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Stoneflies - Plecoptera: Perlidae of Gunnison County, Colorado

Hesperoperla pacifica
Golden Stonefly, Willow fly, Pacific Stonefly, Small golden stone, Golden stone, Big Golden stonefly

(Banks 1900)

Updated 12 Sept 2021
TSN 102972


Nymphs live in swift water in streams and rivers throughout the county and nation.

Life History

H. pacifica remain in the stream as a nymph for 2 or 3 years, the fancy word for that is semivoltine.

Richardson and Gaufin (1971) found that H. pacifica was primarily a carnivore while eating 88% animal and 12% plant matter. They prefer to eat mayflies (Ephemeroptera), midges (Chironomidae) and caddisflies (Trichoptera). The highest proportion of midge larve in their stomachs were found in Hesperoperla from the Taylor River. Richardson and Gaufin thougt a large part of the detritus and plant matter in the guts of these animals is from the gut of their prey.

Fuller and Stewart (1977) noted this species is semivoltine and emerged from June to July in the Gunnison River at Lost Canyon Resort. First year nymph guts were 85% animal material from their first appearance in August - September through the following July. Chironomidae larve always had a high electivity and were over 60% of the gut contents in all months except May. In May Ephemeroptera nymphs showed a higher electivity. Small numbers of other aquatic insects appeared in the guts, but electivity for them was always negative. Second year nymphs also fed on animal matter (85%) in most months. They elected to eat more Trichoptera larvae in the fall and winter inspite of the fact that Chironomid larvae were abundant. By the next June-August, mature nymphs shifted back to Chironomids. H. pacifica showed a consistent negative electivity for Ephemeroptera nymphs except in May during the first year of their development. They either avoided feeding on the common Oligochaetes from July through September or did not encounter them while hunting.

Local Research Results

Small predators preyed on small prey and big predators showed a preference for medium sized prey. Size selectivity varied with predator size. Percent attacks per encounter by small predators were strongly biased towards small prey, Large stoneflies were weakly biased towards large prey. Capture success was greater and handling times were shorter with small prey compared to large prey (Allan et al 1987b).

This Hesperoperla was molting in a tributary of the East River today, 20 July 2011.

Locations Collected

Taylor River, Lake Fork of the Gunnison River, Gunnison River at the Lost Canyon Resort.


Older publications may refer to this species as Acroneuria pacifica.

Good Links

On this website:
Perlidae Introduction

Other Websites:


Adams,R and Simmons,D 1999 Ecological Effects of Fire Fighting Foams and Retardants. Conference Proceedings of the Australian Bushfire Conference, Albury

Allan,JD; Flecker,AS; McClintock,NL 1987 Prey preference of stoneflies: sedentary vs mobile prey. Oikos 49(3) 323-331.
     Abstract: " We investigated the effects of prey size and type (sedentary vs mobile) on prey preference in a predaceous stonefly, based on choice experiments and observations of the predator-prey interaction. We presented three size classes of black fly larvae (Prosimulium) to various sizes of the perlid stonefly Hesperoperla pacifica in laboratory experiments. Analysis by preference indices (α, ε) indicated that small predators preferred small prey, large predators preferred large prey, and H. pacifica of intermediate size exhibited a weak, non-significant trend toward preferring prey of intermediate size. These results using sedentary prey, black fly larvae, are compared to previous results using a mobile prey, the mayfly Baetis. Encounter, attack, capture rates and handling times differ as a function of predator size, prey size, and prey type. The results of preference trials generally can be predicted from differential encounter, attack and capture rates, and similar preference curves may have different underlying causes. Small H. pacifica preferred small prey, mainly due to a much higher capture success. Large H. pacifica preferred large prey, due principally to higher encounter and attack rates. Offered a choice between Baetis and Prosimulium, stoneflies exhibited lower encounter and attack rates with Prosimulium, but much higher capture success, resulting in a net preference for black fly larvae. We suggest that laboratory results for attacks, captures and handling time can reasonably be extrapolated to animals in nature, thus lending insight into preference estimates based on gut analysis. However, encounter rates inevitably are influenced by details of the laboratory design and may bear little relation to nature."

Allan,JD; Flecker,AS; McClintock,NL 1987 Prey size selection by carnivorous stoneflies. Limnology and Oceanograpy 32(4) 864-872. PDF

Allan,JD and Feifarek,BP 1988 Prey preference in stoneflies: a comparative analysis of prey vulnerability. Oecologia, 76(4), pp.496-503.

