Blue-winged Olives
Baetis
Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
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This is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
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Identification: Key to Families of Stonefly Adults, Couplet 6
Identification: Key to Families of Stonefly Adults, Couplet 6
Error: Tried to access a key that isn't live.
Adapted from Merritt R.W., Cummins, K.W., and Berg, M.B. (2019)
This couplet refers figures (usually designated 'sf') from this source.
You will need the source (make sure to get the same edition!) to see them.
This couplet refers figures (usually designated 'sf') from this source.
You will need the source (make sure to get the same edition!) to see them.
| Option 1 | Option 2 |
|---|---|
| Gill remnants conspicuous on thoracic sterna between coxae and on first 2 or 3 abdominal sterna (sf 16.193) | Thoracic gill remnants, if present, restricted to area behind coxae (sf 16.195) and absent from basal abdominal sterna |
| Forewing anal region with two or more rows of crossveins (sf 16.194) | Forewing anal region with, at most, one row of crossveins |
| Remaining families: Chloroperlidae, Perlidae, and Perlodidae | |
5 Example Specimens
This shows the adult and its exuviae.
| 5 Example Specimens
Family-level ID following Merritt, Cummins, & Berg 5th Edition:
1. Thoracic gill remnants absent 2. Arms of mesosternal Y-ridge approach posterior end of furcal pits 3. Submental gill remnants short, obscure, or absent 4. Male. Note that sternum 9 (the long, dark, last segment) appears to be the 8th if you count from the front in the ventral view, because the first segment is not easily visible ventrally. 5. Male abdominal tergum 10 not divided posteriorly; Paraprocts modified as hooks. 6. Male abdominal tergum 10 simple without notches or other prominent processes. This one was tricky, because at first glance it looks like the hooks arise from tergum 10, but in fact they're coming from the paraprocts underneath. There's a medial groove on tergum 10 that could be seen as a "notch" too, but it seems by "notch" the key is referring to a notch in the margin. 7. Abdominal sternum 8 with a conspicuous lobe and sternum 7 without such a lobe. This leads to Isoperla. Among Isoperla species known in Washington, most species are ruled out by different shapes of the vesicle (the rounded posterior bump on sternum 8). Isoperla pinta is ruled out by the lack of a region of stout spinules on tergum 9. The remaining options (without knowing how to properly dissect and image the aedeagus) are Isoperla fulva, Isoperla marmorata, Isoperla tilasqua, and Isoperla gravitans, the latter of which is too large. The other three are all at least slim possibilities, but several described characteristics seem to best match Isoperla fulva, which is also mentioned as the most common western Isoperla. 
I keyed this specimen to Paragnetina, and range maps would seem to rule out every species of that genus except for the common Paragnetina media.
The family ID on this one was a little bit tricky. Just going by the size, shape, and color, it looks like Chloroperlidae. However, the second anal vein of the forewing is does not appear to be forked, and the apical maxillary palpal segment is close to the length of the penultimate segment, both of which rule out that family. The position of the cubitoanal crossvein relative to the anal cell in the forewing -- touching it in this case -- indicates Perlidae (and it really doesn't have the "look" of Perlidae at all), but other characteristics, such as the metathorastic sternacostal sutures and lack of gill remnants, point to Perlodidae. That's the right answer. Moving on to Perlodidae, the key characteristics in Merritt & Cummins lead straightforwarly to Isoperla, and the species key in Jewett 1959 (The Stoneflies of the Pacific Northwest) leads to Isoperla fusca.
There is one caveat: That source does suggest a May-July emergence, whereas this one was collected in mid-September. 
These stoneflies--abundant during midday--seemed at first to be flying around with plain yellow bodies, but on closer inspection turn out to have striking, fiery red abdomens.
|
| Pteronarcyidae | Go to Couplet 7 |
Adapted from Merritt R.W., Cummins, K.W., and Berg, M.B. (2019)
The current couplet is highlighted with darker colors and a icon, and couplets leading to this point have a icon.
