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 is an interesting one. Following the keys in Merritt R.W., Cummins, K.W., and Berg, M.B. (2019) and Jacobus et al. (2014), it keys clearly to Ephemerella. Jacobus et al provide a key to species, but some of the characteristics are tricky to interpret without illustrations. If I didn't make any mistakes, this one keys to Ephemerella mucronata, which has not previously been reported any closer to here than Montana and Alberta. The main character seems to fit well: "Abdominal terga with prominent, paired, subparallel, spiculate ridges." Several illustrations or descriptions of this holarctic species from the US and Europe seem to match, including the body length, tarsal claws and denticles, labial palp, and gill shapes. These sources include including Richard Allen's original description of this species in North America under the now-defunct name E. moffatae in Allen RK (1977) and the figures in this description of the species in Italy.
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Identification: Key to Families of Caddisfly Adults, Couplet 3
Identification: Key to Families of Caddisfly Adults, Couplet 3
Error: Tried to access a key that isn't live.
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 |
|---|---|
| Maxillary palps each with 5 segments | Maxillary palps each of 2, 3, 4, 5, or 6 segments |
| Terminal segment of maxillary palps flexible, curved, and of different structure from the preceding segments, typically at least twice as long as segment 4 (sf 19.564, 19.570) | Maxillary palp segment 5 or 6, if present, similar in structure to preceding segments and about the same length as segment 4 (sf 19.602, 19.603) |
| Remaining families: Apataniidae, Glossosomatidae, Goeridae, Hydrobiosidae, Hydroptilidae, Limnephilidae, Phryganeidae, Rhyacophilidae, Rossianidae, Thremmatidae, and Uenoidae | |
3 Example Specimens
This caddis species was dancing high over the stream, spaced a foot or two apart across most of its width, very much like Ephemera mayfly spinners but with more side-to-side motion mixed in. There were more than enough to get the trout interested, but I wasn't able to stick around until they fell on the water (if they did at all).
This is a really strange specimen. I would guess it's one of the dry caddis pupa that scoots across the surface of the water as a pupa rather than emerging right away. Its "wing pads" sure don't look right, though. Maybe they're deformed and that's why I was able to find this one as a pupa in the first place. It also looks like it might be a caddis adult missing its wings, but since I found three of them, that kind of rules out such an anomalous maiming.
I found this one and one other on a midstream rock. The previous day, I caught a similar creature kicking around on the water's surface. This one died and shriveled a little bit before I could photograph it, but it's basically in its original shape. | 5 Example Specimens
I had some trouble working through the genus key for this one because I'm not great at interpreting caddis wing venation. Fortunately, figure 19.707 in An Introduction to the Aquatic Insects of North America (Fifth Edition) shows the distinctive color pattern of the striking forewings on Hydatophylax argus, which is a perfect match for the pattern as well as venation. As there are no other species in that genus in this area, I can be pretty confident in the species ID.
I first just assumed this was Dicosmoecus based on anglers' conventional wisdom since it's a large orange "October caddis," but Creno set me straight. I should have keyed it out. After another look under the microscope, it lacks an anepisternal wart on the mesopleuron, which rules out Dicosmoecus. The midtibiae have 2 apical spurs and 1 pre-apical spur, and from there the color pattern of the wing points to Onocosmoecus. The location then narrows the species to unicolor.
The setae on the wings make it a big tricky to identify this caddisfly from the "splayed wings" view because they obscure the venation, but several of the side views provide a good look at the important forewing veins. It keys pretty confidently to Ironoquia. Based on species ranges and a photo on BugGuide seemingly of this species and some alternatives, it seems Ironoquia lyrata is by far the most likely option.
