Falling Monarchs

Bad weather kills off millions of monarch butterflies in their ancient resting grounds in Mexico.

Blame it on global climate change. It snows in San Francisco while a heat wave jumpstarts spring fever in the Midwest in February. Now, a recent freak freeze in the cool mountains of Michoacan, Mexico, kills off millions of monarch butterflies which make the Mexican state's fir forests their winter home.

Each fall, millions of monarchs flutter up to 3,000 miles from the eastern United States and Canada to two main sanctuaries about 100 miles south of Mexico City. They roost by the thousands, hanging from oyamel firs in massive clumps until spring, when warmer weather triggers a feeding and mating frenzy. It takes at least two generations for butterflies to get back to their northern milkweed patches. So it's the third and fourth generations that navigate south the following year, roosting in the same tree stands their ancestors did.

Biologist Lincoln Brower, who has studied these monarchs for the past 25 years, estimates that up to 250 million butterflies may have been killed by the recent freeze. Many blame rampant illegal logging by farmers for the extent of the die-off, warning that thinning the forest canopy makes the fragile insects more vulnerable to inclement weather. Brower now believes that clumping is a survival strategy. "The only butterflies that remained dry were the ones deep inside the clusters," he told the Associated Press.

The good news is the species as a whole isn't thought to be seriously threatened. Additionally, World Wildlife Fund-Mexico is leading the way to make the reserves both monarch- and farmer-friendly. They are offering payment, training, and jobs to convert landowners from sanctuary stealers to stewards.