Lisa Fugard, Author of Skinner's Drift

I'VE seen fairies. In the Transvolcanic Mountains in central Mexico of all places. It was late afternoon and thousands of them were flitting among the pencil-straight oyamel fir trees. Now it could be that the altitude of 10,000 feet had made me delirious, but I'm not the first person to think a butterfly might be more than an insect. The Aztecs believed butterflies were the souls of the dead. When I visited the monarch butterfly sanctuary of El Rosario and saw these delicate creatures dancing in the air, a childhood dream of mine was fleetingly realized. I'd stumbled upon a fairy glade.

Mexico is the destination for several migratory creatures. Gray whales travel from the Bering Sea to the Baja peninsula to calve; sea turtles gather on beaches near Huatulco to lay their eggs; and at the end of each summer some 250 million monarch butterflies from southern Canada and the central and eastern United States fly south to the high altitude oyamel forests on a journey that can span 3,500 miles.

Scientists knew that the small population of monarchs west of the Rockies wintered in sheltered bays along the California coastline, but until 1975 they were bewildered as to where the butterflies east of the Rockies migrated. That was when an American salesman in Mexico City, working with a Canadian scientist named Fred Urquart, hiked into the Transvolcanic Mountains in Michoacán and found monarchs clustered thick as bunches of grapes in the oyamel firs. What remains a mystery is how the butterflies return to the same forests year after year. The ones that fly to Mexico each fall have never been there; they are the great-great-grandchildren of the monarchs that left the previous spring.

The Mexican government established the Monarch Butterfly Special Biosphere Reserve, consisting of five sanctuaries in central Mexico, in 1986. A presidential decree passed last year expanded the reserve and connected the five sanctuaries, creating a contiguous corridor of 140,000 acres. The two sanctuaries open to the public -- El Rosario and Chincua -- have become popular eco-tourism destinations. Bringing dollars into the communities helps meet the needs of residents, but the increase in tourism threatens to create new problems for the butterflies.

Last January I visited the sanctuaries on a five-day tour offered by Natural Habitat Adventures, a tour company based in Boulder, Colo. I flew into Mexico City and checked into the Imperial Hotel where I met the eight other tour members, ranging in age from 40 to 70. Our guides were Astrid Frisch, a young Mexican biologist, and her husband, Karel Beets, a founding member of the Mexican Association of Eco-tourism and Adventure Travel.

The next morning we boarded a minibus and traveled west for four and a half hours to the state of Michoacán and a two-night stay in Angangueo, a former mining village snuggled in the folds of the mountains close to both sanctuaries.

Small, brightly painted houses hug Angangueo's steep, narrow streets. Geraniums, irises, roses and nasturtiums bloom in front of the houses, and turkeys forage on hillsides studded with cactuses and maguey plants, a member of the agave family that produces a flower spike resembling a colossal asparagus. When the copper and silver mines were active, Angangueo was home to 35,000 people; now there are 5,000. Most of them are dependent on the tourism that the butterfly migration generates from December to late March. Come April the men must look for work elsewhere.

We checked into the Posada Don Bruno, a charming, terraced hotel. After a lunch of tortillas, chicken, beans and avocado at Margarita's across the street, we squeezed onto benches in the back of a pickup truck and set off for El Rosario, the most visited of the sanctuaries.

The 45-minute drive up the rutted dirt road took us past freshly plowed ejidos, plots of land given to the local communities after the revolution of 1912. A young couple made their way up the dirt road in front of us and the woman, astride a burro, gave an adamant shake of her head when one of our group tried to photograph her.

The steep trail through El Rosario begins at 9,530 feet. I can state that with confidence because Elmar, a witty older gentleman on the tour, sported a watch with an altimeter and we requested frequent readings. The hike was less than a mile, but the altitude gave some of us headaches and left all of us breathless. Sadly, one of our group had a bad knee and had to turn back. We rested often while several Mexican families -- obviously used to the altitude -- and a woman in high heels, escorted by a dapper man, whizzed by.

To our delight, monarchs were sighted almost immediately. After a sunny day of nectaring and puddling -- a term used to describe butterflies gathering at damp areas to drink -- they were returning to their roosting area and the forest sparkled with their flitting presence.

We hiked for about 40 minutes, and at 10,120 feet we reached the area where the colony roosted. I found the sight of oyamel trees pendulous with butterflies to be more peculiar than beautiful. Was I really looking at butterflies? With their black-and-orange wings open, monarchs are luminescent creatures; wings closed and bunched together, they resemble patches of lichen and bundles of dead leaves.

Astrid explained that the oyamel-pine forest creates a perfect winter microclimate for the butterflies. Thinning of the forest is like ripping holes in a sleeping bag, she said. If it gets too cold at night the butterflies freeze to death. And if daytime temperatures are too warm they become overactive and burn up their lipid reserves.

