Introduction to the Mayflies (Ephemeroptera) of Gunnison County, ColoradoUpdated 11 January 2026
TSN 100502 
The Baetis or small minnow mayflies to the right are some of the most common mayflies in the Gunnison basin. They were caught and released from the Gunnison River. Common and abundant in Gunnison county and the entire US, this genus and many others are essential to the aquatic food web. As with many other mayflies in our area, Baetis lives crawling around the rocks of the streambed, grazing on the diatoms and algae that grow on the surface of the rocks.
This mayfly species also "drifts", or releases from the bottom to swim in the current. Of course foraging fish love this behavior, so Baetis and many other mayflies that drift are eagerly sought out as food by the variety of introduced and native fishes in our watersheds. NotesThe scientific name is from the Greek Eøémepos which is the basis for the english word "Ephemeral". It means "enduring but a day" or short lived. Then add the suffix -optera which means winged or "has wings". Adult mayflies may only live for a few hours let alone a whole day!Translations of terms used by Fishermen and ScientistsSubimago = DunImago = Spinner Exuvia = Shuck You may click on a mayfly below to go to their webpage :-) 
Good LinksOther Websites:
ReferencesBrittain,JE 2008 Mayflies, biodiversity and climate change. International Advances in the Ecology, Zoogeography, and Systematics of Mayflies and Stoneflies, pp.1-14.Abstract: "Mayflies (Ephemeroptera) are an ancient order of insects that are globally distributed in both northern and southern hemispheres and have survived major environmental shifts. Despite the problems associated with selection processes operating in both terrestrial and aquatic environments, mayflies have successfully colonized a wide range of freshwater habitats from the tropics to the arctic, a somewhat greater range than other hemimetabolic aquatic insects such as the Plecoptera and Odonata. While many species of Ephemeroptera require specific environmental cues, others display considerable flexibility in life cycle length and timing in relation to environmental changes. This is particularly apparent in arctic and alpine species. Climate change scenarios predict rapid shifts across many environmental gradients, including temperature and the frequency and magnitude of floods and droughts. Changes in the mayfly fauna are hypothesized in the light of the environmental tolerances, life cycle plasticity and the dispersal mechanisms of present day mayflies. During periods of rapid environmental transition certain species traits will be beneficial. Generalists will do better; specialists with strict environmental limits and poor powers of dispersal may become extinct." Clements,WH; Cherry,DS and Cairns,J 1988 Impact of heavy metals on insect communities in streams: a comparision of observational and experimental results. Canadian Journal of Fisheries and Aquatic Sciences 45 11, 2017-2025. Working in the Clinch River of Russell County, Virginia and outdoor experimental streams, they measured population responses of macroinvertebrates to natural conditions and 12 µg of copper and zinc in the artifical streams. They used 6 replicates of substrate-filled trays everywhere and counted all the animals (no subsampling). Both stream mesocosm experiments and Clinch river sites showed similar results. They found abundance or total numbers of aquatic insects declined at all high effluent sites associated with the Clinch River coal-fired power plant, recovering 3- 4 kilometers downstream. Low levels of copper and zinc reduced species richness (number of different taxa) and total numbers as well as caused a shift in the species composition of dominant taxa. Metal contamination caused macroinvertebrate populations to shift from control (clean) sites dominated by Mayflies and Tanytarsini Midges to polluted sites dominated by Hydropsychidae caddisflies and Orthocladiinae midges. Edmunds Jr.,GF; Jensen,SL and Berner,L 1976 The Mayflies of North and Central America. University of Minnesota Press, Minneapolis, Minnesota. 