U of A faculty, students observe massive gathering of monarch butterflies in Mexico central mountainsJan. 12, 2009
Dr. Robert Wiedenmann, Head, Department of Entomology
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By Fred Miller, University of Arkansas Division of Agriculture
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Monarch butterflies cluster
FAYETTEVILLE, Ark. -- Recalling a mountaintop experience in central Mexico, Austin Jones said monarch butterflies, warmed by the early morning sun, rose up like a living wave through the treetops.
"You just look up, and there'd be all these butterflies going overhead, seemingly in all directions at once," Jones said. "They'd all be clustered in a tree, weighing down the branches, and then they'd reach some sort of critical temperature or something and they'd just explode into the air."
Jones, an entomology graduate student at the University of Arkansas, was part of a group of students, faculty and others from the U of A, the University of Kentucky and Illinois who spent a week in Mexico Dec. 30 to Jan. 5. They explored art and history in and around Mexico City and visited three mountain preserves set aside as protected overwintering grounds for monarch butterflies.
Robert Wiedenmann, head of the department of entomology in Dale Bumpers College of Agricultural, Food and Life Sciences at the U of A, led the tour, his third since 2005. The Arkansas group also included Tim Kring, professor of entomology, and his wife, Wendy; post-doctoral researcher Carolyn Lewis; and five graduate students, Jones, Sandra Sleezer and husband Rob, Josh Hannam and wife Holly, Ryan Allen and Ben Von Kanel.
Kring taught a fall semester graduate course about seasonal adaptations of insects, which included a good introduction to the migration and overwintering habits of the monarchs, Wiedenmann said.
Wiedenmann said nearly all the monarch butterflies east of the Rocky Mountains in the United States and Canada -- about three-quarters of the population in North America -- spend winter in the central mountains of Mexico. No one knows how many monarchs make the trip to Mexico, but Wiedenmann said the number has been estimated in past years at more than 100 million.
"It's one of the true biological spectacles of the world," Wiedenmann said.
Monarchs tagged as far north as Canada have been recorded as making the trip to about a dozen sites in the mountains around Angangueo, Mexico, a town of about 5,000 that served as the group's base of operations during their visit.
Over three days, they trekked 2 to 4 miles on foot or horseback to Cerro Pelón, elevation 9,500 feet, El Rosario, 10,500 feet, and Chincua, 11,000 feet. Arriving early each morning, the group not only beat the larger crowds that now visit these sites, but also witnessed the "waking" of the butterflies that Jones described.
"Pictures don't do it justice," Jones said. "Being there, surrounded by the sound of butterfly wings, of enough butterflies to repopulate an entire continent -- it's pretty awe-inspiring."
Wiedenmann said the monarchs suspend their reproduction cycle during the migration and winter stay in Mexico. "They redirect all their energy to the trip and surviving the winter," he said. Because the monarchs do not breed during the winter, the generation that makes the trip to Mexico is the same that begins the return migration to the U.S. and Canada.
The butterflies resume reproduction during the return trip in the spring. Wiedenmann said monarchs go through five to six generations a year, beginning with one generation during the northward migration and a couple more during the summer. The last of these generations then undertakes the migration to Mexico in the fall, heading to the very same wintering grounds that their ancestors left four or five generations earlier.
"How do they know where to go?" Wiedenmann asked. It remains one of the many mysteries of the monarch migration, he said.
"The northward migration lasts longer than the southward one because they are breeding along the way and following the growing season of milkweed, the exclusive food source for immature monarchs," Wiedenmann said.
Grad student Sandra Sleezer said the monarchs were almost magical creatures.
"It was a pretty surreal experience," she said. "It's like being surrounded by animated confetti that never stops."
Sleezer said the sheer numbers of monarchs that gather in the trees is astounding. "It's incredible that enough butterflies can gather to weigh down the branches," she said. "Each one is so light and delicate."
"It's something I'll never forget," Sleezer said. "If I just heard about it in class, I'd think, 'that's interesting,' and move on. But being there -- it's an incredible experience."