Epargyreus clarus californicus
'California' Silver-spotted Skipper
Flies from May into July or early August. Once known mainly (or only) from the San Bernardino Mountains, but Ken Davenport says it has ranged into Kern County and elsewhere. It uses legumes, such as Amorpha fruticosa and Lotus - now Acmispon - species. To the south, we may have subspecies huachuca, which is uncommon in southern California and better known in Arizona and elsewhere. But these may in fact be californicus as well.
Scott (1986) says eggs are green with a bright red top and are laid on upperside of leaves. "Young larvae live in a folded-over flap of a leaf; older larvae live between silked-together leaves.... Pupae hibernate" (p.471). Others add that larvae feed at night and retreat to their shelter during the day. These larvae are said to be very easy to find (Allen, Brock, Glassberg 2005, p.114; there is a good photo of a yellowish caterpillar on the facing page). Todd Stout has great larva/leaf photos on the Butterflies of America website. They overwinter as a pupa, and feed after (the two) flights, so larvae should be looked for from roughly late May/June through September, after which they will go to the ground and pupate, apparently in a kind of shelter (the Emmels cite Comstock 1927 on this point).