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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Mayfly Genus Baetis (Blue-Winged Olives)
The genus Baetis and its species are probably the most misidentified mayflies in angling. Many who see mayflies too small to imitate with a size 16 Adams call them Baetis, especially if they're olive in coloration. In reality, Baetis (though the most prominent) is only one of several very similar and abundant genera in the family Baetidae. It seems species in the family are perpetually being reclassified, and identifying any of them, even to genus level is difficult. The angler who wants to describe what is seen streamside usually has only four choices:
1. Call them "Blue-Winged Olives" as most do. the problem is this name has lost all meaning due to being applied to dozens of species across several families (many of which have neither blue wings nor olive bodies). Besides, the name was originally coined for a species of British ephemerellid, the family where this common name should properly reside.
2. Call them "baetids", the Latin name for referring to members of the Baetidae family as a group. While technically accurate scientifically, it doesn't tell the listener or reader much about their appearance.
3. Call them outmoded scientific names - Even calling them by the updated name is usually risky for most species in the field. Adding to the difficulty by using names from outdated nomenclatures? Talk about confusion...
4. Call them "little (whatever color they are) quills." Perhaps this is the best choice as at least it's more accurately descriptive.
The fact is many are so similar that even alot of the specimens in the hatch pages can't be keyed below the family level with absolute certainty; at least from what's observable in the photos alone. They often require observation with a microscope and extensive knowledge of the subtle differences for accurate determinations. So - the next time a fishing buddy identifies a little olive mayfly from a distance using an obsolete name like Baetis vagans, just smile and nod...
For anglers raised on Schwiebert, Swisher, etc., it is often difficult to locate many important species in the newer literature. When working with older taxonomies and/or angling texts, the following hatch page links may prove helpful:
Baetis devinctus = Diphetor hageni (can be an important eastern species)
Baetis hiemalis = Baetis brunneicolor (important Midwest species with a national distribution)
Baetis insignificans = Acentrella insignificans (can be important in some western locales)
Baetis parvus = Diphetor hageni (very important western species)
Baetis propinquus = Labiobaetis propinquus (important in the West with a national distribution)
Baetis pygmaeus = Acerpenna pygmaea (can be important with distribution across all regions)
Baetis vagans = Baetis tricaudatus (most abundant and important species nationwide)
The relatively new genus Fallceon has two species of interest that are made up of several previous Baetis species. They are distributed nationally and may prove significant as more is learned about the angling opportunities they present, especially in the the South and Southwest.
Where & when
Some Baetis species are often the first major hatches in the spring and the last in the fall, and on especially stable spring creeks they may emerge throughout the winter. The genus is common nationwide.See each species page for more on their distribution and timing.
In 261 records from GBIF, adults of this genus have mostly been collected during July (29%), June (28%), August (14%), May (9%), and April (8%).
In 509 records from GBIF, this genus has been collected at elevations ranging from -30 to 11037 ft, with an average (median) of 3182 ft.
Genus Range
Hatching behavior
Baetis nymphs are normally outstanding swimmers, but they are reported to lose this ability when they emerge. They get to the surface by dead-drifting, buoyed by gas bubbles, or by crawling to the surface on some object and letting go to drift along in the film (rather than crawling out). They have trouble breaking through the surface film, escaping their shucks, and drying their wings to take flight, which means that almost any type of surface fly has its uses. Anglers may need to use deep nymphs, floating nymphs, emergers, cripples, or dun patterns during this emergence. Common wisdom says floating nymph and emerger patterns are the most useful.
Dismal weather invites the best hatches of Baetis mayflies; look for them on overcast, rainy days, as long as the water temperature is above 40°F.
