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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
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.

Case view of a Pycnopsyche guttifera (Limnephilidae) (Great Autumn Brown Sedge) Caddisfly Larva from the Yakima River in Washington
It's only barely visible in one of my pictures, but I confirmed under the microscope that this one has a prosternal horn and the antennae are mid-way between the eyes and front of the head capsule.

I'm calling this one Pycnopsyche, but it's a bit perplexing. It seems to key definitively to at least Couplet 8 of the Key to Genera of Limnephilidae Larvae. That narrows it down to three genera, and the case seems wrong for the other two. The case looks right for Pycnopsyche, and it fits one of the key characteristics: "Abdominal sternum II without chloride epithelium and abdominal segment IX with only single seta on each side of dorsal sclerite." However, the characteristic "metanotal sa1 sclerites not fused, although often contiguous" does not seem to fit well. Those sclerites sure look fused to me, although I can make out a thin groove in the touching halves in the anterior half under the microscope. Perhaps this is a regional variation.

The only species of Pycnopsyche documented in Washington state is Pycnopsyche guttifera, and the colors and markings around the head of this specimen seem to match very well a specimen of that species from Massachusetts on Bugguide. So I am placing it in that species for now.

Whatever species this is, I photographed another specimen of seemingly the same species from the same spot a couple months later.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
Troutnut is a project started in 2003 by salmonid ecologist Jason "Troutnut" Neuswanger to help anglers and fly tyers unabashedly embrace the entomological side of the sport. Learn more about Troutnut or support the project for an enhanced experience here.

