Montana Field Guide

Species within the Capniidae are small winter stoneflies. This family is one of the largest families in the order Plecoptera, containing some 300 species distributed throughout the Holarctic region, 25 species occur in Montana. As their name implies these species are generally cold-water stenotherms and hatch in late-winter through early spring. The adults emerging in the winter are often found walking around on the snow. Their closest relatives are the rolled-winged stoneflies (Leuctridae). Many species are endemic to small ranges, perhaps due to the family's tendency to evolve tolerance for cold (isolating populations in mountain valleys) and winglessness (inhibiting dispersal).

Bolshecapnia missiona is most similar to B. sasquatchi, but it can be separated in the details of the epiproct and the posterior margin of the female subgenital plate. The epiproct is long and very thin apically in B. missiona with a pointed tip, while in B. sasquatchi it is much shorter and ends in a bluntly rounded tip, appearing foot shaped in lateral aspect. Luckily, Bolshecapnia sasquatchi has been determined to not occur in Montana, so, missiona is not as easily confused with the other Bolshecapnia species.

Bolshecapnia missiona is known mostly from first order and small second order streams at elevations from 750 to 1500 meters above sea level. This species is reported from about a half dozen small to medium sized creeks in Flathead, Lake and Missoula Counties. These are generally high to moderate gradient with cobble and boulder dominated substrates. Grant Creek is a freestone stream fed directly by snowmelt and cold seeps. High elevation reaches flow in small cascading pools and riffles over small angular cobble and gravel with an open southerly
exposure. Steep slopes at streamside release cold seepage into thick moss over deep sand and gravel mixed with woody debris (Baumann and Potter, 2007).

Merritt and Cummins (1996) report that members of this family are trophically shredder-detritivores; eating large particulate organic materials such as detritus, leaves and plants.

Cold-water stenotherms and shredder functional feeding group.

Specific threats to MT populations of Bolshecapnia missiona have not been identified. In general, stonefly populations are affected by changes to aquatic habitat such as alteration of flow patterns, streambed substrate, thermal characteristics, and water quality. Alteration and degradation of aquatic habitat and dimisnished snowpack is a primary concern for MT populations.