Mass Die-Off of Western Monarch Butterflies Linked to Pesticides, Study Finds

Photo: Monarch butterfly (Danaus plexippus) on a cosmos flower – captured October 13, 2023 in Oklahoma. Photo credit: Thomas Shahan via Flickr. CC BY 2.0. Article by Paige Bennett. EcoWatch – August 1. 2025. Research article: Environmental Toxicology and Chemistry

A new peer-reviewed study has linked pesticides as a likely cause to a mass die-off of Western monarch butterflies that occurred in 2024. In January 2024, researchers found hundreds of dead or dying monarch butterflies near the Pacific Grove Monarch Sanctuary in California, where Western monarch butterflies typically overwinter. […]

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