|
| Philopotamidae | Go to Couplet 4 |
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 Hydroptilidae:
- Body typically less than 5 mm long
- Mesoscutum without setose warts
- Mesoscutellar warts transverse and meeting mesally to form angulate ridge (sf 19.562)
- Hind wings narrow and apically acute, and often with a posterior fringe of long setae (sf 19.563)
- Adults as in sf 10.194
- Widespread
Leads to Couplet 2:
- Body length variable, often more than 5 mm
- Mesoscutum often with setal warts
- Mesoscutellar warts typically rounded or elongate (sf 19.55)
- Hind wings typically broader than at left and apically rounded (sf 19.589); if posterior fringe of setae present, then setae shorter than at left
Couplet 2
Leads to Couplet 3:
- Head with 3 ocelli dorsally
Couplet 3
Leads to Couplet 14:
- Head without ocelli
Couplet 14
Couplet 3 (You are here)
Leads to Philopotamidae:
- Maxillary palps each with 5 segments
- Terminal segment of maxillary palps flexible, curved, and of different structure from the preceding segments, typically at least twice as long as segment 4 (sf 19.564, 19.570)
Leads to Couplet 4:
- Maxillary palps each of 2, 3, 4, 5, or 6 segments
- Maxillary palp segment 5 or 6, if present, similar in structure to preceding segments and about the same length as segment 4 (sf 19.602, 19.603)
Couplet 4
Leads to Couplet 5:
- Maxillary palps each of 5 segments, segment 2 about as long as segment 1 and often rounded (sf 19.561)
Couplet 5
Leads to Couplet 8:
- Maxillary palps each of 2, 3, 4, 5, or 6 segments, segment 2 longer than segment 1 and slender (sf 19.602, 19.603)
Couplet 8
Leads to Couplet 6:
- Maxillary palps each with segment 2 rounded and globose (sf 19.561)
Couplet 6
Leads to Hydrobiosidae:
- Maxillary palps each with segment 2 not globose, but of same general shape as segment 2 (sf 19.558)
- Southwest distribution
Hydrobiosidae
Leads to Rhyacophilidae:
- Foretibiae each with preapical spur (sf 19.557)
- Adults as in sf 10.191
Leads to Couplet 7:
- Foretibiae without preapical spurs
Couplet 7
Leads to Glossosomatidae:
- Pronotum with mesal setal warts widely spaced (sf 19.559)
- Adults as in sf 10.196
Leads to Hydroptilidae:
- Pronotum with mesal setal warts closely approximated (as in sf 19.562)
- Northeast and northwest distribution
Leads to Phryganeidae:
- Middle tibiae each with 2 preapical spurs (sf 19.576), i.e. spurs typically 2, 4, 4 on the tibiae of the front, middle, and hind legs, respectively
Leads to Couplet 9:
- Middle tibiae each with 1 (sf 19.600) or no preapical spurs, i.e. spurs typically, 1, 2-3, 4 on the tibiae of the front, middle, and hind legs, respectively
Couplet 9
Leads to Couplet 10:
- Hind wings each with anterior margin bearing row of stout, apically hooked setae (sf 19.586)
Couplet 10
Leads to Couplet 12:
- Hind wings with anterior margins bearing only straight or slightly curved, normal setae, or none at all (sf 19.579)
Couplet 12
Leads to Couplet 11:
- Hind wings each with vein R1 complete, extending to apical margin of wing (sf 19.589)
Couplet 11
Leads to Thremmatidae:
- Forewings about 2.5 times as long as broad (sf 19.758, 19.759)
Leads to Couplet 13:
- Small black or dark gray insects
- Length of each forewing 3-8 mm
- Forewing without color pattern
Couplet 13
Leads to Limnephilidae:
- Medium or large insects
- Length of each forewing 12-35 mm
- Forewing with various colors and patterns
- Adults as in sf 10.199
Leads to Rossianidae:
- Hind wings each with fork I sessile or rooted, arising at or basal of one or more crossveins
- Hind wing fork II distal, arising well beyond any other forks or crossveins (sf 19.756)
- Northwest distribution
Rossianidae
Leads to Apataniidae:
- Hind wing each with fork I absent, or petiolate and arising beyond all crossveins
- Hind wing fork II more nearly basal, arising at level of other wing forks and crossveins (sf 19.604-19.608)
- Adults as in sf 10.19
- Appalachian Mountains, North, West
Leads to Couplet 15:
- Maxillary palps each with 5 or 6 segments
Couplet 15
Leads to Couplet 24:
- Maxillary palps each with fewer than 5 segments
Couplet 24
Leads to Couplet 16:
- Maxillary palps each with apparently 6 segments
Couplet 16
Leads to Couplet 17:
- Maxillary palps each with 5 segments
Couplet 17
Leads to Psychomyiidae
(Paduniella nearctica):
(Paduniella nearctica):
- Forewings about 4.5 mm long
- Founds in the Ozark Mountains in Arkansas and Missouri
Leads to Calamoceratidae
(Anisocentropus pyraloides):
(Anisocentropus pyraloides):
- Forewings 11-13 mm long
- Southeast distribution
Calamoceratidae
(Anisocentropus pyraloides)
(Anisocentropus pyraloides)
Leads to Couplet 18:
- Maxillary palps each with terminal segment 5 flexible, different in structure from preceding segments (with numerous transverse striae or annulations) and typically at least twice as long as penultimate segment
Couplet 18
Leads to Couplet 24:
- Maxillary palps each with terminal segment 5 similar in structure to preceding segments and typically about the same length as penultimate segment (sf 19.54), or palp with some segments bearing long setal brush (sf 19.597)
Couplet 24
Leads to Leptoceridae:
- Antennae much longer than body
- Middle tibiae without preapical spurs
Leads to Couplet 19:
