Stoneflies - Plecoptera: Perlodidae of Gunnison County, Colorado Skwala americana
American Stonefly, American Springfly, Little Golden Stonefly(Klapálek, 1912)
Updated 26 02 2026
TSN 568735
Life History
Richardson and Gaufin (1971) found nymphs in Utah were polyphagous (they ate many things), feeding primarily on Ephemeroptera (mayflies) (25%) and Chironomidae (midges) (21%).
Fuller and Stewart (1977) found S. americana's diet was over 75% animal matter in May in the Gunnison River at Lost Canyon Resort. Approximately equal volumes of Ephemeroptera (34%) and Plecoptera (34%) were present in the gut with detritus making up the remaining 24%. Chironomids and Simuliids were insignificant in the diet, suggesting S. americana, Cultus aestivalis and Isogenoides zionensis avoid direct competition through prey resource partioning. Small nymphs appeared in September and were highly carnivorous, showing positive electivity for Chironomidae. Their diet switched from carnivorous to polyphagous eating filamentous algae (30%, mostly Ulothrix) and diatoms (18% mostly Synedra, Fragilaria and Cymbella) in September and October. A similar diet switch was also noted in the Perlids Claassenia sabulosa and Hesperoperla pacifica.
Locations Collected
Gunnison River at the Lost Canyon Resort
Notes
Older publications may refer to this species confusingly as Arcynopteryx americana, Arcynopteryx parallela or in the latter part of the 20th century as Skwala parallela.
Good Links
Other Websites:
Photos, Map, Taxon Identifier Numbers - from the Global Biodiversity Information Facility Skwala americana at GBIF
Photos, Map, Museums, DNA - Barcode of Life Data System
Plecoptera Species File Skwala americana by DeWalt,RE; Hopkins,H; Neu-Becker,U and Stueber,G 2025
References
Baumann,RW; Gaufin,AR and Surdick,RF 1977 The stoneflies (Plecoptera) of the Rocky Mountains. Memoirs of the American Entomological Society 31, 1-208. PDF
Buchwalter,DB; Cain,DJ; Martin,CA; Xie,L; Luoma,SN and Garland,JT 2008 Aquatic insect ecophysiological traits reveal phylogenetically based differences in dissolved cadmium susceptibility. Proceedings of the National Academy of Sciences 105 24, 8321-8326.
DeWalt,RE and Stewart,KW 1995 Life histories of stoneflies (Plecoptera) in the Rio Conejos of southern Colorado. Great Basin Naturalist (55) 1-18. PDF
Abstract: "Thirty-one stonefly species representing eight families were collected during the March 1987 to May 1990 study period. Genera represented by more than one species included Capnia, Utacapnia, Taenionema, Suwallia, Triznaka, Isogenoides, and Isoperla. Peak species richness was recorded on or near the summer solstice in 1988 and 1989. Climatic differences between years were reflected in nymphal development and emergence phenology of most species. New or important corroborative life history data are presented for 11 stonefly species of this assemblage. The hyporheic nymphal development of most chloroperlid species limited the number of early instars sampled and our capacity to interpret voltinism. Limited nymphal data suggested a univoltine-slow cycle for Plumiperla diversa (Frison). Adults of Suwallia pallidula (Banks) and S. wardi (Banks) were present for an extended summer period, but the bulk of their respective emergence times was temporally separated. Isogenoides zionensis Hanson, Pteronarcella badia (Hagen), and Pteronarcys californica Newport were all shown for the first time to have a 9-10-mo egg diapause, and all three species have a semivoltine life cycle. Skwala americana (Klapálek) and Isoperla fulva Claassen were further confirmed to have univoltine-slow cycles. Univoltine-fast and univoltine-slow life cycles are reported for the first time in I. phalerata and I. quinquepunctata, respectively. Regression analysis revealed that six of the eight abundant species had extended emergence patterns (slopes of <5%/d), while only two had synchronous patterns. Warmer spring and summer temperatures in 1989 increased the slopes for five of the eight species studied, but did not change their synchrony designation. Nine of 11 abundant species advanced their median emergence date in 1989 over 1988. This and the higher slope values are consistent with a hurried nymphal development and narrower emergence period due to the warmer thermal regime of 1989."
Frison,TH 1937 II. Descriptions of Plecoptera with special reference to the Illinois species. Illinois Natural History Survey Bulletin 21 3, 78-99.
Discussed as Hydroperla paralella.