Spinner behavior
Timing the return of these mayflies as spinners after they hatch is difficult; some may come back within a few hours, while others take a few days.Baetis females are among the only mayflies to lay their eggs underwater. The females land near the water after mating and crawl down to lay rows of eggs on the downstream side of rocks, sticks, and other objects. They may slip loose during the process or let go after they finish, and wet fly imitations are effective during this time. Ernest Schwiebert gives more detail in Matching the Hatch:
In moving through the surface film she folds her wings about her abdomen and uses the downstream side of the object she has selected. The passing through the surface film is the critical phase of her mating. Once she is under the surface, she inspects the rock or log carefully with her abdomen. Finally she lays her eggs with a circular sweeping motion, which leaves a little row of eggs each time. When her supply of eggs is exhausted she climbs back out of the water or is swept away in the underwater currents.
Nymph biology
Baetis nymphs are found in almost every trout stream, but they produce more broods and thicker hatches in cold, unpolluted, alkaline waters. They inhabit almost every microhabitat in the stream except for silt beds, but gravel and vegetation are especially suitable.Baetis Fly Fishing Tips
Because Baetis mayflies are so often called Blue-Winged Olives, some anglers try to imitate them with flies with blue wings and olive bodies. This is one of the follies of common names. Their wings are various shades of gray, maybe with a slight blue tint, and their bodies are various shades of olive or brown. When you meet a hatch, try to catch one of the live mayflies rather than assuming you know its color.Specimens of the Mayfly Genus Baetis
3 Male Duns
This dun molted most of the way into a spinner (though the wings got stuck) the evening after I photographed it, so I took some more photos of the spinner.
I found a female nearby, probably of the same species.
I found a female nearby, probably of the same species.
This male was associated with a female of the same species.
8 Female Duns
This dun emerged on my desk from a container of nymphs I was sorting, so I was able to get an ID from the nymphs. I also uploaded photos of a female nymph and a male nymph.
This female was associated with a male of the same species.
I found this female in the same area as a male with similar markings, probably of the same species.
This little early-season dun molted into this spinner after I photographed her.
This one emerged from a nymph of this kind in my studio but got a bit waterlogged before I could pull it out to photograph.
I'm guessing this specimen is in the genus Acerpenna because of the very sharp costal process on her hind wing. I'm guessing pygmaea because it is the most common species.
Editor note: Not Acerpenna. This is most likely Baetis. See comments on this male specimen for rationale. Also compare with the female specimen associated with it.
Editor note: Not Acerpenna. This is most likely Baetis. See comments on this male specimen for rationale. Also compare with the female specimen associated with it.
3 Male Spinners
Some notes from identifying this specimen under the microscope:
1. The hind wing has three longitudinal 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.
1. The hind wing has three longitudinal 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.
4 Female Spinners
This female spinner was deceased when photographed, so the posture is unnatural, but it was a substantial hatch and clearly worth imitating (with wet flies to imitate the sunken ovipositing females) so I went ahead with the photos.
It was collected in association with a male spinner.
It was collected in association with a male spinner.
I captured and photographed this specimen as a dun before she molted into the spinner photographed here. Her wings got a bit torn up in the process.
18 Nymphs
A 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 on the abdominal sternites, 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 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 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 in my microscope on the scapes, pedicels, paraprocts, or sterna. I also do not see a pair of dark, bilobed markings on the pronotum. Unless I overlooked these characteristics, proceed to couplet 9.
Couplet 9. Abdominal tergum 5 is a bit paler than adjacent terga, 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 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, whereas vernus should have a lack of visible tracheation in most of the gills.
The fore femur 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.
NOTE: I missed an important key characteristic the first time I tried to identify this one (robust setae on the abdominal sternites, 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 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 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 in my microscope on the scapes, pedicels, paraprocts, or sterna. I also do not see a pair of dark, bilobed markings on the pronotum. Unless I overlooked these characteristics, proceed to couplet 9.
Couplet 9. Abdominal tergum 5 is a bit paler than adjacent terga, 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 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, whereas vernus should have a lack of visible tracheation in most of the gills.
The fore femur 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.
