Blue-Winged Olives
Like most common names, "Blue-Winged Olive" can refer to more than one taxon. They're previewed below, along with 26 specimens. For more detail click through to the scientific names.
These are pretty much always called Blue-Winged Olives.
"These little critters supplant the importance of many other well-known mayfly hatches."
-Fred Arbona in Mayflies, the Angler, and the Trout
Arbona did not overestimate these critters. Their great numbers and multiple broods each season make up for their size, which is rarely larger than size 16 and often smaller than size 20.
Hardly mentioned in angling literature prior to the middle of the last century, baetids have become increasingly important to anglers, rivaling any other family of mayflies in this regard. This is largely due to the extension of fishing seasons that now include the early and late periods when this family’s species usually dominate hatching activity. Another important reason is the tremendous improvement in tackle allowing more practical imitation of these little mayflies. The dramatic ecological changes in many of our watersheds and the subsequent impact this has had on the makeup of taxa populations is also a factor.
Taxonomically speaking, this is a most unruly family. The entomological community seems to be perpetually reclassifying its genera and species to the chagrin of many anglers. These changes are not capricious. The reason is older nomenclatures haven't provided the taxonomic flexibility required as more becomes known about the complexities of baetid relationships. Classification of this family’s genera and species is very much a work in progress. The changes have been so extensive that it is beyond the scope of this hatch page to track the taxonomic history effectively without interjecting even more confusion. If you are frustrated by the inability to find some of the old familiar names, you're not alone. Rest assured these popular hatches are listed here, just under the latest classifications. The old famous names are referenced in their hatch pages.
Common baetid hatches with a national distribution are the species
Acentrella turbida,
Baetis brunneicolor, and
Baetis tricaudatus. In the West,
Baetis bicaudatus,
Diphetor hageni and
Plauditus punctiventris can also be common. In the East and the Midwest, look for
Baetis intercalaris and
Plauditus dubius. The species
Iswaeon anoka is important in both the West and Midwest. Some of the
Procloeon and
Anafroptilum (prev. Centroptilum) species are coming to the increasing notice of anglers across the country.
Stillwater anglers are likely to run across
Callibaetis ferrugineus ferrugineus in the East and Midwest. Western anglers will find
Callibaetis californicus and
Callibaetis ferrugineus hageni to be very important.
Streamside identification of these mayflies to specific and often even generic level has always been difficult. This is now even more so as new taxonomic evidence has shown hind wing conformation (or lack of hind wings) and other features are less dependable as ways to tell the genera apart. Many of the lesser-known species probably produce excellent local hatches but have not caught enough attention to be properly recognized by anglers. The lesson is that we should not assume anything about the identity of many
Baetidae hatches we come across; they may not even be in the
Baetis genus, let alone familiar species.
These are pretty much always called Blue-Winged Olives.
This is one of the most prolific genera of mayflies in North American trout streams. Their small size permits the growth of up to three generations per year, and they are good dry-fly insects because they often hatch in impressive numbers and the duns ride the water for a long time before taking flight.
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.
These are pretty much always called Blue-Winged Olives.
The only species of this genus,
Diphetor hageni, is one of the most important in the
Baetidae family for western anglers. It was previously known as
Baetis parvus in the West and its synonymy
Baetis devinctus in the East.
These are pretty much always called Blue-Winged Olives.
Species of the
Fallceon genus can be identified by having typical
Baetis dark or olivaceous coloration and the hooked process on its hind wings of
Anafroptilum (prev. Centroptilum). This genus has only two species of possible interest to anglers:
Fallceon quilleri - a former species of
Baetis that has had eight former
Baetis species synonymized with it. It has a continental distribution.
Fallceon thermophilos - a former species of
Baetis that has had one species from
Baetis synonymized with it. It has a Northwest distribution.
These are pretty much always called Blue-Winged Olives.
Baetis tricaudatus is undeniably the most widespread and abundant baetid on the continent and arguably the most important mayfly species to trout and anglers alike. Eastern anglers used to know these important mayflies by the storied name of
Baetis vagans. Conversely, the usually much larger and late Fall hatching brood of
Baetis tricaudatus was considered an important Western species with its own tradition. But, entomologists recently determined that they are both in fact the same species. The nomenclature conventions guiding entomologists do not account for a name's regional fame among fishermen, and new or obscure species names may replace their old favorites. Sometimes taxa with disparate traditions are combined.
