Monarch butterflies (Danaus plexippus plexippus) are perhaps the most well-known and beloved butterfly species in North America. Their renowned long-distance, seasonal migration and spectacular winter gatherings in Mexico and California have heralded the transition from fall to winter for thousands of years. Monarchs are also culturally significant; they symbolize the returning spirits of the deceased in the November celebration of Dia de los Muertos.
Throughout the northern states and Canadian provinces, meanwhile, their arrival announces the change from spring to summer. A once-ubiquitous sight in gardens, prairies, and natural areas from coast to coast, the monarch butterfly population has recently declined to dangerously low levels on both coasts—but particularly in the west.
An Epic Migration on the Verge of Collapse
Both the eastern and western migrations have experienced significant decline in a matter of decades. In the 1990s, nearly 700 million 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. Now, researchers and citizen scientists estimate that there has been a decline of more than 80% in the east. In the west, the news is more dire. Monarchs have experienced a decline of 99.4% in coastal California, from an estimated 4.5 million in the 1980s to 28,429 as of January 2019.
Monarchs require suitable habitat that provides host plants for breeding and flowering plants to provide nectar for adults. In the case of monarchs, the loss of milkweed means the loss of breeding habitat. Loss of milkweed from prime migration routes is primarily due to the dramatic increase in the use of the herbicide resistant crops Commonly known as Roundup™ Ready Crops, these corn and soy crops are genetically modified to be resistant to glyphosate, a broad-spectrum herbicide that kills everything other than the resistant crop, including milkweed. Harsher winters in monarch overwintering sites have caused larger than usual die-offs. Erratic weather may also delay the emergence of milkweed in spring and change the bloom time of flowering plants that provide resources to migrating monarchs. Legal and illegal logging in the oyamel fir forests of Mexico where eastern monarchs overwinter has removed important winter cover for the species and impacted microclimates that protect the butterflies from extreme cold and precipitation. In California, many sites where western monarchs overwinter have been lost due to development.
In the three decades since first standing up for monarchs, the Xerces Society has gained extensive experience and accumulated expertise in all aspects of monarch conservation. Our work now extends to protecting and managing the habitats that support all stages of the monarch’s lifecycle throughout the transcontinental range of the butterfly’s migration.
Monarchs in the West
In January 2019, the Xerces Society released a call to action for addressing significant declines in the western monarch population. The California overwintering population has experienced a 99.4% decline since the 1980s, dropping from a population of 4.5 million (larger than the current population of Los Angeles) to a population of 28,429 as of January 2019 (smaller than the current population of Monterey). The Xerces Society has been working to ensure that the western monarch population is included in monarch conservation efforts. Xerces has been working on many fronts, holding workshops to assist land managers in identifying monarch conservation needs, training biologists and volunteers to conduct surveys for milkweed breeding habitat, and developing citizen science programs and tools to better address conservation issues specific to western monarchs. We are redoubling these efforts, and invite you to learn how you can help. Visit our Save Western Monarchs page for more information.
Project Milkweed and Milkweed Seed Finder
Monarchs need milkweed! Locate seed and/or plant vendors near you using our Milkweed Seed Finder. Learn more.
Monarch Nectar Plant Guides
- Managing Monarchs in the West: Best Management Practices for Conserving the Monarch Butterfly and its Habitat
- Native Milkweed in California: Planting and Establishment
- Conservation Status and Ecology of the Monarch Butterfly in the United States
- State of the Monarch Butterfly Overwintering Sites in California
- Protecting California’s Butterfly Groves: Management Guidelines for Monarch Butterfly Overwintering Habitat
- July 2016 Monarch Update: Helping Monarch Conservation Take Flight
- Petition for Protection of the Monarch Butterfly Under the Endangered Species Act
- Joint Statement Regarding Captive Breeding and Releasing of Monarchs
- Milkweeds and Monarchs in the Western U.S.
- Report: Monarch Butterfly Site Management Plan for Lighthouse Field State Beach
Partners and Sponsors
The Xerces Society’s work to protect monarch butterflies and other pollinators has been made possible with generous support from the Alice C. Tyler Perpetual Trust, Audrey & J.J. Martindale Foundation, Aveda, Cascadian Farm, Ceres Trust, Cheerios, Clif Bar Family Foundation, CS Fund, Disney Conservation Fund, Endangered Species Chocolate, LLC, Gaia Fund, General Mills, Hind Foundation, Idaho Department of Fish and Game, Iowa Department of Transportation’s Living Roadway Trust Fund, Irwin Andrew Porter Foundation, J.Crew, National Co+op Grocers, National Fish and Wildlife Foundation, Nature Valley, Nestlé Dreyer’s Ice Cream Company, Sarah K. de Coizart Article TENTH Perpetual Charitable Trust, SeaWorld & Busch Gardens Conservation Fund, Swimmer Family Foundation, The Bay and Paul Foundations, The Dudley Foundation, The Edward Gorey Charitable Trust, The Elizabeth Ordway Dunn Foundation, The Monarch Joint Venture, The New-Land Foundation, Inc., The Oregon Zoo Foundation, The White Pine Fund, Turner Foundation, Inc., U.S. Department of Agriculture Natural Resources Conservation Service, U.S. Department of Agriculture Sustainable Agriculture Research and Education, U.S. Department of the Interior Fish and Wildlife Service, U.S. Geological Survey, Whole Foods Market and its vendors, the Whole Systems Foundation, and Xerces Society members.