Monarch butterflies: The last migration


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By Benjamin Vogt

On May 23 my wife yelled to me from the back door of our house, “There’s a monarch on the allium!” The last two springs, this being our third here, we had not seen a monarch butterfly until around my birthday in mid-July. And frankly, I didn’t expect to see hardly any at all this whole summer. As I dashed out to the garden with my camera in hand, there it was, fighting 40 mph wind gusts, rising and slicing through the air to land on an allium, as bumblebees zipped around it like electrons. I knew the moment wouldn’t last.

In 2007 my wife and I moved into our first home together, new construction on the edge of Lincoln. The holdout American elm in the corner of the quarter-acre lot had barbed wire still wound around its trunk, a property marker for some farmer’s previous field. As a child, I tended her gardens with my mother in Minnesota, and as I grew older, confined to apartments, I knew I’d want a big garden someday. With a can of orange spray paint, and a day or two before the sod came in, I marked off 2,000 feet of beds and borders for an ornamental garden designed specifically for native wildlife and plants. Milkweed was first on the list.

I actually knew little about gardening but meticulously researched Plains and Midwestern plants online, purchasing the right plant for the right spot—the dry hill and the mucky clay valley of my small yard. I dug $10 holes for $1 plants from morning to sunset in 90-degree heat for two summers. Some of the first plants were two Asclepias incarnatas (swamp milkweed) and an Asclepias tuberosa (butterfly weed), larval host plants for the monarch butterfly and named after the Greek god of healing, Asklepios. Milkweed is said to treat warts and poison ivy, remove mucus from the lungs, cool fevers and work as a contraceptive. You never know how you might need your plants.

At night that first summer of gardening, I’d dream of black-laced orange butterflies and dozens of other insects and birds frolicking in my Eden. But I didn’t know what to expect. I was a book-reading graduate student, no botanist or entomologist. In 2008, when I noticed a yellow, white and black striped caterpillar, I really had no idea it was a monarch until I did a Google search. I didn’t know the 30 pen-tip-sized white pegs on the undersides of leaves were eggs that would hatch a few days after being laid. The monarchs had come like magic.

Folklore states that if a butterfly flies into your face, cold weather is imminent. For some, it means that within 10 days sufficient frost will turn the leaves the same color as the butterfly. In central Mexico come fall, the monarch arrives at the end of a 3,000-mile migration from as far as southern Canada on the Day of the Dead, which marks the return of a deceased loved one’s soul. No one knows how these monarchs, several generations removed from their northward-bound ancestors, find their way back to their winter home.

The Mariposa Monarch Biosphere Reserve (138,000 acres) lies in the central Mexican states of Michoacan and Mexico. While Angangueo is considered the unofficial monarch headquarters, the most prominent overwintering site is in El Rosario, where as many as four million butterflies—of an estimated 200 million—roost per acre in the fir and pine trees of the oyamel forests on only 12 mountaintops. The trees provide shelter from cold rains, which can freeze the monarchs, while they also hold in warmth rising from the forest floor. The conditions are precariously perfect, delicate microclimates, and only since 1975—as a result of ads taken out in Mexican newspapers—have scientists known the home location of the world’s only migrating butterfly.

The summer breeding range of monarchs east of the Rockies is over 247 million square acres, but here the insects cluster in only a few colonies that range in size from one to 10 acres. Like massive dreadlocks, they hang from trunks and branches in suspended reproduction or diapause. These monarchs were born in September, and unlike the summer generations that live for only two to four weeks, they will last seven months until the February and March migration back north to Texas and the Gulf states, where they will lay eggs and quickly die.

