All Souls Day, observed on November 2, is a little-known holiday in most of the U.S. outside of some Catholic circles, but in Mexico, the date is heralded by a remarkable natural phenomenon that happens each year in the fir-clad mountains of central Mexico.

Like clockwork, millions of monarch butterflies return to these remote forest sanctuaries during the Dia de los Muertos, the three-day span from October 31 to November 2 when the Christian holy days of All Hallow’s Eve, All Saints Day and All Souls Day are celebrated collectively as the “Day of the Dead.”

Since pre-Hispanic times, the Purépecha have recorded the arrival of the long, flowing cloud of orange-winged butterflies that pours into the Sierra Madre hills above the village of Angangueo at precisely the same time each year.

Each year during the Day of the Dead, local people honor the spirits through festive events focused on the butterfly migration. Historically, this holiday time is one of remembering and rejoicing for the deceased, whose earthly bodies are exchanged for spirits ready to move to the next realm, unencumbered by worldly woes as they transition ultimately to heaven. The gossamer-winged butterflies are thus the perfect manifestation of such liberated souls.

Each year during the Day of the Dead, local people honor the spirits through festive events focused on the butterfly migration. Historically, this holiday time is one of remembering and rejoicing for the deceased, whose earthly bodies are exchanged for spirits ready to move to the next realm, unencumbered by worldly woes as they transition ultimately to heaven. The gossamer-winged butterflies are thus the perfect manifestation of such liberated souls.

They believe that human souls do not die, but rather continue living in Mictlan, a place for spirits to rest until the day they could return to their homes to visit their relatives. Later, as Catholic traditions intermingled with Indigenous cultures, the monarch butterflies came to be regarded as the souls of departed ancestors returning to Earth for their annual visit.

Visitors to Angangueo—or most anywhere in Mexico—will find townspeople dressed up as ghosts, ghouls, skeletons and mummies, parading through the streets with an open coffin containing a smiling “corpse.” Bystanders toss oranges, fruits and candies into the coffin as the mock funeral procession makes its way through the village streets.

Mexican woman with carnation flowers day of the dead

Inside homes, families erect ofrendas, or altars, on which they place photographs of deceased family members and offer flowers, bread and treats, which are partaken of “spiritually” as the spirits return. Later, the living enjoy the offerings in material form. In the evening, the altars are lit by candles that are kept burning all night long.

The festivities commemorate two celebrations that honor the memory of loved ones who have died: On November 1, All Saints Day, the souls of children are honored at the altars, which feature white flowers and candles. On November 2, All Souls Day, departed adults are remembered with a variety of rituals that differ between the various states of the Mexican republic.

Day of the Dead altar in Mexico City's Ex Convent of Acolman

Ofrenda (altar) in Mexico City’s Ex Convent of Acolman.

The state of Michoacán in west-central Mexico is where the butterflies add a vibrant touch to Day of the Dead celebrations. Some 300 million “mariposas” are currently arriving there, having traveled over 2,000 miles from the northeast U.S. and southeastern Canada. The monarch butterfly migration remains a mystery to scientists, who aren’t yet certain how the butterflies manage to find this small, isolated sector of oyamel trees that they have never been to before.  The unique microclimate is perfectly suited for overwintering and breeding, however, and the monarchs will spend four to five months here before making their way northward again for the summer.

Like autumn leaves, monarch butterflies cluster by the hundreds of thousands on the branches of oyamel trees—heavy enough to weigh them down!

Like autumn leaves, monarch butterflies cluster by the hundreds of thousands on the branches of oyamel trees—heavy enough to weigh them down! © Court Whelan

If you’d like to experience for yourself what it’s like to stand among millions of gentle butterflies, join a small-group tour of the butterfly sanctuaries in Mexico this winter. This rare habitat is set aside as the Monarch Butterfly Biosphere Reserve, a UNESCO World Heritage Site, to protect and conserve this extraordinary migration phenomenon, which you’ll get to witness up close on intimate adventures.