Pesticides could be to blame for mass monarch die-off

Pesticides likely caused a large die-off of monarch butterflies in California in 2024, according to new research. Hundreds of monarchs (Danaus plexippus) died in January 2024 at an overwintering site in the Pacific Grove Monarch Sanctuary in California—researchers found them twitching or dead in piles. In a study published in Environmental Toxicology and Chemistry, they tested some of the insects, finding an average of seven pesticides in each individual. “The incident gave us a rare opportunity to directly document pesticide exposure and its impacts on monarchs in the real world,” Staci Cibotti, the study’s lead author and an entomologist and pesticide program specialist with the Xerces Society for Invertebrate Conservation, told The Guardian.

Read more in The Guardian.