WASHINGTON— Two conservation groups, the Center for Biological Diversity and Center for Food Safety, today sued the U.S. Fish and Wildlife Service to force officials to set a binding date to finalize federal protections for monarch butterflies under the Endangered Species Act.

The monarch was proposed for protection in December 2024, making the final listing due in December 2025. The groups argue the delay increases extinction risk for the nationally beloved pollinator.

“Comprehensive protections are urgently needed to ensure a future for these migratory wonders,” said Tierra Curry, endangered species co-director at the Center for Biological Diversity. “Monarchs unite us and it’s disgraceful that their future is being sacrificed to political nonsense.”

Instead of issuing the final listing at the end of 2025, Trump officials delayed the decision as a “long-term action,” with no definitive date for issuance provided. The federal assessment of the monarch’s status found that in the next 60 years western migratory monarchs have up to a 99% chance of going extinct and eastern monarchs have up to a 74% chance.

“The Service must finalize monarchs’ protections from their threats, including and especially pesticides, which have been a major driver of their rapid decline,” said George Kimbrell, legal director at the Center for Food Safety and counsel in the case. “The Service’s duty is to protect monarchs not corporations.”

Migratory monarchs have declined by more than 80% since the 1990s. Last year’s eastern population, who overwinter in the mountains of Mexico, was just one-third of the size needed to be out of the danger zone of collapse. Updated population data will publish this spring, but the population is expected to be about the same level.

The western population, who overwinter in forests on the California coast, is down more than 95% since the 1980s and numbered only 12,260 monarchs this year. That’s the third-lowest tally ever counted.

In 2014 the Center for Biological Diversity, Center for Food Safety, Xerces Society for Invertebrate Conservation, and renowned monarch scientist Lincoln Brower filed a scientific and legal petition with the U.S. Fish and Wildlife Service seeking protection for the butterflies and their habitat under the Endangered Species Act. The butterflies were placed on a candidate waiting list for protection in 2020. The centers filed a lawsuit to elevate them from bureaucratic limbo resulting in the proposed listing in 2024.

Today’s lawsuit was filed in San Francisco in the U.S. District Court for the North District of California.

Background

In one of the longest migrations of any insect, at the end of summer eastern monarchs fly from the northern United States and southern Canada to overwinter together in high-elevation fir forests in Mexico. The population size is determined by measuring the area of trees turned vivid orange by the clusters of butterflies. Scientists estimate that 15 acres of occupied forest is the minimum threshold for the migrating pollinators to be above extinction risk in North America.

Monarchs face tremendous threats. Their initial decline was driven by widespread loss of milkweed, the caterpillar’s sole food source, due to increased use of the herbicide glyphosate on fields of corn and soybeans genetically engineered to resist it. Volatile herbicides sprayed on newer herbicide-resistant crops drift and reduce floral resources required by adult butterflies. All stages of monarchs are harmed by neonic insecticides used in crop seed coatings and on ornamental plants.

Climate change is damaging the forests where monarchs winter and extreme weather events are interfering with reproduction and migration. Grasslands and other green spaces that provide wildflowers for nectaring adults continue to be lost to development.

Millions of monarchs are killed by vehicles annually as they migrate across the continent. In their winter habitat in Mexico, forests and streams are being decimated to grow avocados for unsustainable U.S. demand. In California, more than 60 known overwintering forest sites have been cut down.

Listing has been indefinitely delayed for hundreds of imperiled species in addition to the monarch as their protections have been deemed “long-term actions.” The Fish and Wildlife Service lost 18% of its staff last year, including more than 500 scientists, and the Endangered Species Act listing budget was slashed to 2004 levels.

In 2025 not a single plant or animal was protected under the Endangered Species Act for the first time since 1981.