- The monarch butterfly population in the western U.S. hit a nearly 30-year low in 2024. That’s a 96% drop compared to the population in 2023.
- Experts blamed a combination of vanishing habitats, climate change and pesticides.
- Due to declining populations of pollinators, monarchs are expected to become a protected species in the U.S. in 2025.
Fewer monarch butterflies have spent winter in the western U.S. as factors like pesticides, a disappearing habitat, and climate change have affected the population. The population is now at a 30-year low.
What is known about monarch butterflies in western America?
Since 1997, the Xerces Society for Invertebrate Conservation has been monitoring the overwintering monarch butterfly population west of the Rocky Mountains.
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During the winter, the butterflies migrate to the California coast — northern Baja and inland California — and Arizona.
The society said it recorded its lowest number of monarch butterflies ever in 2024.
When the Xerces Society started tracking the species in 1997, it counted 1.2 million winged insects, the highest number ever recorded in the area.
In 2024, it saw a 96% drop in the population compared to the year before, counting just 9,119 monarch butterflies.
It’s the second-lowest number they’ve ever counted in 28 years of tracking data. The lowest was 1,901 monarch butterflies in 2020.
What’s causing the population decline?
Monarchs across North America have faced mounting threats. The biggest threat is the vanishing milkweed, which is the host plant for caterpillars that metamorphosize into butterflies.
Experts said a combination of drought, wildfires, agriculture and urban development have caused the plants to disappear. Plus, pesticides have contaminated many of those that remain.
However, the Xerces Society said it’s unclear what caused such a massive drop in the Western monarch butterfly population between 2023 and 2024.
Still, it serves as another example of a bigger trend.
In December 2024, the U.S. Fish and Wildlife Service announced it plans to add monarch butterflies to its threatened species list by the end of 2025, making it illegal to kill them purposely or transport them.
What about butterflies in the eastern US?
It’s currently unknown if the eastern U.S. monarch population saw the same drop in 2024.
Monarchs travel to Mexico for the winter and are monitored by the World Wildlife Fund, which has not yet released its 2024 data.
How can Americans help?
There are several ways to help revive the dwindling population of these much-needed pollinators.
The Xerces Society’s website is full of ways Americans can help, from planting certain seeds in their gardens to managing habitats specifically for monarch butterflies.
