Fly Fishing for Trout Home
User Password
or register.
Scientific name search:

> > stages before emergence

This topic is about the Insect Order Ephemeroptera

Mayflies may be the most important insects for trout anglers to understand. They are an ancient order of insects, famous outside the fly-fishing world for their fragile beauty and short adult lifespan, often a single day to mate and die. The mayfly's poignant drama attracts poets and anglers alike, but anglers make the most of it.

Mayflies live more than 99% of their lives as nymphs on the river or lake bottom, filling many crucial roles in freshwater ecosystems as they feed and grow. They eventually emerge from the water as winged sub-adults called "subimagos" by scientists and "duns" by anglers. Duns evolved to be good at escaping the water, with a hydrophobic surface and hardy build, but they are clumsy fliers. Within a day or two they molt one last time into "imagos" or "spinners," the mature adults, a transformation captured in this photo series of a dun molting into a spinner. They have longer legs and tails, and sleeker, more lightweight bodies, giving them the airborne speed, agility, and long grasp they need for their midair mating rituals. They are usually darker than the duns and have shinier, more transparent wings. They die within minutes or hours after mating. Read more...

There are 823 more specimens...

The Discussion

TroutnaboutSeptember 16th, 2006, 7:52 pm
Posts: 20Jason: When do claspers appear on male species?
TroutnutSeptember 16th, 2006, 8:15 pm
Bellevue, WA

Posts: 2737
Good question. They're present in pretty much their final form in the duns, and of course the spinners have them.

I've seen them starting to show on some mature nymphs, I think. The pictures should be somewhere on this site, but I don't remember which specimens. They aren't generally visible on most nymphs, so I'm guessing they start to appear in the last few nymphal instars and don't become really prominent until the dun stage.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
TroutnaboutSeptember 16th, 2006, 8:46 pm
Posts: 20Thanks Jason. Are there any gender distinguishing characteristcs during the nymphal stage?
GONZOSeptember 17th, 2006, 8:24 am
Site Editor
"Bear Swamp," PA

Posts: 1681
Jason is right that the claspers can be seen on mature nymphs. In addition, slight differences in overall size and the size of the eyes can be gender clues with many mayfly nymphs (some color and marking differences can also be noted, but you must be very familiar with the species). So, within a mature population of an Ephemerella species, the smaller, sometimes darker, large-eyed nymphs with claspers are males.

One practical application of this information with regard to Ephemerellidae is that the males typically mature first (dark wingcases). In the early part of a hatching period, males will predominate. With species like the Hendriksons, which often display significant gender differences in size and color among adults, this can be an important trait when fishing over fussy, hard-fished trout.
TroutnutSeptember 17th, 2006, 12:23 pm
Bellevue, WA

Posts: 2737
Thanks Gonzo... that reminds me, somewhere one of my nymph pictures shows those developing eyes in a male nymph pretty well. Again I'm not sure which one, unfortunately.

Figuring out nymph gender would be a great topic for a feature article on this site. I'll have to ask some entomologists about more failsafe ways to do it (if there are any) for earlier nymphs. I bet a dissection knife and microscope are required for many of them.

This brings to mind one thing I've always wondered about. Many of the Ephemerella nymphs come in several different color schemes in each river. This is especially true in E. subvaria, the Hendricksons. Since the male and female adults are usually different colors, I wonder if the same is true in the nymphs. Are some of the colors only for males, and others only for females? This question probably isn't too hard to answer...
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
TroutnaboutSeptember 17th, 2006, 5:40 pm
Posts: 20Thanks Guys! I'm taking an entemology study later this week. I'll tryout some of your suggestions when looking at nymphs. Maybe I'll get some pics too.
GONZOSeptember 17th, 2006, 9:36 pm
Site Editor
"Bear Swamp," PA

Posts: 1681
That's a good question, Jason. In the Yellow Breeches, Sulphur nymphs (E. invaria) have four color variations--nearly black, brown, olive, and amber. All four colors can often be found occupying the same rock. My guess is that these variations have evolved so that a certain percentage of the population will be more or less camouflaged against various backgrounds (which seems to fit with invaria's adaptability to diverse habitats). I don't think these colors are gender-specific, however. If they were, one would expect that all of the black or brown ones would be males, and all of the olive and amber would be female. This does not seem to be the case. I suspect it is more likely that you might detect gender differences within a color group (dark olive vs. light olive), but I'm not sure.

What I can say with regard to Hendriksons, however, is that you can sometimes see gender clues in the belly color of mature nymphs. On the Brodheads, female Hendrikson duns often have pink bellies. I have found fully mature female nymphs (some of which were quite dark in dorsal coloration) that displayed pink bellies.

Other families offer other gender clues as nymphs:

In the Polymitarcyidae, male White Fly nymphs (Ephoron spp.) have a shorter center tail (which they lose). Females, which mate as duns, have three short tails (which they retain).

Among the Ephemeridae, male Yellow Drake nymphs (Ephemera varia), in addition to being smaller and having larger eyes, have a slightly different pattern of dorsal (tergite) markings than females.

Because both groups of nymphs (White Flies and Yellow Drakes) are pale and rather translucent, the color of the developing eggs will impart a yellowish cast to the abdomen of fully mature female nymphs.

Of course, all of these distinctions are for mature nymphs. As for detecting gender differences in earlier instars, I haven't a clue!
TroutnutSeptember 18th, 2006, 10:53 am
Bellevue, WA

Posts: 2737
Thanks! You've listed several interesting characteristics I didn't know yet.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

Quick Reply

You have to be logged in to post on the forum. It's this easy:
Username:          Email:

Password:    Confirm Password:

I am at least 13 years old and agree to the rules.

Related Discussions

TitleRepliesLast Reply
Re: Small BWO
In General Discussion by Lastchance
2Aug 30, 2010
by Lastchance
Re: stupid question
In Male Baetis bicaudatus Mayfly Nymph by Brian314
2Feb 27, 2022
by Brian314
Re: Californicas v. Hex
In the Identify This! Board by Byhaugh
1Feb 19, 2014
by Entoman
Re: Nixe species (kennedyi?)
(2 more)

In the Identify This! Board by Millcreek
4Sep 27, 2014
by Millcreek
Re: Baetid nymph color
In Male Baetidae Mayfly Nymph by Martinlf
1Dec 26, 2006
Re: Male or female?
In General Discussion by Shawnny3
8Apr 9, 2009
Re: Heads
In the Photography Board by Wbranch
6Mar 22, 2009
by DOS
Re: Northern Ontario Canada, Stonefly question.
In General Discussion by Snowsquatch
4Sep 4, 2012
by Entoman
Re: Baetis Nymph, Is this it?
In General Discussion by Lastchance
1Mar 10, 2013
by Martinlf
Re: Arctopsyche Grandis
In the Caddisfly Genus Arctopsyche by Epeorus
6Jul 6, 2014
by Entoman
Most Recent Posts
large free living caddis rhyacophila?
In the Identify This! Board by Kjfeen