Journey of a Lifetime: The Great Migration of the Monarch Butterfly

The migration of the monarch is considered one of the great natural phenomena in the world. Photo by Len Villano.

The monarch is not just a butterfly, it is the butterfly. It’s the iconic insect of North America, easily recognizable and beloved by everyone with a net and some free time in a prairie. They even have a place in the hearts of entomophobics, who deny the relationship between a monarch and the rest of the insect kingdom. Threats of extinction have spurred an international rally around their protection, but it’s hard to protect something so fleeting.

The migration of the monarch is known as one of the great natural phenomena in the world. Unlike birds that fly south in the winter and return in the summer, or a salmon run, where the fish migrates upriver to spawn, a single monarch butterfly will never complete its entire journey.

“The monarchs around here never make it to Mexico. That’s what most people find most surprising,” said Erik Ostrum. Ostrum interned at the Butterfly House on Washington Island in the summer of 2015 while he was finishing his degree in entomology at the University of Wisconsin — Stout. “The ones around here only make it to central or southern United States.”

But the cycle continues.

Ostrum is a bug guy. He feels more at home pinning the fragile bodies of the insects he catches behind the Butterfly House into his collection than at Nelsen’s Hall Bitters Pub with the rest of the island folk. He doesn’t just pick up the caterpillars nesting on the roadside milkweed when he sees the town lawn mowers come through, he brings them home and nurtures them into butterflies.

Ostrum looks out over the prairie behind his home among the insects. “Most people just look at this and don’t see anything but plants.”

It is that naive disconnect that has already endangered the survival of the monarch butterfly.

An article published by Scientific Reports in March of 2016 estimated up to a 57 percent risk of monarch extinction over the next 20 years. Monarch population has declined more than 90 percent in the past 25 years. While the numbers for individual years rise and fall with weather events, the long-term trend is a threat to their existence.

“Habitat destruction in the United States and Mexico, deforestation of their migration areas, pesticides and insecticides on croplands,” Ostrum lists the mounting threats to the monarch, ticking them off on his fingers.

But the threats to the monarch all take place under the journey of their lifelong migration.

Photo: Len Villano

The Mountain of the Butterflies

You could say that the migration of the monarch does not start somewhere, it simply continues. The butterfly is always following the trails of milkweed along roadsides as it comes north with the warmer weather and retreats south during colder months.

If there is any place that a monarch could call home, it is a group of mountains 60 miles west of Mexico City.

The Monarch Butterfly Biosphere Reserve is a 140,000-acre preserve of pine forest that houses a uniquely dense population of the butterflies from October through March. But before it was a designated reserve and a World Heritage Site, a textile engineer from Kenosha and a native Mexican responded to an ad in a Mexican newspaper in 1973.

The ad, printed by Canadian zoologists Fred and Norah Urquhart, sought research associates to help in tracking monarch migration. Ken Brugger was working at a textile company in Mexico City with a passion for nature on the side. Catalina Trail was a native of the country whose Spanish fluency and knowledge of the terrain helped bridge the gap between the locals and the outsiders.

The two amateur naturalists set out to track the monarchs and soon found themselves at the summit of Cerro Pelón, surrounded by millions of monarch butterflies. They covered the tall fir trees and littered the forest floor.

National Geographic featured Trail on the cover of its magazine in 1976. She sits smiling between two pillars of monarchs with butterflies resting on her outstretched fingers, her denim pants covered in blurred orange and black.

From there, things moved pretty quickly.

Mexico’s President José López Portillo designated the reserve in 1980. Research and tourism dollars flowed into the rural mountain area. Local governments enacted laws prohibiting logging in the area and the national government prohibited tourism in many of the roosting sites. In 2008, the United Nations Educational, Scientific and Cultural Organization (UNESCO), named the area a World Heritage Site.

While monarchs west of the Rocky Mountain continental divide often travel to California for the winter, roosting in suburban parks and golf courses along the ocean shore, and monarchs of the eastern United States head for Florida’s warmer weather, the mountains of Mexico are most abundant with monarchs in the winter months.

It is in these mountains that the life cycle of a monarch begins. But when it comes to a monarch, the life cycle is better understood as the journey of many generations rather than a single butterfly.

