Monarch Butterflies

Monarch butterflies (Danaus plexippus) of North America are renowned for their long-distance seasonal migration and spectacular winter gatherings in Mexico and California. The monarch butterfly population has recently declined to dangerously low levels. In the 1990s, estimates of up to one billion monarchs made the epic flight each fall from the northern plains of the U.S. and Canada to sites in the oyamel fir forests north of Mexico City, and more than one million monarchs overwintered in forested groves on the California Coast. Now, researchers and citizen scientists estimate the only a fraction of the population remains, a decline of more than 80% has been seen in central Mexico and a decline of 74% has been seen in coastal California.

WMTC 1997-2015 data


Area occupied by monarchs in Mexico from 1994-2015 (left) and population censuses of western monarchs from 1997-2015 (right). Click to enlarge.


To conserve this animal and its habitat, Xerces works with multiple partners across North America. We believe that by working broadly with multiple stakeholders, we are well-positioned to truly recover these butterflies. See The Xerces Society’s Partnerships for Monarchs for a summary of our recent efforts and ongoing partnerships.

Nationally, Xerces is working to restore monarch breeding habitat through Project Milkweed. Our partnership with the USDA NRCS, has resulted in planting more than 120,000 acres of habitat for monarchs and other pollinators, including tens of thousands of diverse wildflower plantings that include milkweed. We are also working to increase the availability of native seed and to make it less expensive to use in restoration activities.

In the western U.S., Xerces is working to identify, understand, and protect monarch overwintering and breeding habitat. In partnership with the Monarch Joint Venture, we have monitored more than 140 California overwintering sites, trained volunteers to monitor many more as part of the Western Monarch Thanksgiving Count, and created a database of all California overwintering sites that allows us to better understand the status of western monarchs and how pending development projects will affect them. Working with land managers and herbaria, we created a database of more than 25,000 milkweed and monarch breeding locations in eleven western states, to work toward identifying and conserving important monarch breeding areas.

North American Monarch Migration Map

Xerces monarch migration map
Xerces’ monarch migration map shows the principle migration routes, spring and summer breeding areas, and overwintering locations for monarch butterflies in North America. If you require a high-resolution file, please contact us at
The primary threats to the monarch butterfly include the loss of milkweed—the key plant that monarch caterpillars need to survive—from agricultural and natural areas, degradation of overwintering sites, and climate change. The large-scale use of systemic insecticides such as neonicotinoids within the breeding range of the monarch may pose a considerable threat. Natural enemies such as diseases, predators, and parasites likely also influence the size of the monarch population. Loss of milkweed from the American Midwest is primarily due to the dramatic increase in the use of the herbicide Roundup™ (glyphosate), made possible by the mass-planting of Genetically Modified Herbicide Tolerant corn and soy. Illegal logging has threatened overwintering sites in Mexico, and in California, numerous sites have been logged and replaced with housing developments. Extreme weather events may be negatively impacting monarchs in the eastern U.S. and low monarch populations in California are correlated with years of intense drought. Climate change models predict that future climate scenarios will not be suitable to support overwintering monarchs or the oyamel fir trees that they use in Mexico.
What You Can Do to Help Monarchs Recover
  • Plant native milkweed and nectar plants. Find sources of local, native milkweed seed in your state using our Milkweed Seed Finder.
  • Learn more about growing milkweeds on our Project Milkweed page.
  • Avoid using insecticides and herbicides.
  • Support agriculture that is organic or free of Genetically Modified ingredients.
  • Become a citizen scientist and contribute to research efforts to track the monarch population in its breeding and overwintering range.
  • Support the Xerces Society’s monarch conservation efforts.


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Program Features
Program Highlights
  • • The Xerces Society has awarded two $3,750 Joan M. DeWind awards for research into lepidoptera conservation
  • Butterfly-a-thon pledges raise $30 per species that Bob Pyle observes for butterfly conservation work
Additional Information