Seen Any Monarch Butterflies Lately?
I did, yesterday, but I had to go to Olbrich Botanical Gardens “Blooming Butterflies” event in Madison to see them.
It use to be that every year, hundreds of millions of monarch butterflies would about now be on their way on what is believed to be the world’s longest insect migration, traveling between the length of North America and central Mexico – some 3,000 miles.
Yet the great monarch migration is in peril, a victim of rampant herbicide use in faraway corn and soybean fields, extreme weather, a tiny microbial pathogen and deforestation. Monarch butterfly populations are plummeting. The dense colonies of butterflies on central Mexican peaks were far smaller this past winter than ever before.
Scientists say Mexico’s monarch butterfly colonies, as many as several million butterflies in one acre, are on the cusp of disappearing. If the species were to vanish, one of the few creatures emblematic of all North America, a beloved insect with powerhouse stamina that even school kids can easily identify, would be gone.
“We see these things as so delicate. But if they migrate a distance of some 2,000 miles, from Canada all the way down to Mexico, they are pretty tough,” said Craig Wilson, a scientist at Texas A University, in a recent article in The Kansas City Star by Tim Johnson.
Scientists who are studying the monarchs’ decline cite many possible reasons, but they’re focusing now on one major one: the decline in the United States of milkweed, a lowly broadleaf plant that’s widely treated as a weed to be eradicated, doused with herbicides in farmlands and along highway shoulders. Milkweed is most common in the high-grass prairies of the Canadian and U.S. Midwest but its 70 varieties also grow along the Atlantic and Pacific coasts, in the Caribbean and elsewhere.
Monarchs can’t survive without milkweed.
Female monarchs lay eggs on milkweed. When they hatch, the larvae grow into caterpillars that feed on the milkweed’s leaves. Those leaves contain a poison that inoculates the monarchs from their predators. The caterpillars then form chrysalises and emerge as butterflies.
Over the past decade, U.S. fields containing milkweed have declined sharply. Orley “Chip” Taylor, a monarch expert at the University of Kansas, calls the loss “massive.”
“We’ve lost something like 24 million acres because of conversion of land to cropland. That’s an area the size of Indiana,” he said.
The advent of genetically modified corn and soybean varieties that can withstand herbicides has added to that loss. Now farmers employ glyphosate herbicides, such as Monsanto’s Roundup, that kill weeds with a vengeance. It’s had a huge impact on milkweed, which before could grow among crops or at the edges of fields.
“The crops survive but any weeds, including milkweed, don’t,” Wilson said.
Faced with vast reductions in milkweed, the size of the colonies of monarchs escaping northern winters has shrunk radically in central Mexico.
Nearly two decades ago, in the winter of 1996-97, dense monarch colonies covered 44.9 acres of oyamel fir forest. In the 2013-14 winter, the colonies covered only 1.7 acres, a plunge of nearly 44 percent from the previous year. The trend seems inexorable, experts said.
“We must turn the tide for monarchs,” said Omar Vidal, the president of WWF-Mexico, a branch of the Switzerland-based World Wide Fund for Nature.
Most monarchs live only a little more than a month. But one generation each year lives seven or eight months, long enough to migrate to central Mexico before winter sets in, where the butterflies settle into a semi-dormant state, often clustering around the same fir trees as their forebears, perhaps drawn by chemical cues. In the spring, the monarchs return to the north, where they lay eggs on milkweed and die, giving way to a new generation.
Other factors may be hurting the monarch population, including extreme conditions associated with climate change. A debilitating protozoan parasite, known in scientific shorthand as OE, also has exploded since 2002 and now affects 10 to 15 percent of monarchs, said Sonia Altizer, an ecologist at the University of Georgia who’s studied monarchs for two decades.
While the dwindling monarch colonies worry scientists, who fear they may also be a warning of other environmental crises, in this region of Mexico the decline threatens people’s livelihood. Butterfly tourism has grown since scientists first came across the dense winter colonies in 1975.
Indigenous people had long known of the butterflies. The Purepecha people called the monarchs the “souls of the departed” because their arrival in early November coincided with festivals honoring the dead.
Taylor has been instrumental in the Monarch Waystation program, which encourages people to recolonize areas as small as their yards with milkweed to serve as stopping points for migrating butterflies. More than 7,500 “Waystations“ now exist, including 400 in Texas alone, and boosters urge federal and state governments to let milkweed grow undisturbed along highways rather than mow it down.
Despite decades of scientific study, mystery still surrounds the monarch, including how it migrates to the same fir patch colonized by earlier generations.
Some experts worry about a variation of “the butterfly effect,” the concept coined by Edward Norton Lorenz, an American meteorologist and pioneer of chaos theory, who suggested that the flapping of a butterfly’s wings could trigger a hurricane on the other side of the globe weeks later.
That theory of interdependence now seems turned on its head. The question today is: What occurs when the monarch stops flapping its wings?
“If monarchs are in trouble _ and they are a really robust species _ you can practically be assured that there are a number of species like pollinators and birds that also are in trouble because they rely on the same habitats as monarchs,” Altizer said.
Many scientists are concerned about the eastern population of monarchs, which spend summer east of the Rocky Mountains. This group is occurring in ever smaller numbers, and its survival may be threatened by a series of natural disasters in the Mexican wintering grounds, as well as by reduced acreage of milkweed plants in their summer home, according to Natural Geographic’s website.