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2018's Favorable Weather for Eastern Monarchs Leads to Rise in Population

January 30, 2019
Center for Food Safety

2018's Favorable Weather for Eastern Monarchs Leads to Rise in Population

Beleaguered Butterfly Still at Serious Risk of Extinction

WASHINGTON, D.C. â?? The yearly count of monarch butterflies overwintering in Mexico, released today, shows an increase of 144 percent from last year's count. That's good news for a species whose numbers have fallen in recent years, but conservationists say the monarch continues to need Endangered Species Act protection.

Today's count of 6.05 hectares of occupied forest is up from 2.48 hectares last winter. The increase is attributable to favorable weather during the spring and summer breeding seasons and during the fall migration. Monarchs have lost an estimated 165 million acres of breeding habitat in the United States to herbicide spraying and development.

"While an increase is better than a decrease, the overall quarter-century trend in the monarch population is still one of steep decline," said Bill Freese, science policy analyst at Center for Food Safety. "The point here is that one good weather year won't save the monarch in the long run, and more protections are needed for this migratory wonder and its summer and winter habitats."

In 2014 conservationists, led by the Center for Biological Diversity and Center for Food Safety, petitioned the U.S. Fish and Wildlife Service to protect the butterfly under the Endangered Species Act. The Fish and Wildlife Service's initial decision was that endangered species protection may be warranted, and a final decision will be issued by June.

"The question is whether the Trump administration wants to do Monsanto's bidding or protect monarchs for future generations," said George Kimbrell, legal director of Center for Food Safety. "This year's count is a temporary reprieve that doesn't change what the law and science demands, which is that we protect monarchs under the Endangered Species Act before it's too late."

As recently as the mid-1990s, monarchs covered nearly 18 hectares of forest in their wintering ground. The population has declined steeply since then, despite fluctuations from year to year. In 2016, U.S. government scientists estimated an 11% to 57% chance that monarchs as a migratory species east of the Rockies will go extinct over the next 20 years.

About 99 percent of all North American monarchs migrate each winter to oyamel fir forests on 12 mountaintops in central Mexico. Scientists from World Wildlife Fund Mexico estimate the population size by measuring the area of trees turned orange by the clustering butterflies.

Monarch butterflies west of the Rocky Mountains overwinter on the coast of California. Their numbers dropped to fewer than 30,000 this year, down from 1.2 million two decades ago.

A recent study found that if current trends continue, the western population has a 63 percent chance of extinction in 20 years and more than an 80 percent chance of extinction within 50 years. The western population is now at the threshold of extinction.

The caterpillars only eat milkweed, but the plant has been devastated by increased spraying of the herbicide glyphosate in conjunction with corn and soybean crops that have been genetically engineered to tolerate direct spraying with it. In addition to glyphosate, monarchs are threatened by other herbicides and by neonicotinoid insecticides that are toxic to young caterpillars.

Climate change also threatens to disrupt the monarch's migration and render its overwintering habitats unsuitable by the end of the century.


Center for Food Safety's mission is to empower people, support farmers, and protect the earth from the harmful impacts of industrial agriculture. Through groundbreaking legal, scientific, and grassroots action, we protect and promote your right to safe food and the environment.

The Center for Biological Diversity is a national, nonprofit conservation organization with more than 1.4 million members and online activists dedicated to the protection of endangered species and wild places.

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