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By Alyson Foster

Content & Collections Specialist, National Geographic Library

For years, it was a longstanding mystery. After dancing and skimming in summer meadows from Canada to Texas and Florida, where did the monarch butterflies go with the approach of autumn? That they streamed south was certain. That they sometimes congregated in immense numbers along the Gulf Coast was well-attested. But then they seemed to vanish into thin air. Where did they go?

That was the question Dr. Fred Urquhart, a biologist who had marveled at monarchs since he was a boy in Ontario, wanted to answer. In 1950, he and his wife, Norah, started tracking the butterflies using special tags they attached to the butterflies’ wings. In addition to an identifying set of letters and numbers, the tags contained a request for anyone who found the butterflies to send information about their location to Fred Urquhart’s university in Toronto—an early exercise in classic citizen science.

The project was not without its challenges. Finding the right kind of adhesive for the tags had taken years. The first glue the Urquharts used made the butterflies too sticky. Another kind fell off in the rain. Eventually, a friend suggested that they try the type of adhesive used on price tags. That worked perfectly.

There was also a shortage of funding. At first there were so few volunteers working on the project that only a small number of butterflies were being tagged. At one point, the whole effort was almost shut down for lack of money. But financial support from the National Geographic Society helped the tagging continue. And as more and more butterflies were tagged, data about the butterflies’ whereabouts began to flow in, helping to develop an increasingly detailed picture of the monarchs’ migratory route.

By the early 1970s the Urquharts had learned a great deal about their butterfly subjects, including about their reproductive cycles. (Monarch migration consists of several generations, and the butterflies that finish a migration are not the butterflies that began it. An activity on migration and life cycles of the monarchs can be found here.) They had also finally collected enough evidence to conclude that the monarch butterflies of eastern North America did not simply go to ground in the southern U.S. during the winter, as many scientists had believed. They migrated on to some final winter destination. But the question remained: to where? Dr. Urquhart’s theory was to the mountains of Mexico. Still, no one knew exactly where. The final piece of the biologists’ puzzle remained stubbornly missing.

In February 1973, a man named Kenneth C. Brugger offered his help. Brugger lived in Mexico and had read a story in the newspaper about the elusive monarchs. He wrote to the Urquharts offering his assistance, and they gratefully took him up on it.

For the next two winters, as Brugger crisscrossed the Mexican countryside in his motor home, he hunted for monarchs, focusing his attention on areas where he found large numbers of butterflies. When he reached the Sierra Madre mountains, the number of butterflies increased. It was clear he was getting closer. Finally, on the evening of January 9, 1975, he called the Urquharts to inform them that he had located the colony. His voice was shaking with excitement.

“We have found them,” he said. “Millions of monarchs—in evergreens beside a mountain clearing.”

It would be another year before the Urquharts could see the amazing sight for themselves. In January of 1976, they climbed high into the Sierra Madre, finally reaching the fir forests of remote Michoacan. And there they found the butterflies. They covered thousands of trees so thickly that branches were breaking beneath their weight. The forest floor was carpeted to a depth of six or eight inches. Millions and millions were clustered in a few square acres. An entire mountainside was one quivering mass of butterflies; golden-orange showers poured off the trees whenever they were touched by the sun.

The sensational discovery that nearly the entire population of eastern North American monarch butterflies overwintered in one remote mountain range was announced to the world in the August 1976 issue of National Geographic. Scientists were finally able to understand the life history of this elusive insect, and the Mexican government soon declared the site to be a conservation area.

A dozen such sites have now been found, all nestled within these same mountains. They are as fragile as their winter inhabitants, and official protection has sometimes been a matter of name only. Illegal logging, for example, has been decimating the fir forests, with worrisome consequences for the monarchs. Nevertheless, hundreds of thousands of ecotourists make their way to these remote slopes, and many reportedly break into tears at the beautiful sight. Environmental groups are also working to raise awareness about the threats facing monarchs and what people can do to help them.

The “international traveler,” as the monarch has been called, has become an “ambassador” species, stimulating closer cooperation between the conservationists of three nations: Canada, the U.S., and Mexico. Thanks go to the pioneering Fred Urquhart, who died in 2002 at the age of 90.