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The Specimen

Maccaffertium vicarium (March Brown) Mayfly NymphMaccaffertium vicarium (March Brown) Mayfly Nymph View 3 PicturesI keyed this nymph to Stenonema fuscom, which is now synonymized with Maccaffertium vicarium. However, the size, markings, and time of year make me very skeptical of this identification.
Collected June 9, 2005 from the Bois Brule River in Wisconsin
Added to Troutnut.com by on May 26, 2006

The Discussion

EntomanMarch 26th, 2012, 4:19 pm
Site Editor
Northern CA & ID

Posts: 2604
You were right about the markings, Jason. This is one of the paler Summer Cahill species, probably mexicanum. The inverted "U" tergal markings are very distinctive (moved to mexicanum).
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
GONZOJuly 1st, 2012, 11:22 am
Site Editor
"Bear Swamp," PA

Posts: 1681
Kurt, I believe that the original placement of this specimen was correct. Further, all of the nymphs currently in the M. mexicanum section look like M. vicarium to me. In the text for that section, Jason says this:
It may be more likely that they belong to a Midwestern color variety of Maccaffertium vicarium which produces good hatches on the river where they were collected.

The "inverted 'U' tergal markings" that you noticed are not "very distinctive" for mexicanum (integrum). That species (or perhaps species group) typically has a large pale V-shaped mark on tergal segments 7,8, and 9. The sterna are "usually entirely pale except for sternum 9, which often has lateral dark bands that may coalesce anteriorly to form a dark inverted U-shaped mark" (Lewis 1974). Lateral projections on M. mexicanum integrum are on segments 7-9.

In my view, the ventral markings (and lateral projections) on all of these nymphs are fairly typical of M. vicarium. The dorsal appearance is darker and more mottled than might be expected on mature vicarium nymphs, but that pattern is quite common on immature nymphs.
EntomanJuly 1st, 2012, 11:49 am
Site Editor
Northern CA & ID

Posts: 2604
Ah, very good. Immatures ain't easy!:) I'll move them.

I don't remember off the top of my head who's paper(s) I went by (other than they weren't Lewis '74), but I remember it was pretty convincing to me at the time. Again though, they were descriptions of mature nymphs. Thanks for the assistance as we do want to get these as right as possible. This group is tough! If I remember correctly, Bednarik '79 (one I probably used) mentions his keys and descriptions were only dependable for New England and that revisions of descriptions may be necessary for many of the old Stenonema species in other regions.

BTW -

Lateral projections on M. mexicanum integrum are on segments 7-9.

Isn't that where they are with this specimen?
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
GONZOJuly 1st, 2012, 11:55 am
Site Editor
"Bear Swamp," PA

Posts: 1681
Bednarik and McCafferty '79 describe the traits of M. mexicanum nymphs (as S. integrum) in essentially the same ways as Lewis. Perhaps you were misremembering something. (Lewis focused on species in the Ohio River valley, not New England.)

Lateral projections on M. mexicanum integrum are on segments 7-9.
Isn't that where they are with this specimen?
Not in my view. See Bednarik and McCafferty for a discussion of what constitutes a "lateral projection" or "spine" and what does not. However you choose to view that trait in these specimens, you would
have to dismiss the ventral (and dorsal) markings to place them as mexicanum.
EntomanJuly 1st, 2012, 11:58 am
Site Editor
Northern CA & ID

Posts: 2604
Perhaps you were misremembering something.

Perhaps. I'm going to see the Giants this morning but when I get back I'll look it up to see If I can find it. As to the projections, I see in the ventral that the gills were hiding the reduced ones on the upper segs in the dorsal shot. Is that what you are referring to? Gotta go!
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
GONZOJuly 1st, 2012, 1:14 pm
Site Editor
"Bear Swamp," PA

Posts: 1681
Is that what you are referring to?

Yes, IMO, projections are on 3-9 (as in vicarium).
GutcutterJuly 1st, 2012, 2:23 pm
Pennsylvania

Posts: 470
I'm going to see the Giants this morning... Gotta go!

Will you please make them beat the Reds, just once, for me...
All men who fish may in turn be divided into two parts: those who fish for trout and those who don't. Trout fishermen are a race apart: they are a dedicated crew- indolent, improvident, and quietly mad.

-Robert Traver, Trout Madness
EntomanJuly 2nd, 2012, 11:24 am
Site Editor
Northern CA & ID

Posts: 2604
Gonzo -

Perhaps you were misremembering something.

You're right. My memory was confusing Bednarik '79 with Burian '08 yesterday. That wouldn't be so bad if they weren't dealing with different genera.:)

I don't remember my thinking at the time I was working on this, but it is clear that the heavily marked terga convinced me to go a different direction.

However you choose to view that trait in these specimens, you would
have to dismiss the ventral (and dorsal) markings to place them as mexicanum.

Agreed. I wasn't disputing your opinion, just asking for clarification on the lateral projection character. Thanks for the assistance. I will move the specimens to their proper listing.

Tony -

They got 'em! Gotta love those 9th inning walk-offs. After the great run of the last couple of weeks, the Giants' bats went a little cold for this series and they (Reds) uncharacteristically lit up Cain the other day. The Giants were lucky to get out with a split series. My second son is a season ticket holder and took me for a delayed Father's Day gift. Great time.
"It's not that I find fishing so important, it's just that I find all other endeavors of Man equally unimportant... And not nearly as much fun!" Robert Traver, Anatomy of a Fisherman
GutcutterJuly 2nd, 2012, 7:56 pm
Pennsylvania

Posts: 470

Tony -
They got 'em! Gotta love those 9th inning walk-offs...
...Great time.

Thanks for taking care of it for me, Kurt.
Do you know any Dodger fans that can help a guy out?
And Paul, get out there and root for the Rockies, just to keep the Cardinals from nippin' at our heels?
Come on, it's almost as bad as being a Flyer fan. 1979...
Well, at least it's not 1975. :)
All men who fish may in turn be divided into two parts: those who fish for trout and those who don't. Trout fishermen are a race apart: they are a dedicated crew- indolent, improvident, and quietly mad.

-Robert Traver, Trout Madness

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