The correct name for this entity is uncertain. Whatever you call it, it is abundant in Sierra Valley in late spring to early summer, and a few autumn individuals suggest at least the possibility of a second brood. The host is Juniper, Juniperus occidentalis. Males perch on the tree and form leks. They also puddle. Both sexes visit many flowers, especially Yarrow (Achillea) , Yellow Ivesia, Sulphur Flower (Eriogonum umbellatum), and Tansy Mustard (Descurainia). There is a great deal of minor variation in color and pattern.

This is a member of a species complex in evolutionary ferment, apparently in the process of speciating on several host plants of the juniper-cypress family, Cupressaceae. Nelson's Hairstreak feeds on Incense Cedar, Calocedrus decurrens, and is generally abundant in mixed mesic forest at mid-elevation on the Sierran West slope; it occurs irregularly at Washington, near the lower end of its altitudinal range; swarms at Lang Crossing; and is a rare stray at Donner, above the range of Incense Cedar.

An enigmatic species, usually rare but occasionally locally common for a generation. It breeds on pine mistletoes (genus Arceuthobium) on Gray or Foothill Pine (Pinus sabiniana) at low elevations and on Ponderosa and Jeffrey Pines (P. ponderosa, P. jeffreyi) higher.

The steel-blue color on the upper surface is unique in our fauna. This handsome species is generally rare, occurring at our sites as singletons visiting mud puddles, or on Rabbitbrush in autumn. It can be locally common on serpentine, where Gray Pine (Pinus sabiniana) tends to be heavily infested with the butterfly's host, Pine Mistletoe (Arceuthobium). It appears to have 2 or 3 broods per year, but records on our transect are so spotty that the seasonal pattern is less than obvious. Males are territorial perchers high in trees.