The Magnificent and Mysterious Monarch Migration

Monarch butterfly prepares for flight. Photo by ASWang
Monarch butterfly prepares for flight. Photo by ASWang

The moment I laid eyes on a chunky yellow, black and white-striped monarch caterpillar (larva), I was hooked. It is colorful, peaceful and eats a lot. It’s mesmerizing to observe.

But all this munching is in preparation for something profound, a phenomenon known as the monarch butterfly migration, a fierce journey of up to 3,000 miles in about 2 months from this majestic pollinator that faces multiple perils.

After 12 days or so of emerging from its egg and 5 instars later (shedding old skin and emerging into a larger caterpillar each time), it pupates, turning into a lovely light green jewel of a chrysalis speckled with a shimmering gold crown and a matching golden arc pattern beneath, like a priceless pendant worthy of royalty.

Finally, after being motionless for 10-14 days, the chrysalis turns black, then translucent and the great transformation that took place inside is revealed.

A glorious orange and black butterfly emerges, about 4 inches wide. It takes within 10 minutes to 2 hours to unravel its wings, pumping fluid into and flapping them while they dry and prepare for flight.

But even more than being beautiful and graceful, the delicate monarch butterfly is relentless in its keen sense of travel and highly adaptable under pressure.

“They are incredibly robust in their survival strategies… They’re pretty hardy! To fly as far as they do, they have to be!” says Gail Morris, conservation specialist in Arizona.

Among all insects, it stands alone in its determination to survive by an ability deeply rooted in its DNA to migrate to overwintering sites in the oyamel forests of Mexico, the tip of Florida and the coast of California.

But this unique migration is in danger of extinction. Generally speaking, there are two populations of monarchs within the same species, one to the east and one to the west of the Rocky Mountains. And each has its own migration pattern.

The traditional thinking has been that these two populations are completely separate. But recent studies from the Southwest Monarch Study and partners who tagged monarchs in the West, found that some made their way further south, overwintering in Mexico with the predominant eastern population of fall migrators.

According to Dr. Robert Pyle, founder of the Xerces Society and author of Chasing Monarchs, “The Continental Divide is not the absolute dividing line between Mexican and Californian migrants, as has always been said. Basically, the westernmost (coastal, S Oregon, Northwest) monarchs migrate to the California coast, while some of the inland ones migrate to Mexico. We have no idea how many or what determines the destination.”

The monarch migration in the East is better understood and documented than the western migration pattern that is still being discovered.

The monarchs in the East begin their spring migration to the North in the oyamel forest, when the sun warms their bodies and conditions are suitable for travel. It takes about a month to land in the southern parts of the United States, east of the Rockies. The females lay nearly 400 eggs on multiple milkweed plants to ensure the survival of at least 3 into adulthood! The parent monarch, the first generation, then dies.

The spring migration is brutal. The bright colors on the larva and the orange on the butterfly is a warning that they are poisonous, but this does not deter some predators. And not only do the monarchs face wind conditions that often flow against the direction they’re headed, but also the cost of reproduction is a toll on their longevity.

The second generation takes another 4-6 weeks to fly further north, from Texas to North Carolina and even parts of Virginia. They lay their eggs and die. The 3rd and sometimes even a 4th generation continues the cycle and the journey north, finishing the spring migration in the southeastern parts of Canada and northern portions of the United States.

Then the fall migrators emerge. They are in a state of diapause, not mating and so are able to make the dangerous 2-month journey south to Mexico mostly and some to Florida. On this 1,500-3,000 mile trip, depending on where they began, the monarchs are faced with death daily from predators, disease, extreme weather conditions like storms, geographic challenges like vast stretches of water where staying in flight is critical, and a lack of milkweed to sustain their energy.

When the monarchs finally make it to Mexico they overwinter in the trees of the oyamel forest, clustering together to keep warm. It’s a joyous and wondrous time in the village nearby when millions of monarchs descend and the locals believe their ancestors have returned in late October around “Dia de los Muertos,” or the Day of the Dead.

The Monarchs remain there until about March, when this first generation begins the spring migration north and east to mate, lay eggs and die after an exhausting 8-9 months of life, arguably the longest of any butterfly. And the cycle begins again.

The western population appears to have a similar pattern of generational travel, having a fall migration from Washington, Oregon and the southwestern sections of Canada to the coast of California (some even venturing to Arizona and even the oyamel forest of Mexico.)

But travel routes during the spring migration north and the fall migration south to various overwintering sites are not so defined. And both the migration and the overwintering sites are in danger.

According to Sarina Jepsen, Endangered Species Program Director at the Xerces Society, “There’s an art to preserving overwintering sites. Microclimate change can occur when just some of the trees at the site are cut – affecting humidity, shade, sun and protection from wind.”

Though disease and other natural causes threaten the survival of the monarchs, perhaps the most severe threat is from humans.

In the East, the growing culture of genetically modified crops allow for the mass dumping of harsh herbicides, destroying native milkweed plants, the only breeding and feeding grounds for monarchs.

In Mexico, the monarchs’ overwintering habitats are threatened by deforestation of the oyamel forest.

In the West, our drought problem and urban sprawl destroys the milkweed, hence eliminating the monarch’s only food source.

So it’s no surprise that the monarch population has plummeted. According to the Xerces Society, the eastern population has dropped nearly 90% compared to the highest monarch population estimated in 1996-1997, hitting an all-time low this year.

The western population has seen about a 50% decline (taking into consideration a 17-year average) since 1997 when 1.2 million monarchs were counted. The last count in November 2013 recorded around 200,000.

Though the numbers look bleak, there is certainly a surge of interest in preserving this natural work of art and vital piece of our ecology. And protecting the monarchs’ migration is to protect the monarch itself.

“The more you learn about monarchs the more fascinating they become… Monarch butterflies are also ideal for involving citizen scientists and for conducting research with students. This is especially true in the west where we are still developing a culture of effective citizen science.” says Dr. Francis Villablanca, Professor of biological sciences at Cal Poly, San Luis Obispo, director and research advisor for monarch alert.

So to become more educated and help the monarch population recover, try some of the unique activities below.

Visit an overwintering site October-February. There are hundreds along the California coast, from Mendocino County to San Diego, the only place to see overwintering monarch in the United States. According to Dr. Villablanca, “Two of the most spectacular sites are Elwood Main in Santa Barbara, and Pismo Beach State Park.” Another popular site is around the Pacific Grove Museum.

Become a citizen scientist during the Thanksgiving count and help field researchers determine the total number of monarch (October-January).

Learn how to get involved in tagging monarchs and furthering the study of migration patterns.

Visit a vivarium (a house of butterflies) Go to for year-round visits. Or enjoy the butterfly pavilion at the Natural History Museum (April-August)

For a fun family activity in your own yard, create a milkweed garden and become a feeding and breeding waystation for spring migrators headed north., and

Visit my blog for more information on monarchs and to read about my experience raising and releasing monarchs in our home in the San Gabriel Valley.

A special thanks to those who shared their passion for and wisdom about monarchs: Angie Babbit, Pat Flanagan, David James, Sarina Jepsen, Gail Morris, Dr. Robert Pyle and Dr. Francis Villablanca.

Originally published in the Fall 2014 issue of The Quarterly magazine.

By Ann Suk Wang

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