The butterfly effect: Do monarchs’ woes signal broader problems?
ANGANGUEO, Mexico — On a high mountain slope in central Mexico, a patch of fir trees looks dusted in orange and black. In fact, millions of monarch butterflies cloak the trees. The forest murmurs with the whir of their flapping wings.
Every year, hundreds of millions of monarch butterflies _ each so light that 50 together weigh barely an ounce _ find their way on what may be the world’s longest insect migration, traveling the length of North America to pass the winter in central Mexico.
Yet the great monarch migration is in peril, a victim of rampant herbicide use in faraway corn and soybean fields, extreme weather, a tiny microbial pathogen and deforestation. Monarch butterfly populations are plummeting. The dense colonies of butterflies on central Mexican peaks were far smaller this year than ever before.
Scientists say Mexico’s monarch butterfly colonies _ as many as several million butterflies in one acre _ are on the cusp of disappearing. If the species were to vanish, one of the few creatures emblematic of all North America, a beloved insect with powerhouse stamina that even school kids can easily identify, would be gone.
The advent of genetically modified corn and soybean varieties that
can withstand herbicides has added to that loss. Now farmers employ glyphosate herbicides, such as Monsanto’s Roundup, that kill weeds
with a vengeance. It’s had a huge impact on milkweed, which before
could grow among crops or at the edges of fields.
“The crops survive but any weeds, including milkweed, don’t,” Wilson said.
Faced with vast reductions in milkweed, the size of the colonies of monarchs escaping northern winters has shrunk radically in central Mexico.