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Introduction to the Mayflies (Ephemeroptera) of Gunnison County, Colorado

Updated 18 Nov 2018
TSN 100502
The Baetis or small minnow mayflies to the right were caught and released from the Gunnison River. Common and abundant in Gunnison county and the entire US, this genus of mayflies are essential to the food web of many rivers. 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.


The 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 Scientists

Subimago = Dun
Imago = Spinner
Exuvia = Shuck

You may click on a mayfly below to go to their webpage :-)

Epeorus longimanus, Spotted Epeorus or flat headed mayfly mymph. Another Epeorus longimanus, Spotted Epeorus or flat headed mayfly mymph. Young Epeorus mayfly nymph in a pan of water on the bank of West Brush Creek. Small Epeorus mayfly nymph in a pan of water. Epeorus nymphs are everywhere! Another youthful Epeorus mayfly nymph. Another young Epeorus mayfly nymph. Young Epeorus mayfly nymph in a pan of water. Young Cinygmula nymphs from a rocky stream. Cinygmula nymphs from a stream in the Southern Rocky Mountains Immature Cinygmula nymphs from a rocky stream. Big, tanklike Drunella nymph in a pan of water with a bunch of other mayflies

Good Links

On this website:
Key to Adult Mayfly families

Other Websites:


Clements,WH; Cherry,DS; 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,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.

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.

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.

Brown,WS 2005 Introduction to the Ephemeroptera or Mayflies of Gunnison County, Colorado