Basis for Listing
The Uncas Skipper (Hesperia uncas) has an extensive range in western North America, from the Canadian prairie southward into Mexico (MacNeill 1964). Its historic occurrence in Minnesota is restricted to an isolated outlier population in Sherburne County, more than 240km (150 mi.) east of its closest established populations in eastern South Dakota. The Minnesota population is possibly a relict from the early to mid-Holocene dry interval (ca. 10000-4000 B.P.), when major vegetation zones shifted well east of their modern positions in the upper Midwest (Williams et al. 2009). In this scenario, the range of the skipper would have expanded eastward with the expansion of appropriate habitat, and a small population has persisted here in habitat whose xeric character was preserved by special conditions despite the return of a moister climate. This skipper has also been recorded as a rare stray from farther west into southwest Minnesota, but there is no evidence of its persistence there.
The central Minnesota Uncas Skipper population was historically confined to several small remnants of a large complex of fossil sand dunes that formed within an extensive sand plain (Anoka Sand Plain Subsection) during the previously mentioned arid period. With the return to moister conditions, these dune blankets were stabilized by a mosaic of dry sand prairie and open bur oak savanna or scrub separated by wet prairies and oak brushland. The Uncas Skipper was not discovered here until 1961, after a state forest had been established that included much of the dune areas and the planting of pines and other conifers on the dunes was well underway. In 1968, its presence was also discovered in a privately-owned dunes remnant about 11 km (7 mi.) southeast of the state forest location.
Today, most of the former habitat within the state forest has been converted to densely stocked pine plantation and oak forest that has grown up in the absence of fire; dune areas outside the state forest have mostly become housing developments. As the planted conifers matured, the Uncas Skipper disappeared from the locations in the state forest where it had formerly been encountered and by 1972 was feared to have been extirpated. The skipper was confirmed to still be present in the private dunes remnant in 1978. In 1983 it was rediscovered in the state forest in a small private inholding that had not been planted with conifers and in some adjacent state forest land where planted conifers were still small. Because of its extreme rarity in the state and the threats to its remaining habitat, the Uncas Skipper was listed as an endangered species in Minnesota in 1984. The last reported observation of an Uncas Skipper from this relict population was in 1989; repeated efforts since have failed to detect it in either of the historical sites.
Description
The Uncas Skipper is a typical member of the "branded" skippers, or subfamily Hesperiinae. It is a small butterfly with a robust body, narrow angular forewings, and shorter more rounded hindwings. Forewing length (base to apex) is 1.4-1.5 cm (0.55-0.59 in.) in males, slightly greater in females. The antennae are relatively short and have clubbed ends with a sharp, backward-pointing tip. They are strong, fast fliers with a very rapid wing beat that appears as a blur to the human eye.
Males and females differ significantly in appearance on the upper side of the wings. Fresh males are typically a brownish orange, tending towards olivaceous, with diffuse, darker marginal coloration. Several small light-colored spots are visible in the darker area near the forewing tips. There is a narrow, almost linear, black "brand" (technically called a stigma) centrally placed along the long axis of the forewing. This structure contains specialized scent scales used in courtship. The pattern above has lower contrast in males from the central Minnesota population compared with those from farther west. Females are variable but tend to be darker with large whitish spots on the forewings and pale brown spots on the hindwings. The underside of the hindwing (the forewing is mostly hidden at rest) is similar in the two sexes and is distinctively marked with prominent rectangular white spots that are linked by white-scaled veins to form a web-like pattern. This is set off from the yellowish-brown ground color by dark brown shading around the white. Both sexes become darker and duller with age as scales wear off, but the distinctive patterning never disappears.
The underside pattern of the Uncas Skipper will reliably separate it from all other skippers of similar size and shape that may occur in the same area. These include the Long Dash (Polites mystic), the Tawny-edged Skipper (Polites themistocles), and the Sachem (Atalopedes campestris) in central Minnesota. The related Cobweb Skipper (Hesperia metea) could easily be mistaken for Uncas, but its flight period in our region ends in late May to early June, before Uncas adults emerge. There is no confirmed record of the Cobweb Skipper from Minnesota, though it occurs in several northwestern Wisconsin counties bordering Minnesota.
Habitat
The Uncas Skipper inhabits dry native prairie or barrens prairie on sand dune forms. More sparsely vegetated slopes and summits are especially critical. Adults will range more widely in search of nectar.
Biology / Life History
The Uncas Skipper in central Minnesota appears to have only a single generation in a year, though in South Dakota, and throughout most of its range, it produces two or more generations per year (Scott 1986; Marrone 2002). Adults have been observed from mid-June to mid-July, but in any given year the flight period is rarely more than three weeks. No detailed study of the life history of this skipper in Minnesota has been made, but in rearings from eggs the chronology of the various stages was similar to that of the Dakota Skipper (Hesperia dacotae) (personal observation). Larvae reached the fourth or fifth stage before hibernating for the winter and finished larval development the following spring.
