The migration of the Monarch butterfly is one of the most incredible adaptations in the natural world. There is nothing that we observe in the delicate-winged creatures that would predict the immense journey of the butterflies. And yet, they will undertake a 4 generation migration, which will cover 2,000 to 3,000 miles (each way). The migration begins in a remote mountain range in Mexico, goes across America to Canada and back to Mexico again.
The Migration Route
After overwintering in Mexico, the Monarchs begin the migration to Canada. These butterflies are the 4th generation in the cycle, and they are unique. They have made the migration from Canada to Mexico, arriving in October. The following spring they will start the migration back to Canada. They begin the journey by flying to the southern United States, where they will mate and die. The 2nd generation will make it as far as the northern states; they to will mate and die (living only one month). The 3rd generation will settle in various locations in Canada and the northeastern United States (also living one month).
The 4th generation will make the trip to Mexico before winter comes again. They will live almost nine months, and make the epic journey from Canada to Mexico, all on their own. They will have to fly an average of 50 miles per day. On their way the butterflies will cross the Great Lakes, the Great Plains, hundreds of miles of deserts and the Sierra Madre Mountains. Starting from different locations in the northeastern U.S. and Canada, the Monarchs will find their way south and converge in huge flocks near Mexico. Millions of butterflies take part in the 2 month-long migration.
How do They do it?
Naturalists are unable to explain how the Monarch butterfly accomplishes such an incredible flight. Each butterfly weighs less than one fifth of an ounce, and its delicate wings must withstand the journey. Also, a large amount of energy is needed to fly such long distances. A butterfly is built more like a helicopter than an airplane, thus it is not the most efficient flyer. There are, however, ways that they can maximize their energy. They only fly when the conditions are perfect. And they can take advantage of rising columns of air. This occurs when the sun heats the ground, causing the air directly above to become hotter. The hot air gets lighter and then rises, carrying the butterflies up. In this case their light frames are a bonus.
Perhaps the most puzzling question regarding the migration is: how do the Monarchs navigate? The 4th generation will begin the journey from a wide variety of locations, and find their way to a forest in the mountains of Mexico (a place they have never seen). Scientists can only speculate how they do it. Maybe they follow a specific angle of the sun or the earth’s magnetic field. Maybe they are guided by wind directions or follow landmarks. And why is the 4th generation more adept at flying long distances, and able to live much longer?
The Power of Multiple Generations
I find it particularly interesting that multiple generations are needed to accomplish the full cycle of the migration. It brings to mind a comparison with human life. In many ways, recent generations are special. We are special in the sense that we benefit greatly from the labors of past generations. Our modern life is the product of people who are no longer here. Like the Monarchs, each generation has passed on something to the next, and over time it has built up.
Today, humans can achieve great things, because we have been given great opportunities. Much of which we take for granted has come about through multiple generations. For example, democracy, human rights, technology, industry, agriculture and so on. Some challenges are so immense that it takes more than one lifetime to overcome them. We should also keep in mind that we will leave something to the next generation.
On personal note: I live in Atlantic Canada, and I have on occasion observed a passing butterfly. They are beautiful creatures, and seem to have a mystical quality to them. In addition to their vibrant colors and elegant flight, the thought of having come from a grounded caterpillar is remarkable. The transformation from caterpillar to butterfly is one of the most amazing transformations in nature. For me, the Monarch is the most familiar of the butterflies. And even before I knew of the migration, I would still pause in admiration when one flew by.
The story of the Monarch Butterfly is so incredible that if it had not been observed and documented, no one would believe it. In fact, the full extent of the migration was not known until 1975. There are Monarchs in other parts of the world, but only in North America do they migrate such great distances. The Monarch butterfly is clearly one of the most amazing animals on earth. And it shows us that very often nature is more creative than we are.
References: Journey of the Butterflies, Aired November 30, 2011 on PBS