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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 20 Dec 2020
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

Àlvarez,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

Àlvarez,M and Peckarsky,BL 2014 Cascading effects of predatory fish on the composition of benthic algae in high-altitude streams. Oikos, 123(1)120-128. 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

Fuller,MR and Peckarsky,BL 2011 Ecosystem engineering by beavers affects mayfly life histories. Freshwater Biology, 56(5), pp.969-979. PDF

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."

Koch,BJ; Hall Jr,RO and Peckarsky,BL 2020 Nonconsumptive effects of Brook Trout predators reduce secondary production of mayfly prey. Freshwater Science, 39(3), pp.549-558.

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

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

Mihuc,TB and Minshall, GW 1995 Trophic generalists vs. trophic specialists: implications for food web dynamics in post-fire streams. Ecology, 76(8), pp.2361-2372.
     Abstract: "The trophic ecology of 11 benthic macroinvertebrate taxa found in Cache Creek, Yellowstone National Park (YNP) was studied to determine if burned organic matter is an important resource and how resource utilization patterns may be altered in post-fire streams. Laboratory food quality experiments were conducted to determine the growth response of each species when grown on several resource types: burned organic matter, periphyton, unburned coarse particulate material (CPM), and unburned fine particulate material (FPM). The central hypothesis of this research was that benthic macroinvertebrates cannot use burned organic matter as a resource. A secondary hypothesis was that some benthic macroinvertebrates are facultative in trophic function, with the ability to use both allochthonous and autochthonous resources for growth. Of the 11 taxa studied, only one (Paraleptophlebia heteronea) could grow on burned organic matter as a resource, indicating that post-fire food webs probably do not exhibit major shifts in resource utilization to burned material. Two species were generalist detrivores (P. heteronea, Ameletus cooki) able to use both natural FPM and CPM resources. Two species were specialist detritivores (Oligophlebodes sigma, Ephemerella infrequens) growing only on unburned CPM resources, and two (Cinygmula mimus, Epeorus albertae) were specialist herbivores utilizing only periphyton. Five species were generalist herbivore-detritivores (Baetis bicaudatus, Drunella doddsi, D. coloradensis, D. spinifera, Zapada columbiana), exhibiting growth on both detritus and periphyton resources. Based on the experimental results, trophic generalists are common food web components in Yellowstone streams. Two of the most abundant benthic macroinvertebrates during post-fire recovery, B. bicaudatus and Z. columbiana, were trophic generalists, indicating that some generalists may be disturbance adapted. In this study, published functional feeding group classification did not indicate obligate resource utilization (growth on only one resource type) for most taxa studied. Comparison of a food web for Cache Creek based on functional feeding group classification and one based on the results of this study indicates that the inclusion of generalists in the web results in a more realistic approximation of food web relationships such as the link-species scaling law. Our results suggest that future research should include spatial and temporal aspects of resource switching and generalist resource utilization by individual lotic primary consumers."

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), pp.152-164. PDF

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

Peckarsky,BL; McIntosh,AR; Àlvarez,M and Moslemi,JM 2013 Nutrient limitation controls the strength of behavioral trophic cascades in high elevation streams. Ecosphere, 4(9)1-17. PDF
     Abstract: "Indirect effects of predators on primary producers vary over space and time. Key components of the environmental context underlying that variability include the bottom-up supply of resources and the defense, mobility and foraging efficiency of primary consumers. We manipulated key resources that limit primary producers and tested the effects of system enrichment on the strength of top-down interactions between top predators (Salvelinus fontinalis), different types of grazing invertebrates and algae in high elevation streams of Colorado, USA. We added nitrogen and phosphorus to flow-through microcosms powered by stream water and tested the direct effects of chemical cues from brook trout on the behavior of sedentary, predator-resistant (caddisflies) and mobile, predator-vulnerable grazers (mayflies), and the indirect cascading effects of predators on: (1) the biomass of algae mediated by grazer behavior and (2) the impact of grazers on algal biomass accrual. Recognizing the value of whole-ecosystem experiments, we also tested the effects of supplementing nutrients to two headwater fishless streams on the impact of grazers on algae and the performance (growth rates) of four predominant grazer species compared to two adjacent reference streams with ambient (limited) nutrients. In both experiments, algal biomass increased with added nutrients where consumption by grazers was swamped by increased algal accrual due to enrichment. Results of the microcosm experiment were consistent with a context-dependent behavioral trophic cascade whereby predator cues increased the biomass of algae only in treatments with enriched nutrients and mobile, predator-vulnerable grazers (Baetis mayflies). Baetis showed risk-sensitive behavioral responses to fish cues, which resulted in cascading effects on algae only under enrichment. In contrast,behavior of sedentary, predator- resistant caddisflies (Allomyia) was unaffected by predator cues and a cascade was never observed. The whole ecosystem experiment revealed no aggregative responses by grazers but instead, strong developmental responses of all grazer species to nutrient enrichment. Growth rates of grazers increased with mobility, with the highest rates occurring for mobile, predator-vulnerable Baetis mayflies in enriched streams. Our results emphasize the importance of experimentally testing thecontext-dependency of trophic cascades, and are consistent with the hypothesis that nutrient limitation may reduce the strength of trophic cascades."

Poff,NL; Wellnitz,TA and Monroe,JB 2003 Redundancy among three herbivorous insects across an experimental current velocity gradient. Oecologia 134:262-269. PDF
     Abstract: "We conducted streamside experiments to determine if the ability of herbivorous insects to remove algal periphyton varies with local current velocity. We used two mayfly species (Baetis bicaudatus and Drunella grandis) and one caddisfly species (Glossosoma verdona), which differ from one another in body morphology and mobility. Periphyton was grown for 30 days on ceramic tiles in constant velocity to create similar initial forage conditions for grazers. Tiles were transferred to three velocity regimes characteristic of the natural streambed: slow (3-5 cm s-1), medium (15-20 cm s-1) and fast (32-41 cm s-1). Four grazer treatments (Baetis, Drunella, and Glossosoma alone, and all species combined) were repeated for each velocity treatment to isolate the effect of local current on grazer ability to crop periphyton. Grazers differed in their abilities to remove periphyton across current treatments. Glossosoma removed significantly (P<0.05) more periphyton at fast versus either slow or medium velocities; Baetis showed a similar (but non-significant) trend; and, Drunella always removed about 75% of periphyton, irrespective of current. At fast current, periphyton removal was equivalent among the species. At medium current, Drunella removed significantly more than both Baetis and Glossosoma, whereas at slow current, Drunella removed more than Baetis, which removed more than Glossosoma. Periphyton removal under the combined three-grazer treatment was similar qualitatively to the combined effects of individual grazers. More periphyton tended to be removed as current increased, with the fast versus slow contrast showing marginal significance (P=0.10). Under all current regimes, the quantity of periphyton removed did not differ from the null model expectation of simple additive effects among individual grazers (i.e., no facilitation or inhibition). These experiments show that for some species, herbivory varies with current, which suggests that the herbivore "function" of cropping periphyton may vary with the environmental context of local current. Under some local velocities, however, different herbivore species "function" similarly and are potentially redundant with respect to periphytic removal. In naturally heterogeneous streams characterized by sharp gradients in local current velocity, we expect current-dependent species interactions to be common and at least partially contribute to intra-guild co-existence of species."

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