The monarch butterfly is a magnificent and unique beast—the globe's only butterfly species that embarks on an annual round-trip migration spanning thousands of miles, from the northern US and Canada to central Mexico. And monarchs aren't just a gorgeous bug; they're also pollinators, meaning they help keep land-based ecosystems humming. Their populations have been plunging for years, and the number of them hibernating in Mexico last year hit an all-time low, reports University of Minnesota ecologist Karen Oberhauser. Why? Here's Oberhauser:
Tragically, much of their breeding habitat in this region [the US and Canada] has been lost to changing agricultural practices, primarily the exploding adoption of genetically modified, herbicide-tolerant crops in the late 20th and early 21st centuries ... These crops allow post-emergence treatment with herbicides, and have resulted in the extermination of milkweed from agricultural habitats.
In a 2012 post, I teased out how crops engineered for herbicide tolerance wipe out milkweed, the monarch's main source of food, and lead to the charismatic specie's decline. And here's the peer-reviewed paper, co-authored by Oberhauser, that documents the trend.