Thursday, June 16, 2011

Looking for "Mr. Heptagenia" in the Moormans

We didn't find him, or her, though such distinctions hardly apply at this stage of mayfly development.

I went to the Moormans River this morning with a friend who lives on the stream -- a good entomologist and photographer in her own right.  And, yes, we were hoping to find some Heptagenia flatheaded mayflies.  No luck.  We did find this beautiful, pre-hatch, richly colored Maccaffertium flathead.  Quite a color display.  We also found a lot of these little guys --

flatheaded mayflies, genus Leucrocuta.  You may recall from my original entry on flatheaded mayflies (1/8/11) that the genera Leucrocuta and Heptagenia are, anatomically speaking, closely related, but Heptagenia nymphs have fibrilliform present on the gill on segment 7, Leucrocuta nymphs do not.
Leucrocuta nymphs also have this very big head, and you can spot them on rocks because 1) they're very little, and 2) they are very, very fast, difficult to pick up!

Our day was shortened by clouds and sprinkles, making photography pretty darn tough.  But I did manage to find a few, small Perlesta common stoneflies, one genus Acroneuria common stonefly, some common netspinners, a Polycentropodid (Trumpetnet spinner) caddisfly larva, and one lonely small minnow mafly: it turned out to be genus Acentrella.


Describing Perlodid stoneflies:

Since my report today was a brief one, I thought I might do something that some of you are sure to enjoy (I hope all of you do).   The question is: when a specialist looks at a nymph -- a stonefly nymph -- what are some of the things that he or she looks at in terms of colors and patterns that would be relevant in determing species?    Here's our nymph: a Perlodid stonefly, genus Isoperla.

Yesterday, I sent this photo to Steven Beaty (North Carolina, Division of Water Quality) and posed the following question: "There is a prominent, white "X" behind the posterior ocelli (i.e. at the back of the head) -- does that figure into species ID."  Let me walk you through his response, using photos to point out the features that he discusses.  (As always, for best results click on the photo to enlarge it.)

"The white X is composed anteriorly of the ecdysial suture which is not typically factored into color patterns.  The posterior portion appears to be bifurcate.  Of more interest to me is the "ocellar spot" which is the large pale area within the ocellar triangle."   These photos should clarify the features he's talking about.

And for the "ocellar spot"...

He continues, "Also of note is the pale area anterior to the median ocellus which has the form of a rough "M" but with an obscure anteromedian extension (this whole pattern also appears as a transverse dark bar across the median ocellus with dark extensions back through the lateral occelli to the lateral areas of the occiput [back line of the head] -- take your pick)."     Illustration:


And he continues, "Also the longitudinal abdominal striping (including the somewhat interrupted medial stripe) is of note."  Illustration:

Unfortunately, after reviewing that information, he concluded "We have found very similar larvae in VA along the Blue Ridge Parkway and have labeled them as Isoperla n. sp 91... I hate to disappoint you, but I cannot make a reliable species determination on this specimen."  (This was quoted with permission.)

As I told him, I'm not disappointed at all.  I think it's pretty exciting that there are still species out there that have not yet been labeled and named!

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