Adult Mayfly Identification
Text: Roger Rohrbeck
Photos: Jason Neuswanger
For those unfamiliar with genus names, a common name for each genus is provided at the end of this article.
After a bit, weíll walk through the identification of a mayfly, but first we need to set the stage by exploring some physical features of the winged stages of mayflies.
Is it a dun or spinner?
Mayflies are unique in the insect world, in that they have more than one winged lifestage, the dun (sub-adult or subimago), and the spinner (adult or imago).
Under most circumstances, the (dun or spinner) determination is easy to make.
A mayfly dun (subimago) has wings that are dull and opaque.
A mayfly spinner (imago) has wings that are hyaline (shiny and transparent).
Is it male or female?
Three easily observable features can be used to determine sex in the winged stages of mayflies:
- Eyes of male tend to dominate the head; eyes of female donít.
- Fore legs of male are extremely long; fore legs of female arenít.
- Male has forceps (claspers) to hold female during copulation; female doesnít.
While all three of these features will not necessarily be observable, usually one or two are, and can be used to determine the sex of a winged mayfly.
How long is it?
The body of a mayfly is measured from the front of the head to the end of the abdomen, excluding tails. This measurement varies greatly from one type of mayfly to another. It ranges (from 2 mm.) for the smallest species (to 40 mm.) for the largest species.
These are the body length ranges (excluding tails) for most N. American mayfly genera:
Acentrella (4-6 mm.), Ameletus (9-14 mm.), Anthopotamus (7-18 mm.), Asioplax (3-6 mm.), Attenella (6-8 mm.), Baetis (4-10 mm.), Baetisca (10-14 mm.), Brachycercus (3-6 mm.), Caenis (2-4 mm.), Callibaetis (5-10 mm.), Caudatella (8-11 mm.), Centroptilum (5-7 mm.), Cinygma (8-10 mm.), Cinygmula (6-10 mm.) Diphetor (5-7 mm.), Drunella (6-16 mm.), Epeorus (7-14 mm.), Ephemera (10-30 mm.), Ephemerella (5-12 mm.), Ephoron (9-14 mm.), Heptagenia (8-14 mm.), Heterocloeon (5-6 mm.), Hexagenia (16-40 mm.), Ironodes (11-14 mm.), Isonychia (10-21 mm.), Leptophlebia (8-14 mm.), Leucrocuta (5-8 mm.), Litobrancha (15-40 mm.), Maccaffertium (7-16mm.), Metretopus (10 mm.), Nixe (8-11mm.), Paraleptophlebia (6-11 mm.), Plauditus (3-6 mm.), Procloeon (3-9 mm.), Pseudocloeon (4-6 mm.), Rhithrogena (7-11mm.), Serratella (4-9 mm.), Siphlonurus (9-16 mm.), Siphloplecton (13-19 mm.), Stenacron (8-12 mm.), Stenonema (9-11 mm.), Timpanoga (14-16 mm.), Tricorythodes (3-7mm.)
Are wings plain, or are they marked or mottled?
Some mayflies have wings that are plain (uniform in color), and others have wings that are marked or mottled (contrasting in color).
Among mayflies with plain fore wings are the following genera:
Acentrella, Ameletus, Anthopotamus, Asioplax, Attenella, Baetis, Baetisca, Brachycercus, Caenis, Caudatella, Centroptilum, Cinygma, Cinygmula, Diphetor, Drunella, Epeorus, Ephemerella, Ephoron, Heterocloeon, Hexagenia, Ironodes, Isonychia, Leptophlebia, Metretopus, Paraleptophlebia, Plauditus, Procloeon, Pseudocloeon, Serratella, Siphlonurus, Timpanoga, and Tricorythodes.
Marked or mottled wing
Among mayflies with marked or mottled fore wings are the following genera:
Callibaetis, Ephemera, Heptagenia, Leucrocuta, Litobrancha, Maccaffertium, Nixe, Rhithrogena, Siphloplecton, Stenacron, and Stenonema.
What size are the hind wings?
All adult mayflies have fore wings, and most adult mayflies also have hind wings. Whether the hind wings are obvious, minute, or absent is a key to identification.