330 pages pages. Edmunds Jr,GF and McCafferty,WP 1988 The mayfly subimago. Annual review of entomology, 33(1)509-527. PDF Abstract: "Mayflies are unique among present-day insects because they molt after becoming fully winged; in other words, they have a winged preadult life stage. This is the subimago. Because mayfly metamorphosis includes this unique life stage and is thus different from other existing kinds of insect metamorphosis, entomologists have long pondered the exact nature and role of the subimago. Many of the proposed explanations have been based on little or no data. Is the subimago comparable to the adult of other insects or is it perhaps equivalent to the pupa or even the larva? Does it have a functional role or is it merely a relict of a primitive lifestyle? Why and how in certain groups of mayflies has the subimago evidently replaced the adult? Here we review the historical thinking, synthesize the pertinent aspects of available data with considerable unpublished data,and draw conclusions about the function and evolution of the subimago." Edmunds,GF and Tennessen,KJ 1996 Ephemeroptera. In: An Introduction to the Aquatic Insects of North America. 3rd ed. Eds: Merritt,RW; Cummins,KW Kendall/Hunt Publishing Company, Dubuque, Iowa, 126-163. Ogden,TH; Gattolliat,JL; Sartori,M; Staniczek,AH; Soldán,T and Whiting,MF 2009 Towards a new paradigm in mayfly phylogeny (Ephemeroptera): combined analysis of morphological and molecular data. Systematic Entomology, 34(4), pp.616-634. PDF Abstract: "This study represents the first formal morphological and combined (morphological and molecular) phylogenetic analyses of the order Ephemeroptera. Taxonomic sampling comprised 112 species in 107 genera, including 42 recognized families (all major lineages of Ephemeroptera). Morphological data consisted of 101 morphological characters. Molecular data were acquired from DNA sequences of the 12S, 16S, 18S, 28S and H3 genes. The Asian genus Siphluriscus (Siphluriscidae) was supported as sister to all other mayflies. The lineages Carapacea, Furcatergalia, Fossoriae, Pannota, Caenoidea and Ephemerelloidea were supported as monophyletic, as were many of the families. However, some recognized families (for example, Ameletopsidae and Coloburiscidae) and major lineages (such as Setisura, Pisciforma and Ephemeroidea among others) were not supported as monophyletic, mainly due to convergences within nymphal characters. Clade robustness was evaluated by multiple methods and approaches." Ogden,TH and Whiting,MF 2005 Phylogeny of Ephemeroptera (mayflies) based on molecular evidence. Molecular phylogenetics and evolution, 37(3), pp.625-643. PDF Abstract: "This study represents the first molecular phylogeny for the Order Ephemeroptera. The analyses included 31 of the 37 families, representing ∼24% of the genera. Fifteen families were supported as being monophyletic, five families were supported as nonmonophyletic, and 11 families were only represented by one species, and monophyly was not testable. The suborders Furcatergalia and Carapacea were supported as monophyletic while Setisura and Pisciforma were not supported as monophyletic. The superfamilies Ephemerelloidea and Caenoidea were supported as monophyletic while Baetoidea, Siphlonuroidea, Ephemeroidea, and Heptagenioidea were not. Baetidae was recovered as sister to the remaining clades. The mayfly gill to wing origin hypothesis was not supported nor refuted by these data. Mandibular tusks were supported as having at least one loss in Behningiidae and, together with the burrowing lifestyle, possibly two origins. The fishlike body form was supported as plesiomorphic for mayflies with multiple secondary losses. Topological sensitivity analysis was used as a tool to examine patterns concerning the stability of relationships across a parameter landscape, providing additional information that may not have been acquired otherwise." Peckarsky,BL; McIntosh,AR; Àlvarez,M and Moslemi,JM 2015 Disturbance legacies and nutrient limitation influence interactions between grazers and algae in high elevation streams. Ecosphere, 6(11)1-15. PDF Abstract: " Debate about control of interaction strength among species is fueled by variation in environmental contexts affecting food webs. We used extensive surveys and two field experiments to test the individual and interactive influences of variation in the assemblages and associated traits of grazers as shaped by the legacy of disturbance, nutrient limitation and the presence of top predators on the accrual of basal resources. We quantified hydrologic variation and streambed movement to describe the legacy of disturbance and sampled biota of 20 streams over five years in a high-elevation catchment in Colorado, USA. Grazer assemblages switched from