Friday, December 30, 2016

The other small winter stonefly -- Paracapnia angulata

Genus Allocapnia small winter stoneflies are common and plentiful in all of the streams that I visit: this genus isn't.  This is the third or fourth time that I've seen it, and I've only seen it in two small streams in Sugar Hollow.  These.

This is genus Paracapnia, species angulata.  Too uncommon to have a tolerance value assigned.

The keys to identification are: 1) the entire body which is very setose - hairy- as in the photo above, 2) the shape of the wing pads, and 3) the complex pattern on the head.

On the wing pads -- the posterior ends of both pairs are rounded (the rear pads of Allocapnia are truncate).  Paracapnia wing pads look like this.

But let's look at Beaty's description ("The Plecoptera of North Carolina," p. 8) before we go any further.

Genus Diagnosis: Nymphs 6-8 mm.  Head with a purplish-brown reticulate color pattern; pronotum fringed with many long bristle-like hairs, longest at corners; body setose, with numerous long setae.

angulata -- Head pattern of purplish pigmentation outlining entire frontoclypeus, with a short bar from median ocellus to the anterior edge of the frontoclypeus; occiput usually with purplish bars along,  but removed from epicranial stem to postocciptal margin.

The purplish brown pattern is clear from our live shots.

But for the detailed features of the head and pronotum it's best to use a microscope photo.

We should also note that if we find a Paracapnia nymph in our parts, we've found P. angulata since Beaty notes that "Paracapnia angulata is the only known species of Paracapnia in the southeastern United States." (p. 9)


Actually, the reason I went out this morning -- it was cold and blustery -- was to look around for more Uenoids (little northern casemakers).  And I found them of course since they're plentiful at this time of year.  This morning it was  Neophylax consimilis.

In terms of the "longitudinal gradient" (see the entry posted on 12/15),  this one occurs -- in my experience at least -- between N. aniqua and N. mitchelli (further upstream) -- and N. fuscus and N. oligius further down.  (N. mitchelli has a TV of 0.0; N. consimilis is 0.3; N. oligius is 2.4.)

N. consimilis does not have a tubercle on the head, but it does have clavate gills on the first abdominal segment.  The setae count at sa3 (ventral) is 2-3.  Here you go.

On occasion consimilis has a frontoclypeal pale spot  -- like this

-- but in other cases the head is totally brown.  Such was the case on the one that I found this morning.


Good fun, even in freezing weather.

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