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Ephemeroptera: Baetidae of Gunnison County, Colorado

Baetis bicaudatus
Small Minnow Mayfly, Iron Blue Dun, Blue-winged Olive, BWO, Little dark blue winged olive #20

Dodds 1923

Updated 28 Dec 2016
TSN 100823

A Baetis snack for a stonefly. Notice two tails on the Baetis larvae. Caught and released from the Upper East river on 2Aug2011.


This is a classic two-tailed (bi-caudatus) Baetis species. Widespread in Western North America, they have indistinct markings on their body, but a bilobed mark on the pronotum.


This is one of the rhodani group of Baetis species.

Good Links

On this website:
Introduction to Baetis
Key to Baetis Nymphs

Outside websites:
Hatch Chart for the Gunnison Gorge & Black Canyon from Cimarron Creek Guides in Montrose http://cimarroncreek.com/flyfishing/hatchchart.cfm

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


Allan,JD 1978a Diet of brook trout (Salvelinus fontinalis Mitchell) and Brown Trout (Salmo trutta L.) in an alpine stream. Internationale Vereinigung für Theoretische und Angewandte Limnologie Verhandlungen 20, 2045-2050.
     Abstract: "Diurnal drift of stream invertebrates is examined as a predator avoidance adaptation via the hypothesis that those taxa or growth stages which are large, and thus subject to intense predation relative to smaller forms, should be most strongly constrained to nocturnal drift activity. Smaller taxa or stages may be aperiodic or day active. Data from an alpine stream document for the abundant and widespread mayfly Baetis bicaudatus that, on a continuum from small to large size, the risk of predation increases while the propensity to drift during the day decreases. There is supporting and some contrary evidence from the literature for the generality of this pattern."
This research was conducted in Cement Creek, a tributary of the East River in the Gunnison Basin of Colorado.

Allan,JD 1981 Determinants of diet of brook trout (Salvelinus fontinalis) in a mountain stream. Canadian Journal of Fisheries and Aquatic Sciences 38, 184-192. PDF

Allan,JD 1987 Macroinvertebrate drift in a Rocky Mountain stream. Hydrobiologia 144, 261-268.
     The author studied Cement Creek in Gunnison County during the spring, summer and fall of 1975-1978. He found that drift densities (number of animals per 100 m³ of water) was 10 times higher at night. 24 hour totals approached 2000 animals/100m³ in mid-summer down to 500 animals/m³ in the fall. Quote from the abstract: "Ephemeroptera, especially Baetis, dominated the drift." He found that benthic density (number of animals/m² from streambed samples) was the best predictor of 24hr drift rate for Baetis bicaudatus. Adding discharge to the calculation (a stepwise regression) helped predict the number of B. bicaudatus in the drift.

Allan,JD and Russek,E 1985 The quantification of stream drift. Canadian Journal of Fisheries and Aquatic Sciences 42:210-215. PDF

Alvarez,M and Peckarsky,BL 2013 The influence of moss on grazers in high-altitude streams: food, refuge or both? Freshwater Biology, 58(9) 1982-1994. PDF

Ball,SL; Hebert,PDN; Burian,SK; Webb,JM 2005 Biological identification of mayflies (Ephemeroptera) using DNA barcodes. Journal of the North American Benthological Society 24(3) 508-524.

Corkum LD and Clifford HF 1981 Function of caudal filaments and correlated structures in mayfly nymphs, with special reference to Baetis (Ephemeroptera). Quaestiones Entomologicae 17: 129-146. PDF

Cowan CA and Peckarsky BL. 1990 Feeding by a lotic mayfly grazer as quantified by gut fluorescence. Journal of the North American Benthological Society 9(4)368-378. PDF

Dodds,GS 1923 Mayflies from Colorado: descriptions of certain species and notes on others. Transactions of American Entomological Society 69, 93-116.
     Dodds described Baetis bicaudatus in this paper.