Baetis vagans is one such casualty. Fortunately, trout think like Shakespeare:
A rose by any other name would smell as sweet. The rose that was
vagans has lost none of its charm. This species is
multibrooded (Multibrooded: Producing more than one generation in a single year. Baetis mayflies are a classic example. Insects which produce a single generation with two distinct peaks (like the June and September hatches of Isonychia bicolor mayflies) are not multibrooded, because the fall insects are offspring from the previous fall instead of the current year's spring.) with the hatches of Spring being larger flies. As the weather warms the following broods are composed of progressively smaller flies. In the East, they range in size from 16 to 20. In the West, they may run a size larger.
These are often called Blue-Winged Olives.
This genus contains most of the important Blue-Winged Olive ephemerellids that make up some very important hatches across the country.
In the East, there are the morning hatches of
Drunella cornuta (Large Blue-Winged Olive) followed as the season progresses by the smaller
Drunella cornutella and
Drunella lata species, both commonly called Little Blue-Winged Olives. These hatches usually begin in late spring and can continue well into midsummer on many Eastern and Midwestern streams.
In the West, the
Drunella genus is even more prominent. Besides having abundant Blue-Winged Olive hatches represented by the common species
Drunella coloradensis (Little Western Green Drake),
Drunella spinifera (Western Slate-winged Olive Dun) and
Drunella flavilinea (Western Blue-winged Olive or "Flav") the region also has the
Drunella group of famous Western Green Drakes made up of the curious flat-faced nymph species
Drunella doddsii and the three
subspecies (Subspecies: Entomologists sometimes further divide a species into distinct groups called subspecies, which have two lower-case words on the end of their scientific name instead of one. The latter is the sub-species name. For example, Maccaffertium mexicanum mexicanum and Maccaffertium mexicanum integrum are two different subspecies of Maccaffertium mexicanum.) of
Drunella grandis. Coloration ranges widely by region, going from dark brown to bright green. Most commonly they will be in the olive range. The wings too can range from dark slate to medium dun, often with yellow or olive pigment in the
basal (Basal: close to the base; root or beginning) costal region (lower leading edge) of the forewings.
There have been many changes in taxonomic nomenclature affecting the
Ephemerellidae over the years with few impacted more than the species of this genus. Anglers interested in "connecting the dots" with entomological information provided in fishing literature of the past need to take note of this.
Female Drunella tuberculata Mayfly Dun
View 14 PicturesI don't know for sure that this is Drunella tuberculata, but that's my best guess for now.
It certainly has a different look and much more robust body shape from Drunella lata duns I photographed a couple weeks earlier, so I doubt it's that species. Using distribution records to eliminate other choices narrows this down to Drunella tuberculata or Drunella walkeri.
Markings described for the abdominal sternites (Sternite: The bottom (ventral) part of a single segment on an insect's abdomen.) of the male spinner of Drunella tuberculata are suspiciously similar to those on this female dun. Also, this dun is 9.5mm long (my ruler pic isn't very good, but I'm basing this on measuring the real thing). The size range given in the old Allen & Edmunds keys for walkeri females is 7-8mm, while tuberculata is 9-11mm. For these reasons I'm sticking it in tuberculata for now.
This is the only Drunella mayfly I saw all day. I scooped it off the water as it emerged at around 7pm from a big Catskill tailwater.Collected
June 1, 2007 from in
Added to Troutnut.com by on June 8, 2007 These are often called Blue-Winged Olives.
Though not as well known as the Hendrickson and Sulphur hatches of the
Ephemerella genus,
Drunella cornuta (Olive Morning Dun or Large Blue-Winged Olive) is nonetheless an important Eastern hatch.
Lloyd Gonzales, in his book
Fly-Fishing Pressured Water, notes that this attractive olive-green mayfly can provide good-to-excellent morning fishing in the faster sections of many streams. He also mentions that it can hatch in surprising numbers and usually faces less competition for the trout's attention than many of the spring or evening-emerging ephemerellids. Yet,
cornuta and its sister species have largely escaped the limelight. The renowned twilight hatches of big
Ephemera drakes and many other popular mayfly species command fly fisher's attention at this time of year. As the days lengthen, fishing all of the available mayfly hatches would require a pretty long day astream, so most anglers choose to focus on the late afternoon and evening activity.
