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Stoneflies - Plecoptera: Pteronarcyidae

Pteronarcys californica
Salmonfly, Giant Salmonfly, Willowfly, Giant Stonefly

Newport 1848
Updated 23 February 2024
TSN 102473


These big, prehistoric looking nymphs are common in medium-sized rivers below 7500ft, usually in trash piles and leaf packs or under large stones in eddies near shore. Enormous numbers of adults emerging over a few weeks in the Black Canyon and many other western streams are quite the spectacle and a favorite of the trout and flyfishermen alike. There have been attempts to reintroduce them in the Gunnison River above the dams in the Aspinall unit.

Life History

Richardson and Gaufin noted this species eats detritus. All of the specimens they examined had sand in their guts. No sand was found in the hind gut so they assume the nymphs regurgitate the sand as required. Algae was found in many specimens. Traces of animal matter were found in some guts. Laboratory observations of feeding habits on leaf packs led to the observation that P. californica is occasionally cannibalistic. Usually nymphs lie hidden with antennae protruding and waving side to side. When food contacts their antennae the nymphs rush out and seize the food with their maxillae. While searching for food, P. californica nymphs move slowly with their antennae continuously moving back and forth.

Locations Collected

Gunnison River at Soap Creek and McCabe Lane, Black Canyon, Lake Fork of the Gunnison.

Good Links

Species details from plecoptera.species.file

Photo - Nymph from Michael Wigle Photography.

Photo of adult - from the Tree of Life

Another Photo of adult - from the Tree of Life

Hatch chart for East, Taylor, and the Gunnison River through Black Canyon. https://dragonflyanglers.com/fishing-report/#hatch-chart

Photos, Map, Museum specimens, DNA - Barcodinglife.org


Adams,MM; Baxter,CV and Delehanty,DJ 2023 Emergence phenology of the giant salmonfly and responses by birds in Idaho river networks. Frontiers in Ecology and Evolution, 11, p.804143. HTML
     Abstract: "Emergence of adult aquatic insects from rivers is strongly influenced by water temperature, and emergence timing helps to determine the availability of this ephemeral food resource for birds and other terrestrial insectivores. It is poorly understood how spatial heterogeneity in riverine habitat mediates the timing of emergence. Such spatiotemporal variation may have consequences for terrestrial insectivores that rely on aquatic-derived prey resources. We investigated emergence phenology of the giant salmonfly, Pteronarcys californica, at three spatial scales in two Idaho river networks. We examined the influence of tributary confluences on salmonfly emergence timing and associated insectivorous bird responses. Salmonfly emergence timing was highly variable at the basin-scale during the period we sampled (May–June). Within sub-drainage pathways not punctuated by major tributaries, emergence followed a downstream-to-upstream pattern. At the scale of reaches, abrupt changes in thermal regimes created by 10 major tributary confluences created asynchrony in emergence of 1–6 days among the 20 reaches bracketing the confluences. We observed 10 bird species capturing emerged salmonflies, including 5 species typically associated with upland habitats (e.g., American robin, red-tailed hawk, American kestrel) but that likely aggregated along rivers to take advantage of emerging salmonflies. Some birds (e.g., Lewis’s woodpecker, western tanager, American dipper) captured large numbers of salmonflies, and some of these fed salmonflies to nestlings. Emergence asynchrony created by tributaries was associated with shifts in bird abundance and richness which both nearly doubled, on average, during salmonfly emergence. Thermal heterogeneity in river networks created asynchrony in aquatic insect phenology which prolonged the availability of this pulsed prey resource for insectivorous birds during key breeding times. Such interactions between spatial and temporal heterogeneity and organism phenology may be critical to understanding the consequences of fluxes of resources that link water and land. Shifts in phenology or curtailment of life history diversity in organisms like salmonflies may have implications for these organisms, but could also contribute to mismatches or constrain availability of pulsed resources to dependent consumers. These could be unforeseen consequences, for both aquatic and terrestrial organisms, of human-driven alteration and homogenization of riverscapes."

Albertson,LK; Briggs,MA; Maguire,Z; Swart,S; Cross,WF; Twining,CW; Wesner,JS; Baxter,CV and Walters,DM 2022 Dietary composition and fatty acid content of giant salmonflies (Pteronarcys californica) in two Rocky Mountain rivers. Ecosphere, 13(1), p.e3904. PDF
     Abstract: "Many aquatic invertebrates are declining or facing extinction from stressors that compromise physiology, resource consumption, reproduction, and phenology. However, the influence of these common stressors specifically on consumer–resource interactions for aquatic invertebrate consumers is only beginning to be understood. We conducted a field study to investigate Pteronarcys californica (i.e., the “giant salmonfly”), a large-bodied insect that is ecologically and culturally significant to rivers throughout the western United States. We sampled gut contents and polyunsaturated fatty acid composition of salmonflies to compare resource consumption across river (Madison or Gallatin, Montana), sex (male or female), and habitat (rock or woody debris). We found that allochthonous detritus comprised the majority of salmonfly diets in the Gallatin and Madison Rivers, making up 68% of the gut contents on average, followed by amorphous detritus, diatoms, and filamentous algae. Diets showed little variation across river, sex, or length. Minor differences in diets were detected by habitat type, with a higher proportion of diatoms in the diets of salmonflies collected from rocky habitat compared to woody debris. Fatty acid composition generally supported the results of gut content analysis but highlighted the importance of primary producers. The presence of eicosapentaenoic acid (20:5n-3) and alpha linolenic acid (18:3n-3) indicated consumption of diatoms and filamentous green algae, respectively. Our research underscores the importance of a healthy riparian zone that provides allochthonous detritus for invertebrate nutrition as well as the role of algae as an important source of fatty acids."

