Why monarch butterflies, now endangered, are on the ‘edge of collapse’

The migratory monarch butterfly, a North American icon with a continent-spanning annual journey, now faces the threat of extinction according to a top wildlife monitoring group.

Thursday’s decision by the International Union for Conservation of Nature to declare the species endangered comes as years of habitat destruction and rising temperatures have decimated the fluttering orange itinerants’ population.

The species’ numbers have dropped between 22% and 72% over the past decade, according to the new assessment. Monarchs in the Western United States are in particular danger: The population declined by an estimated 99.9%, from as many as 10 million butterflies in the 1980s to fewer than 2,000 in 2021.

“It is difficult to watch monarch butterflies and their extraordinary migration teeter on the edge of collapse, but there are signs of hope,” said Anna Walker, an entomologist at the New Mexico BioPark Society who led the butterfly assessment.

The monarch is not alone. Butterflies across the region are vanishing as the West gets hotter and drier. According to one recent study, a majority of 450 species across a swath of 11 Western states are dropping in numbers.

But it is the decline of the well-known monarch that has grabbed headlines and caused dismay among many wildlife watchers.

The butterfly is famous for its epic migrations from wintering grounds in Mexico and California across the rest of the continent, signaling the start of summer as it fans out into the northern reaches of the United States and Canada.

Despite surviving thousands of miles of migration, threats from humans now abound.

Forest clearing to harvest timber and to make space for farms and homes is creeping into its wintering grounds. Pesticides and herbicides threaten not only the insect itself but also milkweed, which monarch larvae need to live. And climate change is exacerbating droughts and fires that can kill the butterflies and the plants they depend on.

Despite the dangers, wildlife officials in the United States have yet to protect the monarch under the Endangered Species Act.

In 2020, the U.S. Fish and Wildlife Service said the butterfly’s decline is sharp enough to warrant placement on the endangered species list. But the agency declined to do so, saying other species should take priority.