Rob Nixon in the Boston Review:
In coming weeks, the Northeast of the United States will experience the peak of its annual migration of monarch butterflies. The butterflies’ life cycle takes place over an astonishingly broad geographic range. Each year, the monarchs overwinter by the millions in the high-altitude forests of Mexico. Then, in the spring and summer, they head north to the United States and southern Canada, the northern limit of where milkweed, the only plants that the fastidious monarchs breed on, will grow.
Because so many ecological factors have to sync perfectly for this journey to work, in recent decades the monarch population has declined rapidly under pressure of environmental changes. In response, a grassroots network of butterfly defenders has sought to preserve the multiple environments that the butterflies need. In the process, the defenders—and, by extension, the butterflies—have made surprising enemies.