The US Fish and Wildlife Service announced in December 2024 that it was working to list monarchs as threatened, a move that would prohibit anyone from killing, transporting them or making changes that would render their property permanently unusable for the species, such as eradicating all milkweed from the land.
The Xerces Society for Invertebrate Conservation has been counting western overwinter populations along the California coast, northern Baja California and inland sites in California and Arizona for the last 28 years.
Monarchs in the eastern US spend their winters in Mexico, while monarchs west of the Rocky Mountains typically overwinter along the California coast.
Monarch butterfly numbers plummet in US west coast winter habitats Just 9,119 were counted in 2024 – down 96% on previous year and second-lowest mark in nearly three decades.
The number of monarch butterflies spending the winter in the western United States has dropped to its second-lowest mark in nearly three decades as pesticides, diminishing habitat and the climate crisis take their toll on the beloved pollinator.
