|scientific name Hesperia assiniboia |
common name Plains Skipper
Native short grass prairie, and open, sandy areas of the aspen parkland and southern boreal forest.
Peak flight activity occurs in August, with flight dates ranging from late July to late Sept.
Distinguishing species of the genus Hesperia can be a challenge even to the experienced lepidopterist; differences in wing markings are subtle, and are best appreciated by looking at series of individuals from any given locality. There are two species with which the Plains Skipper is most likely to be confused: the Nevada Skipper (H. nevada) and the Common Branded Skipper (H. comma manitoba). The Plains Skipper can be separated from the Nevada Skipper by its smaller size, later flight season and by the ventral hindwing maculation: the spot nearest the anal margin is more or less in line with the adjacent spots in assiniboia, whereas this spot is offset towards the wing base in nevada. The Common Branded Skipper can be separated from the Plains Skipper by the darker colour of the hindwing underside (brown-green vs. yellow or yellow-green) and its occurrence in mountain grasslands (including alpine and subalpine meadows) rather than prairie grasslands (Bird et al. 1995). The Plains Skipper was once considered to be a subspecies of H. comma.
The Peace River grasslands populations of the Plains Skipper represent an undescribed subspecies (Bird et al. 1995), characterized by the yellowish ground colour of the underside with light yellow rather than whitish maculation. Populations from the northern parkland also have yellow rather than silver underside markings (Layberry et al. 1998).
The immature stages of Alberta populations are undescribed. The closely related taxon oregonia (W.H. Edwards) overwinters as an egg on Vancouver Island, BC (Hardy 1954), and it is likely H. assiniboia does so. Larvae of some populations construct silk-lined tunnels under dried cattle droppings (McCabe & Post 1977), which provide shelter during the day; larvae leave these shelters at night to feed (Acorn 1993). Fourth instar larvae have a dark brown head covered with black pits, and the body is covered with short bristles (McCabe & Post 1977).
Adults nectar at Dotted Blazing-star (Liatris punctata) and asters, including Aster canescens (Bird et al. 1995), and males of the Peace River populations congregate at the tops of south-facing river canyons (Guppy & Sheppard 2001).
Although this species can be locally common, its occurrences have declined as a result of habitat loss to agriculture and development. It may be relatively resilient to cattle grazing in native pastures, as it is most common in moderately grazed grassland (McCabe & Post 1977).
The undescribed Peace River populations are globally unique.
Unknown for Alberta. Larvae are reported to feed on grasses in other parts of the species range, including needle grass (Stipa spp.), Fescue (Festuca spp.), Blue gramma (Bouteloua gracilis), June grass (Koeleria cristata), and Brome grass (Bromus spp.) (Bird et al. 1995, Layberry et al. 1998). These records may refer to more than one species and require confirmation. McCabe & Post (1977) list Stipa and Koeleria as likely hosts in North Dakota.
The Plains Skipper is found from the Peace River grasslands south and east through the prairie provinces to Manitoba, south through the northern Great Plains states (Layberry et al. 1998). The Peace River populations are disjunct from the Great Plains populations.
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