It may not be breaking news that monarch butterflies are in decline, but the most recent population figures for this beautiful butterfly are especially alarming, according to an article in the New York Times. The results of a survey done in December 2012 by Mexico's National Commission of Natural Protected Areas, in partnership with the World Wildlife Fund (WWF) and the Mexican cell phone company Telcel, showed a steep drop in the number of monarchs that completed their annual migration to their wintering grounds in the Mexican forest. Where these insects once covered as many as 50 acres of forest, last year they were down to a mere 2.94 acres, a 59 percent decline from the size of the overwintering grounds just a year previous. (Because it is impossible to count the number of individual butterflies, the acreage of forest they cover is used to approximate their population levels.)
According to Omar Vidal, the head the WWF's Mexican operation, there has been a steady decline in monarch numbers over the last seven to eight years. While last year's drought and record-breaking heat in North America is thought to have contributed to this past year's drop, habitat loss is an important underlying and ongoing factor in the monarchs' decline. There has been a rapid expansion of farmland in the U.S.in recent years, with much of this acreage planted to herbicide-resistant soybeans and corn. This has resulted in more herbicide use, which in turn means less milkweed in the fields. Monarch caterpillars feed exclusively on milkweed, and without this food source they can't reproduce. It's estimated that close to 150 million acres of monarch habitat have been lost as a result of these farming changes.
To read more about the monarch population decline, go to New York Times.