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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.

Identification: Key to Genera of Perlidae Nymphs, Couplet 12

Option 1Option 2
Two ocelliThree ocelli
Lateral pronotal fringe completeLateral pronotal fringe incomplete
Closeup of the pronotal fringe of short but distinctive spinules (in red boxes), which in this case do not fully extend laterally around the pronotum.
Arizona and Texas
Remaining genera:
5 Example Specimens
No further information about this genus is available on Troutnut.com at this time.
Go to Couplet 13
The current couplet is highlighted with darker colors and a icon, and couplets leading to this point have a icon.
Occiput with a transverse row of regularly spaced spinules or distinctly elevated ridge
Couplet 2
Occiput either without spinules, except possibly laterally near the eyes or else with a sinuate, irregularly spaced spinule row
Couplet 5
Two ocelli
Three ocelli
Couplet 3
Abdominal terga with more than 5 intercalary bristles
Western North America
Abdominal terga with no more than 4 intercalary bristles
Eastern North America
Couplet 4
Posterior spinule fringe of abdominal sternum 7 complete
Cerci without a long setal fringe
Posterior spinule fringe of abdominal sternum 7 incomplete
Cerci with at least a few long silky setae
Occipital spinules in a sinuate, irregularly spaced row, more or less complete behind posterior ocelli
Couplet 6
No distinct occipital spinule row or a few scattered spinules may be present near the postocular setal fringe (sf 16.106)
Couplet 10
Abdominal terga with
Western North America
Abdominal terga with >5 intercalary bristles
Couplet 7
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
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
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
Cerci with prominent dorsal fringe of long, silky setae
Abdominal terga not speckled
Western North America
Couplet 9
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
No mesal longitudinal row of silky hairs on thorax and abdominal dorsum
Abdominal sternum 7 usually with a complete posterior fringe
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
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
Femora and tibia with dorsal (outer) and ventral (inner) fringes of long silky setae
Eastern North America
Femora and tibia with only dorsal (outer) fringe of lonk, silky setae
Eastern North America
Couplet 12

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Two ocelli
Lateral pronotal fringe complete
Arizona and Texas
Three ocelli
Lateral pronotal fringe incomplete
Couplet 13
Head with large area of yellow in front of median ocellus (sf 16.106)
Eastern North America, Appalachian Mountains and foothills
Eccoptura xanthenes
Head mostly brown, usually with yellow M-shaped mark in front of median ocellus
Couplet 14
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
Cerci without basal fringe of silky setae
Pronotal flange narrow throughout
Eastern North America, Southern Appalachians or Piedmont


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