Photo by Sandy Vandenburg
Migratory Wonder
A tagged monarch drinks from a flower. If the butterfly is recaptured later, the tag will offer scientists valuable information about its travels.
Before National Geographic published its famous 1976 cover story detailing the search for the monarch butterfly’s wintering grounds, nobody knew where these strikingly beautiful creatures vanished when the weather grew cold. A 2,000-mile migration was thought to be a “foolish idea,” said Wanda DeWaard, founder of the outdoor education company Earth Kin LLC, who has led a monarch tagging program in Great Smoky Mountains National Park since 1998. Ever since, this natural phenomenon has fostered fascination among scientists and enthusiasts alike.
But it’s a phenomenon under threat, according to the U.S. Fish and Wildlife Service. Monarch populations east of the Rockies spend the winter in central Mexico, while those in the west migrate to southern California. Today, there are 80 percent fewer monarchs overwintering in Mexico than in the 1980s, and California wintering populations are 95 percent smaller than they were at that time. In response to these figures, the Fish and Wildlife Service issued a proposal to list the monarch butterfly as a threatened species under the Endangered Species Act.
“The iconic monarch butterfly is cherished across North America, captivating children and adults throughout its fascinating lifecycle,” USFWS Director Martha Williams said in a press release announcing the listing proposal. “Despite its fragility, it is remarkably resilient, like many things in nature when we just give them a chance.”
Though isolated populations of monarchs exist in 90 different countries, islands, or island groups worldwide, their lineages all trace back to North America, where the butterfly has a complex life cycle and migratory pattern that scientists still don’t fully understand.
In the spring, overwintering butterflies mate and fly north, eventually stopping to lay eggs once they find milkweed. This new generation continues its northward journey. Over the course of three to five generations, each with a lifespan of two to five weeks, the monarchs arrive in southern Canada. But the last generation lives much longer, with sexual maturity put on hold while they fly south to central Mexico for the winter. When spring returns, they complete their development to mate and lay eggs.
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Photo by Warren Bielenberg
Migratory Wonder
Wanda DeWaard stands at the ready with a butterfly net during a tagging event in Cades Cove.
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Photo courtesy of US Fish and Wildlife Service
Migratory Wonder
A monarch butterfly drinks nectar from a flower. Nectar-producing plants are critical for migrating monarchs, providing them with the energy they need to complete the arduous journey.
“It’s a pretty amazing process,” DeWaard said. “I think it’s important to have a little wonder and awe and mystery in our lives, and they certainly provide it.”
DeWaard has been finding wonder and awe in monarchs since the 1990s, when she first spotted their caterpillars at her home in Pigeon Forge, Tennessee, munching milkweed. She was fascinated and contacted Monarch Watch, a program based at the University of Kansas that includes a monarch tagging program. Tags help researchers better understand how monarchs move across the landscape. At the time, little was known about the monarch’s distribution in the Southern Appalachians.
“Whoever I talked to at Monarch Watch wasn’t even sure monarchs breed in the Smokies,” DeWaard said. “And I said, ‘Well, I’ve seen them in my yard.’”
In the years since, DeWaard has worked to fill that knowledge gap, leading countless groups of people in monarch tagging events. Most of her work takes place in Cades Cove, where prescribed fire keeps the meadows open and encourages the growth of milkweed and other nectar-producing plants. However, monarchs may sometimes be found in other open areas such as Cataloochee and Purchase Knob.
Over the years, DeWaard has witnessed “a very different pattern” of monarch butterfly presence in the Smokies than what she might have expected before she began observing them. The Smokies’ first monarchs usually arrive as milkweed shoots leaf out in April. They lay eggs, and this new generation continues its journey north. Another round of breeding typically occurs in September—a deviation from the typical northward progression of reproductive activity. DeWaard hypothesizes that these butterflies might be dispersing from the more crowded regions in their quest to procreate. Migrating monarchs also stop by in the fall, filling up on nectar in the fields.
DeWaard’s tagging numbers have fluctuated over the years, ranging from fewer than 100 in the early 2000s to a record of more than 1,100 in 2018. She oversaw the tagging of 724 monarchs in 2023, but last year only 154 monarchs were tagged, despite DeWaard holding three to four tagging events each week. It’s difficult to draw inferences from these figures, however, as factors such as number of tagging events, weather, and other issues can impact tagging.
