Tuesday, August 2, 2011

Rich in Small Minnow Mayflies: A Look at Powells Creek

I've become interested in attempting to identify small minnow mayflies to the level of species, so I've been intently looking for nymphs.  I thought Powells Creek in Crozet might be a good place to find some -- and I was right.   In the photo above, we have a Baetis intercalaris small minnow mayfly swimming next to a lovely common stonefly, genus Neoperla.

I found both mature and immature B. intercalaris nymphs.  Here's a look at one of each.


immature (note that the center tail/cerci is broken off):

How have I arrived at the B. intercalaris identification?   I've been given the use of a key that is a "work in progress," not yet published, and therefore one I cannot fairly cite from it.  But I think I can note the key features of this particular species without using quotations.  First (and you might want to click on the photo of the mature sample to enlarge it to follow along), the "tracheation" (veins) in the gills is well developed.  Second, the color is one of the keys: mature nymphs are often gray /brown.  Third,
the abdominal gills have a distinct pattern, with what look like "parentheses" marks at the top of each segment, and there are often three pale dots at the back of the abdominal segment.  All of these features show up very well in the mature sample pictured above.  For a close-up of the abdominal pattern, here is a microscope view.

I found 4-5 nymphs of this species today in a short period of time.  But, I also found several Acentrella small minnow mayflies.  They looked like this.

Two tails, gills well tracheated with a gray pigmented area on the front part (distal) of each gill.  And, like all of the Acentrellas I've found this summer, these seem to have red/orange spots on various parts of the body.  Just look at how one of these looks in a microscope view.

Pretty spectacular!  Needless to say, I'm trying to figure out the species on this one.  I think it's Acentrella parvula -- but I'm trying to get confirmation of that from an expert.  More on that later.

As always, I found a variety of insects today.   A fair number of flatheaded mayflies, genus Maccaffertium and Epeorus vitreus.  There were also lot of common netspinners and a few fingernet caddisflies.  I also found quite a few adult Riffle Beetles (Elmidae): meant to take a few photos, but I simply forgot.

And I did find quite a few common stoneflies, the one Neoperla -- you might recall that this is the only stream in which I've found this particular species -- and quite a few young Acroneurias.  I need to start taking photos soon of the latter to document how they change as they grow.  At the moment, the yellow "M" pattern on the head is still indistinct.  Another shot of the Neoperla.

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