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Stoneflies - Plecoptera: Chloroperlidae of Gunnison County, Colorado
Sweltsa fidelis - Mountain Sallfly

Banks 1920
Updated 22 Dec 2023
TSN 103286


Sometimes brachypterous (short-winged). Male epiproct indistinguishable from Sweltsa revelstoka, however female subgenital plates are very different. Nymphs were described in 2005, see Stark and Stewart.


Since this species suffered a name change, older publications may refer to this species as Alloperla fidelis.

Good Links

On this website:
Introduction to Sweltsa
Key to Chloroperlidae Nymphs
Key to Chloroperlidae Males
Key to Chloroperlidae Females


Banks,N 1920 New Neuropteroid insects. Bulletin of the Museum of Comparative Zoology. 64: 299-362.
     Described as Alloperla fidelis.

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
     Quote from page 179: "This species is abundant in creeks and rivers in the Pacific Northwest. The adults emerge from May to September. "

Delk,JK; Kilgore,MJ; Stark,BP 1998 Comparison of the epiproct structure of two closely related species, Sweltsa fidelis (Banks) and S. revelstoka (Jewett) (Plecoptera: Chloroperlidae). Great Basin Naturalist 58(3) 282-284.
     Abstract: " The male epiprocts of 2 closely related western Nearctic species, Sweltsa fldelis (Banks) and S. revelstoka (Jewett), were examined using SEM. The males of these 2 species have been historically distinguished by epiproct measurements. The ratio of the length from the base to greatest width versus total epiproct length ranges from 0.49 µm to 0.67 µm ( x̄= 0.56) in S. fldelis and 0.55 µm to 0.69 µm (x̄ = 0.60) in S. revelstoka. Similarities in measurement suggest that the location of the greatest epiproct width is not a reliable and consistent character for distinguishing males of these 2 species."

Dieterich,M and Anderson,NH 1995 Life cycles and food habits of mayflies and stoneflies from temporary streams in western Oregon. Freshwater Biology, 34(1), pp.47-60.
     Summary: "1. Field data and results from laboratory rearing are combined to describe life cycles and food habits of the mayflies Paraleptophlebia gregalis and Ameletus n. sp., and the stoneflies Soyedina interrupta, Ostrocerca foersteri, Sweltsa fidelis and Calliperla luctuosa.
2. P. gregalis, A. n. sp., S. interrupta and O. foersteri have univoltine life cycles which are characterized by a high degree of plasticity. S. fidelis and C. luctuosa have semivoltine life cycles which are more tightly synchronized.
3. Laboratory feeding trials and field observations characterize P. gregalis as a collector, A. n. sp. as a scraper, O. foersteri and S. interrupta as shredders and C. luctuosa as a predator mainly of midge larvae. Late-instar larvae of S. fidelis are believed to be scavengers.
4. Laboratory rearing yielded a negative correlation between growth rates (Y) and larval size in autumn (X) for S. interrupta. This indicates compensatory growth by small larvae in order to achieve synchronized emergence. The correlation can be described by the equation: Y = 0.0053-0.0036X (R2= 0.82; P < 0.01; n = 22)
5. The field and laboratory data indicate that photoperiod mainly determines the rate of development and size of emerging subimagos in P. gregalis."

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 394. "This species occurs in mountain streams, but is not as commonly collected as S. coloradensis or S. lamba. Delk et al. (1998) indicated that males of S. fidelis can not be reliably distinguished from S. revelstoka(Jewett). The latter species is not known from Colorado."

Malison,RL; Hand,BK; Winter,E; Giersch,JJ; Amish,SJ; Whited,D; Stanford,JA and Luikart,G 2022 Landscape connectivity and genetic structure in a mainstem and a tributary stonefly (Plecoptera) species using a novel reference genome. Journal of Heredity, 113(4), pp.453-471.
     Abstract: "Understanding how environmental variation influences population genetic structure can help predict how environmental change influences population connectivity, genetic diversity, and evolutionary potential. We used riverscape genomics modeling to investigate how climatic and habitat variables relate to patterns of genetic variation in 2 stonefly species, one from mainstem river habitats (Sweltsa coloradensis) and one from tributaries (Sweltsa fidelis) in 40 sites in northwest Montana, USA. We produced a draft genome assembly for S. coloradensis (N50 = 0.251 Mbp, BUSCO > 95% using "insecta_ob9" reference genes). We genotyped 1930 SNPs in 372 individuals for S. coloradensis and 520 SNPs in 153 individuals for S. fidelis. We found higher genetic diversity for S. coloradensis compared to S. fidelis, but nearly identical genetic differentiation among sites within each species (both had global loci median FST = 0.000), despite differences in stream network location. For landscape genomics and testing for selection, we produced a less stringently filtered data set (3454 and 1070 SNPs for S. coloradensis and S. fidelis, respectively). Environmental variables (mean summer precipitation, slope, aspect, mean June stream temperature, land cover type) were correlated with 19 putative adaptive loci for S. coloradensis, but there was only one putative adaptive locus for S. fidelis (correlated with aspect). Interestingly, we also detected potential hybridization between multiple Sweltsa species which has never been previously detected. Studies like ours, that test for adaptive variation in multiple related species are needed to help assess landscape connectivity and the vulnerability of populations and communities to environmental change."

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.
     The authors note that S. fidelis was the most frequently recorded species out of the 100 different stonefly taxa they collected in their survey of Glacier National park and the Flathead basin in northwestern Montana.

Stark,BP; Stewart,KW 2005 Nymphs of four western nearctic Sweltsa species (Plecoptera: Chloroperlidae). Transactions of American Entomological Society 131 1+2, 189-200.
     Abstract: " Associations were made for four species of western Nearctic Sweltsa nymphs, and a comparative study of selected specimens was initiated to locate characters that might have potential systematic value. Nymphs of S. fidelis (Banks), S. pacifica (Banks), S. revelstoka (Jewett) and S. townesi (Ricker) were successfully distinguished using chaetotaxic features of cerci, mouthparts and femora in combination with pigment patterns of the frons."
Describes characters used to distinguish nymphs of Sweltsa fidelis from S. revelstoka. Has drawings and scanning electron photographs of various little body parts.

Surdick,RF 1985 Nearctic Genera of Chloroperlinae (Plecoptera:Chloroperlidae). University of Illinois Press, Urbana, IL. 146 pages.

Surdick,RF 1995a New western nearctic Sweltsa (Plecoptera: Chloroperlidae). Proceedings of the Entomological Society of Washington 97 1, 161-177.

Brown,WS 2004 Key to the Stoneflies of Gunnison County, Colorado