Pyrgus centaureae freija (Warren, 1924)
Basis for Listing
The grizzled skipper, also known as the Freija's grizzled skipper, is a Holarctic species with three named subspecies in North America. Subspecies loki occurs in the Rocky Mountains. Subspecies wyandot, which some authorities regard as a separate species (NatureServe 2008), occurs in the eastern United States, from Ohio and possibly Michigan to New York and south in the Appalachians to North Carolina. Subspecies freija ranges across northern North America from Alaska to Labrador. Minnesota is on the southern margin of its range, and its occurrence here is the only one in the contiguous United States (if the population in Michigan is indeed wyandot, as some think it is (NatureServe 2008)). The grizzled skipper is known from only a single locality in Minnesota, in Lake County. It probably occurs at other locations in Minnesota, and the absence of additional records may be explained by its spring flight period, when weather is often unsuitable for butterfly activity, and by the poor understanding of its habitat preferences here. However, there is little doubt that it is rare in the state. The grizzled skipper was listed as a special concern species in Minnesota in 1996.
The grizzled skipper is a small, dark butterfly with a wingspan of 2.4-2.8 mm (0.94-1.14 in.). Females are slightly larger than males, but the sexes are otherwise similar in appearance. The upperside is brownish-black with numerous small, angular white spots on the forewings and diffuse, whitish spots on the hind wings. Conspicuous white and black checkered fringes border both wings. Beneath, the sharply angular white spots in a grayish-brown ground create a strongly checkered effect. Adult grizzled skippers typically fly low over vegetation and may disappear into thickets. Their flight has been described as mothlike, not especially fast, but "blurry" because of the rapid wing strokes. The most similar species that occurs in Minnesota is the common checkered skipper (Pyrgus communis). This species is larger on average (wingspan 2.6-3.4 cm; 1-1.3 in.), and is lighter and brighter than the grizzled skipper. The pepper-and-salt skipper (Amblyscirtes hegon) is a small, dark, brownish-gray skipper with whitish markings that bears a superficial resemblance to the grizzled skipper. However, the whitish markings are much less prominent both above and beneath and do not create a checkered effect. At rest, the pepper-and-salt skipper holds its wings together vertically or spreads the hind wings more than the forewings, whereas the grizzled skipper typically rests with the hind and forewings held in the same plane, often spread almost horizontally.
In Manitoba, the grizzled skipper is reported to frequent "forest edges and openings as well as mixed scrub/heath tundra" (Klassen et al. 1989). At the one known location in Minnesota, the skipper occurs in a large, old clearing on sandy soils dominated by grasses, with some willow (Salix spp.), alder (Alnus incana), bilberry (Vaccinium cespitosum), and blueberries (Vaccinium angustifolium and V. myrtilloides). Black spruce (Picea mariana) and tamarack (Larix laricina) swamps border the clearing in places.
Biology / Life History
Development from egg to adult is reported to take two years in the northern part of the grizzled skipper's range, but it is not known whether this is the case in Minnesota. Little appears to be known about the life history of subspecies freija. In the Michigan entity, late-stage larvae overwinter (Nielsen 1999) and this is probably true in Minnesota. Adults may begin to emerge in late May and all die by the end of June. Cloudberry (Rubus chamaemorus) has been reported to be a larval host plant in Canada and in Europe. Shrubby cinquefoil (Potentilla fruticosa) has been reported for subspecies loki, and wild strawberry (Fragaria sp.) is documented in Michigan. All are members of the family Rosaceae. Adults take floral nectar from available flowers and also imbibe from wet soil.
Conservation / Management
The grizzled skipper is listed as a special concern species in Minnesota because it is apparently rare and limited to a small geographic area. Habitat alteration or destruction could easily threaten the continued occurrence of the species in Minnesota, but because so little is known about its biology, the specific nature of the changes that would threaten the species are not known. Forest fires may be detrimental in the short run, but important for creating and maintaining open habitat. Application of insecticides to grizzled skipper habitat would certainly be a threat, as would the use of herbicides that affect broad-leaved plants.
Conservation Efforts in Minnesota
Data on known occurrences of the grizzled skipper are maintained by the Minnesota DNR's Natural Heritage and Nongame Research Program and utilized in reviewing various activities for environmental impact, notably the application of insecticides and herbicides. These records are also available to forest managers. The one known grizzled skipper location was acquired from a timber company and incorporated into the forest plan for the Superior National Forest, which designated the site as a Special Use Area. A management plan to maintain the habitat opening with some mechanical clearing and careful prescribed burning has been implemented. The Minnesota Biological Survey has conducted limited searches for the grizzled skipper. Additional survey work is needed to determine the full range of this species in Minnesota and its abundance within that range.
References and Additional Information
Huber, R. L. 1981. An updated checklist of Minnesota butterflies. Minnesota Entomological Association Newsletter 14(3):15-25.
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.
NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia.
Nielsen, M. C. 1999. Michigan butterflies and skippers: a field guide and reference. Michigan State University Extension, East Lansing, Michigan. 248 pp.