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.
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This specimen keys pretty easily to Onocosmoecus, and it closely resembles a specimen from Alaska which caddis expert Dave Ruiter recognized as this genus. As with that specimen, the only species in the genus documented in this area is Onocosmoecus unicolor, but Dave suggested for that specimen that there might be multiple not-yet-distinguished species under the unicolor umbrella and it would be best to stick with the genus-level ID. I'm doing the same for this one.
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Identification: Key to Genera of Male Leptophlebiidae Spinners, Couplet 8
Identification: Key to Genera of Male Leptophlebiidae Spinners, Couplet 8
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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 |
|---|---|
| Vein MP2 of forewings directly connected to vein MP1 (source figs 13.234, 13.235) | Vein MP2 of forewings not directly connected to vein MP1 |
| Posterior margin of female subanal plate with a shallow median indentation | Posterior margin of female subanal plate with distinctive deep median indentation |
| Remaining genera: Choroterpes and Hydrosmilodon | |
| Go to Couplet 9 | Neochoroterpes |
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:
- Hind wings without costal projections
- Includes every genus commonly found and discussed by anglers
Couplet 2
Leads to Couplet 4:
- Hind wings with distinct costal projections
- Relatively rare genera
Couplet 4
Leads to Leptophlebia:
- Middle tail often shorter and thinner than outer ones
- Hind wings usually relatively large, about 1/3 the length of forewings
- Male penes with long, decurrent appendages (source figs 13.229, 13.230)
Leads to Couplet 3:
- All tails similar to each other
- Hind wings usually relatively small, about 1/4 the length of forewings
- Male penes variable (source figs 13.281--13.283)
Couplet 3
Leads to Paraleptophlebia:
- Male genitalia with at least one pair of appendages that arise from ventral apices of penes and are more or less directed toward their fused base (source fig 13.281)
Leads to Neoleptophlebia:
- Male genitalia with a wide range of apical appendages or processes that may stick out from the apices of penes (source fig 13.282-13.283), but none that are distinctly directed toward their fused base
Leads to Habrophlebiodes:
- Costal projections of hind wings in distal half of wing margin (source fig 13.232)
- Uncommon
Leads to Couplet 5:
- Costal projections of hind wings near the midpoint of wing margin (source figs 13.231, 13.236-13.238)
Couplet 5
Leads to Habrophlebia:
- Vein Sc of hind wings extends well beyond costal projection (source fig 13.231)
- Uncommon
Leads to Couplet 6:
- Vein Sc of hind wing ends at or slightly beyond the costal projection (source figs 13.236-13.238)
Couplet 6
Leads to Thraulodes:
- Vein MP of hind wings forked (source fig 13.238)
- Uncommon
Leads to Couplet 7:
- Vein MP of hind wings simple, unforked (source figs 13.236, 13.237)
Couplet 7
Leads to Couplet 8:
- Costal projections of hind wings rounded (source fig 13.236)
Couplet 8
Leads to Couplet 10:
- Costal projections of hind wings acute (source figs 13.237, 13.269)
Couplet 10
Couplet 8 (You are here)
Leads to Couplet 9:
- Vein MP2 of forewings directly connected to vein MP1 (source figs 13.234, 13.235)
- Posterior margin of female subanal plate with a shallow median indentation
Couplet 9
Leads to Neochoroterpes:
- Vein MP2 of forewings not directly connected to vein MP1
- Posterior margin of female subanal plate with distinctive deep median indentation
Leads to Choroterpes:
- Vein Sc of hind wings straight where it meets the wing margin beyond base of costal projections (source fig 13.234)
- Costal projections without small rounded apical lobe
Choroterpes
Leads to Hydrosmilodon:
- Vein Sc of hind wings curved where it meets wing margin at base of costal projections (source fig 13.235)
- Costal projections with small rounded apical lobe (source fig 13.235)
Hydrosmilodon
Leads to Traverella:
- Hind wings with at least 8 longitudinal veins and at least 12 crossveins (source fig 13.237)
- Male penes with a thin process arising near apex of each lobe and with tips directed inward and down toward fused base
Leads to Farrodes:
- Hind wings with 7 or fewer longitudinal veins and about 3 crossveins (source fig 13.269)
- Male penes with short lateral process near apex of each lobe (source fig 13.271)
Farrodes
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References
- 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.