Xerces Society

The increasing intensity and frequency of extreme heat likely compounds stresses on the iconic butterfly, worrying biologists about how the struggling population will respond.

The population of western monarch butterflies wintering along the California coast has rebounded for a second year in a row after a precipitous drop in 2020, but the population of orange-and-black insects is still well below what it used to be, researchers say.

“It’s just a devastating decline,” said Stuart Pimm, an ecologist at Duke University who was not involved in the new listing. “This is one of the most recognizable butterflies in the world.”