Monday, August 10, 2015

B. appalachia's Western cousin: B. occidentalis

The Brachentrid (humpless case-maker) that I commonly find at the Rapidan River is the one in the photo above -- Brachycentrus appalachia.  The case is important: 4-sided and tapered, made of neatly wound strips of vegetative matter.   The case-maker I found at Rock Creek last week makes a case that looks much the same, though somewhat distinct given the small pieces of leaves in the middle of the case.

Using our descriptions for caddisflies of the Pacific Northwest, this larva keys out at Brachycentrus occidentalis.  ( The shape of the case and the materials used in its construction were a pretty good indication of family and genus, and the deal was sealed when I saw the crease/divot in the pronotum.

Going by the looks of the case, I thought the species was americanus -- "cases typically 4-sided and made of plant pieces, but may incorporate sand other kinds of debris" -- but that didn't work out. B. americanus and B. occidentalis are distinguished by the number of setae on the venter of the first abdominal segment.

americanus -- "1st abdominal segment w/2 (not 4) long, dark hairs in the middle."

occidentalis -- "Underside of first abdominal segment w/4 long, dark hairs in the middle."

Our larva has four.

But there is more.  Two other features of B. occidentalis: 1) "only 1 mesonotal sa1 seta," and 2) "posterior opening of case circular."  Both are clear in these photos.

Brachycentrus occidentalis -- American Grannom.

I was so disappointed that I couldn't get any live photos.  Not much we can do with heavy, overcast skies.

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