March 30, 2010
By Elizabeth Weise
USA Today
This year may be one of the worst on record for the beleaguered monarch butterfly, experts say.
Photo: Monarch butterflies migrate to Mexico every fall. (By Chip Taylor, Science)
Massive hailstorms that dropped 2 inches of ice on the trees where the orange-and-black-winged butterflies spend the winter in Mexico, followed by 15 inches of rain, could mean that as many as 50% were killed this year.
"My fear is that the number was much higher than that," says Chip Taylor, a professor of entomology and director of Monarch Watch at the University of Kansas-Lawrence. "And that's from a population that was pretty small to begin with." He believes it may take several years for the population to recover.
The area northwest of Mexico City where the winged creatures gather was hit hard by the severe weather. "Fifty people died in the area," Taylor says.
Says Lincoln Brower, a zoologist and monarch specialist at Sweet Briar College in Virginia, "I was down there about 10 days ago, and things are in pretty bad shape."
The monarch population is typically measured by the number of acres of pine trees the butterflies fill. This year, scientists found the smallest area of monarchs overwintering in the 16 years they have been looking — down to 4.7 acres from an average of 18.3 acres, Taylor says.
Brower inspected one of the principal colonies, which had been 1.2 acres in size. "All we found was two trees with butterflies in them."
Each female flies 1,000 miles or more on her way north from Mexico, depositing her eggs along the way only on milkweed leaves. She dies, but her eggs hatch and her offspring continue the migration.
It can take three to four generations for the monarchs to reach Canada, Taylor says. Then in the fall, that final generation begins its migration back to Mexico, and those butterflies live for eight months.
"It's one of the mysteries scientists are still working on," says Craig Wilson, a butterfly follower and science educator at Texas A&M University in College Station.
Monarch populations have fallen dramatically because of three things, says Brower, one of the world experts on the species:
- Illegal logging in Mexico has destroyed the butterflies' mountain habitats.
- Climate change is causing severe weather.
- There has been a significant increase in the planting of corn and soybeans in the Midwest genetically engineered to be herbicide-resistant. That allows farmers to spray weed killer without hurting the crops, but it has meant almost no milkweed survive in the fields.
"They've literally eliminated 100% of the milkweed of what once was prime breeding habitat of the butterflies," Brower says.
Monarch Watch has begun a milkweed-planting campaign to encourage the creation of monarch way stations across the nation.
Monarchs are beautiful, but creating habitats where they can thrive also benefits humans, Taylor says. Those habitats also "protect other insects, the little guys whose life's work is to pollinate our nuts, our fruits and our vegetables."
http://www.usatoday.com/tech/science/environment/2010-03-30-Monarchs30_ST_N.htm