Plebejus acmon

This species has been found at all sites on the transect, though it is not certain that it overwinters at Donner (some years) or Castle Peak (at all). It is weedy and highly dispersive. Although some of its host plants (Deer Weed, Lotus scoparius; Wild Buckwheats, especially the Eriogonum nudum group) are perennial and allow it to have >1 generation in the same place, many (annual species of Lotus, especially L. purshianus; Polygonum aviculare group) are ephemeral and do not. It thus has to be constantly on the move, looking for hosts.

Plebejus icarioides

Found at all of our sites except in the Sacramento Valley and Suisun. As recently as the 1970s it still had a presence in the Valley on Lupinus formosus, but seems to be gone now. An extremely variable species with several distinctive subspecies in the Bay Area. The Sierra Valley population frequently has the spot-pattern on the hindwing beneath "blind" or nearly so (white dots without or with only very reduced black centers, on an ashen ground). Similar specimens occur occasionally on Castle Peak. Males are avid puddlers and may be quite abundant.

Plebejus lupini

The name is a misnomer, since this butterfly always breeds on Wild Buckwheats (Eriogonum, family Polygonaceae) and has nothing to do with lupines. However, under the International Code of Zoological Nomenclature, there's nothing one can do about that! The butterfly is very similar to the Acmon Blue, but unlike it, is always single-brooded. Although there are a few lower-elevation colonies in the Sierra, on our transect it occurs only from Lang Crossing (5000') upslope, flying generally in late spring-early summer (May-July).

Plebejus saepiolus

Abundant on cool montane meadows, on our transect Lang Crossing and up (including Sierra Valley), where it flies just above the ground. The sexual dimorphism is extreme, and all our females are brown. High-altitude specimens may have the black spots beneath rather large and squarish. Adults visit low flowers, especially those of clovers, and males puddle. This species usually co-occurs with the Sonoran Skipper and the Nevada Cloudy-Wing and, often, with the Gray Blue.

Plebejus shasta

Despite its name, the Shasta Blue does not occur on Mount Shasta. It is a high-altitude species. It formerly occurred at Donner but seems to be extinct in my site, though it persists at 8000' at Sugar Bowl, e.g. It is common at Castle and Basin Peaks, occurring in alpine rock-garden habitats where it generally flies from mid-season onward (July-October), along with the Sooty Gossamer-Wing. It flies near ground level, often basking with wings open, and visits Sulphur Flower (Eriogonum umbellatum) more than any other flower.