Year after year when autumn comes, following a primeval call that still remains a mystery to Science, the North American Monarch Butterfly undertakes the longest known voyage in the insect world.
After spending the summer in the native fields and forests of central and northeastern United States and southeastern Canada, millions of these fragile insects start, at the end of summer and the beginning of autumn, a three thousand mile journey south and spend the winter in the warmer central Mexico's majestic Sierra Madre Oriental Mountains.
The final migration destination of the monarch butterfly (Danaus plexippus) was for a long time a puzzle for researchers, but in 1975 the Canadian zoologist Dr. Fred A. Urquhart, together with Kenneth Brugger and Rafael Sánchez Castañeda, discovered their secret. The butterflies were spending the cold winter months along the dry river beds and gulches of the high Sierra Madre, at an altitude of around nine to ten thousand feet in an area between the Michoacan state and Mexico state, in the central region of Mexico.
Urquhart wrote about their discovery: "I gazed in amazement at the sight. Butterflies, millions upon millions of monarch butterflies! They clung in tightly packed masses to every branch and trunk of the tall, gray-green oyamel trees. They swirled through the air like autumn leaves and carpeted the ground in their flaming myriads on this Mexican mountainside."
Monarch migration based on diagrams by Harald Süpfle
This discovery provided one of the most amazing revelations regarding the natural world. Suddenly, as if drawn by a powerful magnet, these fragile summer residents of a vast territory that covers over one half of the United States, migrate south in hurried hordes on a voyage that takes them south over prairies, valleys, mountains, deserts and cities, crossing the Mexican border through Texas, to converge by the millions, like orange-colored tributaries of some great river in the sky, into a region in central Mexico where the Sierra Madre and the Volcanic Belt mountains meet.
A relatively small forested area of only 12,500 acres is the sanctuary where the monarch butterflies spend the winter months and mate before flying back north the following Spring.
Although this appeared to be a great discovery for the scientific community, it was common knowledge for the local inhabitants. These creatures had been part of their lives since time immemorial. Pre-Hispanic inhabitants placed great importance on the Monarch Butterfly, which played a significant role in their religion, myths and legends, and was widely depicted within their art.
They were associated with fire and the Sun's movement in the sky, in general all butterflies or papalotl were the souls of warriors that had died in battle or on the sacrificial altar. It was believed that after traveling with the Sun for four years, they would return to earth as butterflies, to feed on the sweet nectar of flowers. This belief, most probably, also applied to Monarchs, "daughters of the Sun" whose yearly migration symbolized the renewing natural cycle.
In 1986, eleven years after Urquhart's discovery, the Mexican Government protected this important ecologically mountain area and created the Monarch Butterfly Biosphere Reserve. A total of around forty thousand acres of forest were declared protected areas for the migration, wintering and reproduction of the Monarch butterflies, as well as to preserve the environment itself.
The Monarch Butterfly’s Summer Residence
During the summer, Monarch butterflies live in an area that covers 1.5 million sq. miles and extends, from coast to coast, from southern Canada to the southern tips of the Sierra Nevada, the Rocky Mountains to the West and the Appalachians to the East within the United States of America. This area has abundant milkweed (Asclepias), the only plant leaves on which the larvae of this species can feed. It also contains a toxic alkaloid that makes the larvae immune to many natural predators, and also provides the pigment which gives these butterflies their unique coloration.
The longer days and high summer temperatures of this region allow the Monarch to mature and reproduce. During those months, their life cycle is as that of any other butterfly. They live from two to six weeks, during which they mate, lay their eggs and, shortly thereafter, die.
However, the generation that emerges from the cocoons under the September sun has a totally different goal than that of its parents and grandparents. After the fall equinox, as the days grow shorter and temperatures drop, the autumn butterflies undergo a series of hormonal changes that inhibit their reproductive system, preventing sexual maturity, and allowing them to save energy and live much longer than their own parents.
Instead of triggering the urge to mate, the shortening days feed a different and ugent need, as important, or even more important for their survival than reproduction... it's an urge to migrate South (a little like many of the US and Canadian tourists when winter really kicks in), toward warmer lands where they can survive the winter freeze, and postponing their mating rituals till the following season.
