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Ephemeroptera: Baetidae of Gunnison County, Colorado

Introduction to Baetis
Small Minnow Mayflies, Blue-winged Olive, BWO, Dark Blue Quill

Leach 1815

Updated 19 Apr 2017
Three live Baetis larvae side by side in a dish of river water

Provisional Species List


The Baetis nymphs on the right were living in the Gunnison River near McCabe Lane in March of 2007. Baetis nymphs earn the name "small minnow mayflies" because they swim like a small fish. They are streamlined for agility swimming and drifting in a current. Most are dark brown or black colored as nymphs. Some have white or reddish colors that help identify them as larvae or adults. The adults have blue or clear wings. They are small and delicate relative to other mayflies such as the Flat-headed (Heptageniidae) or Spiny Crawler (Ephemerellidae) at all ages. The photo below is of a recently emerged Baetis subimago photographed in the Cement Creek drainage in July of 2008. You can see the nymphal exuvia or shuck to the right of the subimago.


The common species; Baetis bicaudatus, Baetis flavistriga, and Baetis tricaudatus were named in the early part of the 20th century. The less common species were named in last 20 years of the century. Baetis taxonomy changed a lot in the 1990s. Many animals are very difficult to identify even with a microscope. More work on various cryptic or high altitude species is continuing today, driven by interest from many top notch taxonomists and the use of genetic analyses. See references and the other species below. You need adults or mature larvae with brown or black colored wing pads to tell these species apart.

Good Links

On this website:
Key to Baetis larvae
Baetidae Introduction

These species used to be included in Baetis, but have been assigned to different genera recently: Acentrella insignificans, Diphetor hageni, Plauditus virilis

Other websites:


Allan,JD 1987 Macroinvertebrate drift in a Rocky Mountain stream. Hydrobiologia 144, 261-268.
     Based at the Rocky Mountain Biological Lab in Gothic, 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) were 10 times higher at night. 24 hour totals approached 2000 animals/m³ 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.

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.

Cain,DJ; Luoma,SN; Wallace,WG 2004 Linking metal bioaccumulation of aquatic insects to their distribution patterns in a mining-impacted river. Environmental Toxicology and Chemistry 23, 1463-1473.

Canton,SP; Cline,LD; Short,R and Ward,JV 1984 The macroinvertebrates and fish of a Colorado stream during a period of fluctuating discharge. Freshwater Biology, 14(3), 311-316. PDF
     SUMMARY. 1. During a 2-year study of the fish and macroinvertebrates of a third-order montane stream, a severe drought in the first year resulted in a temporary cessation of surface flow. Flow was continuous during the second year.
2. Some taxa (e.g. Ophiogomphus severus) exhibited higher density during the drought year, others declined in abundance during low flow (e.g. Baetis spp.), whereas a few (e.g. Tricorythodes minutus) appeared unaffected. Total macroinvertebrate density decreased by 50% during the low flow year compared to the normal flow year. Mayflies were most severely affected, but also exhibited the most dramatic recovery.
3. The collector-gatherer functional feeding group was abundant only during the normal flow year, whereas shredders and predators exhibited increased relative abundance during low flow.
4. Fish populations were severely reduced in the low flow year. However, fishes rapidly invaded the area following resumption of normal flow.

Clements,WH; Kiffney,PM 1994b Integrated laboratory and field approach for assessing impacts of heavy metals at the Arkansas River, Colorado. Environmental Toxicology and Chemistry 13, 397-404. Abstract
     In contrast to Clements research on the Clinch River in Virginia, this study of the Arkansas River near Leadville, Colorado found no change in the total numbers of aquatic insects above and below the Superfund site California Gulch. They did however note a shift in community structure as metal tolerant taxa (Orthocladiinae midges) replaced intolerant taxa (mayflies). "Benthic communities [below California Gulch] were were dominated by Orthocladiinae chironomids."
They ran chronic toxicity tests with Ceriodaphnia dubia and found significantly lower reproduction in water from the site 6 kilometers below California Gulch in the spring. In the fall the sites above California Gulch and the recovery site 45 km below had significantly worse reproduction.
Studying the concentrations of a few heavy metals in water from the Arkansas River they found: "Considerable seasonal variation in metal concentrations was observed at stations downstream from California Gulch. Levels of Cd, Cu and Zn were 7 to 9 times higher at [the station below California Gulch] in spring than in fall and remained elevated at [the recovery station 45 km below] in spring."
They also looked at bioaccumulation of Cadmium (Cd) Copper (Cu) and Zinc (Zn) in algae and the aquatic macroinvertebrates Baetis spp, Arctopsyche grandis and Rhyacophila in fall and spring. They found lots of variation as always but Baetis metal concentrations were usually higher than the other taxa studied. "Levels of Cd, Cu and Zn in periphyton and benthic macroinvertebrates were significantly elevated at stations downstream from California Gulch in both seasons. "

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

Courtney,LA and Clements,WH 2000 Sensitivity to acidic pH in benthic invertebrate assemblages with different histories of exposure to metals. Journal of the North American Benthological Society 19 (1) 112-127.Abstract

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 and Baetis tricaudatus, among other mayfly species in this publication. Quote from page 109 regarding the genus Baetis: "This genus is a difficult one with which to deal. The insects are small and the species hard to distinguish. Characteristics based on coloration seem to be of no use whatever where alcoholic specimens must be used. Other characteristics must be relied upon, preferably structural differences large enough to be readily seen and not subject to great variation. Accordingly in the following notes there are described only a few points, for the imago, chief among them, size, peculiarities of hind wing and male forceps. The nymph is equally difficult, with the added uncertainty of change due to age and phase of molting cycle. Here, the characters that seem to give most useful distinctive characters are size of mature nymph, number and length of cerci, size and form of gill lamellae. The color pattern persists fairly well for a while in alcohol (i.e. arrangement of light and dark areas) and has given confirming evidence. In case of both nymphs and imagos, however, there is no high degree of certainty as to the accuracy of specific lines - the group one calls a species may include more than one species or he may have divided a species by the use of variable characters."

Durfee,R and Kondratieff,BC 1993 Description of adults of Baetis magnus (Ephemeroptera: Baetidae). Entomological News 104 5, 227-232.

Flecker,AS and Allan,JD 1988 Flight direction in some Rocky Mountain mayflies (Ephemeroptera), with observations of parasitism. Aquatic Insects 10(1):33-42. PDF
     Abstract: " Adult mayflies (Ephemeroptera) were sampled using sticky traps at several locations along a Rocky Mountain stream. Eight genera were collected, of which imagos of Baetis spp and Rhithrogena hageni were most common. Baetis was represented almost exclusively by females and flight direction was significantly in the upstream direction. In R. hageni both males and females were included. Females appeared to fly into clearings or downstream, whereas males showed no directionality, or a downstream bias. This difference in adult flight direction may be partly explainable by the greater amount of downstream drift in Baetis relative to R. hageni. Finally, mermithid nematodes were found to be frequent parasites of Baetis but not of R. hageni causing total absence of eggs in infected females."

Gill,BA; Harrington,RA; Kondratieff,BC; Zamudio,KR; Poff,NL and Funk,WC 2014 Morphological taxonomy, DNA barcoding, and species diversity in southern Rocky Mountain headwater streams. Freshwater Science 33(1) 288-301. PDF
     Working in wadeable streams on the Front Range of Colorado, they found 6 species of Baetis; bicaudatus, flavistriga, magnus and three cryptic species identified by DNA barcoding.

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

Jacob,U 2003 Baetis Leach 1815, sensu stricto or sensu lato. A contribution to the genus concept based on species groups with identification keys. Lauterbornia 47: 59-129. [In German, English summary]

Kiffney,PM and Clements,WH 1993 Bioaccumulation of heavy metals by benthic invertebrates at the Arkansas River, Colorado. Environmental Toxicology and Chemistry 12, 1507-1517.

Kiffney,P; Little,E and Clements,W 1997 Influence of ultraviolet-B radiation on the drift response of stream invertebrates. Freshwater Biology, 37(2), 485-492.
     Abstract: " 1. Recent studies have shown that ultraviolet (UV) radiation (280-400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet-B (UVB; 280-320 nm) radiation on the drift response of immature stream insects in laboratory microcosms.
2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid-day conditions at Fort Collins, Colorado (longitude 105º30"; latitude 40º35").
3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB-exposed streams may be a behavioural response and/or a result of injury.
4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats. "

Leach,WE 1815 Entomology. Brewster's Edinburgh Encyclopaedia 9:57-172.
     Describes the genus Baetis for the first time.

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.

McCafferty,WP 1997 Name adjustments and a new synonym for North American Ephemeroptera species. Entomological News 108 4, 318, 320.