How can an insect with the mass of a paperclip make such journeys and endure? As I watch the July monarchs perform aerial courting—the male dive-bombing and grabbing at the female, hoping to get her on the ground for copulation—I find it amazing that their four thin wings don’t shred. In the heat, the wind, the miles of interstate, they dodge death. And then there are blue jays and orioles, who have learned to only eat the thoracic muscles to avoid the poisonous wings that contain cardenolides, which induce vomiting and heart attacks in predators. Tachnid flies lay eggs in caterpillars—maggots emerge weeks later from a newly formed chrysalis. An estimated 90 percent of monarch larvae never develop into butterflies, and the milkweed they depend upon in North America is quickly vanishing as 6,000 acres per day of habitat is destroyed by human development.

Patches of milkweed are few and far between. Counties mow vital highway edges and destroy stands of it and nectar plants. Farmers plant genetically modified corn and soybeans that are herbicide resistant, so chemicals like Roundup are liberally applied, easily killing any nearby milkweed. In Mexico between 1986 and 2006, one-fifth of the Monarch Biosphere—where only some of the winter roosts are located—was illegally logged, resulting in nearly 26,000 acres of deforestation. How does the monarch persist?

In the winter of 2009–2010, massive rain and hailstorms washed away local villages and monarch roosts in Mexico, resulting in an estimated 50–80 percent loss of the record low 4.7 acres of monarchs, down from the average of 18 acres. In 1996, a record high winter population was set at 44 acres, but in 1997, the population was just 15 acres. Again, from 1999–2000, the population went from 22 acres to seven acres, then in 2004 dropped to five acres.

The Commission for Environmental Cooperation does not list the monarch as endangered but does list the migration as such. Scientists agree that with shifting weather patterns due to global warming, the overwintering sites in Mexico will be uninhabitable by 2055 as the Mexican mountains experience more rain. But with the fragmented and vanishing stands of milkweed in North America, it maybe won’t matter. In the spring of 2009, a dry Texas winter meant fewer milkweed for arriving monarchs, and a cold and wet Midwestern spring and summer slowed migration and inhibited milkweed growth.

But perhaps the monarch is just a butterfly, just one organism, just one phenomenon among thousands on the planet. Or maybe the potential disappearance of one species would diminish human culture itself—the Native American Pima tribe cite the creator as having taken the form of a butterfly, for example. The monarch has spread to Australia, Indonesia, the Azores, the Bahamas and Spain through introduction, and the western population is relatively stable (and much smaller) as it migrates from British Columbia to southern California each year, so the monarch won’t vanish entirely. But the metaphor their lives represent is obvious.

In Christianity the caterpillar’s two weeks of life represents our earthly self, the chrysalis our tomb, the emergence (10–14 days later for a monarch) is a casting off of our body and spiritual rebirth. The monarch is more than a reminder of ourselves, it is the center of our moral and ethical beliefs as another species sharing and taking care of the Earth, and in turn ourselves. Organizations like Monarch Watch, MonarchLab and the Commission for Environmental Cooperation are trying to make preservation and ecotourism a physically benign yet economically viable option for Mexicans who harvest the forest to heat homes, cook food and just barely survive. These same organizations work in North America on a seemingly different level—to appeal to our humanity, our compassion, our sense of wonder and aesthetic joy.

Somewhere in the middle is the monarch butterfly. Somewhere in my garden now a female, slightly smaller than a male and missing two pheromone-producing androconium spots on two of its wings, may be laying eggs underneath milkweed leaves. She is tattered and faded, her short summer lifespan nearing an end, but a few of her 400 eggs will emerge as an echo of herself in four weeks, a rebirth noticed by our own ancestors long ago—a symbol of defiance and hope in a new world more reminiscent of small, carefully tended gardens than of one vast nature.



What a well articulated thesis on why we should value these amazing creatures and their unique migration. Thank you for putting it so eloquently. I have never seen the info on the Christian caterpillar symbolism--curious where that came from. Love that. As others have pointed out, asking why we should save the Monarch Migration is like asking why we should save the Mona Lisa. Both are treasures, one natural, the other manmade. Monarch Migration huggers like me are more inclined to ask: why would you not? Thank you again for the thoughtful reading.

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