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.
In California, monarchs are not listed under the California Endangered Species Act (CESA). They are included on the California Department of Fish and Wildlife's (CDFW) Terrestrial and Vernal Pool Invertebrates of Conservation Priority list (PDF) (PDF) and identified as a Species of Greatest Conservation Need in California's State Wildlife Action Plan. California law (Fish and Game Section 1002) prohibits the take or possession of wildlife for scientific research, education, or propagation purposes without a valid Scientific Collection Permit (SCP) issued by CDFW. This applies to handling monarchs, removing them from the wild, or otherwise taking them for scientific or propagation purposes, including captive rearing. To learn more about obtaining a Scientific Collecting Permit, see our SCP page.
CDFW's Monarch Conservation Work
CDFW is an active participant in the Western Association of Fish and Wildlife Agencies (WAFWA) effort to enhance western monarch conservation, along with the other member states Washington, Oregon, Idaho, Utah, Arizona, Nevada, and New Mexico. The 50-year Western Monarch Conservation Plan, adopted in 2019, establishes population size and habitat conservation goals and strategies. See WAFWA's Monarch and Native Insect Pollinator Working Group for more information on priority actions.
CDFW also participates in the California Multi-agency Monarch and Pollinator Collaborative, a group of 13 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.
Monarch overwintering aggregations occur on five properties managed by CDFW and an additional two Department easements. In 2024 CDFW completed habitat assessments on four of the properties. We are currently planning management actions at those sites to reduce fire risk while enhancing resources that support monarchs. We are also working to protect and restore monarch breeding and migratory habitat on CDFW lands throughout the state.
Since 2021, CDFW has co-facilitated a plant materials working group with the Xerces Society focused on developing sources of early-season milkweed for restoration projects. The group currently has over 70 members from a variety of organizations. It is open to the public and you are welcome to join its quarterly meetings. To learn more, contact the CDFW Pollinator Coordinator at wildlifemgt@wildlife.ca.gov, and be sure to include 'plant materials working group' in the subject.
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:
- Add locally appropriate native flowering plants in your home garden or restoration project, focusing on early- and late-blooming species that support the monarch's spring and fall migration.
- Plant native milkweed species appropriate to your location, with a focus on early-season milkweed species such as California milkweed (Asclepias californica), heart leaf milkweed (A. cordifolia), desert milkweed (A. erosa), and woolly milkweed (A. vestita).
- Ensure any plants you purchase from nurseries are pesticide-free.
- Limit pesticide use during bloom periods of plants visited by monarchs, near milkweed hostplants, and adjacent to overwintering sites during the overwintering period (October - March).
- Become a community scientist by volunteering to collect data on monarchs and milkweed that help us make informed decisions: