» Genus Baetis (Blue-Winged Olives)
(Baetis adonis, Baetis alius, Baetis bundyae, Baetis caurinus, Baetis diablus, Baetis foemina, Baetis hudsonicus, Baetis moqui, Baetis notos, Baetis palisadi, Baetis parallelus, Baetis persecutor, Baetis phoebus, Baetis piscatoris, Baetis pluto, Baetis posticatus, Baetis rusticans)
This is page 3 of specimens of Baetis. Visit the main Baetis page for:
- The behavior and habitat of Baetis.
Pictures of 32 Mayfly Specimens in the Genus Baetis:
Baetis tricaudatus (Blue-Winged Olive) Mayfly Nymph
View 20 PicturesA nymph of the same species as this one emerged into a dun in my studio so I got photos of both stages.
NOTE: I missed an important key characteristic the first time I tried to identify this one (robust setae (Seta: Little hairs on insects.) on the abdominal sternites (Sternite: The bottom (ventral) part of a single segment on an insect's abdomen.), which were harder to see than I expected but are clearly present), so I went on a bit of a wild goose chase and landed at a dead end. After spotting that characteristic, this one keys more straightforwardly to either Baetis tricaudatus or the Baetis piscatoris complex. It doesn't seem to be a perfect fit for either one in the key, but I'm going with tricaudatus based on range and abundance. It's not certain.
However, I'm leaving the flawed analysis below with this disclaimer, because some aspects of how I approached that dead end might be informative in the future.
----Incorrect analysis below----
After spending a lot of time with this one under my shiny new microscope, I'm still not quite sure what it is. I botched my attempt to expose the mouth parts that might make the ID more definitive. Based on the key in Webb et al 2018's "Baetis Larvae of North America," here's my reasoning at each key couplet.
Couplet 1. The pronotum (Pronotum: The top of the insect prothorax.) lacks dark, submedian U-shaped markings. Also, if I were to follow through to couplet 2, there seem to be characteristics that rule out each of the options: the intercalaris complex is ruled out by the abdominal markings, and the caudal (Caudal: Toward the posterior tip of the body.) filaments have neither a dark median band (ruling out the flavistriga complex) nor uniform pale coloration (ruling out Baetis notos). This sends me with decent confidence to couplet 4.
Couplet 4. I cannot find robust setae (Seta: Little hairs on insects.) in my microscope on the scapes, pedicels, paraprocts, or sterna. I also do not see a pair of dark, bilobed markings on the pronotum (Pronotum: The top of the insect prothorax.). Unless I overlooked these characteristics, proceed to couplet 9.
Couplet 9. Abdominal tergum (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.) 5 is a bit paler than adjacent 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 "distinctly paler"? The figure for Baetis alius in the paper, as well as a very nice picture posted by Millcreek in the forum here, shows that Baetis alius would have darker tergites (Tergite: The top (dorsal) part of a single segment on an insect's abdomen when it consists of a single chitinous plate (sclerite), or an individual sclerite if the segment has more than one.) surrounding #5. So proceed to couplet 11.
Couplet 11. The length of the gills is obviously less than 2X their width. This leads to the Baetis vernus complex, which could include that species or Baetis brunneicolor. This key doesn't say how to tell those species apart.
Switching over to Burien et al 2018 as the source, the characteristics used to distinguish vernus from brunneicolor seem to rule out either one. Brunneicolor should have more uniformly brown abdominal tergites (Tergite: The top (dorsal) part of a single segment on an insect's abdomen when it consists of a single chitinous plate (sclerite), or an individual sclerite if the segment has more than one.), whereas vernus should have a lack of visible tracheation in most of the gills.
The fore femur (Femur: The main segment of an insect's leg close to the body, in between the tibia and the trochanter.) length is about 3.8x its width.
Also worth noting: In the genus ID, I thought I could see the villipore in my microscope, but I'm not sure. If I back out of Baetis altogether and assume there's no villipore, I end up at Fallceon, but this specimen doesn't seem to have the frontal keel on the head that's supposed to be present on Fallceon quilleri. So that seems like a dead end as well.
Male Baetis tricaudatus (Blue-Winged Olive) Mayfly Spinner
View 12 PicturesSome notes from identifying this specimen under the microscope:
1. The hind wing has three longitudinal veins (Longitudinal vein: Longitudinal veins are the major long veins running length-wise through an insect's wing, connecting the base to the outer margin, or the major branches from those veins.), but the third is faint, short (about half the length of the wing), and close to the wing margin.
2. Then antenna is brown fading into white at the tip, and the base is ringed with white.
3. The joints of the tarsal segments on the middle and hind leg have fine black markings.
It was also collected in association with a female spinner.
Female Baetis bicaudatus (BWO) Mayfly Nymph
View 12 PicturesI collected this one along with a male that was quite a bit smaller but equally ready to emerge in mid April.
I spent (Spent: The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.) quite a while on the identifications, because they really don't look very much like the Baetis bicaudatus nymph I caught last year in Idaho. However, the presence of 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.) rules out Acentrella turbida, the lack of a fringe of long setae (Seta: Little hairs on insects.) on the tibiae (Tibia: A middle segments in the leg of an insect, located between the femur and the tarsus.) rules out Acentrella insignificans, range rules out Heterocloeon and Iswaeon, and the thumb-like projection on the labial palp (
The wing pads on this final instar Baetidae
mayfly nymph are extremely dark.
Palp: A long, thin, often segmented appendage which can protrude from certain insect mouth parts such as the maxillae. Also known as the < />palpus.) points to Baetis. Thus, Baetis bicaudatus is a fairly confident ID, and it's not too surprising that it looked different from my previous specimen because bicaudatus is thought to be a species complex with multiple types that haven't been fully sorted out yet.
The palp on the maxilla of an Ephemerella
nymph (detached and photographed under a microscope) is highlighted in red here.
The microscope pictures for this specimen aren't from the same exact nymph, but a mixture of a few others of the same kind that I didn't mind dissecting.
Female Baetis tricaudatus (Blue-Winged Olive) Mayfly Nymph
View 13 PicturesThese nymphs were highly abundant in my early April kick net samples from the Yakima Canyon, and one of them emerged into a dun, which I photographed immediately. Similar-looking nymphs but with distinctly brighter color patterns were also abundant. I just photographed one. After extensive views under the microscope, it's clear the bright ones are males and the dull ones are females of the same species.
The most likely guess at the species is Baetis tricaudatus, which may be a complex of related species that haven't all been sorted out yet. It isn't a perfect fit to every key characteristic (and I never seem to find a Baetis that matches the expected pronotum (Pronotum: The top of the insect prothorax.) color patterns, but that seems to be the closest.
The microscope images here were taken with different specimens from the main photos (so I could dissect them while preserving that one intact), but clearly the same species.