Armold,MT; Blomquist,GJ and Jackson,LL 1969 Cuticular lipids of insects-III. The surface lipids of the aquatic and terrestrial life forms of the big stonefly, Pteronarcys californica Newport. Comparative Biochemistry and Physiology 31(5)685-692.
1. 1. Surface lipid composition of the adult and naiad big stonefly differ in that a larger percentage of hydrocarbons, wax esters, free fatty acids and sterols are found on the adult, while the naiad surface lipid has more triglyceride.
2. 2. Major qualitative differences between adult and naiad surface lipids exist in the hydrocarbon fraction. Significant quantitative differences were found in all fractions except the sterol fractions.
3. 3. Results of this investigation show that the aquatic naiad form and the terrestrial adult form of the big stonefly have different surface lipid compositions. It appears that this insect's surface lipid composition varies with life stage depending upon the needed water conservation mechanism.

Béthoux,O 2005 Wing venation pattern of Plecoptera (Insecta: Neoptera). Illiesia, 1(9):52-81. PDF

Birrell,JH and Woods,HA 2023 Going with the flow–how a stream insect, Pteronarcys californica, exploits local flows to increase oxygen availability. Journal of Experimental Biology, 226(3), p.jeb244609. PDF
     Abstract: "For insects, life in water is challenging because oxygen supply is typically low compared with in air. Oxygen limitation may occur when oxygen levels or water flows are low or when warm temperatures stimulate metabolic demand for oxygen. A potential mechanism for mitigating oxygen shortages is behavior – moving to cooler, more oxygenated or faster flowing microhabitats. Whether stream insects can make meaningful choices, however, depends on: (i) how temperature, oxygen and flow vary at microspatial scales and (ii) the ability of insects to sense and exploit that variation. To assess the extent of microspatial variation in conditions, we measured temperature, oxygen saturation and flow velocity within riffles of two streams in Montana, USA. In the lab, we then examined preferences of nymphs of the stonefly Pteronarcys californica to experimental gradients based on field-measured values. Temperature and oxygen level varied only slightly within stream riffles. By contrast, flow velocity was highly heterogeneous, often varying by more than 125 cm s-1 within riffles and 44 cm s-1 around individual cobbles. Exploiting micro-variation in flow may thus be the most reliable option for altering rates of oxygen transport. In support of this prediction, P. californica showed little ability to exploit gradients in temperature and oxygen but readily exploited micro-variation in flow – consistently choosing higher flows when conditions were warm or hypoxic. These behaviors may help stream insects mitigate low-oxygen stress from climate change and other anthropogenic disturbances."

Birrell,JH; Meek,JB and Nelson,CR 2019 Decline of the giant salmonfly Pteronarcys californica Newport, 1848 (Plecoptera: Pteronarcidae) in the Provo river, Utah, USA Illiesia, 15(5)53-97. PDF
     Abstract: "Anthropogenic disturbances are causing many aquatic insect species, including those in Plecoptera, to lose geographic range, and, in some cases, succumb to extinction. One species, Pteronarcys californica Newport, 1848, has declined in several rivers in the western United States during the past century. It has been extirpated from the Arkansas River of Colorado and the Logan River of northern Utah and is now in decline in the Provo River of central Utah. We sampled the Provo River for two years (2016–2017) to determine the abundance and distribution of P. californica and other stonefly species. In over 300 samples, we found only 17 P. californica individuals. Our study demonstrates that their abundance and distribution have declined dramatically when compared to baseline values obtained from museum records, unpublished data and publications from the past century. Total stonefly species abundance and richness may also be lower compared to historical data. Because Plecoptera are bioindicators of water quality, this decline indicates that the health of the Provo River is deteriorating, especially in the lower reaches where few stoneflies were found. These findings suggest that active steps should be taken to protect the Provo River and its aquatic biodiversity."

