Oeneis nevadensis

Distinguished from other Oeneis species by larger size and brighter orange-brown upperside coloration. O. n. gigas subspecies is slightly larger and darker than nominate form; O. n. iduna is notably paler above. Biennial flight pattern in even-numbered years separates most populations from O. n. gigas, which flies in odd-numbered years. Sexual dimorphism in eyespot number and distribution of dark scaling on forewing aids identification.

Wingspan 51–63 mm, the largest western Arctic species. Upperside bright orange-brown with dark brown scalloped wing margins. Males display one to two black eyespots on forewing and a large dark patch of sex scales extending from base to near apex. Females bear two to three forewing eyespots with dark scaling restricted to basal area. Both sexes have a small eyespot near hindwing tornus. Underside of forewing matches upperside; hindwing ventral surface uniformly striated dark brown and gray with whitish costa. Some populations show irregular dark median band on hindwing.

Forest clearings, open pinewoods, gravel roads, meadows, slopes, and canyons from sea level to 2,100 m elevation. Along coastal areas, occurs on bare mountain summits. Associated with montane and subalpine zones in the Cascade Mountains.

Cascade Mountains from southern British Columbia to northern California. Subspecies O. n. nevadensis occurs throughout main range; O. n. gigas restricted to southern tip of Vancouver Island; O. n. iduna found in northern coastal California.

Adults fly from early May to late September. Populations exhibit biennial emergence, appearing primarily in even-numbered years. The Vancouver Island subspecies O. n. gigas flies in odd-numbered years.

• Poaceae - larval hostspecific host plant unknown but believed to be grass family

Eggs whitish, oblong, flat-topped. Larva tan with black lateral dorsal stripe, sides striped with brown, greenish brown, and white; head lacks horns, posterior abdomen forked. First-year caterpillar overwinters partially grown; second-year overwinters as fifth instar. Two-year life cycle results in biennial adult emergence.

Adults are associated with high mountain hiking trails and open montane habitats. Biennial flight pattern synchronized across populations, with most appearing in even-numbered years.

• Oeneis macouniiSmaller size, duller coloration, different wing pattern elements
• Oeneis polixenesOverlapping range but smaller with different underside pattern
• Oeneis chryxusSmaller western Arctic with more muted coloration

• butterfly
• Arctic
• biennial
• montane
• Cascade Mountains
• satyrinae
• western North America
• fire-sensitive

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