WASHINGTON — Monarch butterflies are now listed as endangered because of fast dwindling populations in North America. The International Union for the Conservation of Nature announced the designation on Thursday for the orange-and-black butterflies. The group estimates that populations have declined between 22% and 72% over a decade.

Famous for their seasonal migration, millions of monarchs travel from the United States and Canada south to California and Mexico for the winter. They breed new generations along the way that begin the return trip at the end of summer. They are typically spotted in the Midwest during their migration south in August and September.

The butterflies are imperiled by loss of habitat and increased use of herbicides and pesticides for agriculture, as well as climate change. Over the past 20 years, scientists have noted declines in all populations, but especially the California population, which fell to fewer than 30,000 in 2019. Habitat loss is the biggest problem. 

Cities and agriculture have disrupted some of the Monarch’s migration. They need milkweed to survive and the plant is not as widespread before. Conservationists recommend planting milkweed and other sources of nectar to help the butterflies thrive.