Branham,JM and Hathaway,RR 1975 Sexual differences in the growth of Pteronarcys californica Newport and Pteronarcella badia (Hagen) (Plecoptera). Canadian Journal of Zoology, 1975, 53:(5) 501-506.
     Abstract: "Two species of Plecoptera, Pteronarcys californica Newport and Pteronarcella badia (Hagen), were collected seasonally from a single site in the Provo River, Utah. Body weights of the living animals were used to distinguish four size classes in each sex of Pteronarcys californica, and one size class for each sex of Pteronarcella badia. Ovaries, fat bodies, and guts were dissected from Pteronarcys californica. Growth of whole animals and of the organs are discussed with regard to life cycle, sexual development, and age. The importance of weight measurements on insects to be used for physiological studies is discussed."

Clubb,RW; Lords,JL and Gaufin,AR 1975 Isolation and characterization of a glycoprotein from the stonefly, Pteronarcys californica, which binds cadmium. Journal of Insect Physiology 21 (1)53-60.
     Abstract: The present study reports the isolation and characterization of a cadmium-containing glycoprotein from the water-soluble fraction of an aquatic insect. The isolated glycoprotein contained 0·67% cadmium, 62·1% carbohydrate, and 37·2% protein. The glycoprotein appears to be involved in the detoxification of cadmium, because species insensitive to cadmium contain five times the amount of the glycoprotein as do species sensitive to cadmium.

Colburn,T 1986 The use of the stonefly Pteronarcys californica Newport as a measure of biologically available cadmium in a high altitude river system Colorado, USA. Water Quality Bulletin 11, 141-147.
     Concerned about the heavy metal Cadmium in water often used for human consumption in Gunnison County, Colorado, the author exposed P. californica in cages to the water and accompanying sediments in various rivers in the upper Gunnison Basin. She found Cadmium concentrations lowest in the highest elevation cages. An interesting result was that sometimes the stoneflies had higher concentrations of Cadmium that the water samples might indicate. She said this showed that stoneflies indicate the cadmium present in the sediments. She suggests P. californica metal concentrations may be a better way to monitor stream levels of Cadmium than water samples.

Cui,Y; Béthoux,O; Kondratieff,B; Shih,C and Ren,D 2016 The first fossil salmonfly (Insecta: Plecoptera: Pteronarcyidae), back to the Middle Jurassic. BMC evolutionary biology, 16(1) 217 HTML

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."

Elder,JA and Gaufin,AR 1974 The toxicity of three mercurials to Pteronarcys californica Newport, and some possible physiological effects which influence the toxicities. Environmental Research, 7(2), pp.169-175.
     Abstract: "There is little information available on the toxicity of mercurials to aquatic insects. The information that is available is confined to field observations or medium tolerance limit (TLm) values using only one form of mercury.
The TLm values were determined for three different forms of mercury (phenylmercuric-, and methylmercuric-, and mercuric chloride) to the stonefly Pteronarcys californica. The order of toxicity of the three forms was found to be phenylmercuric chloride > methylmercuric chloride > mercuric chloride. The in vivo effect of the three forms of mercury on isolated gylceraldehyde-3-phosphate-dehydrogenase was also measured.
Two possible physiological factors involved in determining the toxicity of mercury (or other metals) to aquatic insects may be the catabolic pathways being employed at any period during the year, particularly during periods of molting, and age of the instar."

Frakes,JI; Birrell,JH; Shah,AA and Woods,HA 2021 Flow increases tolerance of heat and hypoxia of an aquatic insect. Biology Letters, 17(5), p.20210004. PDF
     Abstract: "Recent experiments support the idea that upper thermal limits of aquatic insects arise, at least in part, from a lack of sufficient oxygen: rising temperatures typically stimulate metabolic demand for oxygen more than they increase rates of oxygen supply from the environment. Consequently, factors influencing oxygen supply, like water flow, should also affect thermal and hypoxia tolerance. We tested this hypothesis by measuring the effects of experimentally manipulated flows on the heat and hypoxia tolerance of aquatic nymphs of the giant salmonfly (Plecoptera: Pteronarcys californica), a common stonefly in western North America. As predicted, stoneflies in flowing water (10 cm s-1) tolerated water that was approximately 4°C warmer and that contained approximately 15% less oxygen than did those in standing water. Our results imply that the impacts of climate change on streamflow, such as changes in patterns of precipitation and decreased snowpack, will magnify the threats to aquatic insects from warmer water temperatures and lower oxygen levels."

