Monarch Butterfly’s Migration Still a Mystery, Despite Decades of Study : Environment: No other insect migrates, and scientists are unable to explain the phenomenon. Do they navigate by the sun or by Earth’s magnetic field? No one knows.
Conditions are nearly ideal as John Fales heads briskly out the front door with his butterfly net and a worn green canvas bag slung over his shoulder.
It’s 75 degrees on a mostly sunny afternoon in the early fall. A gentle breeze ripples the waters of Chesapeake Bay, a short walk from Fales’ home at Plum Point in Calvert County, Md.
Fales records the temperature from a gauge atop a pole in his yard and writes down the time. Ready now, he scans the shrubs in his yard and the sky overhead. He is quickly rewarded.
“There goes one,” he says, glimpsing a monarch butterfly as it flutters overhead, too high to catch.
The monarch is flying due south, following an ancient migratory path to its winter home in Mexico.
No other insect migrates as the monarch does. Each fall, millions east of the Rockies from Texas to Canada fly south, to return in the spring. Those in the West winter near the coast in Southern California and Baja California.
Despite decades of study, scientists cannot fully explain the phenomenon. Do they navigate by the sun or take their cue from the Earth’s magnetic field? No one knows. The mystery enhances the allure of one of the most beautiful and popular of butterflies.
The migration is easily observed in early fall. The butterfly’s distinctive wings of burnt orange, black and white as well as its larger-than-average size make it stand out. You can spot monarchs as they stop to feed in gardens, along the beach or at the sides of highways. Or just look up.
“Between Labor Day and the middle of October, on any really sunny day I could go out in the mall and see them flying overhead,” says Robert K. Robbins, research entomologist at the Smithsonian Institution in Washington.
There might be one monarch or many. Philip Kean, a member of the Maryland Entomological Society, once saw thousands clustered in a field of tick weed sunflowers near in Anne Arundel County, “tanking up for the trip home.”
Scientists assume that the monarch has been making this annual journey for thousands of years; whether they can continue it will depend on actions of its worst enemy: people. The butterfly’s winter homes are under assault. In Mexico, poor people living next to the forests of coyumel firs where the monarchs stay have cut into them for timber and to clear land for crops. In California, developers’ projects have destroyed the insects’ habitat.
A number of private organizations and the government of Mexico, however, have taken action in the ‘80s to prevent irreversible damage.
Mexico’s efforts in particular are noteworthy. In an impoverished country where environment often takes a back seat to economy, the national government has established monarch refuges. The refuges, or reservas, are a two-hour drive southwest of Mexico City in an area of about 1,500 square miles. Despite the official designation, however illegal encroachment has occurred. Preservationists believe that the monarch’s security depends on developing economic alternatives for the resentful residents nearby.
“They’re very, very poor people,” said Alfredo Arellano, a biologist with the Monarch Civil Assn., a private group in Mexico City. “They want work.”
Even limited logging can hurt the monarch, however. Thinning of the forest results in higher temperatures in the day and lower ones at night, upsetting an environment that would otherwise be a perfect spot for the mariposa monarch to spend the winter.
Biologists say that if the temperature rises too much, the monarchs become too active, burning energy they need to survive and to make the return flight north. If it becomes too cold, the monarchs die.
In the United States, the Xerces Society and National Wildlife Federation are among the organizations supporting efforts to preserve the monarch. A number of scientists are trying to unravel its secrets, with the assistance of volunteers such as Fales who pass on their observations and tag butterflies so that they can be tracked.
Fales has been collecting butterflies of all kinds since 1942. He was an entomologist for the U.S. Department of Agriculture research facility in Beltsville, Md., until 1972, when he retired and moved with his wife to their small house overlooking the bay.
Fales, who is fit and nimble at age 76, snares the butterflies with a quick snap of his net and tags them with the dexterity of a surgeon.
He spots what looks like a monarch perched in a patch of wildflowers. It turns out to be a viceroy, a look-alike that often fools an untrained eye. The viceroy also fools birds, which generally avoid monarchs because the chemicals derived from the butterflies’ ingestion of milkweed, their favorite food, make them a poisonous meal.
Fales soon nets the real thing. Kneeling, he opens the bag to extracts his tools: a peanut jar containing ethyl acetate, which he uses to kill butterflies he intends to collect, and a small box.
Fales removes the struggling butterfly from the net and lays it on the yellow jar top, his thick fingers holding it gently in place. He takes a marker and, with the pointed end, delicately scrapes off a small patch of scales on both sides of the top right wing, being careful not to poke through the wing membrane. Then he picks up a folded gummed tag a bit larger than a thumbtack and places it on the cleared area of the wing, pressing gently.
The white tag has a number, 1099, and the address of the Natural History Museum in Los Angeles, where monarch research data is collected. So far, none of the butterflies Fales has tagged during the past four years has turned up.
Fales then tosses the tagged monarch into the air. It obstinately heads northward, ignoring Fales’ prediction that it would go the other way. He seems mildly surprised, but the other butterflies he tags this afternoon do fly south.
The typical generation of monarch does not live more than a month, Fales says, but the migrating generation can live long enough to survive the winter and a trip of perhaps 2,500 miles.
Part of the mystery is that no one is sure how far north a monarch makes it back in the spring. Fales has caught tired specimens whose colors have faded and wings have become ragged, suggesting that their trips had started far to the south. Scientists are certain, however, that the butterflies mate along the journey north, producing new generations that join the migration.
“I’ve been monitoring the monarchs for many years,” Fales says. “In the last couple of years, it’s been in short supply. We’re trying to figure out what’s going on.”
In 1987 and 1988, Fales said, there was not a “massive fall migration”--during one of those, you can spot 100 in a 10-minute period. The numbers have so far been small this year, he said, although higher than they were for 1988.
In Mexico, preservationists have discovered four new wintering sites, all in the same region, according to a report last summer by Fred Urquhart. Urquhart is the Canadian scientist who deserves much of the credit for discovering the monarch’s winter homes.
For many years, scientists suspected that monarchs migrated to Mexico, but they did not know where. Finally, in 1975, an American named Kenneth Brugger, using information from Urquhart, found a colony of monarchs. Local residents, of course, had known all along about the butterflies.
In the 14 years since, the butterflies have acquired many friends, the Entomological Society of America among them. The society is one of more than 11 groups seeking to make the butterfly the national insect.
Mexicans are also fond of their colorful visitors, and one refuge is open to the public to accommodate the increasing number of people who want to see an unusual sight.
On a chilly morning last January, for instance, tens of thousands of monarchs--too many to estimate--were clumped like leaves in the branches of tall fir trees in a forest in the state ofMichoacan more than 7,000 feet above sea level. As the sun climbed higher into the sky, warming the air, the butterflies begin to stir. Thousands begin to fly between the trees and to light on bushes. A few settled on the awe-struck people who had trekked up a steep unpaved path to the refuge.
“It’s a glorious silent dance,” whispered Connecticut artist Lois Read as she painted the scene in watercolors.
