Saturday, February 11, 2017

Isoperla season -- and other signs of spring at the Rapidan River

So I'm about to write up today's entry and thought I'd look again at Beaty's description of Isoperla similis -- quite sure that was the ID on the nymph in this photo -- when I discovered that the playing field has changed.  In the latest version of "The Plecoptera of North Carolina," (version 4.0, December, 2015) Isoperla similis is no longer described.  Rather, we are given details on two new groups: the Isoperla similis Group and the Isoperla pseudosimilis Group.  So I turned to  Beaty's detailed study of Isoperla nymphs in North Carolina -- "A morass of Isoperla nymphs (Plecoptera: Perlodidae) in North Carolina: a photographic guide to their identification," (2015) -- where I discovered that the former group consists of I. bellona, I. cherokee, and I. starki: the latter of I. pauli, I. pseudosimilis, I. reesi, and I. stewarti.  I'm behind the times.  Let me send this nymph to Beaty to see if he can help with the ID.  But it looks like the nymphs of all of these species are as yet undescribed.  It might be that the best we can do for now is sort out into which group this nymph is is to be placed.  Stay tuned.


But this was not the only Isoperla I discovered today.

There were a lot of the smaller more common species -- Isoperla montana (Kirchneri Group).

If you're a regular reader, you know that these nymphs are prolific in the Rapidan in the spring: they're all over the leafpacks, and they hatch in April as "Yellow Sallies."  (Gear up fly fishermen!)

And another sign of spring -- the spiny crawler Ephemerella invaria.

Lots of those nymphs as well today though they were still very small.  Along with E. dorothea, these hatch out as Pale Evening Duns in May and June.  Key to the ID of invaria are the tubercles on the terga.  Notes Beaty, "abdominal terga with short, sharp, paired submedian tubercles on segments 2-9, rarely on 2, sometimes barely discernible on segments 3-8, small on 4-7, rarely on 9."  ("The Ephemeroptera of North Carolina," p. 52)

Finally, I was surprised to find 3-4 hellgrammites today, all of them Nigronia (not the common hellgrammite that we see -- Corydalus).

The species?  Nigronia serricornis.  I've found it before in some of the small streams in Sugar Hollow, but it's the first time I've seen them up here.  For the keys to the ID, look back to my entries of 11/21/12 and 11/22/12.  Serricornis is distinguished from fasciatus by the location and size of the repiratory tubes at the end of tergite 8.

These are wide apart, parallel, and relatively short (though they look large in this microscope photo).

Great fun to be out today even though it was fairly dark and cloudy.  Hope to get out to Sugar Hollow on Monday.

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