Oarisma

Small-bodied butterflies with wingspans typically 2.3–3.0 cm. Species within Oarisma are distinguished from similar grass skippers by genitalic and wing pattern characters; precise identification often requires examination of male genitalia. O. poweshiek can be distinguished from the western congener O. garita by subtle differences in wing pattern and genitalic morphology—12 occurrence records in aggregated datasets were misidentified as O. poweshiek when they were actually O. garita.

Prairie and grassland ecosystems. O. poweshiek specifically occupies prairie fens in Michigan, mesic prairie in Wisconsin, and tallgrass prairie in Manitoba. Adults fly almost exclusively within prairie plant communities and are rarely observed in shrub, wetland, or forest communities. Egg-laying microhabitats are characterized as more open with drier microclimates compared to surrounding areas.

Genus distributed throughout the Americas: United States (south to Texas and Florida), Mexico, Central America, Caribbean (Cuba, Hispaniola, Virgin Islands), and South America. O. poweshiek historically occurred in ten U.S. states (Illinois, Indiana, Iowa, Michigan, Minnesota, Nebraska, North Dakota, Ohio, South Dakota, Wisconsin) and southeast Manitoba, Canada; currently extant at only six sites.

O. poweshiek is univoltine with adult flight period mid-June to mid-July. Other species' flight periods vary by latitude and elevation.

Larvae of O. poweshiek feed on graminoid species: Andropogon gerardi, Muhlenbergia richardsonis, Sporobolus heterolepis, and Schizachyrium scoparium (all Poaceae). Larvae alternate between shoots of various host species throughout development. Adult O. poweshiek nectar primarily on Rudbeckia hirta (black-eyed Susan).

• Andropogon gerardi - larval food plantbig bluestem
• Muhlenbergia richardsonis - larval food plantmat muhly
• Sporobolus heterolepis - larval food plantprairie dropseed
• Schizachyrium scoparium - larval food plantlittle bluestem
• Rudbeckia hirta - adult nectar sourceblack-eyed Susan; primary nectar plant for O. poweshiek in Manitoba

Univoltine (one generation per year). Development includes egg, larval (with 5–7 instars observed in O. garita), pupal, and adult stages. O. poweshiek larvae overwinter, with degree-day accumulation from egg hatch to eclosion studied using thermal thresholds of 6°C and 32°C. Overwintering may act to synchronize adult emergence. Ex-situ rearing of O. garita demonstrated that larvae can complete development in 5, 6, or 7 instars without maintaining consistent size ratios between instars, casting doubt on the applicability of Dyar's Rule for instar determination in this genus.

Larvae navigate microhabitats to locate host food plants. Adult O. poweshiek activities are distributed along a soil moisture gradient: egg-laying associated with mesic conditions, resting/basking with drier conditions, and nectar feeding across the gradient. Breeding behaviors in ex-situ settings are positively associated with sunlight intensity and negatively associated with age for both sexes; ambient temperature showed no significant effect on breeding frequency.

Pollinator in prairie ecosystems. O. poweshiek abundance in Manitoba is positively associated with density of Rudbeckia hirta, indicating potential mutualistic relationships with this nectar plant.

O. poweshiek listed as Federally Endangered in the United States and Canada in 2014. Subject to intensive conservation efforts including ex-situ captive breeding, habitat management, and reintroduction programs. Pesticide use limitation areas (PULAs) established in Midwest states to protect remaining populations. Research on this species has informed broader understanding of climate change vulnerability in prairie butterflies and contributed to development of species distribution modeling methodologies with field validation.

• CopaeodesFormerly treated as separate genus; species transferred to Oarisma in 2019 based on taxonomic revision. Some sources still list these species under Copaeodes.
• Oarisma garitaWestern congener similar in appearance to O. poweshiek; distinguished by wing pattern and genitalic characters. Historical misidentifications between these species have occurred in occurrence datasets.

• grass skipper
• prairie obligate
• endangered species
• North America
• univoltine
• conservation
• climate sensitive

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• A Brief Guide to Pesticide Mitigations, Label Changes to Protect Endangered Species
• rusty patched bumble bee and Poweshiek skipperling - Entomology Today
• pesticide use limitation areas - Entomology Today
• Observations on life history of Oarisma powesheik (Parker) 1870
• Endangered Oarisma poweshiek larvae vary their graminoid forage in Manitoba, Canada
• Aggregated occurrence records of the federally endangered Poweshiek skipperling (Oarisma poweshiek)
• Endangered Oarisma poweshiek butterfly larval foraging and adult habitat interactions in Manitoba, Canada
• Life history and ecology of the endangered Poweshiek skipperling Oarisma poweshiek in Michigan prairie fens
• Management practices benefit endangered Poweshiek skipperling (Oarisma poweshiek) in Manitoba tall grass prairie
• Adult activities of endangered Oarisma poweshiek butterflies are associated with a soil moisture gradient in tall grass prairie in Manitoba, Canada
• The role of ambient temperature in the ontogeny of endangered Oarisma poweshiek and their relative O. garita reared ex-situ at Assiniboine Park Zoo, Manitoba
• Conservation genetics of an endangered grassland butterfly ( Oarisma poweshiek ) reveals historically high gene flow despite recent and rapid range loss
• A field‐validated species distribution model to support management of the critically endangered Poweshiek skipperling ( Oarisma poweshiek ) butterfly in Canada
• Breeding Behaviors of the Endangered Prairie Butterfly Oarisma poweshiek (Lepidoptera: Hesperiidae) in Relation to Environmental Factors in an Ex Situ Conservation Setting