The Great Migration

In February and March, after a long winter in the Mexican mountains, the monarch begins travelling north. They find mates and begin laying eggs as they cross the border into Texas. After laying eggs, the monarchs from Mexico die and their offspring are left to continue the northern migration.

This first class of monarch children are known as the first generation and they will continue heading north through the spring as milkweed begins popping up throughout the Midwest.

But the first generations of monarchs are not those we see fluttering around the Door County peninsula. The southern-born butterflies live between two and six weeks, mating and laying eggs on milkweed plants along their journey before dying. Finally, by the third generation, the butterfly makes the trip all the way north to spend the summer.

“In this part of the area, depending on warmth, you get one to three different generations of monarchs,” said Ostrum, happy to see more monarchs on Washington Island than in past years. “In the early summer they’ll hatch and then mid-summer or early fall is the next generation.”

The monarch may not know when school goes back in session and the tourists leave the county, but as the days get shorter and the temperature drops, the butterfly prepares for the final and greatest generation of its migratory cycle.

The fourth generation of monarch develops just like its ancestors, but when it finally takes flight in September and October, it will live up to eight months as it makes the return journey south.

“The tagging programs that tagged [butterflies] in Wisconsin or Minnesota were found in southern Texas, which I think was the longest one they’ve found,” said Ostrum.

The Ridges Sanctuary in Baileys Harbor offers a tagging program where visitors can place small identification stickers on the wings of the monarchs before setting them free.

Shannon Pump, naturalist at The Ridges, led the program in 2015, which contributes to the massive data collection of butterfly migration across the country.

“So we know where they ended when they died and they lay their eggs before they die,” said Pump. “They are going to get there and breed and lay an egg. Then [researchers] tag their migrators and their migrators come back up here, so we’re getting a general consensus of where all of that’s going and that’s kind of the importance of the whole tagging program.”

Every organization that tags monarchs has a special identification code. When a butterfly turns up in Arkansas, you can type the code into an online database and learn that the monarch came from The Ridges up in Wisconsin.

The program helps answer questions such as how far a butterfly can travel during its life cycle and whether butterflies from one area tend to migrate together along the same paths year after year.

“It takes many years of doing that before we get really good data,” said Pump.

The generation of monarchs that leave The Ridges will travel more than 50 miles each day on its 2,000-mile quest, resting on the receding milkweed and red clover fields as they follow the warm temperatures south.

The fourth or fifth generation monarch makes it back to the mountains in Mexico and stays through the winter, right where its great-great-grandparents spent the winter the year before.

“They usually take the same paths every season,” said Ostrum. “Just like other animal migrations, it’s just hardwired into them.”

Rose Hara, 8, releases a tagged monarch butterfly at The Ridges Sanctuary. Photo by Jackson Parr.

Milkweed

For such a graceful creature, milkweed seems like a strange plant to depend on. It is poisonous to birds and smaller animals while feeling at home growing along busy interstates and construction sites.

“Milkweed doesn’t do too bad in disturbed areas,” said Ostrum. “It’s the birds that stay away from it but a lot of insects really don’t have a problem with it.”

This aversion by birds is part of what protects the vulnerable monarch from being eaten. It didn’t take long in evolutionary history for the monarch’s predators to realize the black and orange butterfly is not fit to eat.

Monarchs lay their eggs on milkweed and the plant is the only thing the young caterpillars will eat. Planting milkweed is one of the few things you can do to provide more habitat for the travelling monarchs, especially in the more diverse climate of Wisconsin.

“I read in one study they did in south Texas and the southern states, where milkweed grows year round, that bacteria or virus that’s naturally occurring gets attached to the butterflies down there and kills them off, which doesn’t happen up here because it dies with the milkweed,” said Ostrum. “They’ve started telling people down there to mow or cut down their milkweed once a year so it can grow back.”

But in places with healthy milkweed, roadside mowing is part of what is destroying the nesting areas for monarchs. Some states, such as Minnesota, recognized the limited options in planting beneficial native species that will survive next to an interstate and enacted laws to reduce roadside mowing. Iowa and other states have actively planted milkweed along roadsides.

“When I see the tractor coming to mow all the ditches I go in front of the tractor and pick all the caterpillars off before it goes through,” said Ostrum.

But mowing is just one of the threats to a monarch population that has been dwindling for decades.

Threats to the Monarch

Despite declining numbers, the monarch is not yet designated as an endangered species. Although state and federal efforts have encouraged support for the butterfly, it is not afforded any legal protection against what threatens them.

