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Montana Field Guide

Montana Field Guides

Acmon Blue - Plebejus acmon


Global Rank: G5
State Rank: SNR

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General Description
[From Ferris and Brown 1981; Scott 1986; Opler and Wright 1999; Glassberg 2001; Pyle 2002] Forewing 1.1-1.4 cm. Sexually dimorphic; upperside of male deep blue to greenish-blue, female brown and sometimes with orange along veins. Uppersurface usually with black spot in forewing disk, hindwing with black scaling interior to orange aurora. Undersurface variable, off-white with pattern of black spots, hindwing submarginal orange band with iridescent blue spots, hindwing black marginal line not swollen at veins, fringes unchecked.

Phenology
Many flights in the south, March to October; one flight in the north, mid-June to early July, July to early August above treeline (Scott 1986). Mainly March and April to August and September, almost all year in southern California and Arizona, June to July at high elevation and into Alberta and Saskatchewan (Glassberg 2001).Early April to early October in Oregon and Washington (Pyle 2002; Warren 2005), mid-May to mid-August in British Columbia (Guppy and Shepard 2001).

Diagnostic Characteristics
Best determined by a combination of Uppersurface usually with black spot in forewing disk, hindwing with black scaling interior to orange aurora; submarginal orange band of hindwing undersurface with iridescent blue spots, hindwing black marginal line not swollen at veins, fringes unchecked.

Species Range
Montana Range

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Range Comments
Southwestern British Columbia, southern Alberta and Saskatchewan south through all of western US to northwestern Mexico, east to central Great Plains (Goodpasture 1973; Scott 1986; Opler and Wright 1999; Glassberg 2001); from 1310 m to 3810 m elevation in Colorado (Scott and Scott 1978; Ferris and Brown 1981), to 2438 m elevation in Oregon (Warren 2005). In Montana, reported across the state (Kohler 1980; Stanford and Opler 1993). Mainly common but rare to uncommon east of the continental divide (Glassberg 2001).

Migration
Non-migratory; infrequent eastward dispersal occurs (Scott 1986, 1992).

Habitat
A wide variety of open habitats, including oak woodland, montane conifer woodland, desert chaparral, rocky slopes and flats, prairie hills, sagebrush steppe, weedy areas, roadsides, above treeline in alpine terrain (Scott 1986; Opler and Wright 1999; Glassberg 2001; Guppy and Sheperd 2001; Pyle 2002). In Glacier National Park, Montana, reported from montane xeric meadows and above treeline in alpine terrain (Debinski 1993).

Food Habits
Larval food plants include Astragalus, several species of Eriogonum, several species of Lotus, Lupinus, Melilotus, Polygonum, and Trifolium flowers (Goodpasture 1974; Scott 1986, 1992; Guppy and Shepard 2001; Pyle 2002; Warren 2005). Adults feed on flower nectar (including Asclepias, Astragalus, Baccharis, Brassica, Cirsium, Eriodictyon, Eriogonum, Polygonum) and mud (Scott 1986, 2014; Warren 2005).

Reproductive Characteristics
Females lay eggs often singly (but up to 10) on host plant leaves or flowers (Goodpasture 1974; Scott 1986, 1992). Eggs hatch in about 6 days (depending on temperature). Development from egg-laying to pupation about 28 days, adult eclosion (emergence from pupae) about 7 days after pupation. Larvae do not build nest, remain hidden in host flowers, diapause as L2 or L3 instars, are tended by ants (Aphaenogaster, Formica, Iridomyrmex) in some regions, wander off host plant to pupate in leaf litter (Goodpasture 1973; Scott 1979; Warren 2005; James and Nunnalee 2011). Males patrol throughout the day on flats or hillsides near host plants as they seek females (Scott 1975b, 1986).

References
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Citation for data on this website:
Acmon Blue — Plebejus acmon.  Montana Field Guide.  .  Retrieved on , from