- Antennae typically little, if any, longer than body
- If antennae longer than body, then middle tibiae with preapical spurs (sf 19.593)
Couplet 19
Leads to Couplet 20:
- Mesoscutum with setose warts (sf 19.565)
Couplet 20
Leads to Hydropsychidae:
- Mesoscutum without setose warts or setae (sf 19.572)
- Adults as in sf 10.192
Leads to Couplet 21:
- Mesoscutal setose warts ovoid, their combined area smaller than that of mesoscutellum (sf 19.565)
Couplet 21
Leads to Xiphocentronidae:
- Mesoscutal setose warts quadrate and appressed along median line, their combined area exceeding that of mesoscutellum (sf 19.574)
- Found in Arizona and Texas
Xiphocentronidae
Leads to Couplet 22:
- Foretibiae each typically with preapical spur (sf 19.567)
- If preapical spur absent, then basal segment of tarsus shorter than twice the length of the longer apical spur (as in sf 19.567)
Couplet 22
Leads to Psychomyiidae:
- Foretibiae without preapical spurs
- Basal segment of each tarsus at least twice the length of the longer apical spur (sf 19.569)
Leads to Ecnomidae:
- Forewings each with vein R1 branched near apex (sf 19.571)
- In the US, found only in Texas
Ecnomidae
Leads to Couplet 23:
- Forewings each with vein R1 unbranched (sf 19.573)
Couplet 23
Leads to Dipseudopsidae:
- Forewings each with vein R2 branched from R3 at radial crossvein (sf 19.573)
- Eastern distribution
Dipseudopsidae
Leads to Polycentropodidae:
- Forewings each with vein R2 and vein R3 either fused throughout as vein R2+3 (sf 19.568) or with the two veins separated near apex of wing (sf 19.566)
Leads to Beraeidae:
- Mesoscutum without setose warts and setae (sf 19.594)
- Tarsal segments 2-5 with spines only near their apices (sf 19.595)
- Eastern distribution (highly localized)
Beraeidae
Leads to Couplet 25:
- Mesoscutum with setose warts (sf 19.577, 19.578, 19.582, 19.596, 19.598) or setal areas (sf 19.590, 19.591)
- Tarsal segments 2-5 with spines typically arranged irregularly (sf 19.583)
Couplet 25
Leads to Couplet 26:
- Mesoscutal setae arising in diffuse area over nearly entire length of mesoscutum (sf 19.590, 19.591)
Couplet 26
Leads to Couplet 28:
- Mesoscutal setae largely confined to pair of small, discrete warts (sf 19.577, 19.578, 19.582, 19.596, 19.598)
Couplet 28
Leads to Calamoceratidae:
- Antennae with scapes twice as long as pedicels, head typically with posteromesal ridge dorsally (sf 19.590)
- East, Southeast, Southwest, West Coast
Calamoceratidae
Leads to Couplet 27:
- Antennae with scapes at least 3 times longer than pedicels
- Head without posteromesal ridge dorsally (sf 19.591)
Couplet 27
Leads to Leptoceridae:
- Antennae markedly longer than body
- Pronotum consisting of a pair of lateral erect, platelike warts separated by wide, mesal excavated collar usually hidden by produced, angulate anterior margin of mesonotum (sf 19.591)
- Middle tibiae without preapical spurs (sf 19.592)
Leads to Molannidae:
- Antennae little, if any, longer than body
- Pronotum with warts much closer together, not platelike
- Middle tibiae each with 2 preapical spurs (sf 19.593)
- Adults as in sf 10.198
Leads to Helicopsychidae:
- Head with posterior setose warts relatively large, extending from mesal margins of eyes ot mid-dorsal line and anteriorly to middle of head (sf 19.577)
- Antennae never longer than forewings
Leads to Couplet 29:
- Head with posterior setose warts smaller than at left (e.g. sf 19.596)
- If not as above, then antennae about 1.5 times as long as forewings
Couplet 29
Leads to Couplet 30:
- Mesoscutellum with single median setose wart extending over most or all of its length (sf 19.593)
Couplet 30
Leads to Couplet 31:
- Mesoscutellum with pair of setose warts occupying about half its length (sf 19.582) and sometimes touching along mid-dorsal line (sf 19.598)
Couplet 31
Leads to Odontoceridae:
- Mesoscutellum almost entirely covered by a single setose wart, with setae arising over most of the wart (sf 19.596), except bare mesally in Pseudogoera singularis
- Maxillary palps each 5-segmented, except 4-segmented in male Pseudogoera singularis
Leads to Sericostomatidae:
- Pronotal setose warts fused into single transverse wart on each side of mid-line
- Median fissure of mesoscutum deep (sf 19.579)
Sericostomatidae
Leads to Couplet 32:
- Pronotum with 2 discrete setose warts on each side of mid-line
- Median fissure of mesoscutum not deep as at left (sf 19.582)
Couplet 32
Leads to Brachycentridae:
- Middle tibiae each with 1 or 2 preapical spurs arising at point about one-third distance from apex of tibiae (sf 19.583), or middle tibiae without preapical spurs
- Abdominal segment 5 with internal glands opening in a pair of ventral sclerotized lobes (sf 19.584)
Leads to Lepidostomatidae:
- Middle tibiae each with 2 preapical spurs arising from about mid-point of tibia (sf 19.599)
- Ventral abdominal glands not apparent
- Adults as in sf 10.195
Start a Discussion of this Couplet
References
- Jacobus, L. M., Wiersema, N.A., and Webb, J.M. 2014. Identification of Far Northern and Western North American Mayfly Larvae (Insecta: Ephemeroptera), North of Mexico; Version 2. Joint Aquatic Science meeting, Portland, OR. Unpublished workshop manual. 1-176.
- 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.