Monach Butterfly
Monach Butterfly

Monarch Butterflies Have Declined 90%; Conservationists Seek Extra Protection

A Monarch butterfly sits on a bush at the Pedro Herrada butterfly sanctuary on a mountain in the Mexican state of Michoacan. REUTERS

In the last 20 years, the population of monarch butterflies in the eastern U.S. has declined by 90 percent, greatly worrying environmentalists and researchers. Today, three major conservation groups and a scientist have called on the Fish and Wildlife Service to designate the brilliant orange and black insects as threatened, a move that would provide federal officials with more latitude in efforts to preserve them like designating certain areas as protected.

“We’re at risk of losing a symbolic backyard beauty that has been part of the childhood of every generation of Americans,” said Tierra Curry, a senior scientist at the Center for Biological Diversity, one of the groups calling for the move, in a release. “The 90 percent drop in the monarch’s population is a loss so staggering that in human-population terms it would be like losing every living person in the United States except those in Florida and Ohio.

The Center for Food Safety and the Xerces Society, groups dedicated to sustainable food protection practices and insect preservation, respectively, are also asking the feds to act, as is famed monarch scientist Lincoln Brower.

The butterflies are disappearing in part due to a decline of habitat in the Midwest, specifically the loss of milkweed, the only plant upon which they lay eggs and their larvae feed.

Milkweed is a native plant that provides plenty of value to butterflies, wasps and bees, but is of little use to farmers. In the past, milkweed was spared because the herbicides used by farmers to keep crops healthy were used more sparingly—and in some cases, tilling machines were used to clear weeds.

But in recent years, with introduction of genetically-modified crops likeRoundup-ready corn and soybeans that are resistant to traditional herbicides, farmers have begun to spray more and more Roundup—the Monsanto-made chemical—over wider and wider areas.

This practice, as well as the cultivation of 1 million new acres of land in recent years, driven by higher corn and soybean prices, has destroyed milkweed crops, and greatly hurt monarchs, research shows.

Scientists and environmentalist have urged landowners—especially in the Midwest—to plant milkweed to help the monarch. Obviously participation is voluntary at this point. But if, for example, the U.S. Department of Agriculture offered incentives to farmers to plant milkweed, that could be a potential game-changer in the right direction.



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Monarchs in peril

Monarchs migrate up to 3,000 miles each fall to their wintering area in central Mexico. In the past few years citizen scientists have recorded a sharp drop in the number making the trip.

Map of monarch habitat


Although illegal deforestation and severe weather have contributed to the decline, research done by the World Wildlife Fund Mexico and theMonarch Butterfly Biosphere Reserve suggests that the overwhelming concern is U.S. farms’ large-scale use of herbicides that destroy milkweed. Further studies done by D. T. Tyler Flockhart, of the University of Guelph in Ontario, and his colleagues compared the relative effect of each threat and determined that loss of milkweed had the greatest impact on recent monarch declines.

Milkweed is the only plant on which monarch butterflies will lay their eggs, and it is the primary food source for monarch caterpillars. Despite its necessity to the species, the plant decreased 21 percent in the United States between 1995 and 2013. Scientists, conservationists, and butterfly enthusiasts are encouraging people to grow the plant in their own yards and gardens.

The butterflies’ life span is so short that those making the next migration to Mexico will be the great-grandchildren of the previous migrators. For this winged orange icon, survival is a group effort.








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Milkweed loss in agricultural fields because of herbicide use: effect on the monarch butterfly population

JOHN M. PLEASANTS, and KAREN S. OBERHAUSER, Department of Ecology, Evolution and Organismal Biology, Iowa State University, Ames, IA, USA and Department of Fisheries, Wildlife and Conservation Biology, University of Minnesota, St Paul, MN, USA

Abstract. 1. The size of the Mexican overwintering population of monarch butter- flies has decreased over the last decade. Approximately half of these butterflies come from the U.S. Midwest where larvae feed on common milkweed. There has been a large decline in milkweed in agricultural fields in the Midwest over the last decade. This loss is coincident with the increased use of glyphosate herbicide in conjunction with increased planting of genetically modified (GM) glyphosate-tolerant corn (maize) and soybeans (soya).

2. We investigate whether the decline in the size of the overwintering population can be attributed to a decline in monarch production owing to a loss of milkweeds in agricultural fields in the Midwest. We estimate Midwest annual monarch production using data on the number of monarch eggs per milkweed plant for milkweeds in different habitats, the density of milkweeds in different habitats, and the area occupied by those habitats on the landscape.

3. We estimate that there has been a 58% decline in milkweeds on the Midwest landscape and an 81% decline in monarch production in the Midwest from 1999 to 2010. Monarch production in the Midwest each year was positively correlated with the size of the subsequent overwintering population in Mexico. Taken together, these results strongly suggest that a loss of agricultural milkweeds is a major contributor to the decline in the monarch population.

4. The smaller monarch population size that has become the norm will make the species more vulnerable to other conservation threats. Key words. Glyphosate, GMO, milkweed, monarch butterfly

Key words. Glyphosate, GMO, milkweed, monarch butterfly