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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 Species of Drunella Nymphs, Couplet 10

Option 1Option 2
Larvae have short, marginal, hairlike setae on the heads, legs, and tergitesMarginal setae not well developed on the heads, legs, and tergites
No long setae protruding dorsally from tergites 8 and 9Long setae protrude dorsally from the anterior margins of tergites 8 and 9
Relatively many denticles on tarsal claws, and positioned along the length of the clawRelatively few denticles on tarsal claws, positioned basally
Remaining species:
Drunella tuberculata
Drunella walkeri
Drunella allegheniensis
No further information about this species is available on Troutnut.com at this time.
Go to Couplet 11
The current couplet is highlighted with darker colors and a icon, and couplets leading to this point have a icon.
Western North American species
Couplet 2
Eastern North American species
Couplet 7
Abdominal sterna with prominent friction disc of setae
Couplet 3
Abdominal sterna without prominent friction disc of setae (although felt-like coating of setae may be present)
Couplet 4
Forefemur with margins toothed
Forefemur with margins smooth
Forefemur with margins with prominent teeth
Prosternum with no anterior projection
Couplet 5
Forefemur with margins mostly smooth
Prosternum with prominent anterior projection
Couplet 6
Abdominal terga with paired, narrow spines
Abdominal terga with paired, broadly triangular spines
Abdominal terga 8 and 9 with paired spines more than twice the length of spines on preceding segments
Abdominal terga 8 and 9 with paired spines clearly less than twice the length of preceding pairs
Abdomen without paired dorsal tubercles, but may have paired ridges
Head smooth, without paired occipital tubercles (pictured yellow box)
Couplet 8
Abdomen with paired dorsal tubercles, always well-developed on segments 5-7
Head roughened, with paired occipital tubercles, or with small to large paired occipital tubercles
Couplet 10
Apex of tibial projection sharp and curved
Frontoclypeal projections are short, flat, and do not protrude anteriorly from the surface of the frontoclypeus (Funk et al. 2008)
Median ocellar tubercle relatively small (Funk et al. 2008)
Apex of tibial projection blunt to moderately sharp and straight
Frontoclypeal projections are longer, conical (or curved), and protrude anteriorly from the surface of the frontoclypeus (Funk et al. 2008)
Median ocellar tubercle relatively large (Funk et al. 2008)
Couplet 9
Mature nymph 7.8-11.4 mm long (Funk et al. 2008)
Median ocellar tubercle sharp and relatively long (red box)
Lateral frontoclypeal projections usually semilunar (green boxes above)
Middle and hind tibiae relatively long (Funk et al. 2008)
Mature nymph 6.4-8.5 mm long (Funk et al. 2008)
Median ocellar tubercle blunt to moderately sharp and relatively short
Lateral frontoclypeal projections moderately curved to straight
Middle and hind tibiae relatively short (Funk et al. 2008)
Couplet 10

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Larvae have short, marginal, hairlike setae on the heads, legs, and tergites
No long setae protruding dorsally from tergites 8 and 9
Relatively many denticles on tarsal claws, and positioned along the length of the claw
Drunella allegheniensis
Marginal setae not well developed on the heads, legs, and tergites
Long setae protrude dorsally from the anterior margins of tergites 8 and 9
Relatively few denticles on tarsal claws, positioned basally
Couplet 11
Has a row of long, hairlike setae along the margin of the clypeus
More robust, less flattened general appearance
Almost always has a pair of prominent, paired, stout, suboccipital spines
Lacks a row of long, hairlike setae on the clypeus
Usually a very flattened general appearance
Sometimes has only small bumps, other times more prominent suboccipital spines

References

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