Encalada, AC and Peckarsky, BL 2000 Selective oviposition behavior of the mayfly Baetis bicaudatus in Colorado Mountain Streams. NABS abstract. http://www.benthos.org/meeting/nabs2000/nabstracts2000.cfm/id/262

Encalada,AC and Peckarsky,BL 2002 Does local recruitment of the mayfly Baetis bicaudatis determine local larval abundance? Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, in Life Histories. http://www.benthos.org/database/allnabstracts.cfm/db/Pittsburgh2002abstracts/id/134

Encalada,AC and Peckarsky,BL 2006 Selective oviposition of the mayfly Baetis bicaudatus. Oecologia 148:526-537. Abstract

Gilpin,BR and Brusven,MA 1970 Food habits and ecology of mayflies of the St. Maries River in Idaho. Melanderia 4:19-40. PDF

Harper,PP and Harper,F 1997 Mayflies (Ephemeroptera) of the Yukon. Pp. 152-167 In: H.V. Danks and J.A. Downes, eds. Insects of the Yukon. Biological Survey of Canada (Terrestrial Arthropods). Ottawa, Ontario, Canada. http://www.biology.ualberta.ca/bsc/pdf/harper.pdf

Hernandez,SA and Peckarsky,BL 2014Do stream mayflies exhibit trade-offs between food acquisition and predator avoidance behaviors? Freshwater Science 33(1) 124-133.

Hughes,JM; Mather,PB; Hillyer,MJ; Cleary,C and Peckarsky,B 2003 Genetic structure in a montane mayfly Baetis bicaudatus (Ephemeroptera: Baetidae), from the Rocky Mountains, Colorado. Freshwater Biology 48, 2149-2162.

Kerans,BL; Peckarsky BL and Anderson,C 1995 Estimates of mayfly mortality: is stonefly predation a significant source?. Oikos 74(2):315-323. PDF
     Abstract: " Field experiments and surveys were carried out in a Rocky Mountain alpine stream during the summers of 1990 and 1992 to estimate the proportion of natural losses of the mayfly Baetis bicaudatus resulting from the co-occurring, predatory stonefly, Kogotus modestus. Functional response experiments determined the number of prey consumed by male and female Kogotus by manipulating the densities of prey and the presence or absence of predators in stream-side chambers. Estimates of losses of Baetis and density of Kogotus were based on ten benthic samples collected weekly (except for last sampling date) from one study reach. Concurrently, drift density of Baetis was estimated upstream and downstream of the reach to determine gains or losses of Baetis resulting from migration. In the functional response experiments Kogotus consumed the same number of prey regardless of prey densities. Female predators tended to consume more prey (~ 2 d-1) than males (~ 1 d-1), although the result was only statistically significant in one out of three experiments. Per-capita mortality rates of Baetis declined from 0.01 to 0.001 d-1 (predator m-2)-1 with increasing prey density. In the study reach Baetis density declined 70% during the 4.5 wk and per-capita losses averaged 3.8% d-1. We estimated that predation by Kogotus could cause between 1.6 and 9.5% of the losses of Baetis from the study reach. This occurred because high losses of Baetis were combined with low consumption rates and densities (1.83 individuals m-2) of Kogotus. Baetis drift density was higher at night than during the day. Drift densities of Baetis tended to be higher leaving than entering the reach in nighttime estimates, although the results were not statistically significant. Few replicates resulted in low power to detect differences in upstream and downstream drift densities; therefore, it is possible that some losses could be the result of drift out of the study reach. Nonetheless our results suggest that Kogotus populations had little direct, lethal effect on Baetis populations in this study reach."

Lugo-Ortiz,CR and McCafferty,WP 1998 A new North American genus of Baetidae (Ephemeroptera) and key to Baetis complex genera. Entomological News 109 5, 345-353. Abstract
     The key splitting Baetis species from Labiobaetis, Barbaetis, Heterocloeon, Plauditus and Acentrella is useful. Page 351 has figures illustrating the Baetis traits of thumb on the labial palp (Fig 20) and figure 21 showing abdominal tergal scales.

McCafferty,WP; Durfee,RS; Kondratieff,BC 1993 Colorado mayflies (Ephemeroptera): an annotated inventory. Southwestern Naturalist 38 3, 252-274. PDF
     Quote from page 255: "This is a relatively common mountain species throughout the West. It sometimes is the only mayfly species found in alpine streams of Colorado. It is now known to range into Alaska (Milner, 1987), and the first author and N. Kluge of St. Petersburg, Russia have recently confirmed that it also occurs in Siberia. Another "two-tailed," trout-stream species of Baetis that may eventually be confirmed from Colorado is B. punctiventris (McDunnough), which has often been incorrectly known as Pseudocloeon edmundsi to Salmon River and Yellowstone fly fishermen."

McCafferty,WP and Provonsha, AV The Mayflies of North AmericaSpecies List (Version 8Feb2011)
     Here is the geographic range and synonyms:
Baetis bicaudatus Dodds, 1923 [CAN:FN,NW;USA:FN,NW,SW]
    Baetis minimus Dodds, 1923 (syn.)

McIntosh,AR; Peckarsky,BL; Taylor,BW 2002 The influence of predatory fish on mayfly drift: extrapolating from experiments to nature. Freshwater Biology 47: 1497-1513.

McIntosh,AR; Peckarsky,BL and Taylor,BW 1999 Rapid size-specific changes in the drift of Baetis bicaudatus (Ephemeroptera) caused by alterations in fish odour concentration. Oecologia 118(2) 256 - 264. Abstract Pdf file (288 KB)

McPeek, MA and Peckarsky,BL. 1998 Life histories and the strengths of species interactions: combining mortality, growth and fecundity effects. Ecology 79: 235-247. Abstract

Minshall,GW Robinson,CT and Lawrence,DE 1997 Postfire responses of lotic ecosystems in Yellowstone National Park, U. S. A. Canadian Journal Fisheries Aquatic Sciences 54: 2509-2525.

Newell,RL and Hossack,BR 2009 Large, wetland-associated mayflies (Ephemeroptera) of Glacier National Park, Montana. Western North American Naturalist, 69(3) 335-342. Abstract and PDF

Peckarsky,BL 1980 Influence of detritus on colonization of stream invertebrates. Canadian Journal of Fisheries and Aquatic Sciences 37, 957-963.

Peckarsky,BL 1983 Biotic interactions or abiotic limitations? A model of lotic community structure. In: Dynamics of Lotic Ecosystems. Eds: Fontaine III,Thomas D; Bartell,Steven M Ann Arbor Science, Ann Arbor, Michigan, 303-323.

Peckarsky,BL 1990 Habitat selection by stream-dwelling predatory stoneflies. Canadian Journal of Fisheries and Aquatic Sciences 48, 1069-1076.

Peckarsky,BL 1991a A field test of resource depression by predatory stonefly larvae. Oikos 61 (1) 3-10.

Peckarsky,BL 1991b Is there a coevolutionary arms race between predators and prey? A case study with stoneflies and mayflies. Advances in Ecology 1: 167-180.

Peckarsky,BL 1996 Alternative predator avoidance syndromes of stream-dwelling mayfly larvae. Ecology 77 (6) 1888-1905.Abstract

Peckarsky,BL; Cowan,CA; Penton,MA and Anderson,C 1993 Sublethal consequences of stream-dwelling predatory stoneflies on mayfly growth and fecundity. Ecology 74(6)1836-1846. Abstract

Peckarsky,BL, Encalada,AC and McIntosh, AR 2011 Why do vulnerable mayflies thrive in trout streams? American Entomologist 57(3)152-164.

Peckarsky,BL; Hughes,JM; and Encalada,AC 2002 Is there a genetic basis for the phenotypic differences among Baetis spp. in fish and fishless streams? Presented at the NABS Annual meeting, Pittsburgh, Pennsylvania, in Population Distribution: Studies of Dispersal, Behavior, and Genetics II http://www.benthos.org/database/allnabstracts.cfm/db/Pittsburgh2002abstracts/id/104

Peckarsky,BL; Hughes,JM; Mather,PB; Hillyer,M; Encalada,AC 2005 Are populations of mayflies living in adjacent fish and fishless streams genetically differentiated? Freshwater Biology 50: 42-51. PDF

Peckarsky,BL; Kerans,B; Taylor,BW and McIntosh,AR. 2008 Predator effects on prey population dynamics in open systems. Oecologia 156(2):431-40. Abstract, PDF

Peckarsky,BL; McIntosh,AR; Taylor,BW; Dahl,J 2002 Predator chemicals induce changes in mayfly life history traits: A whole stream manipulation. Ecology 83 (3) 612-618. Abstract

Peckarsky,BL; McIntosh,AR; Caudill,CC; Dahl,J 2002 Swarming and mating behavior of a mayfly Baetis bicaudatus suggest stabilizing selection for male body size. Behavioral Ecology and Sociobiology 51, 530-537.