Obvious hind wing
Among those mayflies with obvious hind wings are the following genera:
Ameletus, Anthopotamus, Attenella, Baetisca, Caudatella, Cinygma, Cinygmula, Drunella, Epeorus, Ephemera, Ephemerella, Ephoron, Heptagenia, Hexagenia, Ironodes, Isonychia, Leptophlebia, Leucrocuta, Litobrancha, Maccaffertium, Metretopus, Nixe, Paraleptophlebia, Rhithrogena, Serratella, Siphlonurus, Siphloplecton, Stenacron, Stenonema, and Timpanoga.
Minute hind wing
Among those mayflies with minute hind wings are the following genera:
Acentrella, Baetis, Callibaetis, Centroptilum, Diphetor, and Heterocloeon.
Absent hind wing
Among the mayflies with absent (no) hind wings are the following genera:
Asioplax, Brachycercus, Caenis, Plauditus, Procloeon, Pseudocloeon, and Tricorythodes.
Does it have 2 or 3 tails?
Winged mayflies have either two or three tails. Donít confuse this with the number of tails the nymph has, as it may be different. Some mayflies have three tails as a nymph, but only two in the winged stages.
2-tailed Families (Genera)
Baetidae (Acentrella, Baetis, Callibaetis, Centroptilum, Diphetor, Heterocloeon, Plauditus, Procloeon, Pseudocloeon)
Ephemeridae (Hexagenia, Litobrancha)
Heptageniidae (Cinygma, Cinygmula, Epeorus, Heptagenia, Ironodes, Leucrocuta, Maccaffertium, Nixe, Rhithrogena, Stenacron, Stenonema)
Metretopodidae (Metretopus, Siphloplecton)
Polymitarcyidae (Ephoron male)
3-tailed Families (Genera)
Caenidae (Brachycercus, Caenis)
Ephemerellidae (Attenella, Caudatella, Drunella, Ephemerella, Serratella, Timpanoga)
Leptohyphidae (Asioplax, Tricorythodes)
Leptophlebiidae (Leptophlebia, Paraleptophlebia)
Polymitarcyidae (Ephoron female)
First, letís "Observe"
Okay, now that weíve explored some physical attributes of the winged stages of mayflies, letís put your new observation skills to use. Weíll assume youíve just parked your vehicle, and are in the process of putting on your waders. At this very moment, a mayfly lands on the back of your hand. You gently lift your arm, and make some observations before the mayfly discovers its mistake, and flies off.
- It looks to be 9 mm. (~3/8Ē) in length, about hook size #14.
- The eyes dominate the head.
- The fore legs are extremely long.
- You arenít sure whether or not it has claspers.
- The fore wings are dark in color and marked with broad white veins.
- The hind wings are minute (luckily, youíre blessed with 20/10 eyesight).
- It has two tails.
Then, some "analysis"
Your new friend didnít have hyaline wings, so it must be a dun. Its eyes dominated the head, and it had extremely long fore legs, so it must be a male.
By consulting the number of tails lists (see above), we can eliminate all but the following genera, which have a length range including 9 mm.
Acentrella, Ameletus, Baetis, Callibaetis, Centroptilum, Cinygma, Cinygmula, Diphetor, Epeorus, Ephemerella, Ephoron (male), Heptagenia, Heterocloeon, Ironodes, Isonychia, Leucrocuta, Litobrancha, Maccaffertium, Metretopus, Nixe, Plauditus, Procloeon, Pseudocloeon, Rhithrogena, Siphlonurus, Siphloplecton, Stenacron, and Stenonema.
By consulting the body length range list, we are able to eliminate all from the above list except:
Ameletus, Baetis, Callibaetis, Cinygma, Cinygmula, Epeorus, Ephoron (male), Heptagenia, Maccaffertium, Nixe, Procloeon, Rhithrogena, Siphlonurus, Stenacron, and Stenonema.
By consulting the fore wings lists, we are able to eliminate all from the above list except:
Callibaetis, Heptagenia, Maccaffertium, Nixe, Rhithrogena, Stenacron, and Stenonema.
By consulting the hind wings lists, we are able to eliminate all from the above list except:
So, as a result of this observation and analysis, you astutely conclude that your new friend must have been a Callibaetis male dun, commonly called a Specklewing.
Too much work?
My goodness (you say), this analysis is way too much work. Do I really have to do all that just to identify a winged mayfly I donít already recognize? For the answer, see paragraph below.
