Seen a little zigzaggy orange and black critter fluttering by lately? An extraordinary migration is occurring in northern Virginia this month, as monarch butterflies (Danaus plexippus), wend their way to Mexico to join millions more and hang snugly together like little gray beards on oyamel fir trees at 9,000 to 11,000 feet all winter.
“This is one of the most extraordinary annual migrations on our planet,” says monarch expert Dr. Lincoln Brower of Sweet Briar College. “This amazing migration eludes explanation.”
The monarch, weighing one-fifth the weight of a penny, is the only butterfly to regularly undertake a two-way migration. Some monarchs, the ones that start in Canada, make a 3,000-mile trip. If a six-foot person made the equivalent journey, it would be 11 times around the world, estimates Dr. David Gibo, a Toronto zoologist. The eastern population, east of the Rocky Mountains, winters in Mexico; the western population in California.
Monarchs got their name from English colonists in the 17th century because
the insect’s bright orange and black hues reminded them of British royalty, the prince of Orange, later King William III.
Every September and October, Burke resident Larry Brindza spends several hours a day studying monarchs passing through the Occoquan Bay National Wildlife Refuge in northern Prince William County. He scans fields
of goldenrod, tickweed sunflowers, snake root and Joe Pye weed and snags
unsuspecting monarchs with the deft swoosh of his net. When they are abundant, he can catch almost one a minute.
Working from what he calls his “laboratory” in the back of his Volvo, he takes measurements and with surgical forceps, meticulously attaches a tiny sticker weighing one one-hundreth of a gram to the underside of the left-hind wing. The tiny polypropylene plastic sticker is a self-adhesive made by 3M especially for Monarch Watch, a Kansas-based advocacy group.
Brindza hopes someone will find and report these tagged butterflies so experts can track their routes and survival. His recovery rate of monarchs tagged at the refuge and found in Mexico is .002 percent. He works also on the Eastern Shore and had 10 recoveries between 2004 and 2012 or a recovery rate of .003 percent. “The first one recovered was like winning the lottery. I was tickled pink,” he replied, when asked what inspires him, given such a low recovery rate.
Scientists say that counting individual monarchs is nearly impossible because they clump together so closely in winter, so observers estimate the size of the population by measuring the area of the forest occupied by overwintering monarchs.
Monarchs covered over 20 hectares in Mexico (a hectare is 2.47 acres) in 1996-1997. In the winter of 2011-2012, they covered only 2.89 hectares. According to Brower, “The 2011-2012 overwintering season in Mexico had the third-lowest numbers in over 18 years. The best estimate is that this is about 40 million monarchs.” Experts expect the 2011-2012 numbers to be
low as well.
The monarch migration is an “endangered phenomenon,” says Brower. In this country, pesticides, herbicides and development are destroying breeding habitat and milkweed plants. Monarch habitat disappears at 6,000 acres a day and overuse of herbicides along highways and elsewhere is creating grassy areas that support few species, contends Chip Taylor, director of Monarch Watch.
An added stressor is that in Mexico, clear-cutting of oyamel trees for lumber destroys the butterflies’ roosts and removes protection and warmth. “The Mexican government has made strides in stopping the massive illegal logging,” says Brower, “but there is still substantial and damaging logging occurring on a smaller scale that must be stopped.”
The Monarch Cycle
In late summer, the monarch larvae or caterpillars fatten up on common milkweed (Asclepias syriaca), transform into a chrysalis and then into an adult butterfly. The ingested milkweed sap offers protection from predators because it is poisonous to small vertebrates, like birds that are repulsed by the taste and toxicity.
When spring temperatures rise in Mexico and nectar sources become available, monarchs mate, head north and females lay eggs. The eggs become adults and this new generation flies north.
How to Help
Support Monarch Watch, http://www.monarchwatch.org/.
Plant common milkweed. You can buy seeds from Monarch Watch.
Plant nectar plants to provide food for adult monarchs.
Create a monarch waystation, http://www.monarchwatch.org/waystations/.
Support the National Wildlife Refuge system and other natural areas. For information on Occoquan Bay refuge, visit