Published in the November 2014 issues of National Geographic magazine
Fewer monarch butterflies are crossing North America to winter in Mexico, says the World Wildlife Fund Mexico. In 2004 an estimated 550 million completed the winter migration; last season an estimated 33 million made it, according to the fund’s count. Although illegal deforestation and severe weather contributed to the decline, recent research suggests that the biggest culprit is farms’ large-scale use of herbicides that destroy milkweed. Monarch caterpillars need to feed on the plant—but it decreased 21 percent in the United States between 1995 and 2013. That doesn’t bode well for the butterflies, whose life span is so short that those making the next migration will be the great-grandchildren of the previous migrators. For this winged orange icon, survival is a group effort.
—Lindsay N. Smith