Monarch Butterflies Go on Global 'Red List'

North America's migratory monarch butterfly, the beloved orange-and-black insect capable of flying 2,500 miles across the continent, is officially an endangered species in the eyes of the leading global authority. The International Union for the Conservation of Nature added migratory monarchs to its Red List of Threatened Species Thursday following its first assessment of the insect, which involved a review of 100 studies and interviews with experts. It found numbers of Western monarchs, which live west of the Rocky Mountains, fell by 99.9% from the 1980s to 2021—when there were just 1,914 known individuals—while numbers of Eastern monarchs fell 84% from 1996 to 2014, per National Geographic.

Female monarchs lay eggs on milkweed plants—the only plant monarch caterpillars can eat—along migration routes from Mexico to Canada. But the use of herbicides has erased the plants from many landscapes, reports the New York Times. Climate change has also taken a toll. "We're starting to see this kind of mismatch between when insects are ready to start the spring and when plants are ready," Anna Walker, the New Mexico BioPark Society entomologist who led the assessment, tells the Times. "There are a ton of unknowns." Experts hope the designation will encourage land owners to plant milkweed that is native to their region as well as native flowers that will bloom when monarchs visit, providing them with nectar.

"Only 1% of insect species have been assessed by the IUCN—so having the monarch listed is significant," per NatGeo. The Committee on the Status of Endangered Wildlife in Canada recognized the butterfly—part of a broader species including non-migratory monarchs in southern Mexico, the Caribbean, and northern South America—as endangered in 2016. The US Fish and Wildlife Service acknowledged the species was at risk of extinction in 2020 but declined to put it on its Endangered Species List, arguing there were other species that took precedence, per the Times. It then proposed listing the monarch as endangered in 2024 "unless its situation improves enough to make the step unnecessary," per the AP. (More monarch butterflies stories.)