Oarisma poweshiek
Critically endangered prairie butterfly that experienced a catastrophic population crash between 2005 and 2015. Dark brown with orange along the forewing costa and white-veined grey hindwing undersides. Fewer than 500 individuals remain in the wild.
Seasonal Activity
Diet
Nectar from a variety of prairie forbs (adult); foliage of native graminoids including prairie dropseed, little bluestem, and mat muhly (larva)
Lifecycle
One generation per year. Adults emerge in late June or early July and exist in the adult form for approximately two weeks, during which they nectar, mate, and lay eggs. Eggs are laid on or near grass host plants. Larvae feed on graminoid foliage, construct shelters, and overwinter as partially grown larvae. Pupation occurs in spring. Historically a common prairie butterfly prior to 2005, the species suffered a catastrophic and poorly understood population crash between 2005 and 2015. The Minnesota Zoo, John Ball Zoo, and Assiniboine Park Zoo all operate captive rearing programs. Over 700 individuals have been released through the Grassland Butterfly Conservation Program, including the first reintroduction at an extirpated site.
Ecology
Native Habitats
Details
Description
The Poweshiek Skipperling (Oarisma poweshiek) is a small, dark skipper butterfly with a wingspan of 24-30 mm. The upperside is dark brown with a narrow orange wash along the costa (leading edge) of the forewing — a key distinguishing feature. The underside of the hindwing is dark grey with prominent white veins, giving it a delicately streaked appearance. Unlike many skippers, the Poweshiek Skipperling has a relatively slender body and a subtle, understated appearance that belies its status as one of North America's most endangered butterflies.
Lifecycle
One generation per year. Adults emerge in late June or early July and are active for approximately two weeks. During this brief flight period, adults nectar on a variety of prairie forbs, mate, and lay eggs on or near grass host plants. Larvae feed nocturnally on graminoid foliage, constructing silk shelters at the base of plants. They overwinter as partially grown larvae and resume feeding in spring before pupating in early summer.
This species was historically a common prairie butterfly throughout its range prior to 2005. Between 2005 and 2015, populations crashed catastrophically for reasons that remain incompletely understood. Fewer than 500 individuals are estimated to remain in the wild. The Minnesota Zoo, John Ball Zoo (Michigan), and the Assiniboine Park Zoo Conservancy (Manitoba) all operate captive rearing and reintroduction programs. The Assiniboine Park Zoo completed the first reintroduction of captive-reared Poweshiek Skipperlings at an extirpated site, releasing over 700 individuals through the Grassland Butterfly Conservation Program.
Ecology
The Poweshiek Skipperling is entirely dependent on intact tallgrass prairie habitat. Adults nectar on a range of native prairie forbs including purple coneflower, black-eyed Susan, and prairie clovers. Larvae feed on a suite of native graminoids — primarily prairie dropseed (Sporobolus heterolepis), little bluestem (Schizachyrium scoparium), and mat muhly (Muhlenbergia richardsonis). The extent of habitat specialization may vary across the species' historical range, with different regional populations potentially using different host grass species.
Habitat loss and degradation from agricultural conversion, overgrazing, invasive species encroachment, and altered hydrological and fire regimes are the principal threats. The species' extreme rarity makes any disturbance — even prescribed fire intended to maintain prairie quality — a potential risk to the few remaining populations. Pesticide drift from adjacent agricultural lands is also a concern.
Host Plants
Larvae feed on native graminoids in intact tallgrass prairie. The specific host species may vary regionally across the historical range.
- Prairie dropseed (Sporobolus heterolepis)
- Little bluestem (Schizachyrium scoparium)
- Mat muhly (Muhlenbergia richardsonis)
- Possibly other native prairie graminoids
Habitat
Historically ranged from the Dakotas east through Minnesota and Iowa to the southern Lower Peninsula of Michigan, with Canadian populations restricted to southeastern Manitoba. Once common in mesic tallgrass prairie and prairie fens, the species is now reduced to a handful of sites. In Canada, the Poweshiek Skipperling is listed as Endangered under the Species at Risk Act (reassessed by COSEWIC as Endangered in 2014, upgraded from Threatened in 2003). In Ontario, the species is considered historically extirpated, though the exact status remains uncertain given the species' rapid decline.