The International Union for the Conservation of Nature (IUCN), the global leading authority on the status of biological diversity, has declared the monarch butterfly an endangered species. According to scientists, the monarch population has declined between 23 and 72 percent in the past decade.
Anna Walker, who led the monarch butterfly assessment, said:
“It’s hard for people to imagine that something that shows up in their backyard is threatened.”
The decline of the monarch butterfly population is attributed to habitat destruction, pesticides, and milkweed, the plant they lay larvae in. The western monarch population, less studied and more at risk, has plummeted 99.9 percent in recent decades, from around 10 million in the 1980s to just 1,914 in 2021. The eastern population declined by 84 percent between 1996 and 2014.
The eastern North American monarch population is notable for its annual southward late summer/autumn migration from the northern and central United States and southern Canada to Florida and Mexico. The western North American population of monarchs west of the Rocky Mountains often migrates to sites in southern California, but has been found in overwintering Mexican sites, as well. During the fall migration, monarchs cover thousands of miles, with a corresponding multigenerational return north.