Fuller,RL and Stewart,K,W 1977 The food habits of stoneflies (Plecoptera) in the Upper Gunnison River, Colorado. Environmental Entomology 6, 293-302.
Discussed as Skwala parallela
Gaufin,AR; Clubb,R and Newell,R 1974 Studies on the tolerance of aquatic insects to low oxygen concentrations. Great Basin Naturalist 34:45-59. PDF
The authors studied the acute short term tolerance of aquatic insects to low oxygen. They used the 96 hour Median Tolerance Limit. They discussed Skwala americana as Arcynopteryx parallela. They did not find a TLm96 for S. americana using their experimental apparatus. Survival was 100% from 2-5mg/l of oxygen.
Hassage,RL and Stewart,KW 1990 Growth and voltinism of five stonefly species in a New Mexico mountain stream. The Southwestern Naturalist, 35 (2)130-134.
Discussed as Skwala parallela Abstract: "The nymphal growth and emergence of five stonefly species were determined by intensive sampling of leaf packs and mineral substrate in a riffle of a mountain stream in northern New Mexico. Isoperla fulva (n = 781) and Triznaka signata (n = 421) had late summer recruitment and slow univoltine life cycles, while nymphs of Prostoia besametsa (n = 2,009) were recruited in late fall and had a fast univoltine life cycle. Nymphs of Skwala parallela were apparently recruited in early summer or spring and were also univoltine. Classenia sabulosa had a semivoltine life cycle with nymphs recruited in late summer and early fall. Although they were of similar size at summer recruitment, nymphs of T. signata were generally smaller than those of I. fulva in fall and winter. Nymphs of P. besametsa grew rapidly during the coldest part of the year, achieving size equivalence with T. signata in December and February. The greatest nymphal growth rate was displayed by S. parallela; nymphs of this species reached 3.5 mm in head capsule width (HCW) by the end of the fall. Growth of C. sabulosa (which ultimately reaches 4-5 mm HCW) was much slower; this species required more than a single year of growth. Adult P. besametsa were first collected in April (n = 130) when they were most abundant; a few were also collected in May (n = 4) and June (n = 1). Skwala parallela adults (n = 13) were only collected in April. Adults of I. fulva (n = 37) were collected only during June, while those of T. signata were abundant in June (n = 22) and July (n = 33) with a single individual collected in August."
Kiffney,PM and Clements,WH 1993 Bioaccumulation of heavy metals by benthic invertebrates at the Arkansas River, Colorado. Environmental Toxicology and Chemistry 12, 1507-1517.
Quote from page 1512: "Variation among taxa: Metal concentrations in organisms collected from station AR-5 [impacted by heavy metal pollution from California Gulch] (fall, spring, summer) varied significantly among taxa (Fig 7). The highest concentrations were generally found in the mayfly Baetis spp., the stonefly Pteronarcella badia, and the caddisfly Arctopsyche grandis, whereas the lowest levels were measured in the two predators, Skwala americana, and Rhyacophila spp."
Klapálek,F 1912 Plécoptères. I. Fam. Perlodidae; [monographische Revision. II. Fam. Perlidae; Subfam. Perlinae, Subfam. Neoperlinae; mongraphische Revision] Series Sélys-Longchamps, Edmond de, baron, 1813-1900. Collections zoologiques; catalogue systematique et descriptif, fasc. 4, pt. 1-2.
Described as Arcynopteryx americana.
Kondratieff,BC and Baumann,RW 2002 A review of the stoneflies of Colorado with description of a new species of Capnia (Plecoptera: Capniidae). Transactions of American Entomological Society 128 (3) 385-401.
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."
Mutch,RA and Pritchard,G 1986 Development rates of eggs of some Canadian stoneflies (Plecoptera) in relation to temperature. Journal of the North American Benthological Society 5(4)272-277.
First page
Discussed as Skwala parallela. Abstract: "The eggs of eight species of Plecoptera from Alberta were reared at constant temperatures between 2 and 25°C. All species' eggs hatched at 2°C but none hatched at 25°C. The relationships between temperature and number of days required for development and hatching were fitted to power equations. Slope values (b) ranged from -1.31 for Skwala parallela to 0.03 for Amphinemura banksi; the remainder fell between -0.94 and -0.68. All of these values, except for that for S. parallela, imply that stonefly eggs develop most efficiently at the lowest temperature within the favorable range or develop with equal efficiency throughout the favorable range."
