Western monarch butterflies face 99% extinction risk by 2080 as pesticides and habitat loss drive decline

A mass casualty event in January 2024 at Pacific Grove Monarch Sanctuary saw hundreds of western monarch butterflies dying with curled abdomens; a toxicology report later revealed a cocktail of pesticides, including residential sprays. The 2025-26 overwintering season counted only 12,260 monarchs across 249 California sites, the third-lowest since 1997. A March 2025 study in Science, co-authored by Scott Black of the Xerces Society, found U.S. butterflies declined 22% from 2000 to 2020, with 24 species dropping over 90%. Ecologist Matt Forister's research detected pesticides in nearly all milkweed samples from California's Central Valley and retail nurseries, with up to 61 different chemicals per plant. In Oregon, the Fender's blue butterfly was downlisted from endangered to threatened after habitat restoration led by Cheryl Schultz. Scientists at Lighthouse Field State Beach are testing ultralight radio tags weighing under 0.1 gram to track female monarchs via the Project Monarch app. Volunteer Diana Magor studies heartleaf milkweed, which sprouts earlier and may help monarchs adapt to earlier springs from climate change. The U.S. Fish and Wildlife Service estimates eastern monarchs face 56-74% extinction by 2080, while western monarchs have a 99% chance of vanishing.