Leads to Couplet 2:
- First (basal) tarsal segment at least as long as the third (apical) tarsal segment
- Tarsi completely sclerotized on venter
Couplet 2
Leads to Couplet 5:
- First tarsal segment much shorter than third tarsal segment
- Mid and basal tarsal segments with well-developed ventral membraneous pads
Couplet 5
Leads to Taeniopterygidae:
- Second (middle) tarsal segment about as long as first (basal) segment (sf 16.178)
- Gill scar present (sf 16.179) or absent on inner coxal surface
Leads to Couplet 3:
- Second tarsal segment much shorter than first (sf 16.176)
- Gill scar absent from inner coxal surface
Couplet 3
Leads to Capniidae:
- Tails multisegmented (sf 16.180)
- Second anal vein of forewing simple and unforked (sf 16.183)
- Usually 1 or 2 intercubital crossveins
Leads to Couplet 4:
- Tails 1-segmented (sf 16.182)
- Second anal vein of forewing forked (sf 18.183)
- Usually 5 or more intercubital crossveins
Couplet 4
Leads to Nemouridae:
- Apical segment of labial palpus circular and larger than preceding segment (sf 16.184)
- Wings lying relatively flat over the abdomen at rest
- Forewing often with an X-pattern of crossveins at cord (sf 16.183)
- Cervical gills sometimes present (sf 16.185)
Leads to Leuctridae:
- Apical segment of labial palpus similar to preceding segment (sf 16.186)
- Wings rolled around abdomen at rest, giving body a slender, needle-like appearance
- Forewings without an X-pattern of crossveins at cord (sf 16.187)
- Gills absent
Leads to Peltoperlidae:
- Ventroapical tibial spurs small and arranged in one or two rows (sf 16.188)
- Metathoracic sternacostal sutures, if present, arise from posterior corners of furcal pits
- Posterolateral angles of metasterna usually project behind coxae (sf 16.189)
- Two ocelli
Leads to Couplet 6:
- Two slightly enlarged ventroapical spurs occur on each tibia, each surrounded by subapical membraneous area (sf 16.190)
- Sternacostal sutures extend laterad of anterior corners of metathoracic furcal pits, often to margins of basisternum (sf 16.191), or sutures incomplete near furcal pits (sf 16.192)
- Posterolateral angles of metasternum not projecting (sf 16.192)
- Two or three ocelli
Couplet 6
Couplet 6 (You are here)
Leads to Pteronarcyidae:
- Gill remnants conspicuous on thoracic sterna between coxae and on first 2 or 3 abdominal sterna (sf 16.193)
- Forewing anal region with two or more rows of crossveins (sf 16.194)
Leads to Couplet 7:
- Thoracic gill remnants, if present, restricted to area behind coxae (sf 16.195) and absent from basal abdominal sterna
- Forewing anal region with, at most, one row of crossveins
Couplet 7
Leads to Chloroperlidae:
- Lateral margins of pronotum not bent downward
- Second anal vein of forewing often forked between anal cell and wing margin (sf 16.196)
- Hind wing anal region usually with less than 5 longitudinal veins
- Body color variable but often green or yellow in life
- Apical maxillary palpal segment often much reduced in size relative to penultimate segment
- Gill remnants absent
Leads to Couplet 8:
- Lateral margins of pronotum usually bent sharply downward, partially covering sides of prothorax (sf 16.197)
- Second anal vein of forewing forked or unforked between anal cell and wing margin
- Hind wing anal region with 5 or more longitudinal veins
- Body color yellow, brown, or black
- Apical maxillary palpal segment not greatly reduced in size
- Gill remnants present or absent
Couplet 8
Leads to Perlidae:
- Metathoracic sternacostal sutures along posterior margin of basisternum not reaching furcal pits, and obscure arched grooves extend anterolad from furcal pits
- Cubitoanal crossvein of forewing usually touching, or very near anal cell
- Thorax (and sometimes paraprocts) often with branched gill remnants or ragged gill stubs (sf 16.195)
Leads to Perlodidae:
- Metathoracic sternacostal sutures extend laterad from anterior corners of furcal pits to margins of basisternum
- Cubitoanal crossvein of forewing often absent, or located on the cubitus beyond (distal of) the anal cell by a distance at least equal to the cubitoanal crossvein's own length
- Thorax and paraprocts without branched gill remnants but finger-like (or forked) gills sometimes occur on submentum, thorax, or sides of abdomen (sf 16.198)
Start a Discussion of this Couplet
References
- Jacobus, L. M., Wiersema, N.A., and Webb, J.M. 2014. Identification of Far Northern and Western North American Mayfly Larvae (Insecta: Ephemeroptera), North of Mexico; Version 2. Joint Aquatic Science meeting, Portland, OR. Unpublished workshop manual. 1-176.
- Merritt R.W., Cummins, K.W., and Berg, M.B. 2019. An Introduction to the Aquatic Insects of North America (Fifth Edition). Kendall/Hunt Publishing Company.