This specimen keys to the Baetis flavistriga complex, which could be either flavistriga or Baetis phoebus.
Under the microscope, this one clearly has hind wingpads.
Here 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 with well-developed medially projecting corner --> Baetis (couple 44). BUT no sign of scale-like setae on abdominal terga. Conflicts at this couplet.
3. Gills on segments I-VII
4. Tarsal claws with denticles, 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
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 antennae has no distal lobe --> rules out Labiobaetis (100 % certain)
2. 38 --> Terminal filament much shorter than cerci --> not Barbaetis benfieldi (100 % certain)
3. 39 --> Terminal filament reduced (100 % certain)
4. 40 --> Tarsal claw denticle count couplet. If two rows of denticles: Either Iswaeon or Heterocloeon. Can't be Iswaeon because cerci 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. Moving on to 42.
5. 42 --> Hind wing pads present (100 % certain)
6. 44 --> Segment 2 of labial palpi with well-developed medially projecting corner (80 % certain), scale-like setae not evident on terga but maybe limitation of my scope --> Baetis (alternative would be Acentrella, but pronotum 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, L-shaped on second and third) matches original species description to a tee.
7. Baetis bicaudatus nymph
1. Hind wingpad present but small and hidden beneath forewing pad
2. Segment 2 of labial palp with well-developed medially projecting corner --> Baetis (couple 44). BUT no sign of scale-like setae on abdominal terga. Conflicts at this couplet.
3. Gills on segments I-VII
4. Tarsal claws with denticles, 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
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 antennae has no distal lobe --> rules out Labiobaetis (100 % certain)
2. 38 --> Terminal filament much shorter than cerci --> not Barbaetis benfieldi (100 % certain)
3. 39 --> Terminal filament reduced (100 % certain)
4. 40 --> Tarsal claw denticle count couplet. If two rows of denticles: Either Iswaeon or Heterocloeon. Can't be Iswaeon because cerci 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. Moving on to 42.
5. 42 --> Hind wing pads present (100 % certain)
6. 44 --> Segment 2 of labial palpi with well-developed medially projecting corner (80 % certain), scale-like setae not evident on terga but maybe limitation of my scope --> Baetis (alternative would be Acentrella, but pronotum 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, L-shaped on second and third) matches original species description to a tee.
This specimen was collected along with a female which was quite a bit larger, different in color, but otherwise seemed the same morphologically.
This nymph keys to Baetis assuming the villipore is present (hard to see in my photos or scope), and within that genus it tentatively keys to the flavistriga species complex, of which Baetis flavistriga itself is by far the most common in Washington state, so that's the most likely ID.
This specimen and many like it were found with other specimens I found to be duller-colored females of the same species. I wasn't aware of such a difference between male and female nymphs in Baetids, but all the morphological characteristics I checked in the key were the same, and the color patterns are, too -- just not the brightness.
These 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 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.
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 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.
I collected this one along with a male that was quite a bit smaller but equally ready to emerge in mid April.
I spent 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 rules out Acentrella turbida and Iswaeon anoka, the lack of a fringe of long setae on the tibiae rules out Acentrella insignificans, range rules out Heterocloeon, and the thumb-like projection on the labial palp 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 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.
I spent 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 rules out Acentrella turbida and Iswaeon anoka, the lack of a fringe of long setae on the tibiae rules out Acentrella insignificans, range rules out Heterocloeon, and the thumb-like projection on the labial palp 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 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.
1 Streamside Picture of Baetis Mayflies:
Baetis spinners trying to lay eggs on my waders
In this picture: Mayfly Genus Baetis (Blue-Winged Olive).
