Rare Species Guide

  Synonyms

Hesperia pawnee

  Basis for Listing

There are two widespread subspecies of Hesperia leonardus: the true Leonard's skipper (H. l. leonardus) in the eastern United States and southeastern Canada, and the Pawnee skipper (H. l. pawnee) in the Great Plains. These are very different in appearance and were until recently treated as different species, but studies of intermediate or "blend-zone" populations in western Wisconsin, eastern Minnesota, and western Iowa indicate substantial recent or continuing gene flow between them, supporting their treatment as subspecific variants of a single species (Scott and Stanford 1981; Spomer et al. 1993). Individuals in eastern Minnesota are highly variable in appearance, but overall these "blend-zone" populations are more similar to true Leonard's skipper (pictured at top right) than to Pawnee (pictured at top left). Populations in western Minnesota are typical Pawnee skipper, with no obvious evidence of gene flow from eastern populations. What appears to be true Leonard's skipper occurs in the southeast corner of Manitoba (Klassen et al. 1989), and specimens taken in adjoining Roseau County, Minnesota, may be the same (Ron Huber, pers. comm.).

Habitat loss is a serious threat to both the "blend-zone" Leonard's skipper and the Pawnee skipper in Minnesota. The dry prairie habitat of the Pawnee skipper has been reduced to a tiny fraction of its historical extent, and overgrazing and gravel quarrying are continuing threats to this habitat. Urban development continues to destroy what is left of the dry sand prairies and savanna habitat of the "blend-zone" Leonard's skipper in eastern Minnesota. None of the protected sites for either subspecies provide enough habitat to support large skipper populations, leaving these isolated colonies at risk of extirpation. For this reason, the Leonard's skipper (including the Pawnee skipper) was listed as a special concern species in Minnesota in 1996.

  Description

The Leonard's skipper (both subspecies) is a typical member of the "branded" skippers, or subfamily Hesperiinae. It is a smallish butterfly with a robust body,narrow, angular forewings, and shorter, broader hind wings. Forewing length (base to apex) of males is 1.5-1.65 cm (0.59-0.65 in.). Females are slightly larger, with more rounded wings. The antennae are relatively short, with clubbed ends that have a sharp, recurved tip. Leonard's 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 have a narrow, black "brand" of specialized scent scales used in courtship centrally placed along the long axis of their forewing. Females lack this, but instead have a pattern of light-colored squarish spots on a darker background; these are translucent in the Pawnee skipper and opaque in the Leonard's skipper. Pawnee skipper males have a brownish-orange ground color on the upperside, with variably extensive dark margins. The orange tends to be reduced in the "blend-zone" Leonard's skipper males. "Blend-zone" Leonard's skipper females also tend to be darker above than Pawnee females, and the spots may be translucent or opaque. Beneath, the two subspecies are strikingly different. Pawnee skippers are ochre colored. Males sometimes have an obscure row of lighter colored spots on the hind wings; females are more frequently spotted, with the whitish spots more evident. The underside of the Leonard's skipper is rust red, with a prominent band of contrasting ochre to white spots on the hind wings. In the "blend-zone" populations, the ground color varies from dark rust-red to brownish ochre, and the band of spots is commonly prominent but may be absent.

The late summer flight period of both subspecies reduces the problem of distinguishing them from other similar skippers. The Assiniboia skipper (Hesperia comma assiniboia) flies at the same time and overlaps the northern part of the Minnesota range of the Pawnee skipper. Generally, the underside of the Assiniboia skipper has a colder, grayish-ochre tone than that of the Pawnee skipper. In the southern part of its Minnesota range, the Pawnee skipper is quite similar to the slightly larger Ottoe skipper (Hesperia ottoe), but the flight period of the Ottoe skipper is usually over by the time the Pawnee skipper adults begin to emerge. A superficially similar skipper, the sachem (Atalopedes campestris), regularly produces a late-summer brood in southern Minnesota. Males of this species have a broad black patch surrounding the forewing brand, and females have a continuous band of light spots on the underside of the hind wing that forms a sharply angled chevron. These characters work to separate sachem individuals from both Pawnee and "blend-zone" Leonard's skippers. In far northern Minnesota (Roseau County), the Laurentian skipper (Hesperia comma laurentina) flies at the same time as Leonard's and in the same habitats, but it is smaller and the ground color of the hind wings beneath is a greenish-brown in contrast to the reddish brown of Leonard's.

  Habitat

For the Pawnee skipper, dry prairie (northern and southern) dominated by mid-height and short grasses is the preferred habitat. The Leonard's skipper in eastern Minnesota is strongly associated with dry habitats on sand, including prairie, savanna, and openings in woodlands. Dominance by native plant species characteristic of these plant community types seems to be an important factor.

