Watch for flashes of silver from the underside of a butterfly’s wings in June on San Bruno Mountain. That’s the telltale sign of the callippe silverspot, a once-ubiquitous Bay Area butterfly that is now on the federal endangered species list.
The callippe silverspot’s population has crashed due to the decline in the populations of its only host plant, the Johnny jump-up.
A relative of the violet, the jump-up is an annual native, and it has mostly wilted by the time the adult butterfly lays her eggs on or near it. The larvae hatch and immediately spin a silk pad on the dormant plant. Then they go into a state of lowered metabolism that lasts through the winter. When the larvae awaken again in early spring, the now-green plant is an essential source of food. The larvae spend two to three months eating and molting; finally, they encase themselves in leaves held together by silk and undergo their metamorphosis.
The silverspot’s adult life lasts but three weeks in early summer, when they feed on flower nectar, mate, and lay eggs. You might spot them sipping nectar from thistles, mints, and other flowers. Their wings, spanning only two-and-a-half inches, are intricate and variable. While the undersides are spotted with the aforementioned silver, the top sides tend to be brown with black spots and lines.
In early June 2008, butterfly counters recorded over 200 silverspots during an annual survey. A walk on the Buckeye Canyon Trail on San Bruno Mountain may be your best chance at spotting this silver butterfly. Historically, the callippe ranged from La Honda in San Mateo County to the Twin Peaks neighborhood of San Francisco, as well as on the inland hill ranges of Contra Costa and Alameda counties. Due to habitat changes brought on by livestock grazing, urban and suburban development, and heavy recreational use, there are not enough healthy Johnny jump-up populations to support the butterflies in most of its historic range. But venture south of San Francisco, to the precious habitat island of San Bruno Mountain, and you may be treated to a vision of silver-speckled wings of this native butterfly.