Hesperia dacotae (Skinner, 1911)
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Basis for Listing
The Dakota Skipper (Hesperia dacotae) is a northern prairie endemic whose historical range extended from southern Saskatchewan and Manitoba through the Dakotas, Minnesota, and Iowa, and east to the Chicago area. Most of its native prairie habitat throughout this range has been lost through conversion to agriculture. The skipper has disappeared south and east of Minnesota and has become increasingly rare and local in its remaining range (Cochrane and Delphey 2002).
The Dakota Skipper is completely dependent upon the survival of its native prairie habitat. There is no evidence to date that reconstructed prairie provides suitable habitat. Although much of the prairie in the four large complexes that formerly supported strong numbers of this skipper is protected from destruction by government or private conservation ownership, portions remain vulnerable to plowing, overgrazing, gravel mining, and housing development. This is also true for many of the smaller sites. However, the recent precipitous decline of the Dakota Skipper makes it clear that protecting prairie is not sufficient to guarantee the survival of this butterfly. At present, there is no obvious explanation for its decline. The use of prescribed burning to mimic the fire regime that was a crucial component of the tallgrass prairie ecosystem has been a concern—burning too much of a site at one time, or too often, may result in unsustainable mortality. However, the skipper has vanished from several sites with no known history of prescribed burning, and much of the one site where it persists has been managed with fire for many years. Another possibility is exposure to insecticides. All of the prairie remnants are tiny islands in a sea of cropland and are thus vulnerable to contamination by insecticides applied to the surrounding crops. Because these patches of habitat are small and widely separated, once the species is eliminated from a patch—by whatever cause— it is highly unlikely that a Dakota Skipper population will be reestablished by immigrants from other patches.
The Dakota Skipper was listed as a threatened species in Minnesota in 1984. In response to the recent deterioration in its situation, the Minnesota Department of Natural Resources elevated its status in 2013 to state endangered. In 2014, its range-wide decline prompted the U.S. Fish and Wildlife Service to list it as federally threatened (USFWS 2014).
The Dakota Skipper is a typical member of the "branded" skippers (subfamily Hesperiinae). It is a smallish butterfly with a robust body, narrow angular forewings, and shorter more rounded hind wings. Forewing length (base to apex) is 1.3-1.4 cm (0.51-0.55 in.) in males, slightly greater in females. The antennae are relatively short with clubbed ends that have a sharp recurved tip. Dakota Skippers are fast fliers with a very rapid wing beat that appears as a blur to the human eye.
Males and females differ in wing markings most notably on the upper surface of the forewings. Males are typically a smooth brownish orange above with diffuse, darker marginal coloration. There is a very narrow, almost linear, black "brand" of specialized scent scales used in courtship located centrally along the long axis of the forewing. Females are more variable but tend to be darker or duller with bands of lighter spots on both hind and forewings. The pattern has a soft smeared look. The underside of the hind wing (the forewing is mostly hidden at rest) is generally a dull yellowish color with an obscurely lighter spot band in males. Females tend to be grayish brown with a more evident lighter spot band. Both sexes become darker and duller as scales wear off with age.
Similar skippers that fly at the same time as the Dakota Skipper and in the same habitat include the Ottoe Skipper (Hesperia ottoe), the Long Dash (Polites mystic), the Tawny-edged Skipper (Polites themistocles), the Sachem (Atalopedes campestris), the Delaware Skipper (Anatrytone logan), and the Iowa Skipper (Atrytone arogos iowa). The Ottoe Skipper is quite similar but is larger and brighter straw-yellow beneath. The Long Dash is usually a richer orange above with a more contrastingly dark border, and the brand on the male forewing is broader and more conspicuous; beneath, the hind wing is a richer yellow-brown, sometimes with reddish tints. There is a broad band of lighter spots, often quite pronounced in females. The orange on the upperside of the Tawny-edged Skipper is restricted to the forward edge of the wing with the remainder very dark brown. The Sachem is larger than the Dakota Skipper, and the male brand is embedded in a large round patch of black scales. Beneath, both the Delaware and Arogos skippers are unmarked clear yellow. Males of both lack the brand on the forewing, and females have no whitish spots.
In Minnesota, the Dakota Skipper seems to prefer native dry-mesic to dry prairie where mid-height grasses such as little bluestem (Schizachyrium scoparium var. scoparium), prairie dropseed (Sporobolus heterolepis), and side-oats grama (Bouteloua curtipendula var. curtipendula) are a major component of the vegetation. In North Dakota, this skipper also occurs in more mesic prairie (Royer and Maronne 1992). The most productive sites in Minnesota feature some topographic variation (Swengel and Swengel 1999). Adults will forage into nearby lowland prairie (mesic and wet prairie) for nectar.
Biology / Life History
The Dakota Skipper has a single annual generation. Adults emerge from pupae during a 2-3 week period beginning near the summer solstice (males a few days earlier than females, on average). Adults can live up to three weeks in captivity, but adult survival in the wild is probably a few days to a week. Eggs hatch in about 10 days. The partly grown larvae enter winter diapause in the fall and complete their growth the following spring. Adults of the new generation emerge after about a 2-3 week pupal stage.
Conservation / Management
Habitat destruction (Minnesota’s Remaining Native Prairie) has been the primary threat to the Dakota Skipper. All prairie habitat that is not protected by permanent dedication for conservation is at risk of destruction for agricultural production, aggregate mining, or development. Wind power development is a recently added threat. This skipper is reportedly sensitive to grazing (McCabe 1981). If not properly managed, long-term grazing can convert prairie to a sod dominated by exotic species that is unsuitable as skipper habitat. Episodic, heavy grazing that does not degrade the prairie may still eliminate the Dakota Skipper by removing all necter flowers during the flight period. Use of herbicides to control weeds or shrubs can permanently eliminate critical nectar sources, and insecticide drift from nearby agricultural fields can kill this skipper in all stages of development. In some locations in Minnesota the habitat is seriously threatened by the encroachment of shrubs and trees. Small isolated colonies of the Dakota Skipper are at high risk of extirpation resulting from both natural events (such as severe drought or hailstorms) and human caused events (such as accidental 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 also a threat (Britten and Glasford 2002).
Conservation Efforts in Minnesota
Much of the prairie habitat that supported each of the four largest known Dakota Skipper populations is protected through ownership and management by public agencies or private conservation organizations. This is also true for several of the sites that had smaller populations. The Minnesota DNR has sponsored or supported several survey efforts to find new locations of Dakota Skippers and updates information on known locations. Guidelines for protecting skipper populations within a fire-management program are employed by the major owners of Dakota Skipper habitat in Minnesota, and efforts have been made to educate other land managers. The U.S. Fish and Wildlife Service has developed conservation guidelines for prescribed fire, grazing, haying, habitat restoration, and weed control activities. Further research on the effects of cattle grazing on this species is needed. The Minnesota Zoo has recently begun a project to breed the Dakota Skipper in captivity to shore up the one remaining Minnesota population if needed and to reestablish populations in former sites. It has also initiated studies of possible insecticide contamination of remnant prairie sites.
Robert P. Dana, Ph.D., MN DNR and Ronald L. Huber, 1988; Robert P, Dana, Ph.D., MN DNR, 2008 and 2017
Britten, H. B., and J. W. Glasford. 2002. Genetic population structure of the Dakota Skipper (Lepidoptera: Hesperia dacotae): a North American native prairie obligate. Conservation Genetics 3:363-374.
Cochrane, J. F., and P. Delphey. 2002. Status assessment and conservation guidelines: Dakota Skipper, Hesperia dacotae (Skinner) (Lepidoptera: Hesperiidae), Iowa, Minnesota, North Dakota, South Dakota, Manitoba, and Saskatchewan. Department of the Interior, U.S. Fish and Wildlife Service, Twin Cities Field Office, Minneapolis, Minnesota. 92 pp.
Dana, R. P. 1991. Conservation management of the prairie skippers Hesperia dacotae and Hesperia ottoe: basic biology and threat of mortality during prescribed burning in spring. Station Bulletin 594-1991. Minnesota Agricultural Experimant Station, University of Minnesota, St. Paul, Minnesota. 63 pp.
McCabe, T. L. 1981. The Dakota Skipper, Hesperia dacotae (Skinner): range and biology, with special reference to North Dakota. Journal of the Lepidopterists' Society 35(3):179-193.
Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the prairie parkland and tallgrass aspen parklands provinces. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 362 pp.
Royer, R. A., and G. M. Maronne. 1992. Conservation status of the Dakota Skipper (Hesperia dacotae) in North and South Dakota. Report to the United States Department of the Interior, Fish and Wildlife Service, Denver, Colorado. 44 pp.
Selby, G. 2009. 2007/2008 Prairie butterfly surveys in western Minnesota. Natural Heritage and Nongame Research Program, Minnesota Department of Natural Resources. 28 pp. + appendices.
Swengel, A. B. 1998. Effects of management on butterfly abundance in tallgrass prairie and pine barrens. Biological Conservation 83(1):77-89.
Swengel, A. B., and S. R. Swengel. 1999. Observations of prairie skippers (Oarisma poweshiek, Hesperia dacotae, H. ottoe, H. leonardus pawnee, and Atrytone arogos iowa) (Lepidoptera: Hesperiidae) in Iowa, Minnesota, and North Dakota during 1988-1997. The Great Lakes Entomologist 32(4):267-292.
U.S. Fish and Wildlife Service. 2011. Species assessment and listing priority assignment form - Hesperia dacotae (Dakota Skipper). U.S. Fish and Wildlife Service, Bloomington, Minnesota. 49 pp.
U.S. Fish and Wildlife Service. 2014. Endangered and threatened wildlife and plants; threatened species status for Dakota Skipper and endangered species status for Poweshiek Skipperling. Federal Register Vol. 79, No. 206:63672-63748.