Sulfurs: Labrador Sulfur (Colias nastes)

(Arthropoda: Insecta: Lepidoptera: Pieridae: Coliadinae)
Profile prepared by Sarah Foltz Jordan and Julia Janicki, The Xerces Society for Invertebrate Conservation

The Labrador Sulfur is a small species of sulfur of green wings with a tint of yellow and white on the upper side, and with light spots in the black wing border. It is a univoltine species and the numbers peak around July or August. It is a circumpolar species that inhabits high elevation wind swept tundra ridges; in North America, it ranges from much of Canada and Alaska, south to the Rocky Mountains and the Cascade Mountains. At this point, global climate change poses the greatest threat to this species.

conservation status
Global Status (2009): G5
National Statuses: United States (N5), Canada (N5)
State/Province Statuses: Montana (S2S3), Washington (S2S3), Alberta (S4), British Columbia (S5), Labrador (S3), Manitoba (S5), Northwest Territories (SNR), Nunavut (SNR), Quebec (S5), Yukon Territory (S5)
(NatureServe 2009).
This species is small for a sulphur, with a wingspan of 3.1 to 4.5 cm (1 1/4 to 1 3/4 in.) (Pyle 2002, Opler et al. 2010’). It is usually greenish both on the dorsal and ventral side, although the upperside can also be a dingy yellowish or dirty white. The amount of green, yellow, grey, or white on the upperside is variable (Pyle 2002, Guppy and Shepard 2001). The dorsal surface of the fore- and hindwing is marked with heavy, black melanic scaling, black basal suffusion, and broken, black marginal borders (Miller and Hammond 2007). Both sexes have light spots in the black wing border—a diagnostic trait in the males, as this is the only sulphur in Oregon and Washington in which the males as well as the females have light spots within the black border (Pyle 2002, Guppy and Shepard 2001). The dorsal surface of the forewings has a small, black discal spot, and the dorsal surface of the hindwings has a small, pale, yellow to orange discal spot (Miller and Hammond 2007). The ventral surface of the hindwings is yellow to deep olive with very heavy, black melanic scaling and a small, white, discal spot ringed with red (Miller and Hammond 2007, Pyle 2002). The ventral hindwing cell spot may be thinly rimmed with pink, often smeared distally (Pyle 2002). The ventral surface of the forewings is white with a dusky yellow apex and a small, black discal spot. Both dorsally and ventrally, the wings have a pale pink fringe (Pyle 2002).

Immature: The larvae of this species are dark moss-green with two red-edged stripes down each side (Pyle 2002). The eggs and pupae are difficult to find and to identify.

life history
The flight period of this univoltine species is timed according to snowmelt, but typically occurs between early July and early September, peaking in July-August (Pyle 2002). Females lay eggs on or near the host plants and caterpillars feed on host plant leaves. The larvae of this species overwinter, possibly for two years if the species is biennial (Pyle 2002).
This circumpolar, holarctic species is found on tundra across northern regions of Eurasia and North America. In North America, its distribution includes much of Canada and Alaska, south to the Rocky Mountains in northwest Montana and the Cascade Mountains in northern Washington (Pyle 2002, Miller and Hammond 2007).

Washington: In Washington, this species is known only from a narrow strip along the Canadian border in the western Okanogan Highlands, Okanogan County (Pyle 2002).

BLM/Forest Service Lands: This species is documented on Okanogan-Wenatchee National Forest.

habitat associations
This species inhabits high elevation wind swept tundra ridges, including sites in Washington at 7,000 and 8,300 feet. It is found in screes, fellfields, and summits, often where red heather (Phyllodoce empetriformis) grows. Caterpillars of this species feed on alpine milkvetch (Astragalus alpinus), white clover (Trifolium repens), slender crazyweed (Oxytropis campestris), sweetvetch (Hedysarum sp.) and other members of the pea family (Fabaceae) (Opler et al. 2010, Pyle 2002, Guppy and Shepard 2001, Scott 1986). Additionally, caterpillars may feed on dwarf willows in the northern Cascades of Washington and British Columbia (D. McCorkle in Miller and Hammond 2007). Adults feed on flower nectar (Opler et al. 2010).
Although this species is demonstrably secure globally it is quite rare in parts of its range, especially at the periphery (NatureServe 2009). Global climate change poses the greatest threat to this species, and warming climatic conditions are expected to eliminate the alpine habitat from much of this species’ southern distribution in the United States (Miller and Hammond 2007). Populations in north-central Washington and northwestern Montana represent the southernmost range of this species, and habitat loss in these areas will severely restrict the overall range of the species (Miller and Hammond 2007). Projected climate changes in this region include increased frequency and severity of seasonal flooding and droughts, reduced snowpack, and increased air temperatures (Field et al. 2007), all of which could impact this species’ habitat unfavorably.
conservation needs
Inventory: This species may be the most difficult Cascadian butterfly to watch, catch, or photograph, and a vast area of potential habitat has not been surveyed for this species (Pyle 2002). Surveys are recommended in northern Washington to determine the species’ status, abundance and distribution in the state.

The last known record of this species in Washington is from 1984, and most sites have not been revisited since the 1960’s or 1970’s. Revisit all known Washington sites and new sites with appropriate habitat, and survey for this species. Since abundance estimates for this species are not known, measure larval and adult abundance by conducting a timed visual search along transects through suitable habitat where food plants for caterpillars and nectar plants for adults are present (Miller and Hammond 2007).

Management: Protect and maintain habitat at sites where this species has been documented, including sufficient densities of the species’ host plants.


Guppy, C.S. and J.H. Shepard. 2001. Butterflies of British Columbia. UBC Press, Vancouver, British Columbia, 414 pp.

Miller, J.C. and P.C. Hammond 2007. Butterflies and moths of Pacific Northwest forests and woodlands. Forest Health Technology Team. 234 pp.

NatureServe. 2009. “Colias nastes”. NatureServe Explorer: An online encyclopedia of life [web application]. NatureServe, Arlington, Virginia. Version 7.1. (2 February 2009). Data last updated: February 2009. Available at: (Accessed 25 August 2010).

Opler, P.A., Lotts, K. and T. Naberhaus, coordinators. 2010. Butterflies and Moths of North America. Bozeman, MT: Big Sky Institute. Available at: (Accessed 15 August 2010).

Pyle, R.M. 2002. The Butterflies of Cascadia. A Field Guide to all the Species of Washington, Oregon, and Surrounding Territories. Seattle Audubon Society. 420 pp.

Scott, J. 1986. The Butterflies of North America. Stanford University Press, Stanford, CA. 583 pp.


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milkweed butterflies
wood nymph (Cercyonis sp.) by Caitlin LaBar