On a Mission to Find Mission Blue Butterflies
With tiny, delicate wings ranging from silvery to dark shades of blue, the Mission blue butterflies are the living sapphires of San Bruno Mountain.
These creatures are as small as a quarter and live in the coastal chaparral and grasslands of San Bruno Mountain; other populations are found throughout parts of the Bay Area such as the Marin Headlands, Twin Peaks in San Francisco, and Milagra Ridge in San Mateo County. Mission blue butterflies take flight during calm and sunny weather, though fluctuating conditions on the mountain can present chilling fog and blustery winds within a day! The upper wings of the male butterflies vary from silvery to violet-blue, whereas those of the females are bluish-brown. Both sexes have silver-gray or brown underwings with black spots.
Mission blue butterflies rely on a few species of lupine plants in order of preference: silver lupines, summer lupines, and varicolored lupines. Their life begins around March and their flight season extends into June, when Mission blue butterflies lay eggs upon the leaves of lupines. The eggs hatch into larvae that immediately starts feeding on lupine leaves and growing. These larvae are small, green, slow, and entirely focused on eating, leaving them vulnerable to predators such as parasitoid wasps. Fortunately, the larvae are protected through a mutualistic relationship with native ants; the ants fend off predators and in return, consume a sugary secretion produced by the larvae.
In the summer, the lupines begin to shift their energy from flower and leaf development to root maintenance; Mission blue larvae are able to sense this change, so they crawl down into the leaf litter at the base of the plant and hibernate for eight months from summer through the end of winter. This state is called diapause, which is akin to hibernation during unfavorable environmental conditions. When spring emerges, the lupines resume their flower and leaf development, triggering the larvae to wake up and resume feeding.
Nearly a month later, a Mission blue larva will crawl down to the lupine stem to form a hard-shelled chrysalis. Inside, its body breaks down to transform and emerge into an adult butterfly ten days afterwards. As the lifespan of an adult Mission blue is about a week, it's a race against the clock as these ephemeral creatures actively search for their mate and continue the circle of life!
Although Mission blue adults can nectar from various flowers to survive, its diet during its larva stage is restricted to lupines, meaning the preservation of the three different host lupine populations is also essential in protecting Mission blues from disappearing. Butterfly populations throughout the Bay Area have declined substantially due to urbanization and fragmentation of their natural habitats. This type of habitat modification that resulted in the mission blue butterfly being listed as a federally endangered species in 1976 and protected under the Endangered Species Act.
From the spring through summer of this year, the SMC Natural Resource Team has been scouring the grasslands of San Bruno Mountain in search of these evasive beauties and their host plants. Recording the whereabouts, weather conditions, and numbers of Mission blue butterflies and lupines will aid researchers in analyzing the most suitable habitats as well as developing restoration plans to improve their populations on this mountain.
If you would like to protect the Mission blue butterfly population and overall environment, we encourage you to join the many habitat restoration projects offered by the San Mateo County Parks Stewardship Corps and other programs across the Bay Area. Activities range from removing invasive plants threatening the natural balance of the ecosystem, to planting native species serving as additional nectaring sources for pollinators. Prevent the spread of significant weeds by cleaning your clothes and shoes before and after going outdoors, and even consider planting a butterfly garden!
Next time you're on the mountain on a calm, bright day during the spring and summer, remember to look out for these rare beauties!