Monarch Butterfly


monarch butterfly nectaring on thistle
USFWS Photo by Brett Billings.
Monarch migration routes in U.S.
Figure 1 from The Xerces Society’s Conservation Status and Ecology of the Monarch Butterfly in the United States (PDF).
overwintering monarch butterfly cluster on eucalyptus
USFWS Photo by Ryan Hagerty.

The iconic black and orange monarch butterfly is known for its astonishing long-distance annual migration and reliance on milkweed 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. 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 in North America (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. Recently the western population has experienced dramatic swings, for a low of less than 2,000 in 2020-21 to over 200,000 in 2021-22 (Xerces Society Western Monarch Count). While it is unclear which of the many factors are driving these dynamics, insect population 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. In December 2020, the U.S. Fish and Wildlife Service found that listing was warranted but precluded by other listing actions on its National Priority List. The monarch is currently slated to be listed in 2024.

In California, monarchs are included on the California Department of Fish and Wildlife's (CDFW) Terrestrial and Vernal Pool Invertebrates of Conservation Priority list (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. Due to the current status of the migratory monarch population, CDFW has also issued a mortarium on certain activities covered with an SCP. To learn more about obtaining a collection permit, see our SCP page.

Actions to Support Monarchs

CDFW is an active participant in the Western Association of Fish and Wildlife Agencies (WAFWA) effort to enhance western monarch conservation with the other member states of Washington, Oregon, Idaho, Utah, Arizona, and Nevada. The 50-year Western Monarch Conservation Plan, adopted in 2019, establishes population size and habitat conservation goals, strategies. See WAFWA's Monarch Working Group for more information on priority actions and focal regions.

The western monarch situation is in flux, with many unknowns, including the rise of a year-round breeding population in coastal areas of California. This quickly evolving situation has raised many questions about what can be done to conserve monarchs, factors affecting them, and permitting requirements in place to protect this vulnerable migratory population. More detailed information on these topics is provided in our regularly updated Frequently Ask Questions (FAQ) document (PDF).

An effective response to monarch declines requires participation from land managers as well as members of the public across the state to continue important recovery efforts. Actions we recommend include:

Wildlife Branch - Wildlife Diversity Program
1010 Riverside Parkway, West Sacramento, CA 95605