Each fall, in one of the greatest mass migrations on Earth, more than 200 million monarch butterflies begin their journey from the United States and Canada to Mexico, seeking relief from the harsh northern winters. This multi-generational odyssey, five thousand miles round trip, would be remarkable for any animal, let alone an insect with a tiny brain navigating over terrain it has never seen before. About 90 percent of the world's monarchs spend the winter in the oyamel fir forests of the central Mexican highlands, clustering in densities of roughly four million butterflies per acre.
But the monarch's wintering grounds are under siege, mainly because oyamel wood is in great demand. Consequently, trees are being felled at a rapid rate, despite regulations aimed at protecting this critical habitat. The forest is like a blanket that shields butterflies from the elements. Cutting holes in the canopy exposes the animals to cold and rain and, at other times, excessive heat. As the forest shrinks, fewer potential sites remain that meet the monarch's stringent requirements for water, ample nectar supplies, and a canopy that lets through the proper amount of light. Unless these trees are saved, butterflies that have survived for millions of years may one day be without a winter resting place.
In 1986, the Mexican government created five monarch sanctuaries covering 140,000 acres, but logging and agriculture have not stopped. Ecotourism has been offered as an alternative source of income for the region's poor farmers, although hordes of tourists that step on butterflies, kick up dust, and accelerate slope erosion also threaten the prized species.
Nor are the problems confined to the mountains of Mexico's Michoacan region. Pesticides sprayed in the United States and Canada foul water supplies that monarchs depend on, while herbicides are wiping out milkweed—a critical food source for monarch larvae. Protecting the butterfly will require multinational cooperation, but it's well worth the effort, according to Mexican conservationist Carlos Gottfried. "If we lose the monarch," he says, "we lose a link with something mysterious and everlasting."
More than 80 percent of the world's 250,000 flowering plants depend on animal pollinators, and roughly 15 to 30 percent of the food eaten throughout the world comes from plants pollinated by these creatures.