Erynnis tristis, Mournful Duskywing, or White-edged Dusky
wing lives on oak leaves.
This is one of those pesky caterpillars you find on coast live oak
trees. The males set at the top of hills and wait for the females to
show up. Females of this species fly up to hilltop to mate.
Other similar species do not.
You'll find this butterfly on a variety of flowers in the areas where
there are oak trees.
Erynnis tristis, Mournful Duskywing on black sage