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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.

Lateral view of a Clostoeca disjuncta (Limnephilidae) (Northern Caddisfly) Caddisfly Larva from the Yakima River in Washington
This one was surprisingly straightforward to identify. The lack of a sclerite at the base of the lateral hump narrows the field quite a bit, and the other options followed fairly obvious characteristics to Clostoeca, which only has one species, Clostoeca disjuncta.
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 Families of Stonefly Adults

Identification: Key to Families of Stonefly Adults

Option 1Option 2
First (basal) tarsal segment at least as long as the third (apical) tarsal segment
The red box surrounds the three segments of the tarsus, with the first and third being about the same length and the second (much shorter) in the middle.
The red box surrounds the three segments of the tarsus, with the first and third being about the same length and the second (much shorter) in the middle. Figure from this Capniidae adult.
First tarsal segment much shorter than third tarsal segment
The third tarsal segment (green box) is much longer than the first (magenta box).
The third tarsal segment (green box) is much longer than the first (magenta box). Figure from this Female Calineuria californica adult.
Tarsi completely sclerotized on venterMid and basal tarsal segments with well-developed ventral membraneous pads
Remaining families: Capniidae, Leuctridae, Nemouridae, and TaeniopterygidaeRemaining families: Chloroperlidae, Peltoperlidae, Perlidae, Perlodidae, and Pteronarcyidae
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:
  • First (basal) tarsal segment at least as long as the third (apical) tarsal segment
  • Tarsi completely sclerotized on venter
Couplet 2
Leads to Couplet 5:
  • First tarsal segment much shorter than third tarsal segment
  • Mid and basal tarsal segments with well-developed ventral membraneous pads
Couplet 5
Leads to Taeniopterygidae:
  • Second (middle) tarsal segment about as long as first (basal) segment (sf 16.178)
  • Gill scar present (sf 16.179) or absent on inner coxal surface
Leads to Couplet 3:
  • Second tarsal segment much shorter than first (sf 16.176)
  • Gill scar absent from inner coxal surface
Couplet 3
Leads to Capniidae:
  • Tails multisegmented (sf 16.180)
  • Second anal vein of forewing simple and unforked (sf 16.183)
  • Usually 1 or 2 intercubital crossveins
Leads to Couplet 4:
  • Tails 1-segmented (sf 16.182)
  • Second anal vein of forewing forked (sf 18.183)
  • Usually 5 or more intercubital crossveins
Couplet 4
Leads to Nemouridae:
  • Apical segment of labial palpus circular and larger than preceding segment (sf 16.184)
  • Wings lying relatively flat over the abdomen at rest
  • Forewing often with an X-pattern of crossveins at cord (sf 16.183)
  • Cervical gills sometimes present (sf 16.185)
Leads to Leuctridae:
  • Apical segment of labial palpus similar to preceding segment (sf 16.186)
  • Wings rolled around abdomen at rest, giving body a slender, needle-like appearance
  • Forewings without an X-pattern of crossveins at cord (sf 16.187)
  • Gills absent
Leads to Peltoperlidae:
  • Ventroapical tibial spurs small and arranged in one or two rows (sf 16.188)
  • Metathoracic sternacostal sutures, if present, arise from posterior corners of furcal pits
  • Posterolateral angles of metasterna usually project behind coxae (sf 16.189)
  • Two ocelli
Leads to Couplet 6:
  • Two slightly enlarged ventroapical spurs occur on each tibia, each surrounded by subapical membraneous area (sf 16.190)
  • Sternacostal sutures extend laterad of anterior corners of metathoracic furcal pits, often to margins of basisternum (sf 16.191), or sutures incomplete near furcal pits (sf 16.192)
  • Posterolateral angles of metasternum not projecting (sf 16.192)
  • Two or three ocelli
Couplet 6
Leads to Pteronarcyidae:
  • Gill remnants conspicuous on thoracic sterna between coxae and on first 2 or 3 abdominal sterna (sf 16.193)
  • Forewing anal region with two or more rows of crossveins (sf 16.194)
Leads to Couplet 7:
  • Thoracic gill remnants, if present, restricted to area behind coxae (sf 16.195) and absent from basal abdominal sterna
  • Forewing anal region with, at most, one row of crossveins
Couplet 7
Leads to Chloroperlidae:
  • Lateral margins of pronotum not bent downward
  • Second anal vein of forewing often forked between anal cell and wing margin (sf 16.196)
  • Hind wing anal region usually with less than 5 longitudinal veins
  • Body color variable but often green or yellow in life
  • Apical maxillary palpal segment often much reduced in size relative to penultimate segment
  • Gill remnants absent
Leads to Couplet 8:
  • Lateral margins of pronotum usually bent sharply downward, partially covering sides of prothorax (sf 16.197)
  • Second anal vein of forewing forked or unforked between anal cell and wing margin
  • Hind wing anal region with 5 or more longitudinal veins
  • Body color yellow, brown, or black
  • Apical maxillary palpal segment not greatly reduced in size
  • Gill remnants present or absent
Couplet 8
Leads to Perlidae:
  • Metathoracic sternacostal sutures along posterior margin of basisternum not reaching furcal pits, and obscure arched grooves extend anterolad from furcal pits
  • Cubitoanal crossvein of forewing usually touching, or very near anal cell
  • Thorax (and sometimes paraprocts) often with branched gill remnants or ragged gill stubs (sf 16.195)
Leads to Perlodidae:
  • Metathoracic sternacostal sutures extend laterad from anterior corners of furcal pits to margins of basisternum
  • Cubitoanal crossvein of forewing often absent, or located on the cubitus beyond (distal of) the anal cell by a distance at least equal to the cubitoanal crossvein's own length
  • Thorax and paraprocts without branched gill remnants but finger-like (or forked) gills sometimes occur on submentum, thorax, or sides of abdomen (sf 16.198)

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References

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