Monarch butterfly numbers plummet to near-record low

The western U.S. monarch butterfly population has plummeted to its second-lowest level in nearly 30 years, with only 9,119 butterflies counted in 2024—a 96% decrease from 233,394 in 2023. This decline is attributed to factors such as pesticide use, habitat loss, and climate change. The Xerces Society for Invertebrate Conservation, which has monitored these populations since 1997, reported that the 2024 count is only slightly above the record low of 1,901 monarchs in 2020. Notably, a site in Santa Barbara managed by The Nature Conservancy saw a drop from 33,200 monarchs last winter to just 198 this year. 

Monarchs face significant challenges, including the decline of milkweed—the sole host plant for their caterpillars—due to drought, wildfires, agriculture, and urban development. Pesticide contamination further exacerbates the issue. Extreme heat in the western states during 2024 may have also hindered breeding, as temperatures above 100°F (37.7°C) can be detrimental to monarchs. For instance, Palm Springs reached a record 124°F (51.1°C) on July 5, and northern California experienced record-breaking heat in early October. 

Despite these setbacks, insects like monarchs have the potential for rapid population recovery. After reaching a low of 1,901 butterflies in 2020, the population rebounded to 247,246 in 2021 and 335,479 in 2022. However, the recent decline underscores the need for continued conservation efforts. The U.S. Fish and Wildlife Service has proposed listing the monarch butterfly as a threatened species, which would implement protections against killing or transporting them and designate critical habitats in seven coastal California counties. Public comments on this proposal are open until March, with a final decision expected by December 2025. 

Additionally, environmental law firm Earthjustice has petitioned the Environmental Protection Agency to require testing of pesticide effects on insects like bees, moths, and butterflies, aiming to address one of the key factors contributing to the monarchs’ decline. 

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