Nature seems to have several recurrent color themes, and one of these is gray-winged/olive-bodied aquatic insects. Perhaps this explains why the name "Blue-Winged Olive" is often held up as the poster child for common name confusion. It has been freely applied to a multitude of mayflies in various families, genera, and species. Prior to having a well-established common name, this mayfly was referred to by Gonzales as the Olive Morning Dun. However, it has already been added to the long list of "BWOs" on many Eastern/Midwestern hatch charts.
These are often called Blue-Winged Olives.
When
Selective Trout was first published in 1971, Swisher and Richards included
Drunella lata (Small Blue-Winged Olive, Slate-Winged Olive) as a Midwestern "superhatch." Although it can also be found in many Eastern trout streams, it is probably more important to Midwestern anglers. Typically a morning emerger, this species often competes for the attention of trout with more abundant
Tricorythodes and small baetids during parts of July and August. For this reason, the authors of
Selective Trout considered the concentrated evening spinner falls to be more important than the somewhat sporadic morning emergence. From an angling standpoint, this situation is nearly the opposite of the earlier
Drunella cornuta emergence in the East, where the morning emergence is usually the main event and spinner falls are often of little consequence.
Currently,
Drunella lata shares its name with another mayfly, the former
D. longicornis. That mayfly can be important in mountainous areas in the Southeast, but they are larger and the nymphs lack the distinctive pale markings mentioned in the Juvenile Characteristics section. (The information on this page does not describe
D. longicornis)
These are often called Blue-Winged Olives.
Although by no means a superhatch, this species can be important. Authors who discuss it lament the general lack of credit it receives for the fine hatches it produces on some streams.
These are sometimes called Blue-Winged Olives.
This intriguing species has received a lot of attention in past angling books. Recent authors suspect that much of this credit was a case of mistaken identity, with
Attenella attenuata receiving praise for the hatches of
Drunella lata and
Dannella simplex. Much of the credit
was legitimate and accurate, but this species is no longer thought to be on par with its most popular cousins in
Ephemerella and
Drunella.
I have several specimens listed under this species, but I'm not positive the identification is correct.
These are sometimes called Blue-Winged Olives.
Few anglers can claim to have fished to hatches of this little olive mayfly, even though the species has been mentioned in popular angling entomologies like Caucci and Nastasi's
Hatches or Knopp and Cormier's
Mayflies. On many of the larger Eastern freestones, their emergence happens after the waters have warmed and dedicated anglers have turned their attention to streams that remain cold: headwaters, spring creeks, or tailwaters. Because good populations are usually not found in tiny streams, it is on some the Eastern tailwaters, like the branches of the Delaware, that fly fishers take notice of this species.
Drunella cornutella looks like a Mini-Me version of
Drunella cornuta. In streams where the two species cohabit, size is the only easy way to tell them apart. Although there is some slight overlap between the largest
cornutella and the smallest
cornuta, the average difference is usually pretty obvious. Both share very similar coloration and
morphology (Morphology: The form and structure of an organism, or the study of the form and structure of organisms.) in all stages, even down to the little curved horns coming out of the frontal shelves of the nymph's heads.
These are sometimes called Blue-Winged Olives.
Ernest Schwiebert had this to say about the hatches of this chunky Eastern
Drunella (Blue-Winged Olive) species:
An imitation is rarely required, but notes show that when it is needed it is needed badly.
See the
Drunella and
Drunella cornuta hatch pages for additional information.
These are very rarely called Blue-Winged Olives.
A cult following is something to which few insects can lay claim, but the tiny
Tricorythodes mayflies certainly qualify. Their widespread, reliable, heavy hatches draw impressive rises of ultra-selective trout which demand the most of a technical dry-fly angler's skills.
It is surprising that such a great hatch took so long to come to the attention of fly fishermen. The Tricos were first introduced to anglers in a 1969 Outdoor Life article by Vincent Marinaro, who misidentified them as
Caenis. By the early 1970s the identification had been corrected but Swisher and Richards still wrote in Selective Trout,
"Few anglers are familiar with these extremely small but important mayflies." The next wave of publications boosted
Tricorythodes to its current fame. I suspect their early dismissal was due in part to tackle limitations; anglers in the 1950s had no means to effectively tie and present size 22-28 flies.
These are very rarely called Blue-Winged Olives.
For trout (if not anglers), this single species is arguably the most important mayfly in North America. In terms of sheer numbers, breadth of distribution and hatch duration, it has a good argument.
