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Mayfly Genus Ephemerella (Hendricksons, Sulphurs, PMDs)

Taxonomic Navigation -?-
Species in EphemerellaNumber of SpecimensNumber of Pictures
Ephemerella aurivillii18109
Ephemerella dorothea dorotheaPale Evening Dun211
Ephemerella dorothea infrequensPale Morning Dun23
Ephemerella excruciansPale Morning Dun524
Ephemerella invariaSulphur Dun45185
Ephemerella needhamiLittle Dark Hendrickson941
Ephemerella subvariaHendrickson34158
Ephemerella tibialisLittle Western Dark Hendrickson11

11 species aren't included.
Common Name
Pictures Below

This is page 4 of specimens of Ephemerella. Visit the main Ephemerella page for:

  • The behavior and habitat of Ephemerella.
  • 37 underwater pictures of Ephemerella.

Pictures of 137 Mayfly Specimens in the Genus Ephemerella:

Specimen Page:1...345...15
Ephemerella aurivillii Mayfly NymphEphemerella aurivillii  Mayfly Nymph View 5 PicturesClose examination under a microscope showed definite small tubercles (
A few (not all) of the abdominal tubercles on this Ephemerella needhami nymph are circled.  They are especially large in this species.
A few (not all) of the abdominal tubercles on this Ephemerella needhami nymph are circled. They are especially large in this species.
Tubercle: Various peculiar little bumps or projections on an insect. Their character is important for the identification of many kinds of insects, such as the nymphs of Ephemerellidae mayflies.
)
on the back of this nymph.
Collected February 5, 2004 from unknown in Wisconsin
Added to Troutnut.com by Troutnut on January 25, 2006
Ephemerella aurivillii Mayfly NymphEphemerella aurivillii  Mayfly Nymph View 3 PicturesI have collected this species in Montana but it is very common in Alaska streams.
Collected June 19, 2010 from the Kwethluk River in Alaska
Added to Troutnut.com by Bnewell on June 26, 2011
Ephemerella subvaria (Hendrickson) Mayfly NymphEphemerella subvaria (Hendrickson) Mayfly Nymph View 4 PicturesThese are two common color patterns on Hendrickson nymphs. I suspect that one is male and the other female, but I don't know for sure.
Collected January 13, 2004 from the Namekagon River in Wisconsin
Added to Troutnut.com by Troutnut on January 25, 2006
Male Ephemerella subvaria (Hendrickson) Mayfly DunMale Ephemerella subvaria (Hendrickson) Mayfly Dun View 5 PicturesThis one hatched around 2 pm on opening day of trout season.
Collected May 1, 2004 from the Namekagon River in Wisconsin
Added to Troutnut.com by Troutnut on January 25, 2006
Female Ephemerella excrucians (Pale Morning Dun) Mayfly DunFemale Ephemerella excrucians (Pale Morning Dun) Mayfly Dun View 3 PicturesSize: 10mm. At emergence the specimen was a fairly bright olive green and there was obvious difference in color between the forewing (med. dun) and the hind-wing (pale cream). It was really noticeable as they floated by. You can just make these features out in the second photo, but not so much in the first that was taken 24 hours after capture. Total time from emergence to molting - approx. 48 hours.

Entoman


Edit 2/25/13 - This specimen was originally posted to E. d. infrequens because of its size. It turns out large size doesn't hold up as a way to tell these two apart. This is because excrucians has much greater variability than previously understood. The assumption by anglers that excrucians is always the smaller of the two is apparently not supported by science. There is a lot left to sort out with western Ephemerella species. This may include new discoveries and/or synonyms (Synonym: A former name of a taxon, usually a species. Entomologists frequently discover that two insects originally described as different species are one in the same, and they drop one of the names. The dropped name is said to be a synonym of the remaining name. These changes take a while to trickle into the common knowledge of anglers; for example, Baetis vagans is now a synonym of Baetis tricaudatus.) as well as reportage on new intraspecific variations broadening the descriptions of recognized species. Based on this specimen's Fall maturity, the best guess is that it is an unusual form of excrucians.

As to color, both species duns (nymphs too) demonstrate a tremendous amount of intraspecific variability from pale yellow to bright green with a multitude of sulfur shadings in between, ranging from pale amber, through orange to cinnamon and even dark brown. I've seen wings from pale cream through tannish and almost every shade of dun except the dark shades. Some have pigment stained leading edges matching their bodies, some don't. Most of these variations are undocumented except in angler references and periodicals. It seems a rare year that a new variation doesn't pop up to the notice of anglers.

Bottom line - size is only reliable if the specimens are smaller than size 16, pointing to excrucians. Otherwise, the only fairly dependable way to tell them apart (especially the females) is by timing as infrequens is the first of the two to appear, rarely lasting longer than a couple of weeks or later than the end of June most years. The problem with using timing for determination is it requires knowledge of the hatch sequences as they actually occurred for a given year on a given piece of water. Obviously, this kind of information is seldom available. Without it, determining between the two duns if they are larger than size 18 is speculative at best - at least until very late in the Summer.
Collected October 16, 2011 from the Fall River in California
Added to Troutnut.com by Entoman on October 21, 2011
Specimen Page:1...345...15
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