In 1996, World Wildlife Fund Mexico counted almost a billion monarch butterflies overwintering in the mountain forests of that country.
By 2014 the number had plummeted to just 57 million, a decline of almost 94 percent.
The numbers were even lower the year before when only 34 million monarchs migrated to Mexico.
“That trendline is headed to zero,” said Elizabeth Howard, founder and director of Journey North, a Vermont-based citizen science project that tracks monarch migration by mapping reports of overnight roosting spots.
The population crash has prompted the Center for Biological Diversity; the Center for Food Safety; the Xerces Society for Invertebrate Conservation; and monarch scientist Dr. Lincoln Brower, professor emeritus at Sweet Briar University in Viriginia; to petition the U.S. Fish and Wildlife Service for monarch protection under the Endangered Species Act.
Different factors are blamed for the monarch’s downfall, but experts point to three primary culprits:
“There are definite issues of illegal logging” and lack of protection of overwintering sites in Mexico, said Dr. Jaret C. Daniels, associate curator and director of the McGuire Center for Lepidoptera and Biodiversity, and an associate professor of entomology at the Florida Museum of Natural History at the University of Florida in Gainesville.
Despite efforts by the Mexican government, forests in the mountains of Michoacan and Mexico continue to be illegally logged, reducing the available habitat for monarchs.
Even thinning those forests is bad, Daniels said. “Penetration of cold into thinned forests can be lethal to monarchs.”
Bad weather and climate change are also blamed for the butterfly’s demise. “Changing temperature regimes at these elevations can be lethal to monarchs,” Daniels said.
But the granddaddy of them all is loss of habitat in the United States and the introduction of genetically engineered crops designed to withstand direct exposure to herbicides like Roundup, Daniels explained.
Monarchs breed almost exclusively on the milkweed plant, which until recently grew in the “margins” of crop fields – between the rows and along the field edges. The introduction of Roundup Ready crops was a “game changer” Daniels said. Such plants are genetically engineered to withstand the popular herbicide, so it can be sprayed directly on the crops. It has “decreased or obliterated milkweed,” producing “vast areas of complete crop deserts.”
Daniels added Florida presents a different set of problems for the butterfly. “Florida is a strategic state. How they do here influences how they do farther north. Urbanization in Florida is definitely a factor,” he said.
Also, “Homeowners and municipalities landscape with a non-native milkweed. It can disrupt migration by offering a resource of breeding. It’s kind of a trap for monarchs.”
The non-native milkweed, called tropical or Mexican milkweed, persists longer than native varieties. If a monarch breeds late in the season and the weather turns cold, the caterpillars or newly emerged adults will die. “They’re goners,” Daniels said.
Brower is a hard-core tropical milkweed hater. He does not mince words: “Get that damn plant, pull it out and don’t let it grow anywhere,” he said.
Tropical milkweed represents a friction point in the world of butterflies. Not all experts believe it is harmful and some, in fact, say efforts to get rid of it are more harmful to monarchs.
Jeffrey Glassberg, president of the North American Butterfly Association, writing in the winter 2014 edition of a publication called “American Butterflies,” said “…there is little evidence to support the idea that planting Tropical Milkweeds will weaken Monarch populations and NO evidence to support the idea that Tropical Milkweeds are ‘trapping’ Monarchs and stopping them from migrating to Mexico.”
Daniels said that if the tropical milkweed is removed from the landscape early enough in the fall it shouldn’t be a problem.
Experts are careful to point out the monarch itself isn’t in danger of extinction. “Monarchs occur throughout many areas of the world,” Daniels said. “What is in danger is the phenomenon of the migration and the loss of that tremendous productivity.”
What is the value of a monarch?
What is the value of a monarch butterfly?
Unlike bees, which pollinate our food crops, monarchs don’t account for a segment of the economy, according to Dr. Richard Rubino, a professor emeritus of regional planning at Florida State University who has been monitoring and tagging monarch populations in the eastern part of the Florida Panhandle. “They exist largely through the benevolence of mankind,” he said.
Still, they have value, both as indicators of an ailing environment and as objects of aesthetic appreciation, scientists say.
“Common species (not just butterflies) can be really hurt by human impacts,” said Dr. Jaret C. Daniels, associate curator and director of the McGuire Center for Lepidoptera and Biodiversity, and an associate professor of entomology at the Florida Museum of Natural History at the University of Florida in Gainesville, who added that scientists are seeing “large declines in even common species.
“I think the message is that the monarch (a universally beloved insect and once abundant) has shown dramatic declines and we need to do something about it,” he said in an email. “It’s an iconic butterfly.”
He pointed out that fireflies are also on the decline. “Generations of children are growing up without having those experiences (of seeing fireflies),” he said.
Dr. Lincoln Brower, a professor of zoology emeritus at the University of Florida and a research professor of biology at Sweet Briar College in Virginia, compared the monarch to a valuable work of art.
“What happens if we lose the Mona Lisa?” he asked.
For additional information, and to order swamp milkweed seeds, visit the Save Our Monarchs Foundation at www.saveourmonarchs.org/.