Author and photographer
Roger Rohrbeck, an entomology enthusiast from the state of Washington, provided the text for this article. The above labor-intensive analysis is automatically performed by the Identification page on his website, http://www.flyfishingentomology.com/. One need only enter their observations, and click the Lookup button.
Jason Neuswanger generously authorized use of his insect photos for this article. In most cases, the photos have been cropped, annotated, or otherwise altered for illustration purposes. Jasonís vast gallery of aquatic insect photos can be viewed on his highly acclaimed website, http://www.troutnut.com/.
Common names for generaAcentrella (Minute Graywinged Brown), Ameletus (Brown Dun), Anthopotamus (Golden Drake), Asioplax (Tiny Whitewinged Olive Quill), Attenella (Golden Drake), Baetis (Bluewinged Olive), Baetisca (Specklewinged Dun), Caenis (Whitewinged Sulphur), Callibaetis (Specklewing), Caudatella (no common name), Centroptilum (Pale Watery Dun), Cinygma (Western Light Cahill), Cinygmula (Dark Red Quill), Diphetor (Iron Blue Quill), Drunella (Green Drake), Epeorus (Slate Brown Dun), Ephemera (Brown Drake), Ephemerella (Pale Morning Dun), Ephoron (White Drake), Heptagenia (Pale Evening Dun), Heterocloeon (Bluewinged Olive), Hexagenia (Hex), Ironodes (Slate Maroon Drake), Isonychia (Leadwing), Leptophlebia (Black Quill), Leucrocuta (Pale Evening Dun), Litobrancha (Dark Green Drake), Maccaffertium (Light Cahill), Metretopus (no common name), Nixe (Western Ginger Quill), Paraleptophlebia (Mahogany Dun), Plauditus (Bluewinged Olive), Procloeon (Bluewinged Olive), Pseudocloeon (Bluewinged Olive), Rhithrogena (Western March Brown), Serratella (Little Dark Hendrickson), Siphlonurus (Gray Drake), Siphloplecton (Speckled Olive), Stenacron (Cahill), Stenonema (Gray Fox), Timpanoga (Great Bluewinged Red Quill), Tricorythodes (Trico).
Friends team up for tailing Redfish and some blue lining for mountain trout
Late summer/ fall False Albacore have a feeding frenzy on the southern coast of North Carolina. Here is my view of one weekend mid-October 2013.
The hunt for the perfect Ostrich plume is over, thanks to OPST (Olympic Peninsula Skagit Tactics)
Check out this massive tube fly streamer using Hedron Falshabou
This is perhaps the best review I have ever received from a customer for any GCO product. After such an investment of both time and resources it is rewarding to see customers appreciating both the aesthetics and value of products such as the Ruby River Fiberglass Fly Rod which literally cost half of other comparable […]
I am very excited to announce that the first shipment of Ruby River fiberglass fly rods have arrived. Those that purchased rods should start receiving email shipping confirmations this evening. It may take a day or two for all order to ship so your patience is appreciated. If you were waiting for the shipment to […]
GEOBASS is a new epic adventure series following four expedition anglers on an around the world ultimate bass slam journey. GEOBASS episode 1 takes place in Colombia for Peacock Bass.
Dally’s Ozark Fly Fisher guide and Umpqua Fly Designer Chad Johnson shows a neat trick for a slender version in four must have colors.
I am happy to announce that I just received a large shipments of hooks in this week. Just in time to help finish up filling your fly boxes before opening day! Click Here for More Info
Matt Grobert and Tightlines Productions team up on a very detailed video on how to tie a red quill. There are some great detailed tips around the winging and the quill body.
A winter themed Hatches Theater with Headhunters fly shop, Scientific Angler, and steelhead
Learn from OPST guide Trevor Covich how to tie a large intruder for big steelhead and king salmon.
GreenCaddis has just launched a new double sided waterproof fly box called the “FlyPad”. Store over 750 flies in one box. Click Here for more Info
I forget where I first learned it, but during a Trico hatch, all you need to do to catch the trout that are snubbing your trico pattern is tie on an ant. Over the last 10 years, I‚Äôve found that ants are a trump card that no trout can refuse. This is especially true when […]
This is a great little, “do anything”, baitfish pattern. Color options are endless, limited only by the available colors of fox. This fly sinks very slowly, and can be worked just under the surface of the water, making it deadly for shallow water predators… Bass, Reds, Snook, baby tarpon… she will do it all.