Hairstreaks belong to the large worldwide family Lycaenidae, which also includes all blues, coppers and metalmarks. Hairstreaks are small butterflies, often with tail-like extensions or “hairstreaks” on their hindwings, particularly in members of the genus Satyrium. In Washington State there are eighteen species of hairstreaks, six of them in the genus Satyrium. Butterflies in the genus Satyrium fly in mid-summer, peaking in July.

Satyrium californica occurs throughout the intermountain west from BC to Baja. A single generation flies in mid- summer, early Jun-early Aug, in low and mid elevation shrub steppe habitats of ID and E WA and OR along the flanks of the Cascade Mtns, plus a few outlier localities. It is rather scarce throughout its range but is sometimes common locally, often found with other Satyrium hairstreaks. The most commonly used host plants in Cascadia are Purshia tridentata (Bitterbrush) and Ceanothus velutinus (Mountain Balm). Beyond the Pacific Northwest Amalanchier (serviceberry), Prunus virginiana (Chokecherry) and Salix (willow) are reported. Both sexes visit buckwheats, milkweeds and mints for nectar.

After mating the females lay eggs in small clusters, usually about 4 eggs per cluster. The eggs are sometimes stacked like partially offset pancakes, typically in small crevices, under loose bark or in a narrow crotch on a woody part of the host plant. Shiny, clear glue securely anchors the eggs in place and helps camouflage and protect them. Eggs overwinter; the following spring the emerging larvae chew a small exit hole but leave the egg shells uneaten and still encased in the thick glue binding them together. Eggs hatch about 5 days after “daylighting” in the spring and the larvae develop to pupae in about two weeks, the adult eclosing another twelve days later. On Bitterbrush larvae feed on leaf buds early, switching to young terminal leaves later. On Ceanothus the larvae likewise feed on buds, beginning growth before any leaves have sprouted.

Ceanothus may be the commonest host here but little is known about it, probably because the larvae develop early in the season. Larvae do not construct nests at any stage and are cryptic, matching the buds and woody parts of the host plant. Protection is based on camouflage and concealment. The larvae are solitary and develop through four instars. Satyrium californica larvae are unique and should not be confused with other species; the magenta color and dark dorsal spots are very distinctive. The same hosts are used by Satyrium behrii and S. saepium, however larvae of these species are green and are easily differentiated. California Hairstreak larvae are difficult to find due to their camouflage and general scarcity. Beating larvae from host plants such as Purshia can be productive for other species, but S. californica larvae cling so tightly to the host that this technique is less successful. It is difficult to obtain oviposition in captivity; females which appear to be gravid are often either unfertilized or devoid of eggs. Eggs are strongly glued to the woody substrate, but if left attached the wood will promote mold growth during overwintering.

Adult California Hairstreaks are easily separated from all Washington hairstreaks except Satyrium sylvinus, the Sylvan Hairstreak, particularly the dark nootka subspecies. The Sylvan Hairstreak is generally less heavily marked on the ventral hindwing. Satyrium sylvinus has fewer marginal orange spots above the blue ‘thecla’ spot (usually only one, sometimes a second pale one) than S. californica which has several such spots. A black spot occurs on both species proximal to the blue thecla spot. In S. californica this spot is distinctly chevron shaped but in S. sylvinus it is nearly straight.

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