Scientists have figured out for the first time how the monarch butterfly uses an intricate interplay of its internal body clock and the sun to guide its extraordinary annual pilgrimage from eastern and midwestern North America to its tiny winter home in the pine woods of central Mexico.

Researchers said yesterday that the monarchs -- the orange-colored denizens of summer gardens all over the United States -- use their body clocks to orient themselves in a southwesterly direction as they fly toward Mexico, guided by the position of the sun as it moves across the autumn sky.

The researchers also found that the sun's ultraviolet light is important, perhaps crucial, in stimulating the butterflies to begin their trip south, but that it has no apparent affect on the functioning of the insects' body clocks.

The analysis breaks new ground in highlighting the possibly crucial role that biological rhythms play in the migratory process, but it still does not explain other important aspects of one of animal biology's most unusual phenomena.

University of Kansas entomologist Orley "Chip" Taylor explained that the monarchs are tropical insects that have evolved in such a way that they emigrate every spring from a 30-acre stand of mountain pines in the Mexican state of Michoacan, west of Mexico City, to populate back yards as far north as Winnipeg, Canada.

Full Article:
Washington Post