A rare snowstorm Saturday in the forests of western Mexico was killing millions of monarch butterflies, a leading environmentalist said.
By midday, seven inches of snow covered the ground, and it was still falling in the five monarch sanctuaries in the mountains of Michoacan state, the species’ principal wintering ground.
One-third of the 11 million to 13 million monarchs hibernating in the region could be dead by Sunday, according to Homero Aridjis of the Group of 100, Mexico’s principal environmental organization.
He said Group biologists were on the scene but there was little they could do.
The vivid orange-and-black monarchs fly about 3,000 miles south from Canada and the United States every year to hibernate in the stands of oyamel trees, similar in appearance to mulberry trees. They return north in the spring.
It rains often in the area, but snow is rare. The last big snowfall, in February 1992, killed 70 percent to 90 percent of the butterflies wintering, Aridjis said. The species has yet to recover.