Tuesday, March 11, 2014

Another look: that free-living caddisfly larva was probably R. glaberrima

Back we go to this free-living caddisfly larva from Entry Run.  On Sunday (3/9) I suggested that it might be Rhyacophila shenandoahensis.  But Steven Beaty, based on the photos I sent him, said that R. glaberrima was a more likely ID.

On R. glaberrima, Beaty has only a little to say: "larva 12/ ?? mm; both apicolateral spur and basoventral hook absent; length of segment 2 of maxillary palpi subequal to segment 1. Relatively rare... Collected during spring and summer in the Mountains and Piedmont." ("The Trichoptera of North Carolina," p. 61)

All of that's true of our larva, but can we find a more detailed description?  Fortunately, one is provided by Flint ("Larvae of the caddis fly genus Rhyacophila in eastern North America," p. 471-473.)

Description: Length, 12 mm.  Head, brownish yellow, slightly darker centrally; muscle scars paler, inconspicuous. ... Thorax, pronotum brownish yellow, darker centrally; muscle scars dark; fore femora very broad.  Abdomen, anal proleg with neither basal hook nor apical spur ... claw with 2 ventral teeth. (p. 472)

While the fore femora does not show up very well in my photos, it is indeed very broad.  And the rest of Flint's description is right on the money.  Note the colors of the head and pronotum.

And we've already seen the lack of the basoventral hook and the presence of two ventral teeth.  The apicolateral spurs would -- if they were present -- stick out to the sides of the anal claws.

(Note: There are also two ventral teeth on Rhyacophilids -- like R. shenandoahensis -- in the R. banksi complex of the R. invaria group.  But, on those larvae, the second tooth is very small; not so here.)

There is one other trait of R. glaberrima that is clear in our photos.  There is an oblique suture on the baso-lateral sclerite, a black line.  This feature is illustrated by Flint on p. 471, and it's very clear in this photo.

So, the evidence suggests a correction in our ID.  That Rhyacophilid was R. glaberrima, not R. shenandoahensis.

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