MONARCHS are not endangered, but the oyamels face intense logging pressure and thus the monarch migration is threatened. The lives of the local farmers, the campesinos, are also held in precarious balance. With the creation of the sanctuaries, land that had been communally owned by the campesinos for decades was taken away with no compensation. Logging, a source of income and fuel, was severely restricted. Butterflies threatened to be their undoing.

Developing a tourist-based economy seems to be the answer.

Diego, a shy swarthy man from Angangueo, drove us up to El Rosario in his pickup; halfway up the mountain we paid a toll to pass through one community's land; we hired a local guide, another requirement, even though we had two guides of our own; we bought T-shirts and mugs from the ramshackle wooden stalls at the entrance to the sanctuary.

Until recently there were communities that weren't benefiting from the tourist trade, and land clearing and logging continued. A new program established by the World Wildlife Fund with the support of the Mexican government hopes to put an end to that. Last November the W.W.F. established a trust fund of $6 million: with the interest it will buy logging permits -- in essence paying campesinos not to log -- and finance conservation activities to be carried out by local people. It sounds like a splendid idea but in an interview, Juan Bazaury-Creel, the director of World Wildlife Fund-Mexico warned ''New ideas don't get accepted overnight.''

The next morning we visited the butterflies at Sierra Chincua, a 45-minute drive north of Angangueo. The trail was over a mile long and took us to 10,700 feet. Young men with horses offered to take us, but, along with four others, I chose to make the hourlong hike accompanied by a local guide, Francisco Ambrosio Martínez.

Chincua is beautiful and feels wilder than El Rosario. Lupines and bright pink thistles flourish on the slopes, along with masses of hoja ancha, a tall plant with yellow flowers that the monarchs frequent. The sanctuary was opened in 1996 but only after intense discussion between the local communities that wanted to benefit from tourism and biologists, like Lincoln Brower, who felt the area should be maintained for research.

Mr. Brower acknowledges that opening the sanctuaries provides income for the campesinos and raises public awareness. But he is distressed by the wear and tear wrought by the deluge of visitors. Most U.S tour groups schedule their visits on fairly quiet weekdays. Saturdays and Sundays, when the day trippers converge, are chaotic: it is estimated that 10,000 people visited El Rosario on a busy weekend last year. Clouds of dust kicked up by tourists threaten to asphyxiate some of the butterflies, and the horses at Chincua are grinding a track into the mountain that will lead to erosion. Even the food stalls at the sanctuaries are a drain on the natural resources -- every stand selling tortillas needs a wood fire on which to cook them.

We crested Sierra Chincua to find a cold wind buffeting the south western slope and the oyamels festooned in clusters of chilly monarchs. A path off the trail led to the heart of the colony. I longed to stand in a cloud of butterflies but Francisco did not want us disturbing them. With binoculars I watched the huddled monarchs transform into miniature winged stained-glass windows when the sun broke through the clouds and warmed them.

That afternoon I roamed Angangueo's sleepy, pastel-hued streets until dusk and returned to the hotel in time for Astrid's talk on the life cycle of the monarchs. I can't say that traveling in a tour group is more eco-friendly than visiting the sanctuaries as an independent traveler. But the information Astrid presented and our three visits to the butterflies allowed me to glimpse the complex issues at stake.

In late February the butterflies mature sexually and whirl together in mating dances that can last for 16 hours. Most of the males die. The females fly north to Texas and Louisiana to lay their eggs on milkweed.

This cycle of females searching out milkweed repeats itself two or three more times during the spring and summer, with each butterfly living no more than eight weeks. The late-summer monarchs put their sexual development on hold and live for six to eight months; they are the ones that migrate to Mexico.
On the third morning we returned to El Rosario for a last visit. The experience was extraordinary, yet it also disturbed me. Sunlit stretches of the trail acted as butterfly funnels and as we hiked up the monarchs streamed past, so close I could hear the pat-pat-pat of their wings. At the roosting area they swirled among the oyamels like embers from a fire.

Monarchs alighted in my hair and clung to my day pack. I felt increasingly oafish among such delicate creatures. Another group, several backpackers and a group of children, hiked up the trail. The air grew dustier and I watched a teenage boy, his arm slung around his girlfriend, step on a butterfly. I know that coral reefs are destroyed if you stand on them, and wandering off trail in alpine areas can impact the plant life, but in El Rosario I had evidence of the effect of my presence on the environment: butterflies floundering in the dust at my feet.

THAT afternoon we drove 70 miles southeast to the resort town of Valle de Bravo, where we checked into the luxurious Avandaro Hotel. The fireside trout dinner was superb, but by the time I settled into bed I wished we had spent one more night in Angangueo.

Eco-tourism is about giving back to the places one visits. I know I received far more. I arrived in Mexico with a head full of facts -- 250 million migrating monarchs, campesinos struggling to survive. I left with something more powerful and challenging: vivid recollections of the young boy from El Rosario who clung to the tailgate of the truck as we drove down the mountain and sang one out-of-tune song after another until we gave him a few pesos, and the shaded oyamels of Chincua wearing their butterflies like widows' weeds.