The NYTimes has this:
Previously:ON the first of November, when Mexicans celebrate a holiday called the Day of the Dead, some also celebrate the millions of monarch butterflies that, without fail, fly to the mountainous fir forests of central Mexico on that day. They are believed to be souls of the dead, returned.This year, for or the first time in memory, the monarch butterflies didn’t come, at least not on the Day of the Dead. They began to straggle in a week later than usual, in record-low numbers. Last year’s low of 60 million now seems great compared with the fewer than three million that have shown up so far this year. Some experts fear that the spectacular migration could be near collapse.“It does not look good,” said Lincoln P. Brower, a monarch expert at Sweet Briar College.It is only the latest bad news about the dramatic decline of insect populations.Another insect in serious trouble is the wild bee, which has thousands of species. Nicotine-based pesticides called neonicotinoids are implicated in their decline, but even if they were no longer used, experts say, bees, monarchs and many other species of insect would still be in serious trouble.
For the past 15 years, scientists have been watching monarch numbers plummet, as much as 81 percent between 1999 and 2010.
Nearly every link in the monarchs’ chain of being, he said, is at risk. Illegal logging in Mexico has reduced their winter habitat — an already vanishingly small area, which is itself being altered by the warming climate. Ecotourists who come to witness the congregation of so many butterflies disturb the creatures they have come to see. But perhaps most damaging is the demise of milkweed.Monarchs have the misfortune to rely exclusively on a plant that farmers all across the Midwest and Northeast consider a weed. There is a direct parallel between the demise of milkweeds — killed by the herbicide glyphosate, which is sprayed by the millions of gallons on fields where genetically modified crops are growing — and the steady drop in monarch numbers.To anyone who has grown up in the Midwest, the result seems very strange. After decades of trying to eradicate milkweed, gardeners are being encouraged to plant it in their gardens, and townships and counties are being asked to let it thrive in the roadside ditches. What looks like agricultural success, purging bean and corn fields of milkweed (among other weeds), turns out to be butterfly disaster. This is the great puzzle of species conservation — it has to be effective at nearly every stage of a species’ life cycle. And this, too, is the dilemma of human behavior. We live in a world of unintended consequences of our own making, which can never be easily undone.