The species, which once numbered in the billions across America, is now down to about 30 million, biologists say. A big reason for the die-off is the disappearance of the milkweed plant, which farmers have destroyed in large numbers while spraying Roundup-ready crops with herbicides. The milkweed is both a food source and a home for the monarch, and without it, the butterflies are struggling to survive. Roundup, a brand of glyphosate sold by Monsanto, is particularly lethal to milkweed.
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