McCafferty,WP; Durfee,RS; Kondratieff,BC 1993 Colorado mayflies (Ephemeroptera): an annotated inventory. Southwestern Naturalist 38 3, 252-274. PDF

McCafferty,WP; Waltz,RD 1990 Revisionary synopsis of the Baetidae (Ephemeroptera) of North and Central America. Transactions of American Entomological Society 116, 769-799.

McIntosh,AR; Peckarsky,BL and Taylor,BW 2004. Predator-induced resource heterogeneity in a stream food web. Ecology 85(8) 2279-2290. Abstract

Meyer,MD and McCafferty,WP 2001 Hagen's small minnow mayfly (Ephemeroptera: Baetidae) in North America. Entomological News 112 4, 255-263.

Monaghan,MT; Spaak,P; Robinson,CT & Ward,JV 2001 Genetic differentiation of Baetis alpinus Pictet (Ephemeroptera: Baetidae) in fragmented alpine streams. Heredity 86 (4),395-403. doi: 10.1046/ j.1365-2540.2001.00843.x http://www.blackwell-synergy.com/links/doi/10.1046/j.1365-2540.2001.00843.x/abs/

Morihara,DK and McCafferty,WP 1979a The Baetis larvae of North America (Ephemeroptera:Baetidae). Transactions of American Entomological Society 105, 139-221. PDF

Morihara,DK and McCafferty,WP 1979b Systematics of the propinquus group of Baetis species (Ephemeroptera: Baetidae). Annals of the Entomological Society of America 72, 130-135. PDF

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; Mather,PB; Hillyer,M; Encalada,AC 2005 Are populations of mayflies living in adjacent fish and fishless streams genetically differentiated? Freshwater Biology 50(1), 42-51. doi: 10.1111/j.1365-2427.2004.01292.x Abstract

Pennack,RW and Ward,JV 1986 Interstital faunal communities of the hyporheic and adjacent groundwater biotopes of a Colorado mountain stream. Archiv für Hydrobiologie Suppl. 74 3, 356-396.
     They found Baetis sp. nymphs in the hyporheic zone of the South Platte river in the Front Range of Colorado at 1863 meters elevation.

Poff,NL; Olden,JD; Viera,NKM; Finn,DS; Simmons,MP; Kondratieff,BC 2006 Functional trait niches of American lotic insects: traits-based ecological applications in light of phylogenetic relationships. Journal of the North American Benthological Society 25 4, 730-755.
     Here are the traits for this species from the Appendix:
Life History Voltinism Bi or multivoltine - more than 1 generation/yr
Development Fast Seasonal
Synchronization of emergence Poorly synchronized
Adult life span Less than 1 week
Adult ability to exit Absent
Ability to survive dessication Absent
Mobility Female dispersal Less than 1km flight before laying eggs
Adult flying strength Weak - cannot fly into light breeze
Occurance in drift Abundant (dominant in drift samples)
Maximum crawling rate Very low - less than 10cm/hour
Swimming ability Strong
Morphology Attachment None (free ranging)
Armoring None (soft -bodied forms)
Shape Streamlined - fusiform
Respiration Gills
Size at maturity Small (less than 9mm)
Ecology Rheophily Depositional and erosional
Thermal preference Cool/Warm eurythermal
Habit Swim
Trophic habit Collector-gatherer

Poff,NL and Ward,JV 1988 Use of occupied Glossosoma verdona (Trichoptera: Glossosomatidae) cases by early instars of Baetis spp.(Ephemeroptera: Baetidae) in a Rocky Mountain stream. Entomological news (USA).

Poff,NL and Ward,JV 1991 Drift responses of benthic invertebrates to experimental streamflow variation in a hydrologically stable stream. Canadian Journal of Fisheries and Aquatic Sciences, 48(10): 1926-1936.
     Abstract: Field experiments were conducted in the regulated upper Colorado River to assess drift responses of lotic macroinvertebrates to streamflow manipulations. In each of three seasons, drift was collected in one control and two experimental riffles. On the first day, no flow manipulations occurred. Six hours before sunset on the second day, streamflow was simultaneously reduced and elevated in two experimental riffles with instream diversion structures. Following flow elevation, both mean daily drift density and drift rate generally increased for 13 taxa across all seasons. Flow reductions generally induced elevated drift densities for most taxa, but drift rates declined for some taxa. Patterns of diel drift periodicity were less frequently modified by flow manipulations. Taxa with typical nocturnal peaks in drift activity (Baetis spp., Epeorus longimanus, Triznaka signata) generally maintained this pattern despite some increases in diurnal drift. For a few taxa, modification of diel drift patterns occurred, either as nocturnal decreases following reduced flow (Paraleptophlebia heteronea, Ephemerella infrequens) or as diurnal drift increases in response to either elevated flow (Lepidostoma ormeam, Chironomidae larvae) or reduced flow (Simuliidae). With some exceptions, observed drift responses could be used to suggest active versus passive processes of drift entry.

