Of The Natural State’s many autumnal delights, perhaps the most anticipated is the annual changing of the foliage, when Arkansas’ mountains and forests come afire with a thousand shades of ochre. But before the trees don their fall colors, another metamorphosis wends its orange-winged way across Arkansas’ hills and fields: the annual migration of the eastern monarch butterfly. Early each October, from her home on Mount Magazine, Lori Spencer waits to glimpse some of the millions of monarchs that journey from Canada and the northern United States to central Mexico each year as they stop to munch on the goldenrods and asters that blanket the ridge.

“I love to see them coming up the side of the mountain,” says Spencer, an entomologist and author of Arkansas Butterflies and Moths, a comprehensive guide to the state’s Lepidoptera. It would be easy to imagine the migration appearing as an invasion in delicate miniature. But in speaking with Spencer, one gets the sense that catching sight of monarchs en route to Mexico is more akin to watching a meteor shower. “We try to count them as they fly by. It could be 10 per hour; it could be a hundred per hour—it depends on the conditions,” she says. “Sometimes, just as you’re ready to go inside, you’ll see 20.”

iStock_000062838646_LargeIf any of this strikes you as less than mystifying—birds migrate south and back every year, after all—consider these few facts: The monarch is the only butterfly known to migrate two ways, as birds do, and the monarchs that migrate to Mexico are the great- or even great-great-grandchildren of the last generation that was there. They are traveling to a place they have never been, with no living relatives to show them the way. How they manage this remains a mystery.

“[It’s] something scientists have been asking for over 50 years now,” Spencer says. “The fact that this butterfly, just this one butterfly, is the one that does all this. There are others that do migrate; they just don’t go to the same places, like the monarch does.”

Although there are other bands of monarchs that chart similar cross-country paths, those migrations aren’t anywhere as spectacular as the one Spencer witnesses each year in Arkansas. Western monarchs flit up and down the Pacific coast, while the Florida monarchs range all across the Atlantic side (some speculate they may even join up with their Eastern counterparts in Mexico). But even then, these other migrations pale in comparison when it comes to sheer numbers. Not to mention drama and mystery.

Every year, Spencer’s monarchs follow many of the same paths to Mexico, though they may get blown around a bit by the wind—something they take advantage of since a good wind could save them a lot of flapping energy, even though their wings are thick and adapted for a long flight. They flock to one of a dozen sanctuaries in the Sierra Madre Mountains and cluster together in the trees—often the same trees every year. “That’s part of what’s so fascinating,” she says. “How do you know where you’re going if you’ve never been there before? They’re not following a map.”

There are theories, as Dr. Ashley P.G. Dowling, an entomologist and associate professor at the University of Arkansas, explains. But those theories seem to raise more questions than they answer. “There was a study in which they painted the antennae of migrating monarchs black, and those butterflies were not able to orient themselves to travel south,” says Dowling. “They just got completely screwed up. Whereas the ones with a clear coat over the antennae had no trouble heading south along the correct path.”

One assumption about the monarch migration is that the angle of the sun has some influence on when and how they fly; though, Dowling says, “we typically don’t think of antennae as sensing light; it’s usually about picking up chemical smells and things like that.” Dowling says he doesn’t think there is a definitive, heavily tested hypothesis for how the butterflies find their way to the exact same places in Mexico every year. And yet, year after year, millions of them do.

Unsurprisingly, one of the best ways to see migrating monarchs is to put yourself where they like to be—namely, the buffet line at the local wildflower joint. “It’s kind of like exiting off the interstate,” Spencer explains. “When you’re going down the interstate and you’re hungry, what are you looking for? You’re looking for a billboard that advertises McDonald’s and Burger King.”

Milkweed and goldenrod may be the Big Mac and Whopper of monarchs, but any natural area with abundant wildflowers can attract them down for a refueling. “They’re tracking resources as they’re heading south,” Dowling says. You might even see them clustered in trees, roosting overnight before continuing on their journey.

On Mount Magazine, as well as the rest of the state, the peak time for the monarchs’ fall migration is late September through early October. But it’s also possible to catch them on their return trip, in the early spring. After spending the winter hibernating, conserving energy for the flight back, something signals the monarchs that it’s time to head north. “Once they get into the southern U.S., specifically Texas and Louisiana, that’s where they’re going to do their mating and breeding,” Dowling says. Successive generations will continue north throughout the spring and summer—stopping off in Arkansas in April and May to feed and perhaps lay eggs on their host plant, milkweed—until the migration south begins again in Canada in the fall.

“Most people see monarchs and don’t even know they’re migrating—they think of them as like every other butterfly,” Dowling says. “It’s a cool story, and from the scientific side of things, it’s cool that we still don’t have a good answer for it.”