  Biology / Life History

The Leonard's skipper (both subspecies) has a single annual generation. Eggs are laid in late summer and hatch in about 10 days. After a short period of feeding, young larvae (first or second instars) enter diapause until the following spring, when feeding and growth resume. Larvae complete their growth in late July and pupate, and adults emerge in August. Males emerge on average a few days earlier than females and quickly begin seeking mating opportunities by perching on taller stems in the prairie and pursuing insects that fly by. Receptive females respond to pursuit by descending into the vegetation, where mating occurs. Females probably mate shortly after emergence and seldom remate. Eggs are matured steadily during the female's lifetime and laid singly. Based on data from the similar Dakota skipper (Hesperia dacotae) (Dana 1991), potential fecundity is probably 200-250 eggs. Female longevity has not been measured in this species, but it is probably less than two weeks.

Larvae feed on grasses, but specific preferences have not been determined. Pawnee skipper females in southwestern Minnesota were observed ovipositing on seven different grass species as well as on three forb species (R. Dana, Minnesota DNR, pers. comm.). Of the two observed ovipositions by "blend-zone" Leonard's females in eastern Minnesota, one was on a grass and one on a forb (R. Dana, Minnesota DNR, pers. comm.). It is probable that this skipper, like the dakota skipper and the ottoe skipper, feeds opportunistically on several grass species in nature. Like other skippers in this genus, the larvae construct shelters from which they forage, and suitability of the grasses for shelter construction may be the most important determinant of use. The details of shelter location, whether up in the foliage or at the base of the plant or even underground, are not known. Adults are avid seekers of nectar; blazing stars (Liatris spp.) are especially attractive, but goldenrods (Solidago spp.) and asters (Aster spp.) are also commonly visited. Males also take moisture from wet soil.

In Minnesota, adults of both subspecies are rarely encountered away from native prairie, savanna, or woodland habitats, suggesting a rate of dispersal out of these too low to be detected by casual observation.

  Conservation / Management

Habitat loss is the primary threat to both subspecies of Leonard's skipper in Minnesota. Aggregate quarrying and overgrazing threaten unprotected habitat remnants of the Pawnee skipper. Wind power development is a recently added additional threat. In eastern Minnesota, habitat remnants for the "blend-zone" Leonard's skipper are severely threatened by residential and commercial development. These habitats are also threatened by succession to woodland and forest in the absence of fire or other disturbance. This is a threat even for habitat that is protected from other destruction.

The sensitivity of the Pawnee skipper to livestock grazing is not known, but grazing that eliminates nectar sources for adults and results in replacement of native grasses by exotic pasture grasses eliminates this skipper. Use of herbicides to control thistles and other pasture weeds and shrubs can also eliminate adult nectar sources. Insecticides are a potential threat to both subspecies: for the Pawnee skipper, drift from adjacent croplands and direct application to control episodic grasshopper outbreaks are the main concerns; for the "blend-zone" Leonard's skipper, some insecticides used for control of the spongy moth (Lymantria dispar) will become a threat as this moth spreads into Minnesota.

The use of prescribed burning to maintain the prairie and savanna habitats of this skipper can also pose a threat. There is circumstantial evidence that fire can cause high mortality to larvae (Swengel 1998; Swengel and Swengel 1999). Unless the shelters of small overwintering larvae are buried in the soil or deep in the bases of grass clumps, high mortality during fall and spring burns should be expected. Experimental investigation is needed. Factors that influence fire intensity, such as fuel load, fuel moisture content, and ambient temperature, are important to consider in planning burns. Subdividing a site and burning the units in a rotation that leaves enough larval habitat unburned to assure population survival and recolonization of burned areas between burns is recommended. This may be difficult for small sites. Haying may provide a suitable option in these cases.

Because most sites that support this skipper are small and isolated from others, their small colonies are at high risk of extirpation from both natural events (such as severe drought or hailstorms) and human caused ones (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 may also be a concern.

Several programs and resources are available to land managers and landowners to help protect and manage remaining prairie parcels including the Native Prairie Bank Program, the Native Prairie Tax Exemption Program, and a prairie restoration handbook.

  Conservation Efforts in Minnesota

The Leonard's skipper occurs in a number of sites in Minnesota that are owned and managed by public agencies and private conservation agencies. These include several moderately large prairie sites in western Minnesota that support fair populations of the Pawnee skipper, and a smaller number of large sites in eastern Minnesota that support fair populations of the "blend-zone" Leonard's skipper. The Minnesota DNR has sponsored or supported several survey efforts to find new Leonard's skipper locations and update information for previously known locations. Guidelines for protecting skipper populations within a fire-management program are employed by most of the major owners of Leonard's skipper habitat in Minnesota, and efforts have been made to educate other land managers. Data on the locations of colonies are maintained by the Minnesota DNR's Natural Heritage and Nongame Research Program and consulted during the state environmental review process, so that projects can be modified to reduce or avoid harm.