Blizzard of life
U of A faculty, students observe massive winter gathering of monarch butterflies in Mexico’s central mountainsJan. 18, 2007
Dr. Robert Wiedenmann, Head, Department of Entomology
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By Fred Miller, University of Arkansas Division of Agriculture
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FAYETTEVILLE, Ark. — Standing in the midst of swarming monarch butterflies, high in the central volcanic mountains of Mexico, Robert Wiedenmann said he felt like he was in a blizzard.
“But the snowflakes were four inches across and black and orange,” Wiedenmann said. “It was nearly disorienting because of the sheer numbers flying by and hitting you in the face and mouth.”
Wiedenmann, head of the entomology department of the University of Arkansas Division of Agriculture and Dale Bumpers College of Agricultural, Food and Life Sciences, with colleagues from Purdue University, the University of Kentucky and the Illinois Natural History Survey, led a group of entomology graduate students Jan. 3-7 to two mountain preserves where millions of monarchs from the U.S. and Canada spend the winter.
The butterfly preserves are near Angangueo in the state of Michoacan, about 150 miles west of Mexico City. The group visited the Chincua preserve, located at an elevation of about 11,000 feet, and El Rosario, between 12,000 and 13,000 feet.
The U of A entomology students were Craig Shelton of Lonoke; Jackie McKern of Mount George; Stephanie Hebert of Rayne, La.; Becky Trout of Lexington, Ky.; Robin Verble of Evansville, Ill.; Tara Wood of East Peoria, Ill.; and John Riggins of Riverton, Neb.
Luis Rodriguez, a colleague from Mexico, and his 9-year-old son, Damian, joined the U of A group. Rodriguez is a researcher with the Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias, Mexico’s equivalent to the USDA Agricultural Research Service.
“It was like a circus,” Wiedenmann said. “But I liked the large, diverse group.”
Chincua and El Rosario are two of only a handful of Mexican preserves set aside for the protection of over-wintering monarchs, Wiedenmann said.
“All monarchs east of the Rocky Mountains, about three-quarters of the population in North America, migrate to these mountains every winter,” Wiedenmann said. “It’s one of the true biological spectacles of the world.”
Pinning down a number for how many monarchs migrate to Mexico is difficult, though the number is likely more than 100 million, Wiedenmann said. Monarchs tagged as far north as Minnesota and parts of Canada have been recorded as making the trip to the mountains around Anquangueo.
Wiedenmann said no other butterflies have migrations on this scale.
“The monarchs cluster overnight high in the trees,” Wiedenmann said. “When the morning sun warms them sufficiently, they ‘explode’ out of the trees and fly down slope to feeding areas.”
“The sound of their wings was heard even above our conversations,” he said. “It was almost like hearing the wind through the trees, but there was no wind.”
One of the most interesting things about the annual migration is that the monarchs in Mexico now have never been there before. Monarchs go through five to six generations a year.
“The monarchs that over-winter in Mexico go through one generation during their northward migration in the spring,” Wiedenmann said. There are a couple more generations in the life cycle over summer, but then the butterflies make the southward migration to Mexico in the lifespan of a single generation, typically returning to the very same trees as their ancestors.
“How do they know where to go?” Wiedenmann asked. It remains one of the many mysteries of the monarch migration, 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 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.
Wiedenmann went to the same area two years ago with a group of entomology department heads from several other institutions. The January excursion was an exploratory tour aimed at making it an annual trip with faculty and students from multiple institutions. Wiedenmann plans to develop a companion short course for credit.
“A trip like this lets the students see this amazing natural event and, at the same time, experience a culture very different from their own,” Wiedenmann said.