An iconic North American migration is in jeopardy. The monarch butterfly migrates back and forth from Mexico to Canada every year, its orange and black sails peppering blue skies. In the past 20 years, almost 1 billion monarchs have gone missing across North America. That’s about 1,000 acres, or 600 soccer fields of dead butterflies laid side by side. This abrupt drop in monarch numbers—estimated to be between 65–75 percent of the population—is causing scientists, policymakers, and conversationalists in Canada, Mexico, and United States to sound the alarm and take steps to reverse the decline.
Monarchs are small organisms but mighty continental travelers with only one menu item for their hungry caterpillars: milkweed. All monarch larvae feed exclusively on members of the genus Asclepius, which are common in disturbed, open habitat. Milkweeds are not viable forage for vertebrates as they contain heart toxins similar to ones used in digoxin heart medication.
