Basis for Listing

The subspecies varuna of Uhler's arctic occurs in the prairie provinces of Canada from Manitoba to British Columbia, and south through Montana and the Dakotas to western Nebraska. Other subspecies occur in the Yukon and Northwest Territories, and in the Rocky Mountains southward to northern New Mexico (Layberry et al. 1998; Opler et al. 2006). Minnesota is on the eastern fringe of this species' range.

Uhler's arctic, also known as the Rocky Mountain arctic, was first documented in Minnesota in 1965. One breeding colony has been repeatedly observed at a large dry prairie site in Clay County. The species was reported from a single site in both Mahnomen and Rock counties in 1968, however confirming specimens are not available from either of these sites. Presumably, the species was never common in the state even before prairie destruction as its dry prairie habitat was a minor component of the prairie landscape. Most dry prairie in Minnesota has been destroyed by overgrazing, conversion to cropland, or aggregate mining, and today potential habitat for the butterfly is rare. The primary threats to the habitat where the one breeding colony occurs are overgrazing and gravel mining. The small size of this colony, and its isolation, make it highly susceptible to extirpation. For these reasons, Uhler's arctic was listed as an endangered species in Minnesota in 1984.

  Description

Uhler's arctic is a medium-sized butterfly with a forewing length (base to apex) of 2.3-2.7 cm (0.91-1.06 in.). Both sexes are similar in color and markings. The wings are somewhat elongate. Beneath, the hind wing and normally exposed tip of the forewing are pale gray, coarsely and intricately striated with dark brown. The striations are thicker in the basal half of the hind wing. There is an arc of dark eyespots near the outer margin of the hind wing and again on the forewing; the size and number of these spots is variable. Above, the butterfly is orange-brown with the eyespot arcs repeated. The underside pattern shows through to some extent. Females are slightly larger than males and have more rounded wings. The butterfly rests with its wings closed above its back, exposing only the cryptically marked undersides, which camouflages it very well among dry grass litter in the prairie.

There is no closely similar butterfly in the habitat of Uhler's arctic in Minnesota. The prairie ringlet (Coenonympha tullia), another member of the subfamily Satyrinae that flies in the same habitat and at the same time, has a superficial resemblance to Ulhler's arctic when glimpsed in flight. The prairie ringlet is a smaller butterfly however, with rounded wings, and the underside is an olivaceous gray without dark striations. Eyespots are nearly absent both above and below.

  Habitat

The habitat of Uhler's arctic subspecies varuna in Canada is described as sandy prairie, lightly grazed areas, and open woods, where it prefers hilltops and ridges where there are bunch grasses (Layberry et al. 1998). In Minnesota, the one breeding colony occurs in dry prairie on sandy, gravelly crests and slopes of former shorelines of Glacial Lake Agassiz. Mid-height and short grasses such as needle-and-thread (Stipa comata), prairie junegrass (Koeleria macrantha), and blue grama (Bouteloua gracilis) are a major component of this prairie.

  Biology / Life History

Uhler's arctic adults emerge in late May and early June, and their flight is over by the end of June. Larval food plant preferences are unreported, although all known members of the genus feed on grasses or sedges (or both). Far northern and alpine populations probably require two years to complete larval development (Scott 1986), but this is unlikely in Minnesota. Overwintering occurs as a partially grown larva, and pupation occurs in a cell just under the soil (Scott 1986). Adults are not often observed nectaring, but yellow composites (Asteraceae) are reportedly favored (Marrone 2002). Ragwort (Senecio spp.) is sometimes visited at the Clay County site (R. Dana, Minnesota DNR, pers. comm.). Males are reported to seek mates by hovering several meters above the grass (Layberry et al. 1998). Nothing is known about dispersal tendencies in this butterfly.

  Conservation / Management

The small size of Minnesota's only known colony of Uhler's arctic makes it highly susceptible to extirpation. This could result from natural events (such as severe drought or hailstorms) or human caused ones (such as insecticide application), as well as from the vagaries of normal population processes (for example, by chance all adults in one generation are males). Loss of genetic diversity in a small, isolated population is also a threat. The nearest known colonies are in North Dakota on the other side of the intensively farmed Glacial Lake Agassiz lakeplain, making immigration to this population extremely unlikely. Any further loss of habitat at the Clay County site is a grave threat to the butterfly's survival here.

The larval stage of Uhler's arctic is probably highly sensitive to fall and spring prairie fires. Pupation in the soil may afford some protection from spring burns to this developmental stage. Fires in the favored habitat will generally be on the cool side as fuel loads are relatively low, but until larval habits are known well enough to permit more precise estimates of risk the use of prescribed fire as a habitat management tool should be judicious. The site should be subdivided and the units burned in a rotation that leaves enough larval habitat unburned to assure population survival and recolonization of burned areas between burns. How the butterfly responds to haying is not known, although much of the prairie in the Clay County site was hayed in the past and some haying continues. Uhler's arctic does not appear to tolerate heavy grazing (Klassen et al. 1989; Layberry et al. 1998). The largest single tract within the Clay County site is a privately owned ranch, and the butterfly has not been observed in its grazed prairie. If grazing pressure on the drier prairie within the ranch were reduced, it would probably benefit the butterfly.

  Conservation Efforts in Minnesota

Some of the prairie habitat supporting the only known colony of Uhler's arctic is protected through ownership and management by public agencies and private conservation organizations. Considerable effort has been devoted to reducing the amount of habitat destroyed by aggregate mining in the non-protected portion. An intensive survey of the site was conducted in 1985 to determine where Uhler's arctic occurred within the site. The Minnesota DNR supported survey efforts in 1987 and 1991 to find new locations and update information for known locations. Guidelines for protecting prairie butterfly populations within a fire-management program are employed by the major owners of Uhler's arctic habitat in Minnesota, and efforts have been made to educate other land managers in the state.

  References and Additional Information

Klassen, P., A. R. Westwood, W. B. Preston, and W. B. McKillop. 1989. The butterflies of Manitoba. Manitoba Museum of Man and Nature, Winnipeg, Manitoba. 290 pp.

Layberry, R. A., P. W. Hall, and J. D. LaFontaine. 1998. The butterflies of Canada. University of Toronto Press, Toronto, Ontario. 280 pp. + color plates.

Marrone, G. M. 2002. Field guide to butterflies of South Dakota. South Dakota Department of Game, Fish, and Parks, Pierre, South Dakota. 478 pp.

Opler, P. A., H. Pavulaan, R. E. Stanford, and M. Pogue, coordinators. 2006. Butterflies and moths of North America: Uhler's arctic (Oeneis uhleri). Bozeman, Montana: NBII Mountain Prairie Information Node. . Accessed 20 July 2006.

Royer, R. A. 1988. Butterflies of North Dakota: an atlas and guide. Science Monograph Number 1, Minot State University, Minot, North Dakota. 192 pp.

Scott, J. A. 1986. The butterflies of North America: a natural history and field guide. Stanford University Press, Stanford, California. 583 pp.

Swengel, A. B. 1998. Effects of management on butterfly abundance in tallgrass prairie and pine barrens. Biological Conservation 83(1):77-89.