3-tailed mayfly (Subimago) - Ephemerella

Ephemerellidae

A female subimago (dun), probably Ephemerella. It looks very much like the species known to fly fishers as the "pale morning duns" or PMDs: E. excrucians or E. dorothea infrequens (formerly E. inermis and E. infrequens).

… Lloyd Gonzales, 28 August, 2008 - 12:24am

Subimago/imago tails

Borealfalcon-

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I am confused now. When I took the subimago and waited for it to turn into an imago I noticed it had gaiend an extra tail filament.

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I have only seen one 3 tailed one, Are they rare?

The likely reason for the imago having 3 tails, whereas its subimago appeared to have only 2 tails, is that one of the subimago’s tails got broken off, probably during transition from nymph to subimago. This is quite common, as they are extremely fragile.

As to whether it is rare for mayfly subimago/imago life stages to have 3 tails, some families (like Ephemerellidae) have genera possessing 3-tailed subimagos/imagos. Some families (like Baetidae) have genera possessing 2-tailed subimagos/imagos. One family (Ephemeridae) has one genus (Hexagenia) possessing 2-tailed subimagos/imagos and multiple genera (Ephemera and Litobrancha) possessing 3-tailed subimagos/imagos. One family (Polymitarchidae) has a genus (Ephoron) whose male members possess 2-tailed subimagos/imagos and female members possess 3-tailed subimagos/imagos.

Hope this lessens your confusion as opposed to contributing to it.

… Roger Rohrbeck, 27 August, 2008 - 4:59pm

I see...

But I have seen hundreds in Alberta and only one 3-tailed, just wondered if it was unusual to see. If i recall the 3-tailed are called spinners?

… Borealfalcon, 27 August, 2008 - 5:40pm

Streams vs. lakes and duns vs. spinners

Borealfalcon-

What you've seen is what you've seen, but trust me on this, winged mayflies with 3 tails are common on Alberta streams. However, the vast majority of winged mayflies on Alberta lakes would be of family Baetidae and genus Callibaetis, and they would only have 2 tails.

Dun is the common name for a mayfly subimago, and spinner is the common name for a mayfly imago. Hope this helps.

… Roger Rohrbeck, 27 August, 2008 - 8:01pm

Thanks for your help on this..

The only water source around I know is the North Saskatchewan River. (is that how you spell it?)

It isn't important if its rare or not, I have been looking for a 3-tail for a long time.

(Spinners came from a book, they called the normal 2-tailed Small minnow mayflies and 3-tailed ones Spinners.)

Thanks for your help anyway, there isn't anywere I can check all this currently, maybe I should start on a book maybe.

… Borealfalcon, 27 August, 2008 - 9:52pm