Eric observed an intriguing butterfly flutter to the ground near our house in Sebastopol this morning. It turned out to be a Pine White (Neophasia menapia). It's the first time we've noticed this species in our yard.
Note the greenish-white background color. The thick, dark outlines of the veins and the orange coloration along the edge of the hindwing indicate that this is a female. (Males are paler and lack the orange.) Some of the darker scales showed a purple iridescence (see below).
Shapiro and Manolis provide this fun description of Pine White behavior in A Field Guide to Butterflies of the San Francisco Bay and Sacramento Valley Regions (2007):
"Adults lek around the tops of pines and occasionally other trees, dropping to near the ground and then rising to near the top in a spiraling motion; they repeat the process again and again. Their flight seems effortless, with infrequent wingbeats, and they have more than once been likened to giant snowflakes wafted in the breeze."
[A lek is a gathering of individuals involved in courtship displays. "Lep" (from the title of this post) is an informal abbreviation for "lepidoptera," the scientific name for butterflies and moths.]
Here's a close-up: