The butterflies are on their way to Mexico. They come from as far north as Winnipeg, Manitoba, and as far east as the islands of Maine. Many take a well-flapped route down the Eastern Seaboard before veering across the Gulf Coast. If they can make it through the gantlet of Texas, they will cross the Rio Grande and converge on a few acres of forest in mountains about 60 miles west of Mexico City. There, they spend the winter roosting, thick as quilts, on the branches of oyamel fir trees. In spring, they’ll head back north.
But it’s not clear how many will make it this year to their Mexican retreat, or what kind of condition they’ll be in when they get there.
They need water. They need flowers. They need nectar. The monarch butterfly is a hardy and vigorous insect, but whatever compels it to migrate south does not tolerate much flexibility in the itinerary. Going through Texas on the way to Mexico is what they’re hard-wired to do. And Texas is scorched.
“They’re going to be encountering a thousand miles of hell as they go through a nearly waterless, flowerless, nectarless landscape,” said Chip Taylor, an insect ecologist at the University of Kansas and the director of the nonprofit organization Monarch Watch.
The migrating monarchs must overcome a host of challenges to their way of life, and their numbers have dropped in recent years. A critical problem is the widespread adoption throughout North America of herbicide-tolerant corn and soybeans, said Lincoln Brower, a professor of biology at Sweet Brier College who has been studying monarchs for decades.
These genetically modified crops enable farmers to spray herbicides on their fields and wipe out weeds without hurting the corn or soybeans. But the milkweeds that are eradicated are crucial to the life cycle of the butterflies. Scorned by farmers, milkweeds are a diverse genus of plants, with more than 120 species identified, that co-evolved over the millennia with the butterflies.
“We’re talking about hundreds of thousands of acres of land that are virtually sterilized except for human food crops,” Brower said.
Conservation groups have encouraged people to plant milkweeds to help the monarchs. And in Mexico, where illegal logging has damaged some of the butterfly’s winter habitat, the Washington-based conservation organization American Forests has teamed with other groups to plant more than 900,000 trees in the past five years, said American Forests spokeswoman Lea Sloan.
But nothing is constant in any ecosystem. Climate change is driving wetter winters that leave soggy butterflies exposed to cold snaps, Taylor said. The butterfly population that migrated north this year was smaller than normal, he said, as is the number heading south. As they fly through southern Kansas, Oklahoma, Texas and into northern Mexico, they are encountering areas hit by what the U.S. government rates as “exceptional drought.”