Frakes,JI; Malison,RL; Sydor,MJ and Woods,HA 2022 Exposure to copper increases hypoxia sensitivity and decreases upper thermal tolerance of giant salmonfly nymphs (Pteronarcys californica). Journal of Insect Physiology, 143, p.104455. PDF
     Abstract: "Many aquatic insects are exposed to the dual stressors of heavy metal pollution and rising water temperatures from global warming. These stresses may interact and have stronger impacts on aquatic organisms if heavy metals interfere with the ability of these organisms to handle high temperatures. Here we focus on the effect of copper on upper thermal limits of giant salmonfly nymphs (Order: Plecoptera, Pteronarcys californica), a stonefly species which is common in parts of western North America. Experimental exposure to copper reduced upper thermal limits by ~ 10 °C in some cases and depressed the hypoxia tolerance (Pcrit) of nymphs by ~ 0.5 mg L-1 DO. These results suggest that copper inhibits the delivery of oxygen, which may explain, in part, the strong reductions in CTMAX that we report. Fluorescence microscopy of Cu-exposed individuals indicated high levels of copper in chloride cells but no clear evidence of damage to or high levels of copper on the gills themselves. Our study indicates that populations of aquatic insects from copper-polluted environments may be further at risk to future warming than those from uncontaminated environments."

Freilich, JE 1991 Movement patterns and ecology of Pteronarcys nymphs (Plecoptera). Freshwater Biology, 25(2) 379-394.
     " SUMMARY. 1. Individually tagged Pteronarcys californica (Newport) nymphs were caught and recaptured over a 3-month period to determine their movement patterns and home range size. Sex/age structure, population density, and food habits (from gut contents) were also recorded. More than 1000 nymphs were tagged of which 256 (25%) were recaptured at least once. Tagged insects were confined to contiguous fast water, cobble riffles. Low velocity, silt-bottomed pools acted as barriers.
2. This stonefly has a 3-year life cycle although only the two oldest nymphet size-classes were tagged. Females were larger than males at all ages. The population sex ratio was skewed 60:40 towards females. Densities averaged 1.7 m-2±0.17 SE (range 0-19 m-2).
3. Most movements were short, indicating that a majority of the stoneflies stayed within a few meters of their first capture point (mean 1.8 m downstream ±0.51 SE, range 44 m downstream to 40 m upstream). Significant patch size is a stream reach 24 m long that would contain 85% of the average individual's movements. Time between captures averaged 16 d ±0.734 SE (maximum 81 d). Eight individuals were notable for extremely rapid upstream movements ranging from 6 to 22 m d-1.
4. Frequency of movements up and downstream differed significantly between the sexes. Pteronarcys distribution was clumped with certain quadrate representing 'zones of attraction.' The stoneflies moved rapidly between zones, then stayed many days in those areas. Movements differed significantly from random walk models.
5. Guts contained 75% diatoms, 15% vascular plant material, and 8% animal remains. Females ate significantly more diatoms than males on a volumetric basis."

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. The TLm96 for P. californica was 3.2-3.9mg/l and 34% oxygen saturation which was the highest tolerance for low oxygen among the stoneflies tested except for Skwala americana.

Gaufin,AR and Hern,S 1971 Laboratory studies on tolerance of aquatic insects to heated waters. Journal of the Kansas Entomological Society 44:240-245. PDF
     Abstract: "The mature larvae of fifteen species of aquatic insects (Diptera, Ephemeroptera, Plecoptera, and Trichoptera) and the scud (Amphipoda) were tested to determine their relative sensitivity to heated waters under laboratory conditions. The temperature at which 50% died after 96 hours (TLm96) was recorded as the lethal temperature. This ranged from 11.7 C for the torrential stream mayfly, Cinygmula par Baton, to 32.6 C for the snipefly, Atherix variegata Walker."
The TLm96 for P. californica was 27.0°C.

Goodyear,KL and McNeill,S 1999 Bioaccumulation of heavy metals by aquatic macro-invertebrates of different feeding guilds: a review. Science of the Total Environment, 229(1) 1-19. PDF

Gregory,JS; Beesley,SS and Van Kirk,RW 2000 Effect of springtime water temperature on the time of emergence and size of Pteronarcys californica in the Henry's Fork catchment, Idaho, U.S.A. Freshwater Biology 45(1) 75

Heinold,BD; Kowalski,DA and Nehring,RB 2020 Estimating densities of larval Salmonflies (Pteronarcys californica) through multiple pass removal of post-emergent exuvia in Colorado rivers. Plos one, 15(4), p.e0227088. PDF
     Abstract: "Traditional methods of collecting, sorting, and identifying benthic macroinvertebrate samples are useful for stream biomonitoring and ecological studies, however, these methods are time consuming, expensive, and require taxonomic expertise. Estimating larval densities through collection of post-emergent exuvia can be a practical and time efficient alternative. We evaluated the use of multiple pass depletion techniques of the post-emergent exuvia of Pteronarcys californica to estimate larval densities at ten sites in three Colorado rivers. Exuvia density was highly correlated with both final-instar larval density (R2 = 0.90) and total larval density (R2 = 0.88) and the multiple pass removal technique performed well. Exuvia surveys found P. californica at three low density sites where benthic sampling failed to detect it. At moderate and high density sites the exuvia surveys always produced lower density estimates than benthic surveys. Multiple pass depletion estimates of exuvia proved to be an accurate and efficient technique at estimating larval densities and provided an effective alternative for traditional benthic sampling when objectives are detecting and monitoring P. californica, especially at low density sites."

