Home | Stonefly Nymph Key | Species List | Bibliography | Glossary

Plecoptera: Capniidae of Gunnison County, Colorado

Introduction to Isocapnia
Snowflies, Slender Winter Stonefly, Small Winter stoneflies, Tiny Winter Blacks

Banks, 1938
Updated 18 Mar 2021
TSN 102740

Provisional Species List

Isocapnia crinita
Isocapnia grandis


Isocapnia means "constant carbon dioxide level" in the medical world. In that usage the word refers to the pressure of carbon dioxide in the alveoli of the lungs. However Nathan Banks also used the word to name a rare genus of winter stoneflies in 1938.


Banks,N 1938 New native neuropteroid insects. Psyche (45) 72-79. PDF
      Isocapnia gen. nov.
Rather large, heavy species; radius not bent at origin of radial sector, an oblique vein beyond end of subcosta, several (five or more) costal cross-veins; setae long, twenty or more joints, four or five or more near base very short; anal area of hind wing not reaching to tip of wing. Much larger species than others of the subfamily. Genotype, Arsapnia grandis Bks. There are at least four species, Capnia crinita Claassen, 74 Psyche [March I. fumosa, herewith described, and a clear winged species in which the radial sector is forked beyond the cross-veins; all are from the northwestern parts of United States and western Canada.

Baumann,RW, Gaufin,AR and Surdick,RF 1977 The stoneflies (Plecoptera) of the Rocky Mountains. Memoirs of the American Entomological Society 31, 1-208.
     Quote from page 77: "The genus Isocapnia is of particular interest because of its rarity and because of the large size of most species compared to other capniids. The known nymphs are distinctive in having a fringe of long swimming hairs running along the cerci. The most interesting feature of the adults is the occurrence of dwarf males in certain species. Such males are characterized by smaller size and very reduced wings. In species which have long-winged males as well as dwarf ones, the former show no tendency toward wing reduction or intergradation with the dwarf forms. "

Malison,RL; DelVecchia,AG; Woods,HA; Hand,BK; Luikart,G and Stanford,JA 2020 Tolerance of aquifer stoneflies to repeated hypoxia exposure and oxygen dynamics in an alluvial aquifer. Journal of Experimental Biology, 223(16). PDF

Malison,RL; Ellis,BK; DelVecchia,AG; Jacobson,H; Hand,BK; Luikart,G; Woods,HA; Gamboa,M; Watanabe,K and Stanford,JA 2020 Remarkable anoxia tolerance by stoneflies from a floodplain aquifer. Ecology, 101(10), p.e03127. PDF
     Abstract: "Alluvial aquifers are key components of river floodplains and biodiversity worldwide, but they contain extreme environmental conditions and have limited sources of carbon for sustaining food webs. Despite this, they support abundant populations of aquifer stoneflies that have large proportions of their biomass carbon derived from methane. Methane is typically produced in freshwater ecosystems in anoxic conditions, while stoneflies (Order: Plecoptera) are thought to require highly oxygenated water. The potential importance of methane-derived food resources raises the possibility that stonefly consumers have evolved anoxia-resistant behaviors and physiologies. Here we tested the anoxic and hypoxic responses of 2,445 stonefly individuals in three aquifer species and nine benthic species. We conducted experimental trials in which we reduced oxygen levels, documented locomotor activity, and measured survival rates. Compared to surface-dwelling benthic relatives, stoneflies from the alluvial aquifer on the Flathead River (Montana) performed better in hypoxic and anoxic conditions. Aquifer species sustained the ability to walk after 4-76 h of anoxia vs. 1 h for benthic species and survived on average three times longer than their benthic counterparts. Aquifer stoneflies also sustained aerobic respiration down to much lower levels of ambient oxygen. We show that aquifer taxa have gene sequences for hemocyanin, an oxygen transport respiratory protein, representing a possible mechanism for surviving low oxygen. This remarkable ability to perform well in low-oxygen conditions is unique within the entire order of stoneflies (Plecoptera) and uncommon in other freshwater invertebrates. These results show that aquifer stoneflies can exploit rich carbon resources available in anoxic zones, which may explain their extraordinarily high abundance in gravel-bed floodplain aquifers. These stoneflies are part of a novel food web contributing biodiversity to river floodplains."

Nebeker,AV and Gaufin,AR 1967 Geographic and seasonal distribution of the family Capniidae of western North America (Plecoptera). Journal of the Kansas Entomological Society 40(3)415-421 Abstract and first page

Ricker,WE 1959 The species of Isocapnia Banks (Insecta, Plecoptera, Nemouridae). Canadian Journal of Zoology, 37(5), 639-653.
     Abstract: " The stonefly genus Isocapnia has 10 known species in the North American Cordillera, 1 in Japan, and 1 in coastal Siberia. Of the American species, fraseri, hyalita, missourii, and mogila are here described as new, as is the Siberian species kudia. Unusual or perhaps unique among stoneflies is the occurrence of dwarf males, having rudimentary wings, along with normal males, in the Japanese and in several American species. "

Stanford JA; Gaufin AR. 1974 Hyporheic communities of two Montana rivers. Science 185:700-702. PDF
     The authors report three Isocapnia species from the hyporheic zone of the Tobacco and Flathead rivers in Montana. They found Isocapnia crinita Isocapnia grandis and I. missouri. They state that the Isocapnia species have at least a two year life cycle.

Stewart,KW and Ricker,WE 1997 The stoneflies of the Yukon. pgs 201-222 in Danks,HV and Downes,JA (Eds.), Insects of the Yukon. Biological Survey of Canada (Terrestrial Arthropods), Ottawa. 1034 pp.
     Quote from page 208: "Eastern Palaearctic and Western Nearctic; 11 Nearctic species distributed in the west, from Alaska and Yukon south to California and New Mexicao. Adults brown to black, some species as large as 15-20-mm; brachypterous dwarf male morphs occur in some large river species. Emergence February-June depending on elevation and latitude. Nymphs occur deep in hyporheic gravel under or adjacent to streams until just prior to emergence. Little detail is known of life histories, but nymphal size variation suggests that at least some species are semivoltine. "

Stewart,KW and Stark,BP 2002: Nymphs of North American Stonefly Genera. 2nd edition The Caddis Press, Columbus, Ohio. 510 pages.

Zenger,JT and Baumann,RW 2004 The holarctic winter stonefly genus Isocapnia, with an emphasis on the North American fauna (Plecoptera: Capniidae) Monographs of the Western North American Naturalist 2(1):65-95. PDF

Brown,WS 2004 Stoneflies or Plecoptera of Gunnison County, Colorado