Discussions of Baetis
Big Green River, Wisconsin, late September
1 replies
Posted by Admiralb on Sep 28, 2013 in the species Baetis brunneicolor
Last reply on Sep 30, 2013 by Entoman
I hosted two visiting delegates to the T.U. National Convention in Madison, WI. on September 25, 2013, taking them to the Big Green River in Grant County near Fennimore. There was a high overcast in the morning, and these mayflies [which I merely called "BWO's" and imitated with #16 parachute dries - thin olive bodies, gray wing posts and dun parachute hackle] - were active. Both of my guests raised browns fishing a gray nymph behind a #16 parachute dry BWO. As long as my flies catch fish, I don't need to be a detailed entomologist. Nevertheless, I do sincerely appreciate the detailed scientific info, because it helps me focus my flytying and fly selection. Thank you.
Baetis flavistriga computatii
7 replies
Posted by CaseyP on Jan 22, 2007 in the species Baetis flavistriga
Last reply on Jan 19, 2009 by Taxon
pleased to report the emergence of a new baetis flavistriga which i have christened computatii
forum visitors using the Firefox browser who put troutnut.com on their bookmarks toolbar have undoubtedly noticed a tiny dark mayfly icon in a blue box next the bookmark.
well, it's breeding. came back this evening from a week out of town to discover that the little troutnut computatii had a pal over next the hotmail.com bookmark where formerly there was only a generic white icon. am waiting for it to show up next the other two sites that have only generic icons.
now our resident boffins will help me with the Latin ending on the new name, (i tried to use the genitive plural) and then we'll ask Jason how he got these virtual flies to multiply.
Casey
flavistriga broods
Posted by Konchu on Jan 17, 2009 in the species Baetis flavistriga
Last reply on Jan 17, 2009 by Konchu
Anyone have observations that they are willing to share of different flavistriga broods?
Jason says that B. flavistriga is a "combination of widely varying types in different places, it's hard to piece the information together into reliable hatch dates for the different broods in any given location." This is stated very well.
As part of my bug work, I'm trying to tease apart some of these "varying types" to see what, if anything, they might represent. Tapping into the experience base here might help.
Jason says that B. flavistriga is a "combination of widely varying types in different places, it's hard to piece the information together into reliable hatch dates for the different broods in any given location." This is stated very well.
As part of my bug work, I'm trying to tease apart some of these "varying types" to see what, if anything, they might represent. Tapping into the experience base here might help.
Start a Discussion of Baetis
References
- Caucci, Al and Nastasi, Bob. 2004. Hatches II. The Lyons Press.
- Fauceglia, Ted. 2005. Mayflies . Stackpole Books.
- Leonard, Justin W. and Fannie A. Leonard. 1962. Mayflies of Michigan Trout Streams. Cranbrook Institute of Science.
- Schwiebert, Ernest G. 1955. Matching the Hatch. MacMillan Publishing Company.
- Swisher, Doug and Carl Richards. 2000. Selective Trout. The Lyons Press.
Mayfly Genus Baetis (Blue-Winged Olives)
Taxonomy
Species in Baetis
Baetis adonis
0
0
Baetis bicaudatusPale Olive Duns
6
48
Baetis brunneicolorBlue-Winged Rusty Duns
0
0
Baetis flavistrigaDark Blue-Winged Olives
3
14
Baetis intercalarisSmall Eastern Blue-Winged Olives
0
0
Baetis magnusIron Blue Quills
0
0
Baetis phoebus
0
0
Baetis piscatoris
0
0
Baetis pluto
0
0
Baetis posticatus
0
0
Baetis rusticans
0
0
Baetis tricaudatusBlue-Winged Olives
13
117
Species in Baetis: Baetis adonis, Baetis bicaudatus, Baetis brunneicolor, Baetis flavistriga, Baetis intercalaris, Baetis magnus, Baetis phoebus, Baetis piscatoris, Baetis pluto, Baetis posticatus, Baetis rusticans, Baetis tricaudatus
11 species (Baetis alius, Baetis bundyae, Baetis caurinus, Baetis diablus, Baetis foemina, Baetis hudsonicus, Baetis moqui, Baetis notos, Baetis palisadi, Baetis parallelus, and Baetis persecutor) aren't included.