Most threats to the monarch fall under the decline of its habitat. Roadside milkweed is not the only thing these butterflies need to survive. Unfortunately, much of this habitat destruction is done illegally and outside the reach of conservationists.

Back in the rural Mexican mountains, it is a socio-economic battle of conservationists and natives. Up until 1980, when the country designated the area a protected reserve, those who lived near the mountain of the butterflies made their living by cutting down the trees that housed the monarchs through the winter.

Deforestation continues, with an estimated 26,000 acres of the forest preserve lost between 1986 and 2006. Those who have lived within the preserve their whole life bristle at the idea of taking their industry away so more tourists can come and view the natural phenomenon.

Some natives in the area have embraced the attraction, offering tours, lodging and crafts to the global visitors. Locals can even make money from conservation groups who pay them to patrol the forest in search of illegal logging activity.

Similar to bees, the adult monarch also relies on the nectar of wildflowers and water sources for sustenance during their journey. The use of herbicides to kill plants in rural fields and water diversion for agriculture use means the butterfly has to spend more energy flying around in search of food. If a tired butterfly gets to Mexico, it is unlikely that it will survive the winter to begin the cycle over again.

“If you can have a healthy balance of something for each part of the season, then you’re going to have a lot of pollinators in your yard,” said Kate Markiewicz, Ostrum’s fellow intern at the Butterfly House, who only entered the world of bugs after seeing Ostrum’s fascination. “People need to realize that we’re all part of one giant ecosystem that is interconnected in every way so there’s always going to be a cause and effect. When it comes to the big picture, humans have a pretty big impact and if we don’t start making a change then there are irreversible effects.”

But some of the biggest butterfly enthusiasts may be hurting the insect the most. Tourism at the Monarch Butterfly Biosphere Reserve brings in 150,000 tourists from around the world every year. The proliferation of businesses to capitalize on the new tourism industry and the thousands that visit the sensitive area every year have disturbed the area enough for many monarchs to abandon it.

Shannon Pump, right, helps visitors tag monarch butterflies at The Ridges Sanctuary. Photo by Jackson Parr.

Changing Paths

“When insects are gone, we’re gone,” said Ostrum. “They feed the small mammals that feed the bigger mammals that we feed on.”

Good weather helped the monarch numbers rebound in 2015, but the broad trend over two decades shows a decline. Despite knowing the threats to the monarch, it is hard to know exactly what is causing this decline.

A series of seven monarch studies published in the Annals of the Entomological Society of America in 2015 provides evidence that summer breeding areas in the United States have not seen as much decline in numbers as the Mexican wintering sites. Another study said that monarchs are laying fewer eggs because they can’t find the milkweed to nest on.

The continuous and rapid life and death of the monarch makes any attempt at counting the insect futile. Some researchers in the studies believe that amateur naturalists voluntarily counting the butterfly are sticking to the prairies and forests where walking around in search of butterflies is pleasant instead of examining interstates and commercial farms, where the impacts to the monarch may be the most severe.

Despite the ambiguity in what is causing the problem, the February 7, 2014 edition of Science Magazine agrees on one thing.

“Over the past 20 years, the number of monarchs returning to the largest known wintering ground in central Mexico’s highland forests has plunged by more than 90 percent.”

Monarchs In Door

The Butterfly House is a modest operation, offering simple education from some college interns and a small prairie out back to see the education in action.

“I’ve had grown men in the back labyrinth with a net trying to catch butterflies and it’s adorable,” said Markiewicz. “I really love that about this place.”

There are dirty plastic containers littered with milkweed that has been chewed into strange shapes. Exhibits often stuck behind glass panes are in the open air, free to touch. It’s hard to know whether the bugs crawling around the floor are part of the experience or just part of the house.

“I had a mother come in the other day and I was showing her kids the monarchs and I said, ‘You can open the containers for the caterpillars,’” said Ostrum, seeing the excitement in their eyes. “She looked at me and said, ‘Why do you do this?’ I was taken aback by that question, just by her tone of voice. That was the first time I was ever asked something like that.

“‘Because I get to study the world that everyone else is oblivious to.’ That would have been a good answer.”

Sources: Texas Butterfly Ranch, National Geographic, Science Magazine, The Monarch Joint Venture