The Monarch butterflies have begun to arrive to Michoacan State’s UNESCO Butterfly Biosphere Reserve, as they do every November, reaching peak butterfly density—perhaps a billion individuals flitting about the trees—by mid-January. Visitors from all over the world come to see the magnificent creatures in the mountainous pine forests just north of Mexico City (though they are often so tuckered out after their 3000km (1800mi) trip, that they just hang there quietly in the trees).
This epic migration of Monarch butterflies remains somewhat mysterious to scientists, who have tagged, tracked, and even sequenced the DNA of Monarchs, looking for some clue as to why these delicate creatures behave so differently from their fellow butterflies. They must migrate, of course, to escape the cold Canadian winters; if the temperature drops below 13°C (55°F) they are unable to fly; much colder and they can no longer move. But how do they find their way, generation after generation, back to Michoacan? No one knows.
The 563-square-kilometer (217-square-mile) reserve is the most important wintering site for migrating Monarchs. They “bend tree branches by their weight, fill the sky when they take flight, and make a sound like light rain with the beating of their wings,” says the UNESCO World Heritage site. Eight of the world’s 14 major colonies spend their winters here, about 70% of the global monarch population. It is incredible.
Unfortunately, a recent and unprecedented uptick in herbicide (specifically Roundup) use over the past decade has decimated wild milkweed throughout North America, the only food source for Monarch caterpillars. The herb bequeaths a toxin to the butterflies that keeps birds at bay, and which mother Monarchs use to inoculate their young against parasites. The drought in Texas has also put stress on the migrating Monarchs. Regardless, the first few million Monarchs are already arriving in Mexico, with many more to come.
Visitors to the Biosphere Reserve can either come on a day trip from Mexico City, or stay in one of the towns closer by. Tiny Angangueo is closest to the reserve and almost entirely dedicated to butterfly tourism, with plenty of operators geared to visiting the Monarchs in and around the reserve. Zitacuaro is a bit farther (about 45 minutes by car) from the reserve, but is larger, with more lodging and dining options.
No matter where you stay, bring your hiking shoes, a camera, plenty of water, and layers, just in case things cool off at higher altitudes.