An amazing phenomenon takes place in Mexico every year and we were fortunate enough to witness it–the annual migration of North America’s monarch butterfly from the U.S. and Canada to the mountainous, cool forests of Mexico.

We visited the Reserva de la Biósfera Santuario Mariposa (The Monarch Butterfly Biosphere Reserve), located in a beautiful forest two hours from Mexico City. We reached the colony of butterflies after an hour and a half steep uphill trek and 2,000 feet climb from 9,000 to 11, 000 feet. The air is thin at 9,000 feet, and as we started our hike into the fir forest, we quickly realized we were in for a work-out. We followed a local guide who knew where to find the colony which can change its location overnight, depending on the weather conditions.

About an hour into the hike, we noticed a few butterflies flying between the tall trees. Severely out of breath, but determined, we continued climbing deeper into the forest. More and more butterflies appeared out of nowhere until suddenly, we reached an area where the fir trees were seemingly alive.

Millions of colorful butterflies hung in clusters on the branches, and hundreds more took to the skies. We were welcomed to the Monarch Butterfly Biosphere Reserve, a UNESCO World Heritage site protected as an ecological reserve by the Mexican government.

The monarchs cluster in huge colonies in the forest’s cool micro-climate, humidity, and sunlight. Tens of thousands of monarchs can cluster on a single tree. Before the sun warms the forest, you can only see the brownish underside of their wings.

But then magic begins when the sun’s rays hit the branches and the butterflies open their wings to show their bright orange and black color. They start moving their wings to warm up and when the sun comes through, they start flying.

Migration

The monarch is the only butterfly known to make a two-way migration as birds do. Monarchs live around the world but one subspecies of monarchs; the Danaus Plexippus performs a miraculous migration every year. Unlike other butterflies that can overwinter as larvae, pupae, or adults, monarchs cannot survive cold winters.

In case you are wondering why they don’t simply live in Mexico year-round? –there is no year-round food source, so they are forced to migrate every fall and spring.

Using environmental cues, the monarchs know when it is time to travel south for the winter using air currents and thermals to travel up to 3,000 miles to reach their winter home. Monarchs can travel between 50-100 miles a day and take up to two months to complete their journey.

Researchers are still investigating whether monarchs find their winter location based on the magnetic pull of the earth and the position of the sun.

This migration is almost a biological miracle. The butterflies flying south to Mexico have never made the trip before, yet they know exactly where to go. They start in the early part of October and they arrive in the Central Mexican mountains by November. These butterflies start their return toward the north, to Canada and the US in mid-March.

No individual monarch butterfly ever makes the entire circular route because adult butterflies have a lifespan of only a month or so. Therefore, it is not possible for them to make the migration from North America to Mexico and back again.

To achieve the migration, it takes them four generations. The 4th generation is the “super generation” because it has a life span that is about 10 times that of a normal butterfly. In the fall, the “super generation” butterflies, migrate southward to Mexico.

These monarchs live through the winter in Mexico and begin their trek back north in the spring. They reach Texas and Louisiana, where they lay their eggs and die. It takes another four or five generations of butterflies to complete their destination to northern US and Canada.

Scientific Discovery of Monarch Migration

Seeing the butterflies is one of the most unique experiences in nature. However, the story of the discovery of their migration is almost as unique and interesting.

Fred Urquhart was a Canadian zoologist who as a child was fascinated by monarch butterflies, and he wondered where they went during the winter. In 1927, when he was 17, he wrote to a scientist who studied insect migration about his belief that the monarch butterfly was a migrating insect.

For 38 years he worked to identify their migration routes and discovered that the migration spans multiple generations of butterflies.

He and his wife tracked the butterflies by tagging the wings of thousands of individual butterflies. They spent years perfecting the right tag to stick on delicate and moisture-sensitive butterfly wings. By 1940, they had created a tag made to stick. The tiny label read “Send to Zoology University of Toronto Canada.

They founded Monarch Watch and recruited hundreds of volunteers who helped in their research by tagging butterflies and reporting findings and sightings. After decades of searching Fred and his wife found the location of millions of monarchs in Mexico 10,000 feet above sea level on a mountain on the border of the States of Mexico and Michoacán in 1975.

A Minnesota Connection

One individual monarch butterfly was tagged by two Hopkins junior high students and Jim Gilbert, the famous MN naturalist, on Sept. 6, 1975, at the Minnesota Landscape Arboretum prairie. The butterfly was recovered in Mexico on Jan. 18, 1976.

The film, Flight of the Butterflies, follows the story of monarch butterfly tag PS 397 which was the one Dr. Urquhart found four months after it was tagged in Minnesota. It was found high in the remote Sierra Madre mountains of Michoacán Mexico after flying over 2,000 miles and for at least two months to get there.

At the time of Dr. Urquhart’s discovery of butterfly 397, there were around a billion butterflies. Today, their numbers have been reduced in half. Dr. Urquhart and his wife’s discovery of monarch migration was called “one of the greatest natural history discoveries of our time.”

Monarchs are legendary

Monarch butterflies have been visiting these mountains for centuries. Indigenous people in pre-Hispanic times believed legends that the butterflies were souls coming back from the dead each year to visit their living relatives on November 1 and 2 when Day of the Dead is celebrated.

Symbolically, butterflies are creatures with the ability to transcend the ordinary and take flight into the heavens. In many spiritual circles, the butterfly represents the spirit or soul.

We believe that the monarch butterflies are beautiful, and their story of migration is amazing. We are so grateful that we were lucky enough to visit their Mexican mountaintop winter home.