Monarch Butterfly Numbers Fall Again

Monarch Butterfly


The annual measurement of the eastern monarch butterfly population that overwinters in Mexico is reported to be 2.83 hectares this year. That is a 53% decrease from last year’s more robust population of 6.05 hectares. After a hopeful increase the year before, this year’s estimate is big disappointment as the population once again falls well below a sustainable, secure level.

The eastern population of monarch butterflies migrates every year from the oyamel forests of Mexico across the central and eastern United States up to Canada and then back again—spanning several generations along the way. At each point along their route, the monarch butterflies need to encounter milkweed for laying eggs. They also need to feed at an abundance of nectar-producing plants to fuel their long journey. Over the last several decades, there has been a drastic decline in milkweed—the monarch caterpillar’s only food source—due to the broadscale use of the herbicide glyphosate (commonly known as Roundup) in connection with genetically engineered crops. The losses are particularly bad in the “corn belt” region of the U.S., located in the Midwest, which is a breeding hotspot for monarchs. With the loss of milkweed and other pollinator habitat, there has been a corresponding decline in the monarch butterfly population.

This year’s population decrease is likely due to a combination of factors from drought in Texas to specific weather patterns at critical points of the population’s journey to the overall availability of milkweed and other nectar sources. While a lot of different organizations, agencies, schools and individuals are hard at work to get more milkweed on the ground, the agricultural landscape continues to be intensively managed with pesticides. These pesticides include herbicides like glyphosate, 2-4D, and Dicamba, which destroy habitat, and insecticides like the now infamous neonicotinoids or “neonics,” which directly harm or kill monarchs as well as bees and other native pollinators. And EPA continues to greenlight these destructive pesticides even as their impacts on pollinators as well as human health become increasingly apparent.

In addition to creating more habitat for monarchs, we need to shift our agricultural practices away from the pesticide-intensive practices that have become the norm for “conventional” farming and back to a more sustainable and holistic approach to pest management, such as the use of diversified crop rotations, cover crops, and innovative approaches like the integration of native prairie into agricultural fields.

NRDC is fighting at both ends of this problem—we are in court challenging EPA’s approval of pollinator-harming pesticides like Enlist Duo and neonics, and we are facilitating the adoption of cover crops, prairie strips, and other practices that are slowly being embraced by a growing “regenerative agriculture” movement.

This transition cannot come more quickly. As spring emerges, monarch butterflies are beginning to make their journey north again. Will they encounter enough milkweed to boost their population numbers? Will they find a patch of prairie to fuel their flight back south? Or will the population continue to fall below sustainable levels?

About the Authors

Sylvia Fallon

Senior Director, Science Integration, Science Office

Join Us

When you sign up you'll become a member of NRDC's Activist Network. We will keep you informed with the latest alerts and progress reports.