Monarch butterfly population hits a new low

The number of monarch butterflies that migrates across the United States each year and overwinters in the forests of Mexico has dropped to an all-time low.  News out of Mexico this morning puts the population at 33.5 million individuals. Although the number of butterflies varies from year to year, this estimate is a precipitous drop from a high of 1 billion in 1997 and down from a long term average of 350 million over the last 15 years.  Furthermore, it represents the 9th consecutive yearly measurement below the long term average.  In other words, this year’s news follows a continuing downward trend. It signals a species in crisis. 


The decline of monarch butterflies over the last decade or more has coincided with the wide-scale adoption of genetically modified crops that are resistant to the weed-killer glyphosate, also known as Round Up.  This change in our agricultural system has led to the near extermination of milkweed from huge swaths of our country.  The problem is that monarch butterflies are dependent on milkweed.  It’s the only type of plant that they use for laying their eggs.

Since the introduction of genetically modified “Round Up Ready” corn and soybeans in the late 1990s their adoption level has reached between 70-90%.  As a result, the use of glyphosate in these crop fields skyrocketed.  Scientists now estimate that in the span of about 10 years (from 1999-2010) there has been 60% decline in milkweeds across the Midwest (in both agricultural and non-agricultural areas) and an 80% decline in monarchs in the Midwest.  Past studies have shown that monarchs from the Midwest comprise 50% of the overwintering population in Mexico. This explains why the loss of butterflies from a specific region could have such a large impact on the overall population size.  

There are, of course, other contributors to the monarch’s decline.  Drought, particularly in Texas, is believed to also be posing a threat to these butterflies as they try to make their way from Mexico across the US to Southern Canada and back in the span of a year.  Climate in general (including drought, but also extreme temperatures) is contributing.  And deforestation of their wintering habitat continues to be a concern.

However, given that the widespread adoption of “Round Up Ready” crops has largely eliminated the monarch’s most essential “habitat” by removing milkweeds from the landscape, it’s time to reconsider whether its continued large-scale use makes sense. Today’s news reminds us just what is at stake. Besides its beautiful appearance and usefulness as a pollinator, the monarch’s long-distance round-trip journey is unique in the insect world, a phenomenon that scientists still don’t fully understand.  If we continue blindly along this path, ignoring the unintended consequences of our actions, we risk losing the monarch’s migration – one of the true natural wonders of our planet.

If you’d like to help the monarchs by planting some milkweed, please visit our green gifts here.  

Photo credit: Image shared via Flickr by Mike Rodriguez

About the Authors

Sylvia Fallon

Director, Wildlife Conservation project

Join Us