Richardson,JW and Gaufin,AR 1971 Food habits of some western stonefly nymphs. Transactions of American Entomological Society 97, 91-121.
Discussed as Arcynopteryx parallela
Ricker,WE 1992 Origin of stonefly names proposed by Ricker and collaborators. Perla, 18(1) 12 pages.
PDF
Quote from page 9: "Skwala Ricker 1943 (as sg. of Arcynopteryx). The name of a clan of Salish Indians living near Sardis, British Columbia. "
Shepard,WD and Stewart,KW 1983 Comparative Study of Nymphal Gills in North American Stonefly Genera and a New, Proposed Paradigm of Plecoptera Gill Evolution. Miscellaneous Publications of the Entomological Society of America 13:1-57
Illustration of nymphal osmobranchiae (gills) on page 52 as Skwala parallela.
Short,RA and Ward,JV 1980 Life cycle and production of Skwala parallela (Frison) (Plecoptera: Perlodidae) in a Colorado montane stream. Hydrobiologia 69(3), 273-275.
Abstract: "The life cycle and production of Skwala parallela, a perlodid stonefly, was investigated in a third-order Colorado montane stream. The species exhibited a univoltine life cycle with a distinct cohort. Small nymphs appeared in May. Rapid growth was exhibited throughout summer and autumn. During winter, growth slowed somewhat but was continuous until April. Maximum density of 34 nymphs/m2 occurred in July. Based upon the instantaneous growth method, annual production was 395.3 mg/m2 or 3.95 kg/ha dry weight with a P/B ratio of 4.4. "
Smith,LW 1917 Studies of North American Plecoptera (Pteronarcinae and Perlodini) Transactions of the American Entomological Society 43(4):433-489. PDF
Discussed as Arcynopteryx americana.
Stark,BP and Szczytko,SW 1988 Egg morphology and phylogeny in Arcynopterygini (Plecoptera: Perlodidae) Journal of the Kansas Entomological Society 61(2) 143-160.First Page
Abstract: Comparative data are provided for eggs of nine of the eleven recognized genera in the Holarctic tribe, Arcynopterygini, and these data are used to generate a preliminary phylogeny for the group. Four generic clusters (Megarcys/Sopkalia; Frisonia/Perlinodes/Oroperla; Arcynopteryx/Neofilchneria/Skwala and Setvena/Pseudomegarcys) are established primarily from egg data, but resolution of the Frisonia and Arcynopteryx trichotomies required data from other character suites. Detailed illustrations of the epiproct complex are given for six Nearctic genera to provide additional support for the current generic classification of the group and a standardized terminology is proposed for systellognathan Plecoptera eggs.
Stewart,KW and Stark,BP 1984 Nymphs of North American Perlodinae genera (Plecoptera: Perlodidae). The Great Basin Naturalist, pp.373-415. PDF
Stewart,KW and Stark,BP 2002 Nymphs of North American Stonefly Genera. 2nd edition The Caddis Press, Columbus, Ohio. 510 pages.
Photo of mature nymph pattern on page 111 figure 6.45. Illustrations of nymph on page 449-450, figures 14.55-14.56
Zuellig,RE; Heinold,BD; Kondratieff,BC and Ruiter,DE 2012 Diversity and Distribution of Mayflies (Ephemeroptera), Stoneflies (Plecoptera), and Caddisflies (Trichoptera) of the South Platte River Basin, Colorado, Nebraska, and Wyoming, 1873-2010. U.S. Geological Survey Data Series 606, 257 p. PDF - caution 46MB
Quote from page 58: "Records reported prior to 1989 were recorded as Isogenus, then Skwala parallela (Frison) which was later synonymized with S. americana (Klapálek) by Zwick (1989)." The elevation range is 5,050-8,650 feet and the adults emerge from March-May.
Zwick,P 1989 Notes on Plecoptera (18) Skwala americana (Klapálek, 1912), comb.n., the valid name for Skwala parallela (Frison, 1936). Aquatic Insects 11(3), 181-182.
Abstract: "A lectotype is designated for Arcynopteryx americana Klapálek, 1912, which is transferred to genus Skwala. The name replaces S. parallela (Frison, 1936), its junior synonym."
Illustrations
 Mesosternal Y-arms.
Only visible easily on mature nymphs. |
Lacinia |
Mandible
Notice the serrated edge on the big tooth. Compare to Arcynopteryx. |
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