caddisfly-dominated to mayfly-dominated as disturbance increased. We manipulated the composition of grazer assemblages and the availability of nutrients (N and P) within flow-through mesocosms assembled adjacent to 10 streams, and also deployed larger in-stream channels manipulating the presence of top predators (brook trout) in five streams varying in disturbance regimes. In both experiments we compared the rate of accrual of benthic algae and the strength of grazer-algal interactions among treatments. We observed no indirect effects of top predators on grazer mobility, grazer consumption of algae, or accrual of algal biomass (no trophic cascades). However, in both experiments accrual rates of algae yielded a unimodal pattern and grazer impacts on algae decreased with increasing disturbance, but only at ambient (limiting) nutrient conditions. When nutrients were amended in the mesocosm experiment, algal accrual was uniformly high and grazer impacts on algae were consistently low. Reduced algae accrual at high disturbance levels may be explained by direct effects of environmental harshness on algae, and at low disturbance by indirect effects on grazer traits (behaviors) rather than on grazer density. In more benign streams per capita and per unit biomass grazer impacts on algae were high and drift dispersal was low, both behaviors that reduced accrual of algae. We conclude that nutrient limitation and indirect effects of disturbance on accrual of algae mediated by grazer traits can be stronger than indirect effects of predators on algae, providing a new contribution to the debate about the influence of environmental context on the strength of food web interactions." Perry,JA and Schaeffer,DJ 1987 The longitudinal distribution of riverine benthos: A river dis-continuum?. Hydrobiologia, 148(3) 257-268. They studied Tomichi Creek in Gunnison County. Schloss,AL and Haney,JF 2006 Clouds, shadows or twilight? Mayfly nymphs recognise the difference. Freshwater Biology, 51(6), 1079-1089. PDF Summary: "1. We examined the relative changes in light intensity that initiate night-time locomotor activity changes in nymphs of the mayfly, Stenonema modestum (Heptageniidae). Tests were carried out in a laboratory stream to examine the hypothesis that nymphs increase their locomotion in response to the large and sustained reductions in relative light intensity that take place during twilight but not to short-term daytime light fluctuations or a minimum light intensity threshold. Ambient light intensity was reduced over a range of values representative of evening twilight. Light was reduced over the same range of intensities either continuously or in discrete intervals while at the same time nymph activity on unglazed tile substrata was video recorded. 2. Nymphs increased their locomotor activity during darkness in response to large, sustained relative light decreases, but not in response to short-term, interrupted periods of light decrease. Nymphs did not recognise darkness unless an adequate light stimulus, such as large and sustained relative decrease in light intensity, had taken place. 3. We show that nymphs perceive light change over time and respond only after a lengthy period of accumulation of light stimulus. The response is much lengthier than reported for other aquatic organisms and is highly adaptive to heterogeneous stream environments. " Sartori,M and Brittain,JE 2015 Order Ephemeroptera. In Thorp and Covich's freshwater invertebrates (pp. 873-891). Academic Press. PDF Brief History and Paleontology: "Extant Ephemeroptera represent what is left of a much diversified group of primitive flying insects (Ephemerida), the origin of which goes back to the Carboniferous. Permian data confirm that the group was already present at the end of the Paleozoic. Ephemerida reached their greatest diversity during the Mesozoic, mainly in the Jurassic and Cretaceous. All of these species share the presence of a costal brace at the base of the forewing and a reduction in the anal region of the hindwing with modern mayflies. However, contrary to them, they had homonomous wings (i.e., fore- and hind-wing of the same size), and their aquatic stages could possess up to nine pairs of abdominal gills (compared with a maximum of seven in extant species). Some species also had a wing span over 90 mm. All of these lineages, including Permoplectoptera (e.g., Protereismatidae or Misthodotidae), went extinct by the