Oeneis uhleri varuna (W. H. Edwards, 1882)
Click to enlarge
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 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.
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.
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.