So, in order to survive, they must travel, they must go South. If they can survive the dangerous journey, they'll end up living as long as nine months, twelve times longer than any other butterfly.
The Great Monarch Butterfly Migration
After storing enough energy and body fat during the summer months, these tireless travelers will fly as much as three thousand miles to reach their Mexican wintering grounds. The butterflies fly all day long, and rest during the night, sleeping on tree branches in groups of up to six hundred individuals.
Depending on the winds, they can travel at speeds from nine to twenty-seven miles per hour, covering as much as eighty miles in daily eight-hour shifts. Their favorite routes lie along low open valleys, where they can take best advantage of the north winds to push them along in open-winged glides, which allows them to fly long distances effortlessly. This is how Monarch butterflies can finish their 3000 mile journey in only one month.
By mid-November, the green ravines of the Mexican Butterfly sanctuaries, inhabited by oyameles or firs, oaks and spruces, change from dark green into shades of ochre, brown and orange. Leaves and pine needles become frosted with a singular texture created by the wings of the millions of butterflies that hang in thick clusters from the tree branches. Here they survive the winter cold, in a state of semi-hibernation that allows them to save their energy and fat until the next spring arrives.
The Monarch Butterflies Return
Warming days and longer daylight hours send the signal to the sleeping monarchs that spring is back. They begin to stir and shake off the slumber of their long winter trance. Slowly they open their wings and let the sun and heat soak and warm their bodies.
Little by little the air comes alive with orange tones, hundreds and hundreds of butterflies flutter around from flower to flower collecting the sweet nectar that will nourish and give them the strength necessary for their homeward journey.
Light, heat, and their new-found freedom awaken their sexual maturity, now their buried instincts take over, giving way to courting rituals and mating, and then, without further circling, just as suddenly as they commenced their trip south five months before, once again controlled by an internal clock that urges them to go back home, they begin their journey north. Clouds of butterflies rise up into the air, their beating wings creating a muted throb that searches air currents that will carry them away.
Their original numbers have already dwindled, many have died from rain and the winter cold. Mating has also taken its toll on most of the males, who invested their last spare energies in the reproductive ritual and have now died, but among the survivors are a large number of fertilized females who, on their way back home, will deposit their eggs during their nocturnal rest stops along the journey. Two weeks later these eggs will hatch into caterpillars, that will soon become chrysalides that, in late spring, will metamorphose into a new generation of butterflies.
Of these, only a few will remain to repeat the cycle there where they were born. The rest will continue northward to a home they do not yet know, where, like countless generations before them, they will live, mate and die. The impressive part there is that it will not be their offspring, or their offspring's offspring, but the next generation of butterflies, those born at the end of summer that will again respond to the "Go South" migration call, as their ancestors did the year before, beginning a new cycle.
The Mysteries of the Monarch Butterfly
It's still a mystery how these tiny, delicate insects know which route to follow, since the winter visitors were born in the far-off forests of the United States and Canada, and the monarchs conceived in Mexico never return to their birth place.
How does a whole generation of monarchs travel a several thousand mile route that neither they, nor their parents, have ever flown before? How do their descendants, those born after the winter hibernation on the route back north, manage to return to their parents' original starting point? And again, how does such a small, frail and vulnerable creature manage to survive the rigors of traveling such long distances exposed to sun, rain, cold and the depredation of man? Where does such a tiny body store so much energy? What makes it so tireless? How can an insect be so magnificent?
A weather of theories have been set forward as answers for these enigmas, but still none are considered definitive, even so, one thing is clear, the Monarch Butterfly is one of the most astonishing creatures on this planet, and, the more we learn, the more amazing it becomes.
This long distance traveler, citizen of the world, is the most delicate and beautiful symbol of the transformation and renewal in Nature, and above all, is a prime example of a species' instinct to survive.
No wonder our ancestors adored the Monarch Butterfly, and there is no doubt about just how important they are and that we invest as many efforts as possible to protect them for future generation to admire.
Written by Guadalupe Quintana Pali
Minor improvements by M. A. Gallardo