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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.

Dorsal view of a Zapada cinctipes (Nemouridae) (Tiny Winter Black) Stonefly Nymph from the Yakima River in Washington
Nymphs of this species were fairly common in late-winter kick net samples from the upper Yakima River. Although I could not find a key to species of Zapada nymphs, a revision of the Nemouridae family by Baumann (1975) includes the following helpful sentence: "2 cervical gills on each side of midline, 1 arising inside and 1 outside of lateral cervical sclerites, usually single and elongate, sometimes constricted but with 3 or 4 branches arising beyond gill base in Zapada cinctipes." This specimen clearly has the branches and is within the range of that species.
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.
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Identification: Key to Genera of Perlidae Nymphs

Identification: Key to Genera of Perlidae Nymphs

Option 1Option 2
Occiput with a transverse row of regularly spaced spinules or distinctly elevated ridge
Red squares enclose 3 ocelli, and a light blue rectangle encloses a portion of the neat row of regularly-spaced spinules, which are difficult to see in this image.
Red squares enclose 3 ocelli, and a light blue rectangle encloses a portion of the neat row of regularly-spaced spinules, which are difficult to see in this image. Figure from this Claassenia sabulosa nymph.
Zoomed-in closeup of the image above, showing more clearly the regularly-spaced spinules on an occipital ridge (elevation hard to see in a 2D image) at higher magnification.
Zoomed-in closeup of the image above, showing more clearly the regularly-spaced spinules on an occipital ridge (elevation hard to see in a 2D image) at higher magnification. Figure from this Claassenia sabulosa nymph.
Occiput either without spinules, except possibly laterally near the eyes
Occiput with no spinule row (in the red boxed area), but with spinules on the postocular fringe (blue boxes).
Occiput with no spinule row (in the red boxed area), but with spinules on the postocular fringe (blue boxes). Figure from this Acroneuria abnormis nymph.

or else with a sinuate, irregularly spaced spinule row
Example of an irregularly spaced, sinuate spinule row.
Example of an irregularly spaced, sinuate spinule row. Figure from this Calineuria californica nymph.
Remaining genera: Agnetina, Claassenia, Neoperla, and ParagnetinaRemaining genera: Acroneuria, Anacroneuria, Attaneuria, Beloneuria, Calineuria, Doroneuria, Eccoptura, Hansonoperla, Hesperoperla, Perlesta, and Perlinella
5 Example Specimens
5 Example Specimens
Go to Couplet 2 Go to Couplet 5
The current couplet is highlighted with darker colors and a icon, and couplets leading to this point have a icon.
Couplet 1

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Couplet 1 (You are here)
Leads to Couplet 2:
  • Occiput with a transverse row of regularly spaced spinules or distinctly elevated ridge
Couplet 2
Leads to Couplet 5:
  • Occiput either without spinules, except possibly laterally near the eyes or else with a sinuate, irregularly spaced spinule row
Couplet 5
Leads to Neoperla:
  • Two ocelli
Leads to Couplet 3:
  • Three ocelli
Couplet 3
Leads to Claassenia
(Claassenia sabulosa):
  • Abdominal terga with more than 5 intercalary bristles
  • Western North America
Leads to Couplet 4:
  • Abdominal terga with no more than 4 intercalary bristles
  • Eastern North America
Couplet 4
Leads to Agnetina:
  • Posterior spinule fringe of abdominal sternum 7 complete
  • Cerci without a long setal fringe
Leads to Paragnetina:
  • Posterior spinule fringe of abdominal sternum 7 incomplete
  • Cerci with at least a few long silky setae
Leads to Couplet 6:
  • Occipital spinules in a sinuate, irregularly spaced row, more or less complete behind posterior ocelli
Couplet 6
Leads to Couplet 10:
  • No distinct occipital spinule row or a few scattered spinules may be present near the postocular setal fringe (sf 16.106)
Couplet 10
Leads to Hesperoperla:
  • Abdominal terga with
  • Western North America
Leads to Couplet 7:
  • Abdominal terga with >5 intercalary bristles
Couplet 7
Leads to Attaneuria:
  • Pronotum laterally fringed with a complete, close-set row of long setae (sf 16.114)
  • Posterior fringe of abdominal terga with numerous long setae whose length is 3/4 or more the length of abdominal segments
  • Eastern North America Uncommon
Attaneuria
Leads to Couplet 8:
  • Pronotum fringed laterally with short setae, not so closely set
  • Posterior fringe of abdominal terga mostly of short setae whose length is about 1/4 the length of abdominal segments
Couplet 8
Leads to Perlesta:
  • Cerci without a dorsal fringe of long silky setae
  • Abdomen of most species speckled (dark pigment at bases of intercalary setae)
  • Primarily Eastern North America
  • common
Leads to Couplet 9:
  • Cerci with prominent dorsal fringe of long, silky setae
  • Abdominal terga not speckled
  • Western North America
Couplet 9
Leads to Doroneuria:
  • Dorsum of thorax and abdomen with a mesal, longitudinal row of long, fine, silky setae (best seen in lateral view)
  • Abdominal sternum 7 usually with incomplete posterior fringe
Leads to Calineuria
(Calineuria californica):
  • No mesal longitudinal row of silky hairs on thorax and abdominal dorsum
  • Abdominal sternum 7 usually with a complete posterior fringe
Leads to Couplet 11:
  • Postocular fringe reduced to 1-3 long setae (sf 16.107)
  • Pronotal fringe of 2-3 setae at corners
  • Eyes set forward on head
Couplet 11
Leads to Couplet 12:
  • Postocular fringe with a close-set row of several thick spinules
  • Pronotal fringe well developed, consisting of a close-set row of spinules or setae, occasionally incomplete laterally
Couplet 12
Leads to Perlinella:
  • Femora and tibia with dorsal (outer) and ventral (inner) fringes of long silky setae
  • Eastern North America
Perlinella
Leads to Hansonoperla:
  • Femora and tibia with only dorsal (outer) fringe of lonk, silky setae
  • Eastern North America
  • Rare
Hansonoperla
Leads to Anacroneuria:
  • Two ocelli
  • Lateral pronotal fringe complete
  • Arizona and Texas
Anacroneuria
Leads to Couplet 13:
  • Three ocelli
  • Lateral pronotal fringe incomplete
Couplet 13
Leads to Eccoptura
(Eccoptura xanthenes):
  • Head with large area of yellow in front of median ocellus (sf 16.106)
  • Eastern North America, Appalachian Mountains and foothills
Eccoptura
(Eccoptura xanthenes)
Leads to Couplet 14:
  • Head mostly brown, usually with yellow M-shaped mark in front of median ocellus
Couplet 14
Leads to Acroneuria:
  • Cerci with fringe of long, silky setae, sometimes reduced, but at least on basal segments (sf 16.119)
  • Pronotal flange wider at posterior angles than along lateral margins
  • Widespread
Leads to Beloneuria:
  • Cerci without basal fringe of silky setae
  • Pronotal flange narrow throughout
  • Eastern North America, Southern Appalachians or Piedmont
Beloneuria

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References

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