Ephemerella excrucians or Pale Morning Dun usually follows its larger sibling
Ephemerella dorothea infrequens with which it shares the same common name. What it often lacks in size by comparison is made up for with it's duration, often lasting for months with intermittent peaks. This close relationship with
infrequens has led many anglers to confuse Pale Morning Dun biology with that of the
multivoltine (Multivoltine: Having more than one generation per year.) Baetidae species, having disparate broods that decrease in size as the season advances. Sharing the same common name has not helped to alleviate this misconception.
Until recently,
Ephemerella excrucians was considered primarily an upper MidWestern species of some regional importance commonly called Little Red Quill among other names. Recent work by entomologists determined that it is actually the same species as the important Western Pale Morning Dun (prev.
Ephemerella inermis), and the lake dwelling Sulphur Dun of the Yellowstone area, (prev.
Ephemerella lacustris). Since all three are considered variations of the same species, they have been combined into
excrucians, being the original name for the type species reported as far back as the Civil War. Angler speculation had simmered for some time that the stillwater loving
Ephemerella lacustris was much more widespread, inhabiting more water types then previously thought and could account for many large sulfurish ephemerellids found in still to very slow water locations throughout the West. With the revisions, this discussion is now moot.
Ephemerella excrucians variability in appearance, habitat preferences, and wide geographical distribution are cause for angler confusion with the changes in classification. They can be pale yellow 18's on a large Oregon river, creamy orange 14's on western lakes and feeder streams, large olive green on CA spring creeks as well as tiny sulfur ones in many Western watersheds. Then there's the little Red Quill on small streams in Wisconsin. Yet, all are the same species.
Female Ephemerella excrucians (Pale Morning Dun) Mayfly Dun
View 3 PicturesSize: 10mm. At emergence the specimen was a fairly bright olive green and there was obvious difference in color between the forewing (med. dun) and the hind-wing (pale cream). It was really noticeable as they floated by. You can just make these features out in the second photo, but not so much in the first that was taken 24 hours after capture. Total time from emergence to molting - approx. 48 hours.
Entoman
Edit 2/25/13 - This specimen was originally posted to E. d. infrequens because of its size. It turns out large size doesn't hold up as a way to tell these two apart. This is because excrucians has much greater variability than previously understood. The assumption by anglers that excrucians is always the smaller of the two is apparently not supported by science. There is a lot left to sort out with western Ephemerella species. This may include new discoveries and/or synonyms (Synonym: A former name of a taxon, usually a species. Entomologists frequently discover that two insects originally described as different species are one in the same, and they drop one of the names. The dropped name is said to be a synonym of the remaining name. These changes take a while to trickle into the common knowledge of anglers; for example, Baetis vagans is now a synonym of Baetis tricaudatus.) as well as reportage on new intraspecific variations broadening the descriptions of recognized species. Based on this specimen's Fall maturity, the best guess is that it is an unusual form of excrucians.
As to color, both species duns (nymphs too) demonstrate a tremendous amount of intraspecific variability from pale yellow to bright green with a multitude of sulfur shadings in between, ranging from pale amber, through orange to cinnamon and even dark brown. I've seen wings from pale cream through tannish and almost every shade of dun except the dark shades. Some have pigment stained leading edges matching their bodies, some don't. Most of these variations are undocumented except in angler references and periodicals. It seems a rare year that a new variation doesn't pop up to the notice of anglers.
Bottom line - size is only reliable if the specimens are smaller than size 16, pointing to excrucians. Otherwise, the only fairly dependable way to tell them apart (especially the females) is by timing as infrequens is the first of the two to appear, rarely lasting longer than a couple of weeks or later than the end of June most years. The problem with using timing for determination is it requires knowledge of the hatch sequences as they actually occurred for a given year on a given piece of water. Obviously, this kind of information is seldom available. Without it, determining between the two duns if they are larger than size 18 is speculative at best - at least until very late in the Summer. These are very rarely called Blue-Winged Olives.
Drunella flavilinea (Flav) Mayfly Nymph
View 6 PicturesAlthough the identification is not certain because the nymph is not yet mature, the configuration of tubercles (
A few (not all) of the abdominal tubercles on this
Ephemerella needhami nymph are circled. They are especially large in this species.
Tubercle: Various peculiar little bumps or projections on an insect. Their character is important for the identification of many kinds of insects, such as the nymphs of Ephemerellidae mayflies.) on this one--particularly the forefemora--seems to best match Drunella flavilinea.Collected
July 2, 2019 from in
Added to Troutnut.com by on July 18, 2019