Banks,N 1900 New genera and species of Nearctic Neuropteroid Insects. Transactions of the American Entomological Society 26:239-259.
     Described as Acroneuria pacifica.
Description of the stonefly Hesperoperla pacifica

Baumann,RW; Gaufin,AR; Surdick,RF 1977 The stoneflies (Plecoptera) of the Rocky Mountains. Memoirs of the American Entomological Society (31) 1-208.
     Quote from page 162: "This species is the most widely distributed stonefly species in the Rocky Mountains. Throughout its range it exibits a wide variation in size, wing length, coloration and shape of the female subgenital plate. However, in all cases studied, the aedeagus and ova are uniform. The adults emerge from April to October."

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

Buchwalter,DB; Cain,DJ; Martin,CA; Xie,L; Luoma,SN; 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,R Edward; Stewart,Kenneth W (1995): Life histories of stoneflies (Plecoptera) in the Rio Conejos of southern Colorado. Great Basin Naturalist 55, 1-18. PDF

Fuller,RL and Stewart,KW 1977 The food habits of stoneflies (Plecoptera) in the Upper Gunnison River, Colorado. Environmental Entomology (6) 293-302.
     Abstract: " Gut contents of 1,463 stonefly nymphs, comprising 10 species, from the Gunnison River, Colorado, were analyzed from Dec., 1974-Oct., 1975, in relation to food availability. Pteronarcella badia fed primarily on detritus and moss. Perlidae and Perlodidae mature nymphs were all carnivorous, but showed considerable seasonal-developmental shifting in diets and preference during earlier stages. Early instar Isoperla fulva nymphs were herbivore-detritivores, then gradually shifted through an omnivorous to carnivorous diet as development proceeded. Claassenia sabulosa and Hesperoperla pacifica remained carnivorous throughout development. Dominant prey groups were chironomids, mayflies and caddisflies. Horn's Coefficient of Dietary Overlap showed significance among all predator species for major food categories, but subtle mechanisms such as prey species-and size-selectivity and temporal succession provided sufficient partitioning of the abundant food resources to allow for coexistence. Large Claassenia sabulosa nymphs in August selected more mayflies after dark than in the afternoon. No behavioral selection by predacious stoneflies was indicated for the chironomids Ablabesmyia sp., Cricotopus sp., Prodiamesa sp., and Rheotanytarsus sp."

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 Hesperoperla pacifica as Acroneuria pacifica. The TLm96 for H. pacifica was 1.6mg/l and 14% oxygen saturation. This was the least tolerance for low oxygen among the 8 stonefly species tested.

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.
     Quote from page 395: " This extremely widespread western North American species can be collected in almost all types of streams, ranging from rheocrenes to large rivers throughout the Mountain and Plateau Provinces of Colorado."

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).

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

Mangum,FA and Madrigal,JL 1999 Rotenone effects on aquatic macroinvertebrates of the Strawberry River, Utah: a five-year summary. Journal of Freshwater Ecology, 14(1), 125-135. PDF
     Abstract: " Before treatment with a 3 mg/1 Noxfish (0.15 mg/1 active ingredient; rotenone) for 48 hours, benthic invertebrate communities were quantitatively sampled with a modified Surber net. Then spring, summer, and fall post-rotenone samples were taken monthly at each of four Strawberry River stations for five years. Statistical analyses of the data indicated that the application of rotenone had a significant effect on the following species density: Cinygmula sp., Pteronarcella badia, Hesperoperla pacifica, Hydropsyche sp., and Brachycentrus americanus. Thirty-three percent of the benthic invertebrate taxa at the four stations showed resistance to rotenone. Up to 100% of Ephemeroptera, Plecoptera and Trichoptera species were missing after the second rotenone application. Forty-six percent of the taxa recovered within one year, but 21% of the taxa were still missing after five years. Of the 19 taxa still missing, 47% were Trichoptera, 21% were Ephemeroptera, 16% were Plecoptera, 11% were Coleoptera, and 5% were Megaloptera. "

Martin,CA; Luoma,SN; Cain,DJ and Buchwalter,DB 2007 Cadmium ecophysiology in seven stonefly (Plecoptera) species: delineating sources and estimating susceptibility. Environmental science & technology, 41(20), pp.7171-7177. PDF

