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Montana Field Guide

Montana Field Guides

Western White - Pontia occidentalis

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 2.0-2.5 cm. Base color milky white. Uppersurface of forewing with black discal cell end bar, 5-6 marginal chevrons ("V" spots) joined on outer third and cell ends, lighter and contrasting with blackish submarginal band. Undersurface for forewing apex and hindwing with veins outlined in gray-green (more strongly in spring flight), never bright green or heavy.

One flight, mostly July near treeline, June to early July in far north; two flights May through July at lower elevations and latitudes; three flights April to September in low elevation areas of Colorado (Scott 1986). Mainly two flights April to September, one flight July to August at high elevation (Glassberg 2001). Late May to early September in Colorado (Scott and Scott 1978), mid-June to September near treeline in California (Shapiro 1977), mid-March to mid-September in Oregon and Washington (Pyle 2002), early April to mid-September in Oregon (Warren 2005), June to September in British Columbia (Guppy and Shepard 2001), late April to October in southeastern British Columbia (Threatful 1988).

Diagnostic Characteristics
Best determined by a combination of uppersurface of forewing with 5-6 marginal chevrons ("V" spots) joined on outer third and cell ends, lighter and contrasting with blackish submarginal band; undersurface of hindwing with veins outlined in gray-green (more strongly in spring flight), never bright green or heavy.

Species Range
Montana Range Range Descriptions


Range Comments
Alaska, Yukon, western Northwest Territories south to central California, northern Arizona, northern New Mexico east across boreal Canada to central Ontario, the Great Lakes region, western South Dakota, extreme western Nebraska (Scott 1986; Opler and Wright 1999; Glassberg 2001); 1707 m to 4206 m elevation in Colorado (Brown 1957; Scott and Scott 1978), 12 m to at least 2957 m elevation in Oregon (Warren 2005), 456 m to at least 2500 m elevation in British Columbia (Threatful 1988; Guppy and Shepard 2001). In Montana, reported from all counties (Kohler 1980; Stanford and Opler 1993), to at least 2026 m elevation at Logan Pass in Glacier National Park (FLMNH Lepidopterists' Society database). Range expanding eastward across Northern Great Plains (Opler and Wright 1999) and locally in disturbed habitats such as railroad yards (Pyle 2002). Uncommon to common (Glassberg 2001).

Observations in Montana Natural Heritage Program Database
Number of Observations: 85

(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)


Open habitats, including montane meadows, dry forest openings, dry subarctic and alpine tundra, open plains, railroad yards, fields, roadsides (Shapiro 1977; Scott 1986; Threatful 1988; Opler and Wright 1999; Glassberg 2001; Pyle 2002). In Glacier National Park, Montana reported from mesic montane meadows and above treeline in alpine terrain (Debinski 1993); in the Greater Yellowstone Ecosystem, reported from hilltops, clearings, lowlands, roadsides, alpine terrain (Debinski and Pritchard 2002).

Food Habits
Larval food plants are native and exotic mustards, including Anelsonia, Arabis (several species), Athysanus, Barbarea, Brassica, Cardaria, Chorispora, Caulanthus, Descuriana, Draba (multiple species), Lepidium (multiple species), Phoenicaulis, Rorippa, Sisymbrium, Streptanthus, Thelypodium, Thlaspi; also the non-mustard Cleome (Emmel et al. 1970; Shapiro 1977; Ferris and Brown 1981; Scott 1986, 1992, 2006; Pyle 2002; Graves and Shapiro 2003; Warren 2005). Adults feed on flower nectar (including Achillea, Agoseris, Berteroa, Castilleja, Chrysothamnus, Cirsium, Cleome, Delphinium, Epilobium, Erigeron, Gaillardia, Heterotheca, Heuchera, Hymenoxys, Leucelene, Ligusticum, Machaeranthera, Medicago, Potentilla, Raphanus, Rhinanthus, Salix, Sedum, Senecio, Solidago, Symphyotrichum, Trifolium) and mud (Pyle 2002; Ezzeddine and Matter 2008; James and Nunnallee 2011; Scott 2014).

Reproductive Characteristics
Females lay eggs singly on host plant leaves (often undersurface), stems, flowers (Scott 1986, 1992, 2006; James and Nunnallee 2011). Eggs hatch in about 3 days, develop rapidly (depending on temperature) L5 instar and pupae in 15-20 days, adults eclose (emerge from pupae) in about 10 days; sometime pupate after reach L4 instar (James and Nunnallee 2011). Larvae feed on all parts of host plant, build no nest, overwinter as pupae (Scott 1979, 1986; James and Nunnallee 2011). Males patrol throughout the day on hilltops and around host plants in search of females (Scott 1975b, 1986; Shapiro 1977; Guppy and Shepard 2001; Pyle 2002; James and Nunnallee 2011).

  • Literature Cited AboveLegend:   View Online Publication
    • 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.
    • Emmel, J.F., O. Shields, and D.E. Breedlove. 1970. Larval foodplant records for North American Rhopalocera Part 2. Journal of Research on the Lepidoptera 9(4): 233-242.
    • Ezzeddine, M. and S.F. Matter. 2008. Nectar flower use and electivity by butterflies in sub-alpine meadows. Journal of the Lepidopterists' Society 62(3): 138-142.
    • 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.
    • Graves, S.D. and A.M. Shapiro. 2003.Exotics as host plants of the California butterfly fauna. Biological Conservation 110: 413-433.
    • 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.
    • 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.
    • 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.
    • 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.
    • Caruthers, J.C., and D. Debinski. 2006. Montane meadow butterfly species distributions in the Greater Yellowstone Ecosystem. University of Wyoming National Park Service Research Center Annual Report, 2006. Vol. 30, Art. 14. 85-96.
    • Forister, M.L., C.A. Halsch, C.C. Nice, J.A. Fordyce, T.E. Dilts, J.C. Oliver, K.L. Prudic, A.M. Shapiro, J.K. Wilson, J. Glassberg. 2021. Fewer butterflies seen by community scientists across the warming and drying landscapes of the American West. Science 371:1042-1045.
    • Forister, M.L., E.M. Grames, C.A. Halsch, K.J. Burls, C.F. Carroll, K.L. Bell, J.P. Jahner, et al. 2023. Assessing risk for butterflies in the context of climate change, demographic uncertainty, and heterogeneous data sources. Ecological Monographs 93(3):e1584.
    • Layberry, R.A., P.W. Hall, and J.D. LaFontaine. 1998. The Butterflies of Canada. University of Toronto Press. 280 pp. + color plates.
    • 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 White — Pontia occidentalis.  Montana Field Guide.  .  Retrieved on , from