Peckarsky,BL; McIntosh,AR; Caudill,CC and Dahl,J 2002 Stabilizing selection on male body size of high altitude populations of Baetis bicaudatus (Ephemeroptera: Baetidae). Behavioral Ecology and Sociobiology 51:530-537. Abstract

Poff,NL; Wellnitz,TA and Monroe,JB 2003 Redundancy among three herbivorous insects across an experimental current velocity gradient. Oecologia 134:262-269

Richards,C and Minshall,GW 1988. The influence of periphyton abundance on Baetis bicaudatus distribution and colonization in a small stream. Journal of the North American Benthological Society 7(2):77-86.

Stewart,KW and Szczytko,SW 1983 Drift of Ephemeroptera and Plecoptera in two Colorado rivers. Freshwater Invertebrate Biology. 2(3)117-131. PDF

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

Vance,SA and Peckarsky,BL 1996 The infection of nymphal Baetis bicaudatus by the mermithid nematode Gasteromermis sp. Ecological Entomology 21: 377-381.

Vance,SA 1996 The effect of the mermithid parasite Gasteromermis sp. (Nematoda: Mermithidae) on the drift behaviour of its mayfly host, Baetis bicaudatus (Ephemeroptera: Baetidae): a tradeoff between avoiding predators and locating food. Canadian Journal of Zoology 74: 1907-1913.

Vance,SA and Peckarsky,BL 1997 The effect of mermithid parasitism on predation of nymphal Baetis bicaudatus (Ephemeroptera) by invertebrates. Oecologia 110: 147-152.
     They found that Kogotus modestus ate significantly more parasitized than unparasitized B. bicaudatus. However, Rhyacophila hyalinata caught and ate equal numbers of parasitized and unparasitized nymphs. They attribute this to the behavior of parasitized nymphs and different hunting behaviors of the predators. Parasitized nymphs drifted less, which increased encounter rates with Kogotus nymphs. However R. hyalinata larvae are ambush predators and catch parasitized and unparasitized nymphs equally. They hypothesize that avoiding fish predation by drifting less is a greater advantage to the parasite than the losses suffered by increased stonefly predation.

Vance,SA 1996 Morphological and behavioural sex reversal in mermithid-infected mayflies. Proceedings of the Royal Society of London B 263: 907-912.
     She studied Baetis bicaudatus from the East River near Gothic. B. bicaudatus were either unparasitized with a normal morphology or parasitized with a "female" or intersex morphology. No parasitized mayflies showed complete male characteristics. Through the use of flow cytometry she discovered the "female" mayflies were probably about half males who had suffered sex reversal as a result of Gasteromermis parasitism. Parasitized individuals also tended to fly upstream and were observed crawling under the water, all of which are female behaviors that allow the nematode to emerge from the mayfly and burrow into the substrate to complete its life cycle.

Wellnitz,T 2014 Can current velocity mediate trophic cascades in a mountain stream?. Freshwater Biology, 59(11) 2245-2255. PDF

Wilcox,AC; Peckarsky,BL; Taylor,BW; and Encalada,AC 2008 Hydraulic and geomorphic effects on mayfly drift in high-gradient streams at moderate discharges. Ecohydrology 1(2) 176-186.

Zuellig,RE; Kashian,DR; Brooks,ML; Kiffney,PM and Clements,WH 2008 The influence of metal exposure history and ultraviolet-B radiation on benthic communities in Colorado Rocky Mountain streams. Journal of the North American Benthological Society, 27(1), 120-134. PDF


The middle tail is only a stub or apparently missing. Consider that nymphs of other species may look like B. bicaudatus initially, but will gain tail segments with each new instar.

Brown, WS 2004 Mayflies (Ephemeroptera) of Gunnison County, Colorado, USA