In recent years, Andy Davis, assistant research scientist at the University of Georgia’s Odum School of Ecology, has been working to paint a more complete picture of how monarch populations fare when they leave their winter strongholds. In 2022, his team published a paper analyzing more than 135,000 citizen science monarch observations stretching from 1993 to 2018, gathered during an annual summer data collection event conducted by the North American Butterfly Association. While some areas saw net increases and others saw net decreases in monarch populations, “overall, there’s no long-term decline in the numbers of monarchs in the summer over the last 30 years,” Davis concluded.
Davis’ data indicates that, while steep declines in the number of overwintering monarchs are well-documented, successful breeding in the warmer months make them “perfectly capable of bouncing back in the summer.” He surmises that plummeting winter populations are due to a “transit problem.”
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Photo by Jim Hudgins, courtesy of the US Fish and Wildlife Service
Migratory Wonder
A monarch caterpillar clings to a milkweed leaf. Monarch caterpillars feed exclusively on plants from this genus, storing up the toxins they contain to ensure they are distasteful to predators.
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Photo by André Brousseau, courtesy of Smokies Life
Migratory Wonder
Smokies Life Park Keepers listen as Wanda DeWaard explains the monarch tagging process during a fall tagging event.
“There has been a clear decline in the success rate of monarchs actually reaching Mexico,” he said. “By the time they get to Texas, their numbers have dwindled to 80 percent less than they were 20 years ago. It’s a massive, massive decline that is pretty much going unnoticed.”
In its listing proposal, the Fish and Wildlife Service says that habitat loss, insecticide exposure and climate change are driving the decline in overwintering monarchs. In the Midwest, for example, an important region for summer breeding, milkweed stems decreased by nearly 40 percent between 1999 and 2014. About 90 percent of corn and soybean crop acreages are planted to tolerate herbicides that kill milkweed and other native plants.
The listing proposal calls for an increase in milkweed and nectar-producing plants, protection and enhancement of overwintering sites, reducing the impact of insecticides and herbicides to monarchs and their environment, and maintenance of public support for monarch conservation.
Davis said his research shows that the increasing prevalence of Ophryocystis elektroscirrha (OE), a protozoan parasite that affects monarchs worldwide, is having a larger impact on migration. Migrating while infected is like “running a marathon with the flu,” Davis said. Sick monarchs usually die on the journey.
In nonmigratory populations, OE infection rates as high as 100 percent have been observed, but rates in migratory monarch populations have historically been extremely low, around 1 percent. In recent decades, however, the OE infection rate has skyrocketed, he said. Davis attributes this to non-native tropical milkweed species, often planted by well-meaning people looking for a way to help monarchs. Because they remain in leaf longer, tropical milkweeds accumulate a buildup of OE, which then infects any monarch using the plant.
Another well-intentioned intervention may also be having an impact. Monarchs raised in captivity grow up weak and directionally challenged, Davis said, with some research indicating a migratory success rate only about one-third that of their wild-grown relatives.
“My message to people is, we just need to be hands-off,” he said. “You can have a butterfly garden in your backyard, but leave the monarchs alone and don’t interfere.”
Both DeWaard and Davis said they expect the monarch will continue to survive as a species; it’s the migration that’s under threat. Biologically speaking, it’s an important phenomenon, cleansing the population of weak or sick individuals and bringing butterflies from all over the continent together to exchange genes, keeping the species strong and resilient.
But more than that, it’s a mystical marvel, drawing attention and appreciation to the important roles insects play in the world we share.
“The migration is what makes the monarchs so charismatic,” Davis said. “It’s a special thing that’s almost unique among butterflies. It’s part of their story, and if we were to lose that, it would be a great tragedy.”
About the author: Holly Kays is the lead writer for the 29,000-member Smokies Life, a nonprofit dedicated to supporting the scientific, historical, and interpretive activities of Great Smoky Mountains National Park by providing educational products and services such as this column. Learn more at SmokiesLife.org or reach the author hollyk@smokieslife.org.
Learn more
To learn more about the monarch listing proposal or comment by March 12, search docket number FWS-R3-ES-2024-0137 on regulations.gov. To help monarchs and other pollinators, plant native flowers, avoid pesticides and herbicides, mow less, and participate in citizen science efforts to monitor populations. Contact DeWaard at earthkin@bellsouth.net to get involved with monarch conservation efforts in the Smokies.