By the time they all converge in the transverse Neo-Volcanic Mountain Range in Mexico, there are millions flying together, perhaps as their ancestors have for millennium. They start arriving on the first of November, at the same time as the national festival of Los Dias de Muertos, Days of the Dead. The local people believe the monarchs are old souls returning to the sacred mountains.

Here, at altitudes of 9,000 to 12,000 feet, they overwinter, roosting in oyamel trees at night in groups estimated to be hundreds of thousands strong per tree. In the warmth of the morning sun, they fly low, landing to drink the morning dew and dampened earth near natural springs.

As the sun moves higher, they flights are more energetic, millions of golden fluttering wings rustling the air in the sound and beauty of ever changing patterns of movement.

As spring approaches, the monarchs mate and by the end of March, they head north. Searching out the choicest milkweeds, each female will oviposit about 400 eggs. Her life cycle will then end. Only one to two percent of the caterpillars will survive. These caterpillars mature into butterflies who continue their parents’ northward migration. It can take as many as three or four generations to re-colonize the entire northern habitat range. The summer monarchs complete their life in about three weeks. The monarchs born in autumn have a life cycle of about ten months. In September, they begin their southward migration, as their ancestors have for time immemorial.