Hornig,CE and Brusven,MA 1986 Effects of suspended sediment on leaf processing by Hesperophylax occidentalis (Trichoptera: Limnephilidae) and Pteronarcys californica (Plecoptera: Pteronarcidae). Western North American Naturalist 46 (1) 33-38 PDF
     Abstract: "The effects of suspended sediments on stream invertebrate detrital processing were investigated under replicated conditions in light and temperature-controlled chambers in the laboratory. The leaf-shredding insects Pteronarcys californica and Hesperophylax occidentalis were studied. Mean daily ingestion rates were lower among insects subjected to suspended sediments (1.5 and 3.0 g/l) than insects held in suspended sediment-free environments for seven of the eight trials. In five of the eight trials, mean ingestion rates were suppressed by ?41% when compared to insects held in suspended sediment-free environments. Feeding inhibition was typically greater at the end of the feeding trials (14 days) than at the beginning (0-4 days). The effects of suspended sediments on ingestion were apparently related to the feeding status of the insects at the time of a trial. Insects in an active feeding mode were less influenced by suspended sediment than those in an inactive feeding mode. We conclude that, depending on the season and the duration of impact, suspended sediment can suppress processing of coarse particulate organic matter and thus adversely influence important nutrient and energy pathways in low-order streams. "

Illinois Natural History Survey (INHS) accessed 15 Jan 2010 http://www.inhs.uiuc.edu/
Cat. # Species Stream Location County State Country Date
5805 Pteronarcys californica Gunnison River Gunnison [Gunnison] Colorado United States of America 7 June 1954
5806 Pteronarcys californica Gunnison River Gunnison [Gunnison] Colorado United States of America 7 June 1954
5807 Pteronarcys californica Gunnison River Gunnison [Gunnison] Colorado United States of America 7 June 1954

Kauwe,JSK and Shiozawa,DK 2004 Phylogeographic and nested clade analysis of the stonefly Pteronarcys californica (Plecoptera: Pteronarcyidae) in the western USA. Journal of the North American Benthonlogical Society 23(4)824-838. PDF
     Abstract: "Long-distance dispersal by aquatic insects can be difficult to detect because direct measurement methods are expensive and inefficient. When dispersal results in gene flow, signs of that dispersal can be detected in the pattern of genetic variation within and between populations. Four hundred seventy-five base pairs of the mitochondrial gene, cytochrome b, were examined to investigate the pattern of genetic variation in populations of the stonefly Pteronarcys californica and to determine if long-distance dispersal could have contributed to this pattern. Sequences were obtained from 235 individuals from 31 different populations in the western United States. Sequences also were obtained for Pteronarcella badia, Pteronarcys dorsata, Pteronarcys princeps, Pteronarcys proteus, and Pteronarcys biloba. Phylogenies were constructed using all of the samples. Nested clade analysis on the P. californica sequence data was used to infer the processes that have generated the observed patterns of genetic variation. An eastern North American origin and 2 distinct genetic lineages of P. californica could be inferred from the analysis. Most of the current population structure in both lineages was explained by a pattern of restricted gene flow with isolation by distance (presumably the result of dispersal via connected streams and rivers), but our analyses also suggested that long-distance, overland dispersal has contributed to the observed pattern of genetic variation."

Kowalski,DA and Richer,EE 2020 Quantifying the habitat preferences of the stonefly Pteronarcys californica in Colorado. River Research and Applications, 36(10), pp.2043-2050. PDF
     Abstract: "The salmonfly (Pteronarcys californica) is a large stonefly species that is ecologically important and recreationally significant to anglers in coldwater river systems throughout the western United States. Salmonflies are sensitive to disturbance and pollution and are considered an indicator of quality coldwater stream habitat. They are declining in range and abundance in some river systems and their extirpation from several western rivers has led to restoration attempts including habitat improvement projects and direct reintroductions. These efforts could be improved with a clear understanding of the causes of these declines, a quantitative description of the species' preferred habitat, and practical management recommendations for the restoration of habitat where it has been lost. The objective of this study was to measure variables that describe the physical habitat of sites supporting varying densities of salmonflies in Colorado. Width to depth ratio, bed slope, D50 sediment size, percent fine sediment, and embeddedness were measured at 18 riffle sites and compared to an index of salmonfly density estimated over 3 years. Correlation analysis and multiple linear regression with model selection were used to identify important variables. Salmonfly density was highest at sites with low amounts of fine sediment, low cobble embeddedness, and large cobble size. Fine sediment (particles < 2 mm) was the single best predictor of salmonfly density and ranged from 0–6% at sites with high salmonfly densities. As habitat characteristics influence the range and density of salmonflies in Colorado and elsewhere, results from this study can inform land use practices, flow management, and river restoration activities to benefit this important indicator species."

