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Insects by Common Name
Pale Olive Duns
Scientific Names
| Match | Scientific Name |
 | Tricorythodes allectus |
| Baetis bicaudatus |
| Tricorythodes minutus |
Like most common names, "Pale Olive Dun" can refer to more than one taxon. They're previewed below, along with 1 specimen. For more detail click through to the scientific names.
Mayfly Species Tricorythodes allectus
These are sometimes called Pale Olive Duns.
Mayfly Species Baetis bicaudatus
These are sometimes called Pale Olive Duns.
Baetis bicaudatus is a western taxon of some local importance.
Baetis bicaudatus (BWO) Mayfly Nymph
View 5 PicturesHere I'm just copying and pasting, without cleaning up, my notes from spending a long time with this one under the microscope (and keying with Merritt & Cummins 5th Ed) only to end up confirming the most likely guess.
7. Baetis bicaudatus nymph
1. Hind wingpad present but small and hidden beneath forewing pad
2. Segment 2 of labial palp (
Palp: A long, thin, often segmented appendage which can protrude from certain insect mouth parts such as the maxillae. Also known as the < />palpus.) with well-developed medially projecting corner —> Baetis (couple 44)…. BUT no sign of scale-like setae (Seta: Little hairs on insects.) on abdominal terga (Tergum: the dorsal part of an abdominal segment or segments (terga). Also used to describe the entire abdominal dorsum or the thoracic dorsal segments of Odonata.). Conflicts at this couplet.
3. Gills on segments I-VII
4. Tarsal claws (Tarsal claw: The claws at the tip of the tarsus, on an insect's "foot.") with denticles (Denticle: Small tooth-like projects, often appearing like serrations on the tarsal claws of certain mayfly nymphs.), seemingly 2 rows but very hard to tell… and the key options with 2 rows don’t make sense
5. Assuming no villipore, we land confidently at couplet 48
6. Leads to Fallceon, except antennal scape doesn’t have robust setae (Seta: Little hairs on insects.)
7. Treated as Baetis, leads to brunneicolor, but McDunnough et al 1932 (Can Ent 64) suggests middle tail should be 5/6 as long as outer ones
8. Keys VERY confidently to couplet 36 in M&C (villipore)
9. If assuming villipore present:
1. 37 —> Scape of anntenae has no distal (Distal: Far from the point of attachment or origin; near the tip.) lobe —> rules out Labiobaetis (100 % certain)
2. 38 —> Terminal filament much shorter than cerci (Cercus: The left and right "tails" of an insect are known as the cerci or caudal cerci. The middle tail of a three-tailed insect is not.) —> not Barbaetis benfieldi (100 % certain)
3. 39 —> Terminal filament reduced (100 % certain)
4. 40 —> Tarsal claw (Tarsal claw: The claws at the tip of the tarsus, on an insect's "foot.") dentical count couplet. If two rows of denticles (Denticle: Small tooth-like projects, often appearing like serrations on the tarsal claws of certain mayfly nymphs.): Either Iswaeon or Heterocloeon. Can’t be Iswaeon because cerci (Cercus: The left and right "tails" of an insect are known as the cerci or caudal cerci. The middle tail of a three-tailed insect is not.) lack dark median band. Can’t be heterocloeon because it’s not in the Platte drainage or in Texas. Thus, it must be one row of denticles (Denticle: Small tooth-like projects, often appearing like serrations on the tarsal claws of certain mayfly nymphs.). Moving on to 42.
5. 42 —> Hind wing pads (
Wing pad: A protrusion from the thorax of an insect nymph which holds the developing wings. Black wing pads usually indicate that the nymph is nearly ready to emerge into an adult.) present (100 % certain)
6. 44 —> Segment 2 of labial palpi with well-developed medially projecting corner (80 % certain), scale-like setae (Seta: Little hairs on insects.) not evident on terga (Tergum: the dorsal part of an abdominal segment or segments (terga). Also used to describe the entire abdominal dorsum or the thoracic dorsal segments of Odonata.) but maybe limitation of my scope —> Baetis (alternative would be Acentrella, but pronotum (Pronotum: The top of the insect prothorax.) shape is all wrong for those, although not an official characteristic)
7. CONFIDENT in Baetis bicaudatus after distinctive leg markings (J-shaped light mark on first femur (
Femur: The main segment of an insect's leg close to the body, in between the tibia and the trochanter.), L-shaped on second and third) matches original species description to a tee.