end of the late Jurassic. A recent study described adults and nymphs of a peculiar fossil insect order, the Coxoplectoptera, which could be the true sister group of modern Ephemeroptera (Staniczek et al.,2011). Although the adults have homonomous wings, the nymphs possess seven pair of gills as in the modern mayflies, a single tarsal segment (compared with five tarsal segments in the nymphs of Protereismatidae), and a single pretarsal claw (compared with paired claws in Proteiresmatidae). Heteronomous mayflies with reduced hindwings had appeared by the end of the Jurassic. The Tertiary fauna, as documented by fossils in Baltic or Dominican amber, is definitely contemporary with the presence of extinct and living genera of modern families." Sinitshenkova,ND and Grimaldi,D 2000 New Jersey amber mayflies: the first North American Mesozoic members of the order (Insecta; Ephemeroptera). Studies on Fossils in Amber, with Particular Reference to the Cretaceous of New Jersey. Backhuys Publishers, Leiden, Netherlands, pp.111-125. PDF Abstract: "The following new genera and species of mayflies are described from Upper Cretaceous (Turonian) amber from Sayreville, New Jersey, U.S.A: Cretomitarcys luzzii (imago male), (Polymitarcyidae: Cretomitarcyinae, new subfamily), Borephemera goldmani (imago male, Australiphemeridae), Amerogenia macrops (imago female) (Heptageniidae) and Palaeometropus cassus (subadult male) (Ametropodidae). Previously no mayflies were described from the Mesozoic of North America. Ametropodidae and Heptageniidae are newly recorded for the Mesozoic, and Australiphemeridae for the Upper Cretaceous. The mayflies in this amber probably inhabited a medium-sized or large river. Zoogeography of Upper Cretaceous mayflies is briefly discussed; with particular emphasis on significant faunistic differences between the temperate and subtropical areas." Sun,L; Sabo,A; Meyer,MD; Randolph,RP; Jacobus,LM; McCafferty,WP and Ferris,VR 2006 Tests of current hypotheses of mayfly (Ephemeroptera) phylogeny using molecular (18s rDNA) data. Annals of the Entomological Society of America, 99(2), pp.241-252. PDF Abstract: "Partial 18s rDNA sequences from 22 exemplar mayfly species (Ephemeroptera) representing 20 families were analyzed to obtain a best phylogenetic tree for comparison to previous phylogenetic hypotheses. With respect to relationships among the three major groupings, our molecular data support the hypothesis that Pisciforma and Setisura comprise a monophyletic sister group to the Furcatergalia, rather than the hypothesis that Setisura and Furcatergalia comprise a monophyletic group stemming from the Pisciforma. Within Pisciforma, acceptable trees show that Baetidae separates at the base of the Pisciforma clade. The data suggest that Pisciforma is paraphyletic and do not support the grouping of all Southern hemisphere families as a monophyletic group. An evolutionary sequence favored by the data suggests a grouping of Siphlonuridae, Rallidentidae, Nesameletidae, and Ameletidae and a grouping of Oniscigastridae, Ameletopsidae, and Acanthametropodidae. The data support the monophyly of Setisura (Heptageniidae, Arthropleidae, Pseudironidae, Oligoneuriidae, Isonychiidae, and Coloburiscidae). Within Setisura, a bootstrap/jackknife test places the families Heptageniidae, Arthropleidae, and Pseudironidae in one clade at 100% frequency. Also supported are hypotheses that Pseudironidae is a sister group to a Heptageniidae-Arthropleidae group and that a sister relationship exists between the latter two families. Hypotheses that Pseudironidae separated from other Setisura families at an earlier stage and comprises a sister group to a Heptageniidae-Oligonuriidae lineage or that Pseudironidae should be moved out of Setisura are not supported." Waltz,RD and Burian,SK 2008 Ephemeroptera. In: An Introduction to the Aquatic Insects of North America. 4th ed. Eds: Merritt,RW; Cummins,KW; Berg,MB Kendall/Hunt Publishing Company, Dubuque, Iowa, 181-236. 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. Wiggins,GB and Mackay,RJ 1978 Some relationships between systematics and trophic ecology in nearctic aquatic insects, with special reference to Trichoptera. Ecology 59 6, 1211-1220. PDF Brown,WS 2005 Introduction to the Ephemeroptera or Mayflies of Gunnison County, Colorado www.gunnisoninsects.org "When one tugs at a single thing in nature, they find it attached to the rest of the world." - John Muir |