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The disappearance of the monarch butterfly
The number of monarch butterflies that have migrated from the United States to the forest covered peaks of the Sierra Madre in Mexico has continued to decline this year. In December 2013 only 35 million individuals of the most popular butterfly in the whole of North America migrated, coming to inhabit 6,700 square metres of
The number of monarch butterflies that have migrated from the United States to the forest covered peaks of the Sierra Madre in Mexico has continued to decline this year. In December 2013 only 35 million individuals of the most popular butterfly in the whole of North America migrated, coming to inhabit 6,700 square metres of forest according to the Mexican government and the WWF. To get a feel for the size of this area note that a football field covers 7,000 square metres.
This is the smallest surface area on record, a ways away from the 1996 record when the butterflies coloured a surface of over 182,000 square metres.
The decline of the species has been on course for years, yet according to Karen Oberhauser of the University of Minnesota, who has been studying monarch butterflies for decades, this is the third consecutive year that there has been such a drastic free fall, constituting a frightening phenomenon. According to Oberhauser, the very act of migration of these animals is at risk.
The causes of the decline
The shrinking monarch butterfly population is in part attributable to a couple of seasons of bad weather, especially in Texas. But the principle cause behind it is the agricultural boom that has affected tens of thousands of hectares of the Midwestern United States.
This thesis is supported by evidence presented in the Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population study conducted by Oberhauser and John Pleasants of the Department of Ecology of Iowa State University. Cultivation of corn and soy has increased exponentially especially following the growth in demand for biofuels.
The explosion in their use has brought to an increase in the use of herbicides, in particular Monsanto’s agro pharmaceutical Roundup, which is sprayed directly onto the leaves of genetically modified plants. In 2013 82% of corn and 93% of GM soy cultivated in the US (almost 63 million hectares) were treated with this herbicide, which destroys a specific type of grass known as milkweed that is the only kind that monarch butterfly larvae will eat.
Nothing is coincidental, then: “We have this smoking gun. This is the only thing that we’ve actually been able to correlate with decreasing monarch numbers,” Oberhauser said. Though the data is alarming, all is not lost. Hopefully the weather conditions of the next Texan spring will be more favourable, and conservation organisations will take an interest in the problem and fight for the creation of herbicide-free areas where every type of grass is allowed to grow.
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