San Bruno Mountain, nestled in the northernmost part of San Mateo County, is an island of picturesque mountains that boasts green grassland, coastal scrubs, an intricate watershed, and dunes. If you’re lucky, when you visit you might catch the iconic flutter of three of the mountain’s vibrant butterflies: the Mission Blue, San Bruno Elfin, and Callippe Silverspot. Although 42 kinds of butterflies call San Bruno Mountain home, these three are of special concern because they’re on the Federal Endangered Species List.
Meet the Endangered Butterflies of San Bruno Mountain
As suggested by its name, the Mission Blue is an iridescent blue with a white underwing. The San Bruno Elfin has a rusty brown coloration on its wings. The Callippe Silverspot, the biggest of the three butterflies, is known for its orange-brown color and for the silver spots on its underwing area. Native plants on the mountain such as lupine, the California golden violet, and stonecrop provide food and habitat for the butterflies throughout their various stages of growth and are essential to their ability to grow and maintain their presence on the landscape. Another rare butterfly, the Bay Checkerspot, was recently re-introduced to San Bruno Mountain. (Read more about the Bay Checkerspot butterfly here.)
Why have these butterflies, almost extinct everywhere else, managed to survive on San Bruno Mountain? The answer lies in the uniqueness of the mountain’s geology and climate, which has created an island of rare plants and wildlife surrounded by a sea of urbanization. With 14 endangered plant species in addition to the endangered butterflies, San Bruno Mountain is an astonishingly biodiverse habitat area – right here in the middle of the San Francisco Bay Area.
Unfortunately, the Mission Blue, San Bruno Elfin, and Callippe Silverspot butterflies are under threat even on San Bruno Mountain from development/urbanization, pollution, and invasive species.
How You Can Help
An important part of the work towards reestablishing healthy butterfly population numbers involves removing nonnative grasses that have taken root on the mountain. These grasses have outcompeted the native plants historically present, including ones that all three butterflies need. Removing them to make space for lupines, stonecrops, and the California golden violet to thrive is critical for the butterflies’ survival. If you’d like to volunteer with one of the local groups working to remove these invasives and restore butterfly habitat on San Bruno Mountain, check out their website here.
Threats From Development: Guadalupe Quarry Redevelopment Project
In addition to threats from invasive species, the butterflies of San Bruno Mountain are at risk from continued development. The most recent proposal, the Guadalupe Quarry Redevelopment Project, would destroy butterfly habitat in order to build a giant Amazon-style warehouse and distribution center. Read Green Foothills’ article about this project for more information. We will keep you updated about this proposal. If you’re not already signed up for our email list, sign up to receive alerts.
The Mission Blue, San Bruno Elfin, and Callippe Silverspot depend on the continued ecological restoration of San Bruno Mountain to survive. Their preservation has played a key part in keeping the mountain in the condition that we see it today and it is imperative to maintain this as we move forward into the future.