“Feeding on a weed seems like a good evolutionary bet. And for a long time, it worked well for the monarch butterfly.
“The butterfly’s life cycle is exquisitely synchronized to the seasonal growth of milkweed, the only plant its larvae will eat. In a game of hopscotch, successive generations of monarchs follow the springtime emergence of milkweed from Mexico as far north as Canada.
“The hardy plant once flourished in grasslands, roadsides, abandoned lots, and cornfields across much of the continent.
“It fueled a mass migration that ended each winter with more than 60 million butterflies converging on pine forests in the Sierra Madres.
“Then came Roundup.”
Read more: Slate.com
