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Montana Field Guide

Montana Field Guides

Western Tailed Blue - Cupido amyntula

Native Species

Global Rank: G5
State Rank: S5

Agency Status


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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. Tailed, fringes unchecked. Uppersurface of male blue, female brown with blue at wing base, hindwing of both sexes with a few marginal black spots. Undersurface chalky-white with indistinct black spots (spots sometimes absent), a single reduced orange spot on hindwing margin at base of tail.

Several flights, March to April in southern California, late April to mid-August in most of west; one flight, late May to mid-July in north, mid-June through July in Arctic (Scott 1986). March/April to August, with partial second flight in southern lowlands (Glassberg 2001). First flight April to June, second partial flight in August in Rocky Mountain states (Ferris and Brown 1981). Late April to late August in Colorado (Emmel 1964; Scott and Scott 1978; Scott and Epstein 1987), late March to mid-September in Oregon and Washington (Pyle 2002), late April through July in Oregon (Warren 2005), late April to July in British Columbia (Threatful 1988; Guppy and Shepard 2001).

Diagnostic Characteristics
Best determined by presence of tail, uppersurface bluish, undersurface chalky-white with indistinct black spots (spots sometimes absent), a single reduced orange spot on hindwing margin at base of tail.

Species Range
Montana Range Range Descriptions


Range Comments
Alaska south through western North America and all western mountains to northern Baja California (also shown by Oppler and Wright [1999] in northern Sierra Madre, Mexico), east across Canada's prairie provinces to northern Michigan, Ontario, and the Gaspé Peninsula of Quebec (Scott 1986; Opler and Wright 1999; Glassberg 2001); 1646 m to 3200 m elevation in Colorado (Brown 1957; Scott and Scott 1978), above 2591 m elevation in Donner Pass area, California (Shapiro 1977), near sea level to 1829 m elevation in Oregon (Warren 2005), 456 m to 549 m elevation in southeastern British Columbia (Threatful 1988). In Montana, reported statewide except the eastern 1/4, from 1030 m to about 2804 m elevation (Kohler 1980; Stanford and Opler 1993; FLMNH Lepidopterists' Society database; Butterflies and Moths of North America database). Mainly common to abundant (Glassberg 2001).

Observations in Montana Natural Heritage Program Database
Number of Observations: 7

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)


Undisturbed open areas, shrubsteppe, chaparral, foothill oak woodland, mesic montane meadows, streamsides, trailsides, above treeline in alpine fellfield (Emmel 1964; Shapiro 1977; Scott and Scott 1978; Scott 1986; Threatful 1988; Opler and Wright 1999; Glassberg 2001; Pyle 2002; Warren 2005); significantly more abundant in forest than grassland in northern Idaho (Pocewicz et al. 2009). In Glacier National Park, Montana reported from montane mesic meadows (Debinski 1993); in the Greater Yellowstone Ecosystem, reported from moist meadows, roadsides, sandy clearings, forest margins (Debinski and Pritchard 2002).

Food Habits
Larval food plants include Astragalus (several species), Lathyrus (several species), Lotus, Oxytropis, and Vicea (several species) (Scott 1986, 1992, 2006; Pyle 2002; Warren 2005). Adults feed on flower nectar (including Allium, Apocynum, Astragalus, Centaurea, Cerastium, Draba, Eriogonum, Lathyrus, Potentilla, Rhus, Sedum, Symphyotrichum, Taraxacum, Thlaspi, Trifolium, Vicea), horse manure, coyote dung, urine, and mud (Pyle 2002; Warren 2005; Scott 2014).

Reproductive Characteristics
Females lay eggs singly on host plant flowers and young seed pods, sometimes in crack on stems near leaf base, up to 3 eggs on a single plant (Scott 1986, 1992, 2006; James and Nunnallee 2011). Number of eggs per ovariole (1/8 of total) about 80 (Ehrlich and Ehrlich 1978). Eggs hatch in about 4-5 days (depending on temperature), develop rapidly from L1 instar to mature L4 instar or pupae in about 14-25 days. Most larvae overwinter as mature L4 instar and delay pupation until exiting winter diapause. Adults eclose (emerge from pupae) in about 11-14 days (James and Nunnallee 2011). Larvae solitary, feed on host plant flowers and fruits, build no nest (but may be contained entirely within seed pod), cannibalistic when crowded, tended by ants (Conomyrma bicolor, Formica obscuripes, and Lasius niger in the wild, F. pilicornis reported in captivity), overwinter as mature L4 larvae (Scott 1979, 1986; Ballmer and Pratt 1991; James and Nunnallee 2011). Males perch and often patrol throughout the day in low depressions between shrubs, hillsides, at gully mouths, awaiting passing females (Scott 1975b, 1986).

