Monarch Butterfly Listed as Threatened Under the Endangered Species Act
The U.S. Fish and Wildlife Service listed the monarch butterfly as Threatened under the Endangered Species Act on December 4, 2024, extending federal protection to North America’s most recognized migratory insect after decades of documented decline.
The decision closed out one of the longest-running listing questions in recent ESA history. The monarch had been a candidate for listing since 2014, when USFWS determined that protection was warranted but precluded by higher-priority species — a designation that acknowledges the need without providing the remedy. A formal proposed rule followed in December 2020, and the final Threatened determination came four years after that.
A Collapse Measured in Orders of Magnitude
The population figures behind the listing are stark. The western monarch population, which breeds across the West and overwinters in groves along the California coast, fell from an estimated 4.5 million butterflies in the 1980s to fewer than 30,000 counted at overwintering sites in 2020 — a decline exceeding 99 percent. The much larger eastern population, which winters in the oyamel fir forests of central Mexico, declined by roughly 80 percent over the same period.
Those two flyways are usually discussed separately, but Colorado sits where they meet. Monarchs breed throughout the state wherever milkweed grows — the only plant genus their caterpillars can eat — and fall migrants funnel south along the Front Range corridor, compressed between the Rocky Mountains and the Great Plains, on their way toward Mexico each autumn.
What the Listing Changes
A Threatened designation carries real regulatory weight. It triggers Section 7 consultation requirements, obligating federal agencies to evaluate whether their actions — permits, funding, land management — are likely to jeopardize the species or its habitat. It also brings Section 9 prohibitions against take into play, though the specific protections applied to a Threatened species are shaped by the rules issued alongside the listing.
Recovery work concentrates on three fronts: restoring milkweed and nectar plants across breeding habitat, reducing pesticide and herbicide impacts on both butterflies and their host plants, and protecting the Mexican overwintering forests, where illegal logging and a warming climate continue to erode the narrow band of montane habitat that shelters most eastern monarchs each winter.
Colorado’s Part
The Front Range — particularly the Palmer Divide and the Arkansas River valley — is a documented autumn migration route. Late-season wildflowers such as rabbitbrush and goldenrod supply the nectar that fuels southbound butterflies. Planting milkweed species native to your elevation and region, rather than tropical varieties sold in many garden centers, is among the most direct contributions a Colorado resident can make.
Read the full species profile: Monarch Butterfly