Environmental destruction and violence threaten one of the world’s most extraordinary insect migrations.
Photography by Brendan George Ko
Text by Carolyn KormannFebruary 8, 2021
Every November, around the Day of the Dead, millions of monarch butterflies descend on a forest of oyamel firs in the mountains of central Mexico. The butterflies have never seen the forest before, but they know—perhaps through an inner compass—that this is where they belong. They leave Canada and the northeastern United States in late summer and fly for two months, as far as three thousand miles south and west across the continent. The journey is the most evolutionarily advanced migration of any known butterfly, perhaps of any known insect. But climate change and habitat loss, both in the forest (photographed here in February last year) and in the U.S., are fast eroding the monarchs’ numbers.
Turn Volume On Icon
Click to unmute and listen
to the butterflies as you read.
Monarchs take flight as the sun rises
and begins to warm them up.
Once the sun sets, the butterflies
cluster in the oyamel-fir trees until
the next morning.
A pair of monarchs mating.
Soon they will migrate, and
the fertilized eggs will be laid
en route, spawning a new
generation to continue the journey.
Monarchs in the early morning.
They hibernate from November
until the beginning of March.
With warmer temperatures, they
become sexually mature, mate, and
begin their northerly migration.
The Monarch Butterfly Biosphere Reserve, a partnership between the Mexican government and the World Wildlife Fund, is a hundred-and-thirty-nine-thousand-acre area, straddling the border between the states of Mexico and Michoacán, sixty miles northwest of Mexico City. The monarchs hibernate here, at an altitude of around ten thousand feet, for four months. The reserve comprises land belonging to dozens of groups, including indigenous communities and communal-land villages called ejidos. Before the reserve was founded, locals relied on logging and mining for income. Now they also get revenue from roughly a hundred and twenty thousand tourists who visit the reserve each year.
Roughly a hundred and twenty thousand
tourists visit the reserve each year, diversifying
the income of local communities, which
previously relied on logging and mining.
Michoacán is a battleground for drug cartels, whose activities extend to land theft and the lucrative timber trade. In January of last year, Homero Gómez González, a former logger who had become the supervisor at El Rosario, the most visited butterfly colony in the reserve, disappeared after attending a festival in the nearby city of Ocampo. Two weeks later, he was found drowned, with blunt-force injuries to the head, at the bottom of an irrigation pond. Then a tour guide who worked for him was found dead. Authorities reported that the deaths were under investigation, but most people are afraid to speak up.
While in Mexico, the monarchs look
for water but do not feed, relying on fat stores
accumulated in the course of migration.
The W.W.F. monitors the reserve’s forest cover each year, and issues checks to local communities based on their performance. Since 2005, thirty-seven thousand acres have been replanted. According to Eduardo Rendón-Salinas, the head of the W.W.F. monarch program in Mexico, the two communities that have pursued conservation most strictly, keeping timber harvests minimal and sustainable, “have the most beautiful forests in all of the reserve.” But the sense of heightened danger makes already challenging work much harder. Workers, including those at other local conservation-minded projects—thirty-four mushroom greenhouses, a trout farm, and thirteen tree nurseries—are scared.
Oyamel firs grow at between
nine thousand and eleven thousand
feet above sea level.
Despite the reforesting efforts, the monarchs’ migration remains in grave danger. Last winter, the area they covered in the reserve decreased by fifty-three per cent, probably because the previous spring in Texas, the first main stop on the journey north and where they start laying eggs, was unusually chilly. The monarchs go through around four generations during their northward migration, each living four to five weeks; cooler temperatures limited the growth of milkweed, the only plant on which they lay their eggs, and slowed the growth of caterpillars—all of which made later generations smaller. The journey back to Mexico, in late summer, is accomplished in a single generation—known as the Methuselah generation, because its butterflies live for eight months.
The microclimate of the forest is also changing. Violent storms, high temperatures, and dry conditions have disrupted the equilibrium on which the monarchs depend. Weak, parched trees succumb to bark beetles and other pests. A forest geneticist, Cuauhtémoc Sáenz-Romero, has experimented with planting oyamel firs farther up the mountains. It seems that the trees can survive a decrease in temperature of two degrees Celsius, the equivalent of being planted four hundred metres higher. The monarchs, however, are already near the top of the mountains, so Sáenz-Romero is looking to plant oyamel-fir groves on higher peaks, outside the reserve. These would be far from where the monarchs have ever been. Even if the planting is successful, will the butterflies find them?
Published in the print edition of the February 15 & 22, 2021, issue, with the headline “The Butterfly Forest.”