1. Troutnut Forum
›
2. Site Update Comments
›
3. Dinking around catching bugs in obscure Idaho waters

One key characteristic not clearly photographed, but clear in under the microscope: this specimen's midtibiae have 2 apical spurs and 1 preapical spur.

I spent 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 of 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. This doesn’t fit any of the species they described. 2. The labrum is almost completely dark brown, maybe a bit paler toward the apex. 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 2-8 (100 % rules out similior and celer) —> 3 2. Couplet 3 : Posterior margins of sternites 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 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 patterna and gill shape rules out pritchardi (which is not reported in Idaho anyway). Additional features (antennae, labrum color) rule out a small velox. 6. Backtrack to call the mesal 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 coloration and timing rule out vernalis, and color pattern rules out bellulus. Mesal 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 without well-defined longitudinal stripe —> cooki. However, tergite 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 colors don’t fit. Mesal extension should be larger and tracheation lighter, to be this species. 2. sparsatus: Antenna and labrum colors don’t fit. Mesal extension should be larger. Postero-lateral spines should be very prominent, not barely noticeable. 3. suffusus: Also bad fit to antenna and labrum colors, mesal extension, and especially gill tracheation.

Identification notes from the microscope: Gills on segment 1 extend anteriorly below the body, but not all the way to touching; posterolateral spines minor; femora without fuscous macula.

This nymph was one of several mature Cinygmula nymphs collected at the same time as this female dun emerged, so they're probably the same species. Unfortunately there aren't species keys for either stage.

This specimen unfortunately was blown away by the wind mid-way through the photographs, so I wasn't able to preserve it for an ID or get some of the other angles.

Here I'm just copying and pasting, without cleaning up, my notes from spending a long time with this one under the microscope (and keying with Merritt & Cummins 5th Ed) only to end up confirming the most likely guess. 7. Baetis bicaudatus nymph 1. Hind wingpad present but small and hidden beneath forewing pad 2. Segment 2 of labial palp with well-developed medially projecting corner --> Baetis (couple 44). BUT no sign of scale-like setae on abdominal terga. Conflicts at this couplet. 3. Gills on segments I-VII 4. Tarsal claws with denticles, seemingly 2 rows but very hard to tell… and the key options with 2 rows don’t make sense 5. Assuming no villipore, we land confidently at couplet 48 6. Leads to Fallceon, except antennal scape doesn't have robust setae 7. Treated as Baetis, leads to brunneicolor, but McDunnough et al 1932 (Can Ent 64) suggests middle tail should be 5/6 as long as outer ones 8. Keys VERY confidently to couplet 36 in M&C (villipore) 9. If assuming villipore present: 1. 37 --> Scape of antennae has no distal lobe --> rules out Labiobaetis (100 % certain) 2. 38 --> Terminal filament much shorter than cerci --> not Barbaetis benfieldi (100 % certain) 3. 39 --> Terminal filament reduced (100 % certain) 4. 40 --> Tarsal claw denticle count couplet. If two rows of denticles: Either Iswaeon or Heterocloeon. Can't be Iswaeon because cerci lack dark median band. Can't be heterocloeon because it's not in the Platte drainage or in Texas. Thus, it must be one row of denticles. Moving on to 42. 5. 42 --> Hind wing pads present (100 % certain) 6. 44 --> Segment 2 of labial palpi with well-developed medially projecting corner (80 % certain), scale-like setae not evident on terga but maybe limitation of my scope --> Baetis (alternative would be Acentrella, but pronotum shape is all wrong for those, although not an official characteristic) 7. CONFIDENT in Baetis bicaudatus after distinctive leg markings (J-shaped light mark on first femur, L-shaped on second and third) matches original species description to a tee.

This female dun emerged from a creek loaded with mature Cinygmula nymphs including this specimen, so they're probably the same species. Unfortunately there aren't species keys for either stage.