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Ephemeroptera: Heptageniidae of Gunnison County, Colorado

Introduction to the mayfly genus Epeorus
Slate Dun, Quill Gordon, Flat Headed Mayfly, Yellow Quill, Little Maryatts

Eaton 1881
Updated 8 Oct 2020
TSN 100626

Black wing pad Epeorus nymph on a rock
Notice the black triangular shaped wingpads on this Epeorus. That indicates this animal will emerge as an adult today or in the next few days. Ideally, when identifying larvae you have animals with dark or black wingpads. This is the sort of mayfly you want when an identification key states that it only works with "mature" nymphs.

Species Checklist

Epeorus albertae
Epeorus deceptivus
Epeorus grandis
Epeorus longimanus

How to distinguish adult male and female Epeorus

Trait Male Female
Eyes Large, touching in the middle Small, widely spaced, not touching
Forelegs Extremely Long (used to clasp females) About the same length as the other legs
Abdomen Claspers between tails No claspers

The stonefly Megarcys signata appears to be chasing an Epeorus nymph who is swimming away. These animals were caught and released from the upper East River on the 17th of July 2009.

Good Links

On this website:
Introduction to Iron
Heptageniidae Introduction

Other Websites:
Photos of Epeorus larvae from the McKenzie River, Oregon http://zebu.uoregon.edu/~dmason/Mckenzie/bugs/epeorus.html

This animal was under a rock in a stream in the upper East River Valley 18 July 2007.


Allan,JD 1978 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.

Allan,JD; Flecker,AS 1989 The mating biology of a mass-swarming mayfly. Animal behavior 37, 361-371.

Buchwalter,DB; Luoma,SN 2005 Differences in dissolved cadmium and zinc uptake among stream insects: mechanistic explanations. Environmental Science and Technology 39, 498-504.

Eaton AE. 1881 An announcement of new genera of the Ephemeridae. Entomologist's Monthly Magazine 18:21-27.
     The genus Epeorus is described on page 26.
Description of the mayfly genus Epeorus.

Edmunds,GF; Allen,RK 1964 The Rocky Mountain species of Epeorus (Iron) Eaton (Ephemeroptera: Heptageniidae). Journal of the Kansas Entomological Society 37 4, 275-288. PDF
     This paper discusses all of our Epeorus species except for E. grandis, because E. grandis was named Ironopsis grandis when this paper was published.

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.
     Working in wadeable streams on the Front Range of Colorado, they found a cryptic species of Epeorus alongside E. albertae, deceptivus and longimanus.

Jensen,SL 1966 The Mayflies of Idaho (Ephemeroptera). M.S. Thesis, University of Utah, Utah. 364 p.
     Quote from page 161: " The following combinations of characters serve to distinguish this genus from all other genera of Heptageniidae occurring in Idaho: Male Imagos. (1) Basal segment of the foretarsi equal to or slightly longer than the second segment. Female Imagos. Either (1) the subanal plate is broadly rounded with only a shallow posterior margin of the head deeply emarginate; or (2) the subanal plate with the postero-median emargination usually well developed, and with the basal crossveins of forewings weakly developed, appearing detached anteriorly (Fig 65). Nymphs. (1) Two caudal filaments present, the median terminal filiment absent (fig. 62)."

Lehmkuhl,DM 1968 Observations on the life histories of four species of Epeorus in western Oregon (Ephemeroptera: Heptageniidae). Pan-Pacific Entomologist 44(2):129-137. PDF

Mebane,CA; Dillon,FS and Hennessy,DP 2012 Acute toxicity of cadmium, lead, zinc, and their mixtures to stream-resident fish and invertebrates. Environmental Toxicology and Chemistry, 31(6), 1334-1348. PDF

