Thursday, February 17, 2011

Flatheaded Mayflies: Changes and Additions

Judging by the feedback I'm getting from "Blogspot," the most popular entry with readers -- at the moment -- is the one on "Flatheaded Mayflies" (1/8/11).  So I thought I might add some comments on this mayfly that a lot of us are so used to seeing.

First of all, I've decided it's time for me to switch from "Stenonema" to "Maccaffertium" for our most prevalent flatheaded genus (in this part of the country at least).  If "" has done it, who am I to keep holding out?  Of course, I hate to think of how many fly fishing books are now out of date -- but alas!  (By the way, the genus name "Stenonema" has been reserved for a single species of flathead -- Stenonema femoratum.)

Therefore, I think the flathead pictured above -- which I found last week at Lickinghole creek --  is Maccaffertium vicarium -- what fishermen call the "March Brown" (even though it normally hatches in April!).   I can't swear to this "species level" identification.  And it's based on evidence that is not the best kind to use -- other people's photos from "" and "".  One of the key features, however, seems to be the "red bands" on the femora.  Here's a better look.  They're quite unique.

If someone knows that I'm wrong with this identification, please let me know by posting a comment.

The second note I want to add on flatheaded mayflies has to do with a genus that I left out of my earlier entry: the genus Nixe.  I left it out because I've never seen it in our watershed streams.  Still, Peckarsky, (Freshwater Macroinvertebrates of Northeastern North America, p. 31) do include it in their key -- so readers in other parts of the state, or elsewhere on the East coast, might encounter this genus.

Nixe, anatomically speaking, is closely related to the genera Heptagenia and Leucrocuta (the reader might want to look again at the entry of 1/8/11).  You may recall that the main difference between those two genera is that Heptagenia nymphs have fibrilliform behind the gill on abdominal segment 7; Leucrocuta nymphs do not.  Some photos.  First, let's look at the nymphs.



Now, let's look at the gills on abdominal segment 7.  The fibrilliform behind the Heptagenia gill is quite clear: that it's missing from the Leucrocuta nymph might be difficult for us to see: you may have to take my word for it!



Best I can do.  Now, where does the genus Nixe fit into this mix?  Nixe, like Leucrocuta, has no fibrilliform behind the gill on segment 7.  But, there are no fine hairs ("intrasegmental setae") on the caudal filaments (tails) of the nymph Leucrocuta; there are on the nymph Nixe.  Some photos, and let me start with a photo of a Nixe nymph in its entirety.  (The Nixe specimens in my collection were brought back from Montana.)

And here is a look at the gills on segment 7.

Now let's look at the tails (caudal filaments).



The hairs are short and fine -- but they're there.  So, you might run into this genus: please let me know if you do.


A final note about "websites" for macroinvertebrate photos".  The three I rely on the most for excellent photos (both of nymphs/larvae, and the adults) are:

3.     Tom Murray's photos are stunning!

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