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Mayfly Genus Ameletus (Brown Duns)

Taxonomic Navigation -?-
» Genus Ameletus (Brown Duns)
Species in AmeletusNumber of SpecimensNumber of Pictures
Ameletus celerBrown Dun00
Ameletus lineatusBrown Dun00
Ameletus ludensBrown Dun00
Ameletus oregonensisBrown Dun00
Ameletus sparsatusBrown Dun00
Ameletus subnotatusBrown Dun00
Ameletus validusBrown Dun00
Ameletus veloxBrown Dun00
Ameletus vernalisBrown Dun00

25 species aren't included.
Common Name
MatchCommon Name
***Brown Duns


Pictures Below ↓

This is page 3 of specimens of Ameletus. Visit the main Ameletus page for:

  • The behavior and habitat of Ameletus.

Pictures of 21 Mayfly Specimens in the Genus Ameletus:

Specimen Page:123
Ameletus (Brown Duns) Mayfly NymphAmeletus (Brown Duns) Mayfly Nymph View 6 PicturesI spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.) ages trying to identify this one but ultimately couldn't narrow it down to species. I'm guessing it's either a species that has not yet been reported from Idaho or a species with some variation in characteristics not accounted for in the current key (Zloty 1997), which is only for Alberta but happens to contain all the species documented in Idaho except for one (which is rare and only in a different part o the state from this one).

Here are my raw notes from the microscope session:

8. Ameletus nymph (genus 100 % based on mouth parts under microscope)
1. This is probably a species with the nymph either not described yet or not reported in Idaho (or Alberta).
2. There is a key to the species of nymphs in Alberta (Zloty 1997) which includes all but one (A. tolae) of the species listed in Idaho by IDFG (https://idfg.idaho.gov/species/taxa/8607), and A. tolae is only listed from one drainage in north-central Idaho. So my specimen should be in that key. However, it doesn’t fit any of them.
1. The antennae are pale with brown at the apex (Apex: The uppermost, outermost, or culminating point; the tip.). This doesn’t fit any of the species they described.
2. The labrum (Labrum: The platelike structure forming the roof of the mouth of insects; the upper lip.) is almost completely dark brown, maybe a bit paler toward the apex (Apex: The uppermost, outermost, or culminating point; the tip.).
3. Following the key in Zloty 1997 basically rules out every species reported in Idaho except for tolae, which would be outside its range:
1. Couplet 1 : There definitely aren’t strong ganglionic markings on sternites (
One sternite of this Isonychia bicolor mayfly spinner is highlighted in red.
One sternite of this Isonychia bicolor mayfly spinner is highlighted in red.
Sternite: The bottom (ventral) part of a single segment on an insect's abdomen.) 2-8 (100 % rules out similior and celer) —> 3
2. Couplet 3 : Posterior (Posterior: Toward the back of an organism's body. The phrase "posterior to" means "in back of.") margins of sternites (
One sternite of this Isonychia bicolor mayfly spinner is highlighted in red.
One sternite of this Isonychia bicolor mayfly spinner is highlighted in red.
Sternite: The bottom (ventral) part of a single segment on an insect's abdomen.) 6-8 lack large spines (80 % sure) but other characteristics rule out the species if there were spines (validus, oregonensis, subnotatus) —> 6
3. Couplet 6 : Mesal (Mesal: Toward the middle.) gill extension present, but pretty slim… similar to Fig. 23B or 23G —> 7
4. Couplet 7 : Obviouly gos to 8
5. Couplet 8 : Small size and time of year rules out velox, tergite (
One tergite of this Isonychia bicolor mayfly spinner is highlighted in red.
One tergite of this Isonychia bicolor mayfly spinner is highlighted in red.
Tergite: The top (dorsal) part of a single segment on an insect's abdomen when it consists of a single chitinous plate (sclerite), or an individual sclerite if the segment has more than one.) patterna and gill shape rules out pritchardi (which is not reported in Idaho anyway). Additional features (antennae, labrum (Labrum: The platelike structure forming the roof of the mouth of insects; the upper lip.) color) rule out a small velox.
6. Backtrack to call the mesal (Mesal: Toward the middle.) gill extension “well developed” —> 9
7. Couplet 9 : Tail coloration obviously —> 10
8. Couplet 10 : Supposing it’s a small specimen of a “larger species” leads to 11, in which femora (
The femur of this Isonychia bicolor mayfly spinner is highlighted in red.
The femur of this Isonychia bicolor mayfly spinner is highlighted in red.
Femur: The main segment of an insect's leg close to the body, in between the tibia and the trochanter.) coloration and timing rule out vernalis, and color pattern rules out bellulus. Mesal (Mesal: Toward the middle.) extension on gills from species description very conclusively rules out bellulus. Therefore, calling it a “smaller species” is the correct path —> 12
9. Couplet 12 : Sternites (
One sternite of this Isonychia bicolor mayfly spinner is highlighted in red.
One sternite of this Isonychia bicolor mayfly spinner is highlighted in red.
Sternite: The bottom (ventral) part of a single segment on an insect's abdomen.) without well-defined longitudinal stripe —> cooki. However, tergite (
One tergite of this Isonychia bicolor mayfly spinner is highlighted in red.
One tergite of this Isonychia bicolor mayfly spinner is highlighted in red.
Tergite: The top (dorsal) part of a single segment on an insect's abdomen when it consists of a single chitinous plate (sclerite), or an individual sclerite if the segment has more than one.) color patterns don’t even come close to matching ANY of the 3 species from this point on (cooki, sparsatus, suffusus). From the species descriptions:
1. cooki: Antenna and labrum (Labrum: The platelike structure forming the roof of the mouth of insects; the upper lip.) colors don’t fit. Mesal (Mesal: Toward the middle.) extension should be larger and tracheation lighter, to be this species.
2. sparsatus: Antenna and labrum (Labrum: The platelike structure forming the roof of the mouth of insects; the upper lip.) colors don’t fit. Mesal (Mesal: Toward the middle.) extension should be larger. Postero-lateral (Lateral: To the side.) spines should be very prominent, not barely noticeable.
3. suffusus: Also bad fit to antenna and labrum (Labrum: The platelike structure forming the roof of the mouth of insects; the upper lip.) colors, mesal (Mesal: Toward the middle.) extension, and especially gill tracheation.
Collected August 4, 2020 from Green Lake Outlet in Idaho
Added to Troutnut.com by Troutnut on August 20, 2020
Ameletus (Brown Duns) Mayfly NymphAmeletus (Brown Duns) Mayfly Nymph View 2 Pictures
Collected March 5, 2005 from the Flathead River-lower in Montana
Added to Troutnut.com by Bnewell on June 28, 2011
Male Ameletus (Brown Duns) Mayfly SpinnerMale Ameletus (Brown Duns) Mayfly Spinner View 1 PicturesThis specimen is close to Ameletus vernalis but the wing coloration is missing.
Collected June 10, 2011 from the Touchet River in Washington
Added to Troutnut.com by Bnewell on June 26, 2011
Male Ameletus subnotatus (Brown Dun) Mayfly SpinnerMale Ameletus subnotatus (Brown Dun) Mayfly Spinner View 1 Pictures
Collected July 2, 2008 from the Jocko River in Montana
Added to Troutnut.com by Bnewell on June 26, 2011
Male Ameletus vernalis (Brown Dun) Mayfly SpinnerMale Ameletus vernalis (Brown Dun) Mayfly Spinner View 1 Pictures
Collected April 25, 2012 from the Touchet River in Washington
Added to Troutnut.com by Bnewell on April 26, 2012
Male Ameletus vernalis (Brown Dun) Mayfly DunMale Ameletus vernalis (Brown Dun) Mayfly Dun View 1 Pictures
Collected April 25, 2012 from the Touchet River in Washington
Added to Troutnut.com by Bnewell on April 26, 2012
Male Ameletus vernalis (Brown Dun) Mayfly DunMale Ameletus vernalis (Brown Dun) Mayfly Dun View 1 Pictures
Collected May 15, 2012 from the Touchet River in Washington
Added to Troutnut.com by Bnewell on May 25, 2012
Ameletus (Brown Duns) Mayfly NymphAmeletus (Brown Duns) Mayfly Nymph View 2 PicturesThese two exuviae are my sad little consolation prize after collecting a couple of really cool, large, mature mayfly nymphs I didn't recognize from a tiny, probably fishless, spring-fed tributary of a slightly less tiny trout stream. I saw the nymphs in the kicknet samples and carefully transferred each one to my holding cooler before going to collect more samples. When I got home, I carefully went through the whole sample and couldn't find either one of them. Getting worried, I did it again and even more carefully. This time, I found both exuviae. By process of elimination, pretty much the only possibility is that both of them hatched out of my cooler and flew away during the 10 minutes or so that I had the lid off to collect more samples.

I was really excited about them for the whole three-hour drive home and seriously bummed that they disappeared. In the field I thought they might be one of the families of swimmer nymphs I don't have yet, like Ametropodidae, but keying the exuviae takes me to Ameletus, so at least I didn't miss some great rarity. Still, they were much larger and darker than any other Ameletus I've collected and probably a species I don't have yet.
Collected July 28, 2019 from Mystery Creek #199 in Washington
Added to Troutnut.com by Troutnut on July 30, 2019
Specimen Page:123
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