ANGANGUEO, Mexico — They travel thousands of miles, unerringly, every year between Canada and Mexico. No one knows how they find their way.

Las mariposas — the butterflies — come by the millions to mate and then die. They arrive in Mexico's heartland, the Sierra Madre in Michoacan state, every November. Five sanctuaries are established to protect them and to let visitors see the miracle.

Guide Andres Orosco and I start the three-hour drive from Morelia to Santuario in the morning.

PROTECTED ZONES

Rosario is the original butterfly sanctuary in Mexico and the largest. The Mexican government in 1986 established two zones that form a Monarch Butterfly Biosphere Reserve — protected from logging and development — although Rosario was considered a sanctuary before that.

The mountains of Michoacan have what the monarchs need: The black-and-orange insects cluster on oyamel pines in the remote mountains, and the area provides just the right temperature and moisture.

Indians in the area before Columbus arrived depicted butterflies in their drawings. The wintering grounds were first noted by scientists in the 1970s.

In 2001, the government and private sources set aside millions of dollars for a fund called the Monarch Trust to pay local residents to stop cutting down the trees. Today, some of the farmers make their living as guides.

Tourists have plenty to see in Michoacan before they get to Angangueo. Just outside Morelia, for example, one town sells fresh, round loaves of Mexican bread so close you could touch them from the car.

In another town, San Lucas Pio, outdoor vendors sell baskets woven using ancient techniques. The town is one of many in the area where artisans create goods made there for centuries. Paracho is a guitar town, and in Santa Clara del Cobere, coppersmiths create jewelry, pots and more.

LIKE A MEXICAN IMU

Between villages, the roadsides are lined with the cornfields of subsistence farmers and barbacoa — pit-roasted meats — stands.

We stop near Querendaro to eat at one called Borrego Feliz — Happy Sheep. I'm not so sure about that, because we are eating mutton.

The barbacoa, sprinkled with lime, cilantro and onion, and served with chiles de arbol, is amazing — delicate and spicy at once.

This is a family enterprise. The father is slicing the mutton, which Orosco says was raised by the family and butchered, then buried for about a day in an underground cooking pit piled with maguey cactus for fuel. Two or three daughters are making tortillas and cooking them on a charcoal-fired griddle.

As we drive on toward the sanctuary, Orosco's spiel about the monarchs helps distract me from his fast driving.

CROSSING A CONTINENT

The insects leave Canada in September and arrive at their winter homes in Mexico around Nov. 2, the Day of the Dead. They fly about 2,500 miles, resting in trees by night. Some 40 million come to Santuario Rosario alone.

"They come here to die," Orosco says. The males live only 72 hours after mating. The females live on to lay eggs in the trunks and branches of oyamel fir trees in the mountains. A monarch butterfly's total life span is nine months at the longest.

In March, their offspring hatch and fly away toward Canada. Subsequent generations continue traveling north, reproducing and then dying; the process repeats several times along the way. Several generations later, new offspring reach Mexico.

One theory is that the butterflies navigate by smell, Orosco says. But no one really knows.

Blue-and-white signs showing the way to the santuario start to appear as we get closer. The streets narrow in the towns with their central cathedrals and white-walled buildings. Farmers, their hats hanging down their backs, trudge down the road, and skinny cows stare out at the cars.

Finally, we are in Angangueo. Every older woman is wrapped up in a rebozo (shawl) despite the unseasonably warm February weather. At the santuario, the whole enterprise looks a lot more touristy than I'd expected.

A STEEP CLIMB

Orosco immediately starts marching up the path, which is steep and lined with food vendors.

Butterflies have begun to drift down the mountainside, just a few here and there.

As the climb grows steeper, the crowd gets thicker, and so do the flocks of butterflies. We begin to see hundreds at a time.

They alight on bushes right beside us. Kids are kneeling beside a flock of them on a creek bed, giggling.

Orosco urges me to climb a little higher, where the colonies are easier to see.

They are not what I expected. Still distant, high up in the firs, they hang in clusters. They look like orangey infestations from here. Andres says the migration was viewed by the indigenous peoples of Mexico as a plague. The Spaniards, he says, thought the butterflies were people's souls.

We are ready to leave, and the butterflies soon will be, too. The monarchs make the long journey back to Canada in early March. They will repeat the cycle again, their internal road map still a mystery to us.