Tronstad,LM; Hotaling,S; Giersch,JJ; Wilmot,OJ and Finn,DS 2020 Headwaters fed by subterranean ice: potential climate refugia for mountain stream communities?. BioRxiv, p.788273.
     Abstract: "Near-term extirpations of macroinvertebrates are predicted for mountain streams worldwide as a warming climate drives the recession of high-elevation ice and snow. However, hydrological sources likely vary in their resistance to climate change and thus streams fed by more resistant sources could persist as climate refugia for imperiled biota. In 2015-2016, we measured habitat characteristics and quantified macroinvertebrate community structure along six alpine streams in the Teton Range, Wyoming, USA. Strong differences in habitat characteristics (e.g., temperature, bed stability, conductivity) confirmed three major stream sources: surface glaciers, perennial snowfields, and subterranean ice. Subterranean ice-fed streams - termed "icy seeps" - appear common in the Teton Range and elsewhere yet are globally understudied. Midges in the family Chironomidae dominated our study sites, representing 78.6% of all specimens sampled, with nematodes, caddisflies (Neothremma), and mayflies (Epeorus) also common. At the community-scale, glacier-and snowmelt-fed streams differed significantly in multivariate space, with icy-seep communities intermediate between them, incorporating components of both assemblages. Because the thermal environment of subterranean ice, including rock glaciers, is decoupled from large-scale climatic conditions, we predict that icy seeps will remain intact longer than streams fed by surface ice and snow. Furthermore, our results suggest that icy seeps are suitable habitat for many macroinvertebrates occupying streams fed by vulnerable hydrological sources. Thus, icy seeps may act as key climate refugia for mountain stream biodiversity, an idea in need of further investigation."

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

Webb JM; McCafferty WP. 2006. Contribution to the taxonomy of Eastern North American Epeorus Eaton (Ephemeroptera: Heptageniidae). Zootaxa 1128: 57-64.

Wellnitz,TA; Poff,NL; Cosyleón,G and Steury,B 2001 Current velocity and spatial scale as determinants of the distribution and abundance of two rheophilic herbivorous insects. Landscape Ecology, 16(2), 111-120. PDF
     Abstract: "Organisms frequently show marked preferences for specific environmental conditions, but these preferences may change with landscape scale. Patterns of distribution or abundance measured at different scales may reveal something about an organism's perception of the environment. To test this hypothesis, we measured densities of two herbivorous aquatic insects that differed in body morphology and mobility in relation to current velocity measured at different scales in the upper Colorado River (Colorado, USA). Streambed densities of the caddisfly larva Agapetus boulderensis (high hydrodynamic profile, low mobility) and mayfly nymph Epeorus sp. (low hydrodynamic profile, high mobility) were assessed at 3 spatial scales: whole riffles, individual cobbles within riffles, and point locations on cobbles. Riffles were several meters in extent, cobbles measured 10-30 cm in size, and the local scale was within a few centimeters of individual larvae (themselves ca. 0.5-1.0 cm in size). We also quantified the abundance of periphytic food for these herbivores at the cobble and riffle scales. Agapetus favored slow current (<30 cm s-1) across all scales. Epeorus, by contrast, favored fast current (60-80 cm s-1) at the local and riffle scale, but not at the cobble scale. Only Agapetus showed a significant relationship to current at the cobble scale, with greatest larval densities occurring at velocities near 30 cm s-1. We had predicted an inverse correlation between grazer density and periphytic abundance; however, this occurred only for Agapetus, and then only at the cobble scale. These data suggest that organisms respond to environmental gradients at different spatial scales and that the processes driving these responses may change with scale, e.g., shifting from individual habitat selection at local and cobble scales to population responses at the riffle scale. This study also highlights the importance of using the appropriate scale of measurement to accurately assess the relationship between organisms and environmental gradients across scale. "

Zitnan,D; Zitnanová,I; Spalovská,I; Takác,P; Park,Y and Adams,ME 2003 Conservation of ecdysis-triggering hormone signalling in insects. The Journal of Experimental Biology 206, 1275-1289. Full Text
     One of their study animals was Epeorus sp.