Robinson,CT and Minshall,GW 1986 Effects of disturbance frequency on stream benthic community structure in relation to canopy cover and season. Journal of the North American Benthological Society, 237-248. PDF
     Abstract: " Field experiments were conducted to examine the effects of disturbance frequency on invertebrates and periphyton colonizing bricks in a third order Rocky Mountain (USA) stream. After an initial colonization period (30 days), sets of bricks were turned over at intervals of 0, 3, 9, 27, or 54 days. Invertebrate species richness and density were reduced as disturbance frequency increased. These trends were evident for both seasons (summer and fall) and sites (open vs. closed canopy). Invertebrate species diversity (H') displayed no effect during the fall experiment; however, H' was reduced at high frequencies of disturbance during the summer experiment. Baetis tricaudatus was the most abundant invertebrate on the substrata at both sites and seasons. Alloperla, Baetis, Cinygmula, Chironomidae, Drunella grandis, Hydropsyche, and Seratella tibialis increased in absolute abundances as disturbance frequency decreased. Four other abundant taxa (Capnia, Cleptelmis, Glossosoma, and Isoperla) displayed no clear response to disturbance in either absolute or relative abundances. Species in low abundance tended to colonize only the less frequently disturbed bricks. During both seasons, periphyton biomass increased as disturbance frequency decreased at the open canopy site, while no trend was apparent at the closed canopy site. Periphyton accumulation monitored over time and among treatments revealed that frequent disturbances maintained low standing crops at an open canopy site. These data suggest that disturbance frequency can directly influence the benthic community at the scale of individual rock "islands" by reducing invertebrate richness, total animal density, and periphyton biomass. The effect of disturbance on species diversity (H') was seasonal, further emphasizing the importance of considering seasonality in stream field studies. "

Roline,R 1988 The effects of heavy metals pollution of the upper Arkansas River on the distribution of aquatic macroinvertebrates. Hydrobiologia 160: 3-8.
     They sampled the Arkansas River upstream and downstream of mine drainage and clean water inputs in 1979 and 1980. After compositing 3 surber samplers in the field, they identified the macroinvertebrates to genus level and used a diversity index to evaluate the health of the macroinvertebrate community. Higher diversity is better. Diversity decreased downstream of heavy metal pollution from the Leadville Drain and California Gulch and increased downstream of clean water inputs.
Quote from pages 7-8: "The Ephemeropteran, Baetis, was found in general abundance throughout the study reach and was found to be quite tolerant of heavy metals pollution."

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

Waltz RD; McCafferty WP. 1987. New genera of Baetidae for some Nearctic species previously in Baetis Leach (Ephemeroptera). Annals of the Entomological Society of America 80:667-670.

Wang,TQ; McCafferty,WP 1996 New diagnostic characters for the mayfly family Baetidae (Ephemeroptera). Entomological News 107 2, 207-212.

Wiersema,NA; Nelson,CR; Kuehnl,KF 2004 A new small minnow mayfly (Ephemeroptera: Baetidae) from Utah, USA. Entomological News 115 3, 139-145.
     They provide a key for Baetis larvae to species. Abstract: "Baetis moqui, new species, is described from larvae collected from the Escalante Canyon Region of Garfield County in south-central Utah. The new species is unique among North American Baetis in having gill number one highly reduced or absent. Labial morphology and overall setation characteristics indicate a close relationship between B. moqui and the northern California species Baetis alius and the eastern North American species Baetis pluto. An updated key to the North American Baetis larvae is provided. "

Wipfli,MS, Hudson,J and Caouette,J 1998 Influence of salmon carcasses on stream productivity: response of biofilm and benthic macroinvertebrates in southeastern Alaska, U.S.A. Can. J. Fish. Aquat. Sci. 55(6): 1503-1511 Abstract

Brown, Wendy S. 2004 Mayflies (Ephemeroptera) of Gunnison County, Colorado, USA