Methuselah generation.” As autumn approaches in their sites of migratory origin, a very special generation of butterflies is born. Unlike their parents, grandparents, great-grandparents, and great-great-grandparents — all of whom had ephemeral lives measured only in weeks — these migratory butterflies survive seven or eight months. In human terms, given our average life span of 75 years, this would be like having children who lived to be 525 years old!
This generation performs the incredible feat of flying from Canada and the United States to the center of Mexico — after which they begin the northward journey again. Once they reach the United States, a kind of relay race begins: their short-lived offspring, with only four or five weeks to live, continue making the trek northward over several generations.
The Monarch of Migration
Of all migrations by small creatures, few are as astonishing as the one performed by the Monarch butterfly. The embodiment of fragility, these insects travel between 1,200 and 2,800 miles or more between their starting and ending points — a feat without parallel. What is even more remarkable is that the ones that return to the places where Monarchs hibernate have never been there before. These are the great-great-great-grandchildren of those that performed the intrepid journey from southeast Canada and the United States to central Mexico.
Like several species of birds, bats and whales, the Monarch butterfly of Canada and the United States migrates to places where the climate is less extreme. Winters are too cold in the places where the butterflies reproduce; Monarchs would not be able to withstand either heavy snowfall or the lack of plants on which larval caterpillars feed. As such, the Monarch heads south each fall, where it will stand a greater chance of survival-as well as the chance to “return” to reproductive sites in North America and give rise to future generations of reproductive adults that will complete the annual cycle.
The Monarch butterflies that migrate southward in the autumn are guided by the sun’s orbit as they travel through North America. Even on cloudy days they stay on track thanks to an internal biological compass that functions according to the movement of the sun.
The migration moves at a pace of about almost 50 miles a day, though there are some butterflies that have flown up to 80 miles in a day. Throughout the migration, they continue to store and replenish energy each day by extracting nectar from flowers they encounter along the way. But the butterflies also suffer from illnesses and infections that can be fatal, and must face other dangers including bad weather, predation by birds during hibernation, and big losses in the population due to winter storms.
At the end of October and the beginning of November, after traveling two months, the butterflies settle into hibernation colonies in the mountains of central Mexico, where the States of Mexico and Michoacan meet. There they will spend the winter hibernating.
From mid-November until mid-February, the Monarchs’ hibernation colonies remain relatively stable. During the second half of February, when temperatures rise and humidity decreases in the forests, the butterflies come down from the slopes to mate. And the butterflies that survive the hibernation in Mexico return in the spring to the southern United States.
The Monarch Butterfly website allows you to track the butterflies migration. If you have butterflies in your classroom this site is a good thing to let your students look at once a week to see how far the butterflies have gone. To take the lesson futher you could have the students track the butterflies on a map and calculate how far the butterflies have gone and how long it took them to get to Mexico.
