Published: April 8, 2019

Following the Monarch Butterflies to Mexico

Abigail Derby Lewis, Conservation Tools Program Director, Keller Science Action Center

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The hidden forest where they spend the winter is a sight to behold. 

Dozens of orange and black monarch butterflies perch on tree branches, practically perching on top of one another. Some are blurred as they flap their wings.

While Chicago was inundated with snow, ice, and sleet in January, a different kind of winter wonderland was underway in Michoacán, Mexico. Fourteen Field Museum members joined me in a trek to see the monarch butterflies at their overwintering grounds in central Mexico. I have worked in many forests throughout the tropics, but this experience was completely new to me. This ecosystem felt as if it were actually humming from the energy of so many butterflies.

First, we visited El Rosario Sanctuary, which is the largest monarch overwintering site inside the Monarch Butterfly Biosphere Reserve. It is also the most-visited sanctuary, and for a good reason; it’s estimated that over half of the monarch population occupies this forest site between November and March, making it an unrivaled location for viewing the highest number of monarchs in one area.

The monarch population this year is estimated to be 225 million, the highest recorded number since 2006 and an increase of 144 percent from last winter. Being in the forest and actually seeing the scale of this migratory phenomenon simply takes your breath away. At first, it’s not even clear what exactly you’re looking at. It takes a moment to focus and to realize that the trees are completely covered with monarchs! A butterfly is resting on every single pine needle of every branch and covering every square inch of the tree trunk.

There are so many butterflies that they weigh down even the tallest and most majestic fir trees, giving the appearance the whole forest is dripping with monarchs.

Abigail Derby Lewis
Monarch butterflies cover every branch of a tree, causing it to droop and making it appear almost fuzzy.

Monarchs coat the trees in the forest where they overwinter, huddling together to keep warm.

A monarch butterfly with a small round sticker on the underside of its wing, lying on a white cloth. The sticker has small black and red text.

A tagged monarch in a sea of butterflies is a rare find. The lightweight, adhesive tags don’t interfere with flight. Butterflies are tagged with a unique number on the southward trip and hopefully spotted again in Mexico.

Monarchs and the "magic towns"

El Rosario Sanctuary is a short drive from where we stayed in the mountain town of Angangueo, one of Mexico’s Pueblos Mágicos or “Magic Towns.” A small community 75 miles west of Mexico City, Angangueo is surrounded by the pine-oak forests hovering over 8,000 feet above sea level along the Trans-Mexican Volcanic Belt. The tile roofs, stucco buildings, churches, cobblestone lanes, and brightly colored homes clinging to steep hillsides are imbued with beautiful artistry and history.

For centuries, the indigenous Purépecha Indians who lived in Michoacán tracked the butterflies’ fall arrival, calling them the Parákata, or “harvester butterfly,” because their return signaled it was time to harvest the corn. The Purépecha also believe monarch butterflies are the souls of their deceased ancestors who annually return for a brief visit (see our storybook on the Legend of the Parákata). Today there is still a strong connection between the people living in Angangueo and the monarchs.

A painted mural shows the sun with a face, and orange and black monarch butterflies flying out of its mouth. The monarch life cycle is also depicted, showing caterpillars and chrysalises.

A scene from a six-part mural telling the history of Angangueo. The butterfly’s image appears prominently throughout the town.

An uncertain future—but there’s something we can do

Forests, and nature in general, are the places I often feel most spiritually connected. Witnessing a migration of this magnitude in such a special place was restorative on so many levels. It was a deeply satisfying and joyful feeling to look around and know that many of these butterflies may be the children of the monarchs we raised in our backyards last summer, or perhaps even the individuals we saw stopping to feed and fuel up on asters, goldenrod, and other late-blooming native flowers in the Chicago region last fall as they made the southward journey back to Mexico.

My family and I planted a pollinator garden in our yard in 2017.

Now, when the garden is in full bloom, it's a stopping point for butterflies and other pollinators.

The population increase is certainly something to celebrate, and I was thrilled to hear the good news shortly after returning from my trip. It’s important to bear in mind, however, that the annual population does rise and fall, and it’s had an overall downward trend for the past 20 years. The numbers this year represent the minimal threshold experts think is needed to keep a viable migrating population. I think the increase certainly reflects some success of large-scale efforts to create habitats in the summer breeding grounds of the United States as well as to reduce illegal logging at the overwintering sites in Mexico.

But the boost in numbers likely also reflects a Goldilocks effect in last year's weather: not too hot, not too cold, and few storms. As climate change begins to increase temperature, drought, and the frequency of extreme storms throughout the monarchs’ range, they will no doubt face additional challenges—making actions to provide more milkweed and nectar sources for them even more critical.

To be able to see this wondrous part of their life cycle helped me fully appreciate the complexity and remarkable nature of this species. It fueled my desire to double down on our efforts to engage communities in scaling the creation of habitat throughout metropolitan areas in the Midwest and beyond. Our research shows that adding milkweed and native flowers to our backyards, community gardens, balcony pots, and rooftops will help monarchs and a whole host of other pollinators, too—what we plant really matters.

Spring is upon us, and it’s time to start thinking about what to plant. Need some ideas to get started? Browse our monarch habitat Field Guide for recommendations on plants that will support monarchs and other pollinators.


Abigail Derby Lewis
Conservation Tools Program Director, Keller Science Action Center

Abigail is the Conservation Tools Program Director in the Keller Science Action Center, a division dedicated to translating museum science into lasting results for conservation and cultural understanding. Her work as a conservation ecologist focuses on landscape conservation planning and climate change adaptation for urban nature. She is a Commissioner for the Illinois Nature Preserve Commission and Co-Chairs the Chicago Wilderness Climate Committee.