Identification: Key to Genera of Perlodidae Nymphs, Couplet 19

Identification: Key to Genera of Perlodidae Nymphs, Couplet 19

Option 1Option 2
Mesosternal Y-arms meet or approach anterior corners of furcal pits
Figure from this Skwala nymph.
Mesosternal Y-arms meet or approach posterior corners of furcal pits
Mandibles deeply cleft, separating teeth into two major cusps
Deeply cleft mandible of a Skwala nymph, with the serrate outer cusp boxed in green.
Deeply cleft mandible of a Skwala nymph, with the serrate outer cusp boxed in green. Figure from this Skwala nymph.
Mandibles not deeply cleft
Remaining genera: Frisonia and SkwalaRemaining genera: Baumannella, Chernokrilus, Clioperla, Cultus, Diploperla, Diura, Helopicus, Hydroperla, Isogenoides, Isoperla, Malirekus, Oconoperla, Pictetiella, and Yugus
3 Example Specimens
5 Example Specimens
Go to Couplet 20 Go to Couplet 22
The current couplet is highlighted with darker colors and a icon, and couplets leading to this point have a icon.
Leads to Couplet 2:
  • Gills present on one or more thoracic segments (sf 16.145)
Couplet 2
Leads to Couplet 6:
  • Gills absent from thoracic segments
Couplet 6
Leads to Couplet 3:
  • Prothoracic gills present (sf 16.145)
Couplet 3
Leads to Setvena:
  • Prothoracic gills absent
  • Western North America
Leads to Oroperla
(Oroperla barbara):
  • Lateral abdominal gills present (sf 16.146)
  • California and Nevada
Leads to Couplet 4:
  • Lateral obdominal gills absent
Couplet 4
Leads to Perlinodes
(Perlinodes aurea):
  • Cervical gills present (sf 16.145)
  • Western North America
Leads to Couplet 5:
  • Cervical gills absent
Couplet 5
Leads to Salmoperla
(Salmoperla sylvanica):
  • Prothoracic gills reduced to nipple-like stubs
  • Mesothoracic and metathoracic gills forked (sf 16.35)
  • California and Oregon
Leads to Megarcys:
  • Prothoracic gills well developed
  • Mesothoracic and metathoracic gills simple and thumb-like (sf 16.147)
  • Western North America
Leads to Couplet 7:
  • Lacinia unidentate, except bidentate in early instar Kogotus
Couplet 7
Leads to Couplet 10:
  • Lacinia bidentate
Couplet 10
Leads to Isoperla:
  • Abdomen with dark longitudinal pigment bands (sf 16.15)
Leads to Couplet 8:
  • Abdomen without dark longitudinal pigment bands
Couplet 8
Leads to Remenus:
  • Lacinia broad basally, abruptly narrowed into a long terminal spine (sf 16.150)
  • Eastern North America
Leads to Couplet 9:
  • Lacinia gradually narrowed from base to terminal spine
  • Western North America
Couplet 9
Leads to Kogotus:
  • Mesosternum without transverse anterior furrow
  • Western North America
  • common
Leads to Rickera
(Rickera sorpta):
  • Mesosternal furcal pits often connected by a transverse anterior furrow, sometimes difficult to discern in young nymphs (sf 16.151)
  • California, Oregon, Washington, Nevada
  • rare
Rickera
(Rickera sorpta)
Leads to Couplet 11:
  • Abdomen with longitudinal pigment bands
Couplet 11
Leads to Couplet 19:
  • Abdomen usually without longitudinal pigment bands, having various lateral pigment bands, spots, or various other patterns instead However, at least some Skwala may have a longitudinal dorsal stripe on the abdomen
Couplet 19
Leads to Couplet 12:
  • Abdomen with pale, median, longitudinal pigment band
Couplet 12
Leads to Couplet 14:
  • Abdomen with dark, median, longitudinal pigment band (may be a dark stripe embedded within a light band)
Couplet 14
Leads to Osobenus
(Osobenus yakimae):
  • Apical lacinial tooth about as long as rest of lacinia (sf 16.152)
  • Mesosternal Y-arms with secondary furrows extending to anterior corners of furcal pits (sf 16.153)
  • British Columbia, California, Oregon, Washington
Leads to Couplet 13:
  • Apical lacinial tooth much shorter than rest of lacinia (sf 16.154)
  • Mesosternal Y-arms lacking secondary furrows extending to anterior corners of furcal pits
Couplet 13
Leads to Isoperla:
  • Inner lacinial margin with row of at least 4-5 long setae
  • No prominent knob bearing pegs below subapical lacinial tooth (sf 16.155)
  • Widely distributed
Leads to Susulus:
  • Inner lacinial margin lacking a row of long setae
  • Prominent knob below subapical lacinial tooth bearing 3-4 stout peg-like setae (which may appear as a 3rd tooth under low-power magnification) (sf 16.154)
  • California
Susulus
Leads to Couplet 15:
  • Lacinia quadrate (sf 16.156)
Couplet 15
Leads to Couplet 18:
  • Lacinia triangular or subquadrate
Couplet 18
Leads to Couplet 16:
  • Lacinia with a dense brush of stout setae (sf 16.156)
  • Inner lacinial margin glabrous
Couplet 16
Leads to Couplet 17:
  • Lacinia with one or more rows of stout setae (sf 16.155 and 16.157)
  • Inner lacinial margin setose
Couplet 17
Leads to Cascadoperla
(Cascadoperla trictura):
  • Apical cercal segments fringed with fine hairs dorsally and ventrally (sf 16.158)
  • Western North America
Cascadoperla
(Cascadoperla trictura)
Leads to Isoperla:
  • Apical cercal segments fringed along ventral margins or not at all
  • Widely distributed
Leads to Calliperla
(Calliperla luctuosa):
  • Cerci without marginal fringe
  • Mesosternal Y-arms enclosing an area of abundant clothing hairs (sf 16.159)
  • California, Oregon, Washington
Calliperla
(Calliperla luctuosa)
Leads to Isoperla:
  • Cerci with ventral fringe on apical segments (sf 16.160)
  • Mesosternal Y-arms enclosing an area with few or no clothing hairs
  • Widely distributed
Leads to Cosumnoperla:
  • Mesosternal Y-arms sinuate (sf 16.161)
  • Cerci lacking fine setal fringe
  • California
Cosumnoperla
Leads to Isoperla:
  • Mesosternal Y-arms straight
  • Cerci with fine setal fringe (sf 16.160)
  • Widely distributed
Couplet 19

