The iconic black and orange monarch butterfly is known for its astonishing long-distance annual migration and reliance on milkweed (Asclepias spp.) as its obligate larval host plant. Though genetically similar, there are two subpopulations of monarchs in North America, with the eastern population overwintering in Mexico and breeding in the midwestern states, and the western population overwintering in coastal California and fanning out across the west from Arizona to Idaho to breed. Outside the U.S., there are at least 74 known populations of resident, non-migratory monarchs that have established around the world in the past 200 years, all with origins from the North American populations (Nial et al. 2019).
Both North American migratory populations have declined over the past twenty years due to a suite of interrelated factors including habitat loss in breeding and overwintering sites, habitat degradation, disease, pesticide exposure, and climate change. The western population has experienced dramatic swings, including a low of less than 2,000 individuals counted at overwintering sites in 2020-21 to over 300,000 in 2022-23 (Xerces Society Western Monarch Count).
While the key factors driving these dynamics remain unclear, insect populations commonly fluctuate from year to year. The overall downward trend remains concerning, particularly if the threats are not ameliorated. Though more research is needed, a stable population for western monarchs is likely closer to the historic averages in the 1980's, which are estimated to have ranged between one to four million overwintering butterflies.
Conservation Status of Monarch Butterflies
In 2014, monarchs were petitioned to be listed under the federal Endangered Species Act (ESA). In December 2020, the U.S. Fish and Wildlife Service (Service) found that listing was warranted but precluded by other listing actions on its National Priority List. On December 12, 2024, the Service proposed listing the monarch as threatened with a 4(d) rule and designated critical habitat in California in the western population's overwintering range. The Service will accept public comments on the proposal through March 12, 2025. They will then evaluate comments and any additional information on the species and determine whether the monarch butterfly should be listed. You can learn more about the federal ESA listing process here.
WWW also participates in Multi-agency Monarch and Pollinator Collaborative, a group of state and federal agencies working to identify and enact shared priorities to catalyze monarch conservation in the state. Learn more about the group and access compiled resources at the Collaborative's website.
Since 2019 we have engaged in a plant materials working group with the Monarch Watch focused on developing sources of early-season milkweed for restoration projects. The group currently has members from a variety of organizations.
Actions You Can Take to Support Monarchs
An effective response to monarch decline requires an 'all-hands-on-deck' approach, including participation from land managers and members of the public across the state. We recommend the following actions:
Plant native milkweed species appropriate to your location, with a focus on early-season milkweed species milkweed such as Asclepias syriaca.
