Rare & Endangered Species

Mission Blue Butterfly

The Mission blue butterfly (MBB) is an exceptionally striking butterfly species. The upper wings of the male butterflies display a vivid iridescent blue, a color rarely seen in nature, while females are brown, often with a blue shimmering overlay. Both females and males are marked with dark spots on their undersides.

With a wingspan just over an inch, the MBB inhabits windy hilltops in select Bay Area locations, notably San Bruno Mountain, the Marin Headlands, and Twin Peaks. Urbanization and the spread of invasive plant species have severely reduced viable Mission blue habitat within San Francisco. In 1976, the federal government listed the Mission blue butterfly as an endangered species and granted it special protection under the law. The decline of lupine, the MBB host plant, contributed to their disappearance from San Francisco.

In spring of 2009, the San Francisco Recreation and Park Department (SFRPD) initiated its Natural Resources Division, aiming to increase MBB populations in the city through translocations and habitat management. Twenty-two female Mission Blue Butterflies were transferred from San Bruno Mountain to Twin Peaks, and efforts to plant lupine and other native wildflowers intensified. 15 years later, the MBB recovery project at Twin Peaks Natural Area has seen continued success. Monitoring MBB eggs emerged as a successful strategy for tracking conservation progress, providing reliable estimates of the butterfly population. By closely monitoring MBB eggs, researchers estimated a population of 128 females in 2023, similar to the previous year.  This is a remarkable increase from the low numbers observed in earlier years, indicating positive trends in population recovery.

Habitat management remains a crucial initiative, with ongoing efforts to maintain grassland habitats and increase the number of lupine host plants. Lupine planting has significantly scaled up, with thousands of seeds planted in strategic locations to support butterfly populations. Other habitat management efforts include scrub removal, weed control, and trail maintenance, all of which are ongoing priorities to create an ideal environment for MBBs to thrive. Additionally, plans for future translocations and continued monitoring underscore the commitment to ensuring the long-term success of the MBB recovery project.

Looking ahead, priority tasks for 2024 include repeating the lupine mapping/census, continuing habitat management efforts, and monitoring the MBB population through larval and egg surveys. While translocations may not be necessary in 2024 due to stable population estimates, ongoing collaboration, and funding support from organizations like the Disney Butterfly Conservation Initiative, and Partners for Fish and Wildlife, and the University of Florida remain crucial for sustaining conservation efforts and preserving the Mission blue butterfly population at Twin Peaks.

We need your help to continue these incredible conservation efforts!

Let's ensure our exploration of Mission Blue territory is both enjoyable and respectful! Visitors to Twin Peaks are encouraged to utilize designated paths to avoid disturbing any vegetation, while cyclists should stick to paved paths and roadways for a smoother journey. If you're accompanied by a pet, always keep them leashed to prevent any disruption to the surrounding habitat and ensure they don’t dig or defecate in Mission Blue territory. Your cooperation plays a crucial role in our conservation efforts, and we appreciate your commitment to preserving this San Francisco treasure.