You are here
Couplet 19 (You are here)
Leads to Couplet 20:
  • Mesosternal Y-arms meet or approach anterior corners of furcal pits
  • Mandibles deeply cleft, separating teeth into two major cusps
Couplet 20
Leads to Couplet 22:
  • Mesosternal Y-arms meet or approach posterior corners of furcal pits
  • Mandibles not deeply cleft
Couplet 22
Leads to Frisonia
(Frisonia picticeps):
  • Apical lacinial tooth short, much less than 1/3 the outer lacinial length
  • Ventral submarginal lacinial setae extending well onto apical tooth as a closely set row (sf 16.164)
  • British Columbia, California, Nevada, Oregon, Washington
Frisonia
(Frisonia picticeps)
Leads to Couplet 21:
  • Apical lacinial tooth long, greater than 1/3 the outer lacinial length
  • Ventral submarginal lacinial setae end at inner base of apical tooth
Couplet 21
Leads to Skwala:
  • Outermost cusp of both mandibles serrate
  • Mesal tufts of silky setae on occiput
  • Abdominal segments 1–2 divided by pleural fold
  • Western North America (the range maps below are off, because they also include compacta)
Leads to Skwala
(Skwala compacta):
  • Outermost cusp of both mandibles unserrated, or with indistinct serrations on left mandible only
  • Occiput without mesal tuft of silky setae
  • Abdominal segments 1–3 divided by pleural fold
  • Western North America and higher latitudes of Eastern North America
Leads to Oconoperla:
  • Femora and tibiae without long setal fringe
  • Posterolateral margins of pronotum notched
  • Southern Appalachians
  • Rare
Oconoperla
Leads to Couplet 23:
  • Femora or tibiae or both with long setal fringe
  • Posterolateral margins of pronotum smoothly rounded
  • Widespread
  • Some genera common
Couplet 23
Leads to Isogenoides:
  • Mesosternum with median longitudinal suture connecting fork of mesosternal Y-arms with transverse suture (sf 16.166)
  • Widely distributed
Leads to Couplet 24:
  • Mesosternum without median longitudinal suture
Couplet 24
Leads to Couplet 25:
  • Submental gills conspicuous, projecting portion usually 2 times or more as long as basal diameter (sf 16.37)
Couplet 25
Leads to Couplet 28:
  • Submental gills absent or barely projecting beyond submentum
Couplet 28
Leads to Pictetiella:
  • Apical lacinial tooth about half the total outer lacinial length
  • Western North America
  • Uncommon
Leads to Couplet 26:
  • Apical lacinial tooth about 1/3 or less the total outer lacinial length (sf 16.149)
  • Eastern North America
  • Usually common
Couplet 26
Leads to Malirekus:
  • Ventral lacinial surface with a basal patch of about 50 dark clothing hairs (sf 16.149)
Malirekus
Leads to Couplet 27:
  • Ventral lacinial surface without dark clothing hairs, a patch of about 10 setae may be present (sf 16.167)
Couplet 27
Leads to Hydroperla:
  • Transverse dark pigment band of frons lateral to median ocellus interrupted by circular yellow areas (sf 16.168)
  • Ventral lacinial surface with outer patch of about 10 setae (sf 16.169)
  • Right mandible with 4 teeth
Leads to Helopicus:
  • Transverse dark pigment band of frons uninterrupted by enclosed yellow areas (sf 16.170)
  • Ventral lacinial surface without outer patch of setae
  • Right mandible with 5 teeth
Leads to Couplet 29:
  • Inner lacinial margin with a low knob below subapical tooth (sf 16.149)
Couplet 29
Leads to Couplet 31:
  • Inner lacinial margin without a low knob below subapical tooth (sf 16.155)
Couplet 31
Leads to Malirekus:
  • Outer ventral lacinial surface with basal patch of about 50 dark clothing hairs (sf 16.149)
  • Eastern North America
Malirekus
Leads to Couplet 30:
  • Outer ventral lacinial surface with fewer than 50 basal clothing hairs (sf 16.167)
Couplet 30
Leads to Yugus:
  • Marginal lacinial setal row extending from near subapical tooth to near base (sf 16.167)
  • Labrum with yellow longitudinal mesal band
  • Submental gills very short, if present
  • Eastern North America
Yugus
Leads to Diura:
  • Marginal lacinial setal row restricted to apical half (sf 16.171)
  • Labrum without longitudinal band
  • Submental gills absent
  • Western North America and higher latitudes of Eastern North America
Leads to Couplet 32:
  • Occiput or anterolateral prothoracic margins or both with a row of short stout setae
Couplet 32
Leads to Couplet 36:
  • Occiput and anterolateral prothoracic margins without rows of short, stout setae (a few long setae may be present)
Couplet 36
Leads to Clioperla
(Clioperla clio):
  • Ocellar region transversed by dark band connecting lateral ocelli and eyes but not covering anterior ocellus (sf 16.38); a dark form lacking the light medial area of head, with light M-line
  • Abdominal terga with pale media, paired spots
  • Eastern North America
Leads to Couplet 33:
  • Ocellar triangle more or less covered by dark pigment
  • Abdominal terga with 3 pairs pale or dark spot, or lacking such spots
Couplet 33
Leads to Baumannella
(Baumannella alameda):
  • Outer mandibular cusp serrate
  • Abdominal terga with anterior narrow dark mesal bands and conspicuous transverse row of dark spots
  • California
Baumannella
(Baumannella alameda)
Leads to Couplet 34:
  • Major mandibular cusp without serrations
  • Abdominal terga with variable color pattern
Couplet 34
Leads to Chernokrilus:
  • Mesosternal Y-arms with indistinct anterior extensions which approach furcal pits (sf 16.172)
  • California, Oregon
Chernokrilus
Leads to Couplet 35:
  • Mesosternal Y-arms without anterior extensions
  • Widely distributed
Couplet 35
Leads to Diura:
  • Occipital area with a pair of pale oval markings adjacent to compound eyes; posterior margins of ovals marked by dense irregular rows of short, thick setae (sf 16.173)
  • Western North America and higher latitudes of Eastern North America
Leads to Isoperla:
  • Occipital area without pale oval markings margined by short, thick setae
  • Widely distributed
Leads to Cultus:
  • Mesosternal Y-arms with basal stem and fork
  • Widely distributed
Leads to Diploperla:
  • Mesosternal Y-arms without stem and fork (sf 16.175)
  • Eastern North America
Diploperla

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References

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