Butterfly migration takes a surprising twist

Robert Michael Pyle will always remember an amazing sight on the Bonneville Salt Flats: a flock of monarch butterflies rising above one of the most inhospitable regions on Earth.

Pyle, a biologist and renowned butterfly expert, will give a free public lecture on monarchs starting at 2 p.m. Saturday at the Patagonia Outlet, 2292 Highland Drive. A resident of Washington state, he is the author of "The Audubon Society Handbook for Butterfly Watchers" and other works on these surprising insects.

The lecture, illustrated by slides, is sponsored by the Utah Museum of Natural History, Utah Lepidopterists' Society and Patagonia Outlet.

The large butterflies, which are orange, yellow and black, are famous for their yearly migration of thousands of miles. They are found throughout much of North America and go to Mexico or California for the winter.

Until recently, biologists subscribed to the idea that Eastern monarchs wintered over in the mountains near Mexico City while those from the West traveled to California.

"I call it the Berlin Wall model of butterflies, with the Rocky Mountains separating the Eastern and Western monarchs," Pyle said in a telephone interview. "All the (migration) maps were drawn that way, with a great line down the Rockies showing East, West, with these two different destinations."

Eastern monarchs do fly into Mexico — but the flight patterns of the Westerners, including those that visit Utah, turned out to be more complex, he discovered.

Monarchs usually leave their summer homes around the end of August or early September. Millions show up in the mountains west of Mexico City in November, "and they stay there all winter." Others go to the California coastal "fog belt . . . where they can remain torpid all winter and conserve their energy" before flying back in the spring.

The monarchs that start out aren't the ones that return.

Butterflies mate on the spring migration, "lay their eggs, then they die, and it's their offspring that continue on their way north," he said. Monarchs flying into Utah "are probably the great-great-grandchildren of the ones that left the previous autumn."

Pyle was determined to find out the details of the migration by following them in person.