Molles,MC and Pietruszka,RD 1983 Mechanisms of prey selection by predaceous stoneflies: roles of prey morphology, behavior and predator hunger. Oecologia 57(1) 25-31. Abstract

Newell,RL; Baumann,RW and Stanford,JA 2008 Stoneflies of Glacier National Park and Flathead River basin, Montana. International Advances in the ecology, zoogeography, and systematics of mayflies and stoneflies. University of California Publications in Entomology, Berkeley and Los Angeles, pp.173-186. PDF
     Quote from page 176: "Stoneflies recorded from hyporheic habitats (pumped wells) included: Alloperla severa, Capnia confusa, Claassenia sabulosa, Diura knowltoni, Hesperoperla pacifica, Isocapnia crinita, I. grandis, I. integra, I. vedderensis, Isoperla fulva, Kathroperla, Paraperla frontalis, and P. wilsoni"

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."

Rader,Rb and Belish, TA 1999 Influence of mild to severe flow alterations on invertebrates in three mountain streams. Regulated Rivers: Research & Management. 15(4)353 - 363.
     Discussing Hesperoperla pacifica among a few other critters, they comment that "some stoneflies declined or were even locally extirpated" by severe flow alterations due to dams and water abstraction of their habitat.

Richardson,JW; Gaufin,AR 1971 Food habits of some western stonefly nymphs. Transactions of American Entomological Society 97, 91-121.
     Discussed as Acroneuria pacifica.

Sandberg,JB 2009 Vibrational communication (drumming) of the western nearctic stonefly genus Hesperoperla (Plecoptera: Perlidae). Illiesia 2009 5(13):146-155. PDF

Sheldon,AL 1980 Coexistence of perlid stoneflies (Plecoptera): predictions from multivariate morphometrics. Hydrobiologia, 71(1) 99-105. 1st two pages

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

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 46.

Stark,BP and Green,S 2011 Eggs of western Nearctic Acroneuriinae (Plecoptera: Perlidae). Illiesia 2011 7(17):157-166. PDF

Stark,BP; Gaufin,AR 1976 The nearctic genera of Perlidae (Plecoptera). Miscellaneous Publications of the Entomological Society of America 10, 1-80. page 30.

Stewart,KW and Stark,BP 2002 Nymphs of North American Stonefly Genera. 2nd edition The Caddis Press, Columbus, Ohio. 510 pages.
     Illustrations of nymph on page 344-345, figures 13.21-13.22

Stewart,KW and Zeigler,DD 1984 The use of larval morphology and drumming in Plecoptera systematics, and further studies of drumming behavior. Annals of Limnology, 20 (1-2):105-114.

Thorp,RA; Kondratieff,BC; Thorp,EC; Odenbeck,PB and Jarrett,MJ 2008 The life cycles of Claassenia sabulosa and Hesperoperla pacifica (Plecoptera: Perlidae) in two Colorado streams. Western North American Naturalist, 68(3) 311-318. PDF
     Abstract: "We compared the life cycles of Claassenia sabulosa (Banks 1900) and Hesperoperla pacifica (Banks 1900) (Plecoptera: Perlidae) in allopatry and sympatry by studying 4 populations in 3 streams of the South Platte River Watershed, Colorado. We estimated 2-year life cycles for both C. sabulosa and H. pacifica in allopatry and sympatry. Evidence of egg diapausing and extended larval recruitment was noted for both species in allopatry and sympatry. There were no apparent differences in larval growth, larval recruitment, or adult emergence periodicity between allopatric and sympatric populations of C. sabulosa. In contrast, allopatric and sympatric H. pacifica populations exhibited differences in the timing of larval growth, larval recruitment, and adult emergence. We feel that the differences in the life cycles of these populations were likely related to water temperature because a substantial water temperature difference (degree days of 1761 and 2563) occurred between study reaches. In sympatry, H. pacifica adults began emerging 2 weeks earlier than C. sabulosa, when water temperature reached 9°C. The emergence of H. pacifica was synchronous and male biased. The emergence of C. sabulosa was protandrous and male biased and began when water temperature reached 17°C. Claassenia sabulosa emergence was extended and lasted for 6 weeks during July and August. The abundance of C. sabulosa adults during this period corresponded closely to fluctuations in water temperature."

The United States Geological Survey (USGS) National Water Quality Assessment Data Warehouse (NAWQA) shows this species is present in Gunnison County. Data as of 1Sep2005

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 Hesperoperla pacifica nymph on page 66.

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.


subgenital plate

genital hooks


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