  • Literature Cited AboveLegend:   View Online Publication
    • Ballmer, G.R. and G.F. Pratt. 1991. Quantification of ant attendance (myrmecophily) of lycaenid larvae. Journal of Research on the Lepidoptera 30(1-2): 95-112.
    • Brown, F.M. 1957. Colorado Butterflies. Proceedings; Numbers Three through Seven. Denver Museum of Natural History, Denver, Co.
    • Debinski, D. 1993. Butterflies of Glacier National Park, Montana. Occasional Papers of the Museum of Natural History, the University of Kansas, Lawrence, Kansas. No. 159: 1-13.
    • Debinski, D.M. and J.A. Pritchard. 2002. A field guide to the butterflies of the Greater Yellowstone Ecosystem. Lanham, MD: Roberts Rinehart Publishers. 107 p.
    • Ehrlich, A.H. and P.R. Ehrlich. 1978. Reproductive strategies in the butterflies: I. Mating frequency, plugging, and egg number. Journal of the Kansas Entomological Society 51(4): 666-697.
    • Emmel, T.C. 1964. The ecology and distribution of butterflies in a montane community near Florissant, Colorado. American Midland Naturalist 72(2): 358-373.
    • Ferris, C.D. and F.M. Brown (eds). 1981. Butterflies of the Rocky Mountains. Univ. of Oklahoma Press. Norman. 442 pp.
    • Glassberg, J. 2001. Butterflies through Binoculars: A Field Guide to the Butterflies of Western North America. Oxford University Press.
    • Guppy, C.S. and J.H. Shepard. 2001. Butterflies of British Columbia: including western Alberta, southern Yukon, the Alaska Panhandle, Washington, northern Oregon, northern Idaho, northwestern Montana. UBC Press (Vancouver, BC) and Royal British Columbia Museum (Victoria, BC). 414 pp.
    • James, D.G. and D. Nunnallee. 2011. Life histories of Cascadia butterflies. Corvallis, OR: Oregon State University Press. 447 p.
    • Kohler, S. 1980. Checklist of Montana Butterflies (Rhopalocera). Journal of the Lepidopterists' Society 34(1): 1-19.
    • Layberry, R.A., P.W. Hall, and J.D. LaFontaine. 1998. The Butterflies of Canada. University of Toronto Press. 280 pp. + color plates.
    • Opler, P.A. and A.B. Wright. 1999. A field guide to western butterflies. Second edition. Peterson Field Guides. Houghton Mifflin Company, Boston, Massachusetts. 540 pp.
    • Opler, P.A., K. Lotts, and T. Naberhaus, coordinators. 2010. Butterflies and moths of North America. Big Sky Institute, Bozeman, MT. Available at: (Accessed 15 June 2015).
    • Pocewicz, A., P. Morgan, and S.D. Eigenbrode. 2009. Local and landscape effects on butterfly density in northern Idaho grasslands and forests. Journal of Insect Conservation 13: 593-601.
    • Pyle, R.M. 2002. The butterflies of Cascadia: a field guide to all the species of Washington, Oregon, and surrounding territories. Seattle Audubon Society, Seattle, Washington. 420 pp.
    • Scott, J.A. 1975b. Mate-locating behavior of western North American butterflies. Journal of Research on the Lepidoptera 14:1-40.
    • Scott, J.A. 1979. Hibernal diapause of North American Papilionoidea and Hesperioidea. Journal of Research on the Lepidoptera 18(3): 171-200.
    • Scott, J.A. 1986. The butterflies of North America: a natural history and field guide. Stanford University Press, Stanford, California.
    • Scott, J.A. 1992. Hostplant records for butterflies and skippers (mostly from Colorado) 1959-1992, with new life histories and notes on oviposition, immatures, and ecology. Papilio new series #6. 185 p.
    • Scott, J.A. 2006. Butterfly hostplant records, 1992-2005, with a treatise on the evolution of Erynnis, and a note on new terminology for mate-locating behavior. Papilio new series #14. 74 p.
    • Scott, J.A. 2014. Lepidoptera of North America 13. Flower visitation by Colorado butterflies (40,615 records) with a review of the literature on pollination of Colorado plants and butterfly attraction (Lepidoptera: Hersperioidea and Papilionoidea). Contributions of the C.P. Gillette Museum of Arthopod Diversity. Fort Collins, CO: Colorado State University. 190 p.
    • Scott, J.A. and G.R. Scott. 1978. Ecology and distribution of the butterflies of southern central Colorado. Journal of Research on the Lepidoptera 17(2): 73-128.
    • Scott, J.A. and M.E. Epstein. 1987. Factors affecting phenology in a temperate insect community. American Midland Naturalist 117(1): 103-118.
    • Shapiro, A.M. 1977. The alpine butterflies of Castle Peak, Nevada County, California. Great Basin Naturalist 37(4): 443-452.
    • Stanford, R.E. and P.A. Opler. 1993. Atlas of western USA butterflies: including adjacent parts of Canada and Mexico. Unpubl. Report. Denver and Fort Collins, Colorado 275 pp.
    • Threatful, D.L. 1988. A list of the butterflies and skippers of Mount Revelstoke and Glacier National Parks, British Columbia, Canada (Lepidoptera). Journal of Research on the Lepidoptera 27(3-4): 213-221.
    • Warren, A.D. 2005. Lepidoptera of North America 6: Butterflies of Oregon, their taxonomy, distribution, and biology. Contributions of the C. P. Gillette Museum of Arthropod Diversity, Colorado State University. Fort Collins, Colorado. 406 pp.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Allen, T.J., J.P. Brock, and J. Glassberg. 2005. Caterpillars in the field and garden: a field guide to the butterfly caterpillars of North America. Oxford University Press.
    • Brock, J.P. and K. Kaufman. 2003. Kaufman Field Guide to Butterflies of North America. Houghton Mifflin Company, New York, NY 284 pp.
    • Debinski, D. M. 1991. Inventory and monitoring of biodiversity: an assessment of methods and a case study of Glacier National Park, MT. Ph.D. Dissertation. Montana State University, Bozeman. 205 p.
    • Maxell, B.A. 2016. Northern Goshawk surveys on the Beartooth, Ashland, and Sioux Districts of the Custer-Gallatin National Forest: 2012-2014. Montana Natural Heritage Program. Helena, MT. 114pp.
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Western Tailed Blue — Cupido amyntula.  Montana Field Guide.  .  Retrieved on , from