Study Links Pesticides to Monarch Butterfly Deaths in Pacific Grove : Indybay

Study Links Pesticides to Monarch Butterfly Deaths in Pacific Grove : Indybay

PORTLAND, Ore.; July 25, 2025 — A new study published in Environmental Toxicology and Chemistry documents a mass mortality event of monarch butterflies near one of California’s most iconic overwintering sites and links the deaths to pesticide contamination. In late January 2024, hundreds of monarchs were found dead or dying on a private property near the trees of Pacific Grove Monarch Sanctuary, where they typically cluster during the winter.