Luedtke,RJ and Brusven,MA 1976 Effects of sand sedimentation on colonization of stream insects. Journal of the Fisheries Board of Canada, 33(9), pp.1881-1886. PDF
     P. californica was one of the species that was limited in thier ability to to crawl upstream through slow moving sandy sections. They tended to drift downstream instead.
Abstract: " Driftnets, basket samplers, and artificial streams were used to investigate the influence of heavy sand accumulations on insect drift, colonization, and upstream movements in Emerald Creek, northern Idaho. Most riffle insects successfully passed through low-velocity, sandy reaches 80 m long. Upstream movements on sand were impeded by flows as low as 12 cm/s, except for the heavily cased caddisfly Dicosmoecus sp."

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."

Malison, R.L., Frakes, J.I., Andreas, A.L., Keller, P.R., Hamant, E., Shah, A.A. and Woods, H.A., 2022 Plasticity of salmonfly (Pteronarcys californica) respiratory phenotypes in response to changes in temperature and oxygen. Journal of Experimental Biology, 225(18), p.jeb244253.
     Abstract: "Like all taxa, populations of aquatic insects may respond to climate change by evolving new physiologies or behaviors, shifting their range, exhibiting physiological and behavioral plasticity, or going extinct. We evaluated the importance of plasticity by measuring changes in growth, survival and respiratory phenotypes of salmonfly nymphs (the stonefly Pteronarcys californica) in response to experimental combinations of dissolved oxygen and temperature. Overall, smaller individuals grew more rapidly during the 6-week experimental period, and oxygen and temperature interacted to affect growth in complex ways. Survival was lower for the warm treatment, although only four mortalities occurred (91.6% versus 100%). Nymphs acclimated to warmer temperatures did not have higher critical thermal maxima (CTmax), but those acclimated to hypoxia had CTmax values (in normoxia) that were higher by approximately 1°C. These results suggest possible adaptive plasticity of systems for taking up or delivering oxygen. We examined these possibilities by measuring the oxygen sensitivity of metabolic rates and the morphologies of tracheal gill tufts located ventrally on thoracic segments. Mass-specific metabolic rates of individuals acclimated to warmer temperatures were higher in acute hypoxia but lower in normoxia, regardless of their recent history of oxygen exposure during acclimation. The morphology of gill filaments, however, changed in ways that appeared to depress rates of oxygen delivery in functional hypoxia. Our combined results from multiple performance metrics indicate that rising temperatures and hypoxia may interact to magnify the risks to aquatic insects, but that physiological plasticity in respiratory phenotypes may offset some of these risks."

Myers,LW and Kondratieff,BC 2017 Larvae of North American species of Pteronarcys (Plecoptera: Pteronarcyidae). Illiesia, 13(16):192-224. https://doi.org/10.25031/2017/13.16 PDF
     Abstract: " Larvae of the eight North American Pteronarcys (Plecoptera: Pteronarcyidae) species have been difficult or impossible to identify over the past century. This stems from the lack of rigorous comparisons of reared material. The absence of a reliable key diminishes the importance of Pteronarcys larvae in aquatic ecological and biomonitoring studies. We provide comparative larval descriptions and a key illustrated with high resolution photographs of important diagnostic characters for the eight North American species of Pteronarcys. Earlier descriptions are reviewed and supplemented with new photographs, illustrations and morphometric data to aid in the separation of morphologically similar species."

Needham,JG and Claassen,PW 1925 A Monograph of the Plecoptera of North America. Entomological Society of America, Lafayette, Indiana. 397 pages.

Nehring,RB 1976 Aquatic insects as biological monitors of heavy metal pollution. Bulletin of Environmental Contamination and Toxicology 15 2, 147-154.
     The author established TL50s of 10.1 - 13.9 mg/l for Copper, greater than 19.2 mg/l for Lead, .004 -.009 mg/l for Silver and greater than 13.9 for Zinc. A TL 50 is the median lethal concentration at which half the population dies. This is a standard laboratory toxicity test used for chemicals (among other things). [Yikes, these are such handsome animals, this would be a difficult experiment to do.] Nehring also measured bioaccumulation of the metals. Clean Pteronarcys that were placed in artifical streams with various amounts of metals concentrated those metals 100 times and more over background levels. The author suggests using bioaccumulation in these animals or others to estimate small amounts of metals in water. Analysis of metals in aquatic insects may help figure out what happened if collected shortly after a fish kill.

Nelson,CH 2009 Surface ultrastructure and evolution of tarsal attachment structures in Plecoptera (Arthropoda: Hexapoda). Aquatic Insects, (31)523-545. Html
     The author used scanning electron microscopy (SEM) to image the plantar surfaces of the stonefly tarsomeres and pretarsus of Pteronarcys californica and a number of other species.

Nelson,CH and Hanson,JF 1971 Contribution to the anatomy and phylogeny of the family Pteronarcidae (Plecoptera). Transactions of the American Entomological Society (1890-), 97(1), pp.123-200.

