Search Field Guide
Advanced Search
Montana Field Guide

Montana Field Guides

Shasta Blue - Plebejus shasta


Global Rank: G5
State Rank: S5

Agency Status
USFWS:
USFS:
BLM:


 

External Links





 
General Description
[From Ferris and Brown 1981; Scott 1986; Opler and Wright 1999; Glassberg 2001; Pyle 2002] Forewing 1.0-1.3 cm. Lacking tails. Uppersurface of both sexes with forewing cell bar, male dull to dark iridescent blue with black marginal line and brownish submarginal band, female brown with some blue basally, hindwing with row of submarginal black spots capped with orange crescents on inward side. Undersurface gray with black spots, brown blotches, pale wing veins giving mottled appearance; hindwing with a pale orange submarginal band capped with inward-pointing black chevrons and containing metallic blue-green spots, hindwing postmedian spots dark brown to pale gray-brown but not black.

Phenology
One flight; mostly late June through July, mid-July to mid-August at or above treeline (Scott 1986). June to September (Glassberg 2001). Early June to early September (Emmel and Shields 1978). Mid-July to mid-August in Colorado (Scott and Scott 1978), mid-July to late August in Oregon (Pyle 2002; Warren 2005).

Diagnostic Characteristics
Best determined by a combination of uppersurface of male with black marginal line and brownish submarginal band, female brown with some blue basally, hindwing with row of submarginal black spots capped with orange crescents on inward side. Undersurface mottled, hindwing with a pale orange submarginal band capped with inward-pointing black chevrons and containing metallic blue-green spots, hindwing postmedian spots dark brown to pale gray-brown but not black.

Species Range
Montana Range

Click the legend blocks above to view individual ranges.
 


Range Comments
Oregon, southern Alberta, southern Saskatchewan, south in mountains and intermountain west to central California, southern Nevada, southern Utah, southern Colorado, also to western North Dakota, Black Hills region of South Dakota, western Nebraska (Scott 1986; Opler and Wright 1999; Glassberg 2001), not yet reported from Washington and British Columbia (Guppy and Shepard 2001; Pyle 2002); lower elevation subspecies 1525 m to 3048 m elevation in Colorado, high elevation subspecies above treeline to at least 3962 m elevation (Brown 1957; Scott and Scott 1978; Ferris and Brown 1981), 1554 m to 3505 m elevation in Wyoming (Emmel and Shields 1978), 1920 m to 3719 m elevation in California (Emmel and Shields 1978), 1829 m to 3475 m elevation in Nevada (Emmel and Shields 1978; Austin 1980), 914 m to 2957 m elevation in Oregon (Warren 2005). In Montana, reported from at least 26 counties across the state, rarely west of the continental divide (Kohler 1980; Stanford and Opler 1993; FLMNH Lepidopterists' Society database). Locally common (Glassberg 2001).

Migration
Non-migratory.

Habitat
Alpine fellfield, subalpine rocky slopes and ridges, well-drained forest openings, blowouts, sagebrush-steppe, prairie hills (Emmel and Shields 1978; Austin 1980; Scott 1986; Opler and Wright 1999; Glassberg 2001; Pyle 2002). In Greater Yellowstone Ecosystem, associated with xeric montane meadows dominated by sagebrush (Debinski et al. 2013).

Food Habits
Larval food plants include Astragalus (multiple species), Lupinus (multiple species), Oxytropis, and Trifolium (multiple species) (Emmel and Shields 1978; Scott 1986, 1992). Adults feed on flower nectar, including Arnica, Cistanthe, Erigeron, Eriogonum, Haplopappus, Heterotheca, Sedum, and Solidago (Pyle 2002; Scott 2014).

Reproductive Characteristics
Females lay eggs singly on underside of host plant leaves, sometimes on stems, seed pods, on ground litter near base of plant (Emmel and Shields 1978; Scott 1986, 1992). Larvae feed on young leaves and flowers of host plant, pupation occurs in litter near base of host plant and on undersides of rocks, adults eclose (emerge from pupae) in about 14 days. Biennial; hibernate first winter as egg, second winter as nearly mature larvae (Emmel and Shields 1978; Scott 1986, 1992). Post-diapause larvae in natural conditions in California tended by ants (four species of Formica) (Emmel and Shields 1978), also by Formica in captivity (Ballmer and Pratt 1991). Males patrol throughout the day low to the ground (< 10 cm) near host plants in cushion-plant communities on sparsely-vegetated ridges and slopes in search of females (Scott 1975b, 1986).

References
Login Logout
Citation for data on this website:
Shasta Blue — Plebejus shasta.  Montana Field Guide.  .  Retrieved on , from