Every year at the beginning of November, Mexico is set alight with the sights, smells and sounds of its Día de los Muertos (Day of the Dead) celebrations. The holiday is one of remembrance and reunion: stories of loved ones are shared over pan de muertos (traditional sweet bread), and families gather by candlelight to arrange ofrendas (offerings) to the dead. Heavy fragrances of marigold and copal incense fill the air, coaxing the souls of ancestors back to the world of the living.

This year, one of the holiday’s many symbolic faces will return with a new urgency: the monarch butterfly, whose lifespan expresses a different sort of tradition.

Each fall, like clockwork, clouds of monarchs descend upon the highland forests of central Mexico. Their arrival marks the finish line of a 3,000-mile journey: once in a lifetime, the butterflies fly south from their summer breeding grounds in Canada and the United States and return to the same oyamel fir forests as generations before them.

Millions of fluttering orange wings blanket the forest, enveloping the branches that will shelter them throughout the winter months to come. How the monarch’s internal compass navigates them, generation after generation, to the same overwintering site remains a mystery. To add to the mystique, the annual migration coincides with the Day of the Dead celebrations.

For all their intrigue, monarchs are now an endangered species. The butterfly was added to the IUCN’s Red List in July 2022 following an estimated population decline of nearly eighty percent since the mid-1990s. Monarchs face the same threats that endanger all biodiversity: a cumulative mix of climate change, environmental pollution, and habitat destruction. But for Mexico, conservation of the nationally iconic species has both cultural and environmental gravity.