Newport,G 1848 On the anatomy and affinities of Pteronarcys regalis Newman; with a postscript containing descriptions of some American Perlidae, together with notes on their habits. Transactions of the Linnean Society of London 20: 425-452.

Peterson,MG; O’Grady,PM and Resh,VH 2017 Phylogeographic comparison of five large-bodied aquatic insect species across the western USA. Freshwater Science, 36(4), pp.823-837. PDF
     Abstract: "Glacial legacy, barriers to migration, and dispersal abilities are important determinants of intraspecific genetic diversity. Genetic comparisons can elucidate the distribution of genetic variants among populations, but for many groups of organisms the concordance of population genetic structure and historical refugia among co-occurring species remains unclear. We compared phylogeographic histories of 4 stoneflies (Calineuria californica, Hesperoperla pacifica, Pteronarcys californica, and Pteronarcys princeps) and 1 caddisfly (Dicosmoecus gilvipes) across their species ranges. Study species had large body and wing sizes that suggest strong flying ability and dispersal potential. Nevertheless, riverine habitat restrictions and mating behaviors can inhibit dispersal. We used mitochondrial and nuclear gene sequences to examine population genetic structure relative to potential past and present barriers to dispersal in the western USA. North–south population genetic structure was present for each species but was more pronounced for 2 stoneflies (C. californica and P. californica) and the caddisfly. For these 3 species, phylogenies indicated concordant clades north and south of San Francisco Bay, a large, saltwater estuary in California. Basal phylogenetic nodes and regional centers of haplotype diversity suggested common historical refugia in northern California or southern Oregon, similar to that found in previous studies of salamanders. For 1 stonefly (C. californica) and the caddisfly, distinct populations in the Sierra Nevada Mountains suggested potential barriers to gene flow. The presence of population genetic structure suggests vulnerability to loss of intraspecific diversity under climate change scenarios, particularly for populations at high elevations."

Richardson,JW; Gaufin,AR 1971 Food habits of some western stonefly nymphs. Transactions of American Entomological Society 97, 91-121.
     They examined the guts of 275 nymphs from the Provo River in Utah and the Gunnison River in Colorado. Their results were that on average, P. californica guts contained 79.7% detritus. 99.6% of the animals they looked at had sand particles in their guts as well. Filamentous green algae was 6.6% of the diet while diatoms were only 2.1 percent. Traces of animal material were found in 149 of the 275 nymphs. Baetidae and Ephemerella sp. were the most common mayflies found in the guts.

Rockwell,IP and Newell,RL 2009 Note on mortality of the emerging stonefly Pteronarcys californica on the Jocko River, Montana, USA. Western North American Naturalist 69(2) 264-266.PDF

Ruesink,JL and Srivastava,DS 2001 Numerical and per capita responses to species loss: mechanisms maintaining ecosystem function in a community of stream insect detritivores. Oikos 93(2) 221-234.
     Abstract: "We experimentally reduced the diversity of detritivorous stream insects in field enclosures, and measured the effects on an ecosystem function, processing of leaf litter. Two dominant species were removed separately, the stonefly Pteronarcys californica and the caddisfly Lepidostoma unicolor. In principle, processing could be maintained after species loss in two ways: the remaining species could increase their rates of shredding (per capita response), or they could increase in abundance (numerical response). We imposed a numerical response in some treatments by experimentally increasing abundances of either all the remaining species or the other dominant species so that expected metabolic capacity of the assemblage returned to full-diversity levels. Numerical responses were generally effective in maintaining leaf breakdown when either Lepidostoma or Pteronarcys was removed, except that the treatment in which Lepidostoma was replaced by an equivalent metabolic capacity of all remaining species showed less leaf loss than the full-diversity treatment. Per capita responses by other species appeared effective in compensating for the removal of Pteronarcys (although there were other explanations) but were not effective in compensating for the removal of Lepidostoma. In summary, the consequences of reduced biodiversity varied with which species was lost and how the remainder responded. Thus there was no simple relationship between biodiversity and ecosystem functioning. However, when numerical or per capita compensation does occur, stability of function should rise with diversity in such “interactive” assemblages."

Sanders,HO and Cope,OB 1968 The relative toxicities of several pesticides to naiads of three species of stoneflies. Limnology and Oceanography 13(1) 112-117. First page