All observed ovipositions have been on hairy grama (Bouteloua hirsuta), a small tufted grass that is common on dune slopes. Females typically lay only a single egg before moving on to another tuft. Larvae live in a series of increasingly larger shelters that they construct of plant materials and silk. Details of larval behavior have not been described. Partly grown larvae have been observed hibernating in shelters burrowed into the soil beneath the grass tufts (personal observation).
So far as is known, hairy grama is the obligate host plant for larvae of the central Minnesota Uncas Skipper population. The very similar relative, blue grama (Bouteloua gracilis), is most commonly reported to be the larval host throughout the skipper's western range. Adults are avid seekers of nectar. They visit almost any flowers available, but hairy puccoon (Lithospermum caroliniense) and hairy golden aster (Heterotheca villosa) are favorites of the Minnesota population.
Based on what is reported for other species in the genus, female Uncas Skippers probably mate shortly after emergence and rarely remate. Males seek receptive females primarily by perching on low vegetation or bare sand and pursuing any passing insect that might be a female Uncas Skipper. Uncas Skipper males elsewhere in the range frequently perch on soil or rock. Receptive females respond to pursuit by descending into the vegetation, where coupling follows almost immediately. Loose aggregations of perching males form on upper slopes and tops of prominences. It may be that unmated females are drawn to these same features. The dispersal behavior of mated females is not known. In particular, it is not known how much of a barrier to movement among the patches of open habitat the woodland that now separates them is.
Conservation / Management
Small population size due to past habitat loss and further habitat destruction are the primary threats facing the Uncas Skipper in Minnesota. The largest remaining continuous patch of habitat in the state is privately owned and vulnerable to development. The colony in the state forest is confined to a few small habitat patches separated from each other by dense woodland or forest, and it is separated from the colony on private land by over 11 km (7 mi.) of forest and increasing suburban development. Such small isolated colonies are at high risk of extirpation as a result of natural events (such as severe drought or hailstorms) or human-caused events (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 is another possible threat.
Survival of the Minnesota Uncas Skipper population will depend upon protection of the large private tract and on reclamation of habitat in the state forest from conifer plantation and oak woodland. The latter will take a number of years, though removing young conifers from the remaining habitat patches and opening corridors between these can be accomplished quickly. The use of prescribed fire as a habitat management tool must be very conservative; the core habitat areas on the dune slopes should probably not be burned at all. Abundance of the host grass, hairy grama, appears to be susceptible to rapid change, and maintenance of adequate amounts to sustain the fragile butterfly population may require special management intervention. Research is needed into the factors driving population dynamics of this grass in the dune habitat.
Additional potential habitat is present in the large Sherburne National Wildlife Refuge adjoining the state forest, and the U. S. Fish and Wildlife Service has been using fire to restore much of the upland within the Refuge to its original prairie and savanna condition. Searches in the 1980s of a small area of dune forms in the Refuge just north of the areas in the state forest inhabited at the time by Uncas Skipper were unsuccessful, despite the close similarity of the habitat there to the sites inhabited by the skipper (personal observation). If the skipper had been present in the Refuge, the aggressive fire management may have eliminated it.
Insecticides are a potential threat; oaks are among the preferred larval hosts of the Spongy Moth (Lymantria dispar) and when this moth spreads into Minnesota and infests the oaks that typically occur in or near this skipper’s habitat, pressure to spray these areas is likely to be intense.
Conservation Efforts in Minnesota
Most of the Uncas Skipper habitat remaining in the state forest has been dedicated as a state Scientific and Natural Area and is being managed to protect and restore the native sand prairie and savanna. Conifers in the core habitat patches have been removed and management to open up additional habitat and to restore intervening woodlands to oak scrub are underway. There have also been discussions about removing conifers from the rest of the remaining habitat patches that are within a recreation area in the state forest.
Authors/Revisions
Robert P. Dana, Ph.D. (MNDNR), 2025
(Note: all content ©MNDNR)
References and Additional Information
Lindsey, A. W. 1942. A preliminary revision of Hesperia. Denison University Bulletin, Journal of the Scientific Laboratories 37:1-50 + 6 plates.
MacNeill, C. D. 1964. The skippers of the genus Hesperia in western North America, with special reference to California (Lepidoptera: Hesperiidae). University of California Publications in Entomology 35:1-230.
Marrone, G. M. 2002. Field guide to butterflies of South Dakota. South Dakota Department of Game, Fish, and Parks, Pierre, South Dakota. 478 pp.
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.