View 5 PicturesHere I'm just copying and pasting, without cleaning up, my notes from spending a long time with this one under the microscope (and keying with Merritt & Cummins 5th Ed) only to end up confirming the most likely guess.7. Baetis bicaudatus nymph
1. Hind wingpad present but small and hidden beneath forewing pad
2. Segment 2 of labial palp (
The palp on the maxilla of an Ephemerella nymph (detached and photographed under a microscope) is highlighted in red here.
3. Gills on segments I-VII
4. Tarsal claws (Tarsal claw: The claws at the tip of the tarsus, on an insect's "foot.") with denticles (Denticle: Small tooth-like projects, often appearing like serrations on the tarsal claws of certain mayfly nymphs.), seemingly 2 rows but very hard to tell… and the key options with 2 rows don’t make sense
View Full Size
5. Assuming no villipore, we land confidently at couplet 48
6. Leads to Fallceon, except antennal scape doesn’t have robust setae (Seta: Little hairs on insects.)
7. Treated as Baetis, leads to brunneicolor, but McDunnough et al 1932 (Can Ent 64) suggests middle tail should be 5/6 as long as outer ones
8. Keys VERY confidently to couplet 36 in M&C (villipore)
9. If assuming villipore present:
1. 37 —> Scape of anntenae has no distal (Distal: Far from the point of attachment or origin; near the tip.) lobe —> rules out Labiobaetis (100 % certain)
2. 38 —> Terminal filament much shorter than cerci (Cercus: The left and right "tails" of an insect are known as the cerci or caudal cerci. The middle tail of a three-tailed insect is not.) —> not Barbaetis benfieldi (100 % certain)
3. 39 —> Terminal filament reduced (100 % certain)
4. 40 —> Tarsal claw (Tarsal claw: The claws at the tip of the tarsus, on an insect's "foot.") dentical count couplet. If two rows of denticles (Denticle: Small tooth-like projects, often appearing like serrations on the tarsal claws of certain mayfly nymphs.): Either Iswaeon or Heterocloeon. Can’t be Iswaeon because cerci (Cercus: The left and right "tails" of an insect are known as the cerci or caudal cerci. The middle tail of a three-tailed insect is not.) lack dark median band. Can’t be heterocloeon because it’s not in the Platte drainage or in Texas. Thus, it must be one row of denticles (Denticle: Small tooth-like projects, often appearing like serrations on the tarsal claws of certain mayfly nymphs.). Moving on to 42.
5. 42 —> Hind wing pads (
The wing pads on this final instar Baetidae mayfly nymph are extremely dark.
6. 44 —> Segment 2 of labial palpi with well-developed medially projecting corner (80 % certain), scale-like setae (Seta: Little hairs on insects.) not evident on terga (Tergum: the dorsal part of an abdominal segment or segments (terga). Also used to describe the entire abdominal dorsum or the thoracic dorsal segments of Odonata.) but maybe limitation of my scope —> Baetis (alternative would be Acentrella, but pronotum (Pronotum: The top of the insect prothorax.) shape is all wrong for those, although not an official characteristic)
7. CONFIDENT in Baetis bicaudatus after distinctive leg markings (J-shaped light mark on first femur (
The femur of this Isonychia bicolor mayfly spinner is highlighted in red.
See 2 more specimens...
Mayfly Species Tricorythodes minutus
These are sometimes called Pale Olive Duns.
Jargon Defined:
Cerci: The left and right "tails" of an insect are known as the cerci or caudal cerci. The middle tail of a three-tailed insect is not.
Denticles: Small tooth-like projects, often appearing like serrations on the tarsal claws of certain mayfly nymphs.
Distal: Far from the point of attachment or origin; near the tip.
The femur of this Isonychia bicolor mayfly spinner is highlighted in red.
Nymph: The juvenile, underwater stages of mayflies, stoneflies, dragonflies, and damselflies and other aquatic insects whose juvenile stages are covered by hard exoskeletons. The word can also refer to the fishing flies which imitate these creatures, in which case it is used as a blanket term for flies imitating any underwater stage of an invertebrate (except for crayfish and leeches).
The palp on the maxilla of an Ephemerella nymph (detached and photographed under a microscope) is highlighted in red here.
Pronotum: The top of the insect prothorax.
Setae: Little hairs on insects.
Tarsal claws: The claws at the tip of the tarsus, on an insect's "foot."
Terga: the dorsal part of an abdominal segment or segments (terga). Also used to describe the entire abdominal dorsum or the thoracic dorsal segments of Odonata.
The wing pads on this final instar Baetidae mayfly nymph are extremely dark.
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