Schultheis,AS; Booth,JY; Vinson,MR and Miller,MP 2008 Genetic evidence for cohort splitting in the merovoltine stonefly Pteronarcys californica (Newport) in Blacksmith Fork, Utah. Aquatic Insects: International Journal of Freshwater Entomology, 1744-4152, 30(3) 187-195. PDF
     Abstract: "The life cycles of many stream insects results in the simultaneous existence of multiple cohorts within populations. If larval development is fixed in these long-lived species, successive cohorts may be reproductively isolated and genetically distinct. We examined levels of genetic differentiation in a 333 bp region of the mitochondrial cytochrome-b gene among cohorts of the stonefly Pteronarcys californica (Newport) (Plecoptera, Pteronarcyidae) at two sites along Blacksmith Fork, Utah. Body measurements were collected from 224 specimens. The frequency distribution of (head width) X (head + thorax length) suggests four (Low site) and five year (High site) life cycles comprising an ∼one year embryonic diapause followed by either three or four years of larval development. Seventy-seven individuals were sequenced, from which we detected five unique mtDNA haplotypes. The overall AMOVA suggested moderate genetic differentiation among cohorts (F ST = 0.11, p = 0.01; ΦST = 0.11, p = 0.007). However, pairwise analyses indicated that a single cohort drove the overall ΦST value. Thus, we conclude that there is considerable gene flow among most cohorts of P. californica in Blacksmith Fork."

Sheldon,AL 1999 Emergence patterns of large stoneflies (Plecoptera: Pteronarcys, Calineuria, Hesperoperla) in a Montana river. Great Basin Naturalist 59: 169-174. PDF

Smith,LW 1917 Studies of North American Plecoptera (Pteronarcinae and Perlodini). Transactions of the American Entomological Society 43(4)433-489.
Lucy Smith's description of the salmonfly Pteronarcys californica page 449 Lucy Smith's description of the salmonfly Pteronarcys californica, page 450
Plate 29 illustrations of adult male and female Salmonfly genitalia

PLate 31, illustrations of salmonfly nymph genitalia

Stark,BP and Szczytko,SW 1982 Egg morphology and phylogeny in Pteronarcyidae (Plecoptera). Annals of the Entomological Society of America, 75(5), pp.519-529.

     Abstract: "Egg descriptions and scanning electron microscope photomicrographs are provided for the 10 nearctic pteronarcyid species, and the data are used to test current ideas of the phylogeny of the family. The data suggest Pteronarcys sensu Zwick (1973) is polyphyletic and a revised classification is proposed in which Allonarcys is placed in synonymy with Pteronarcys."

Sutton,MQ 1985 The California salmon fly as a food source in northeastern California. J. Calif. & Great Basin Anthropol. 7(2): 176-182.
     The Modoc, Wintu, Achumawi and Atsugewi Indians along the Pit River and other rivers in Northeastern California ate lots of salmonflies. References within this paper said the Wintu people collected adults in the morning and then boiled them to eat now or dried them for later use. The Atsugewi people also collected Salmonflies in the morning and removed their wings before boiling the bodies.

Townsend,GD and Pritchard,G 2000 Egg development in the stonefly Pteronarcys californica Newport (Plecoptera: Pteronarcyidae) Aquatic Insects: International Journal of Freshwater Entomology, 1744-4152, 22(1)19-26.
     Abstract: "Eggs of Pteronarcys californica Newport were incubated at fixed temperatures between 5 and 20°C in the laboratory and at field temperatures in the Crowsnest River, Alberta. The regression of rate of development on temperature between 5–15°C gave a developmental zero of 3.125°C. Within the range 10–20°C, highest hatching success and fewest days to median hatch occurred at 15.0 or 17.5°C, but physiological time (day-degrees) for egg hatching increased with temperature throughout, markedly so above 15°C. A minimum of 182 days was required for 50% hatch in the laboratory, with no observable development for approximately 80 days. Eggs placed in the river on 25 May 1993 started to hatch on 17 October 1993, and the pulse of larval recruitment in the field population occurred between April and August, 11 to 15 months after oviposition. Eggs hatched over periods of 130–322 days at different temperatures in the laboratory, and over an 11-month period in the field. The placement of diapause early in embryonic development is suggested as a cause of extended recruitment. The variety of embryonic development in Plecoptera is briefly reviewed."

Walters,DM; Wesner,JS; Zuellig,RE; Kowalski,DA and Kondratieff,MC 2018 Holy flux: spatial and temporal variation in massive pulses of emerging insect biomass from western US rivers. Ecology, 99(1)238-240. HTML

Ward,JV, Kondratieff,BC and Zuellig,RE 2002 An Illustrated Guide to the Mountain Stream Insects of Colorado. 2nd ed. University Press of Colorado, Boulder, Colorado. 219 pages.
     Illustration of P. californica nymph on page 66, figure 26.

Ziegler,DD and Stewart,KW 1977 Drumming behavior of eleven Nearctic stonefly (Plecoptera) species Annals of the Entomological Society of America. 70(4)495-505.

"There is no such thing as a blank day for a fisherman. It will be saved for him by the white-throated weasel, who watches his fishing from a hole in the wall under which is lying a fish that refused all flies; or by the excitement of identifying insects; or by the apple-blossom in a nearby orchard; and no one would call that day a blank on which he has seen a king-fisher." -- Arthur Ransome Rod and Line, 1929
Brown, WS 2004 Plecoptera or Stoneflies of Gunnison County, Colorado