Sunday, October 8, 2017

And already a new one to add: Long-horned casemaker, Oecetis avara

While going through some vials I had tucked away in my lab, I just found this little larva (5mm).  I knew right away that it was a long-horned caddisfly -- the length of the hind legs tells us that much -- but the case is one that I don't remember seeing before.

Hmm... time to look at our key.  (p. 356)

141 Maxillary palpi extending far beyond labrum; mandibles long and blade-like with sharp apical tooth separated from remainder of teeth; cases of various types and materials....Oecetis

Oecetis for sure.

On to the species. (p. 370)

171  Dorsal hump of abdominal segment 1 with 4-6 rows of micro-hooks on each side....Oecetis (Pseudosetodes) avara

171' Dorsal hump of abdominal segment 1 without micro-hooks..... 172

Have a look.

If only every ID were so easy!  Oecetis avara.  Just for fun, I thought I'd look at Steve Beaty's description as well.  ("The Trichoptera of North Carolina," p. 92)

O. avara -- larvae 6.5-9 mm; dorsal hump with 4-6 rows of conspicuous micro-hooks on each side.  Case of sand, tapered, an curved in early instars.  Lotic.  Uncommon in the Mountains and Sandhills.

Well, the key feature -- the rows of micro-hooks -- is exactly the same, but our larva is quite a bit smaller, and our case is clearly not made of sand.  The size can be explained -- our larva is possibly immature.  As for the case...hmm... could it be that even though our larva is still pretty small, it no longer lives in the type of case used by "early instars"?  That's the only way that I can explain it.

I'm disappointed that I don't seem to have a live photo of this larva.  There are two possibilities for why that is so.  1) I had put this case into a vial before I saw what it was (trust me, I've done it!), and 2) it's a larva that's been in my possession from the time that I still worked with StreamWatch 7 long years ago.  In any event, the ID is certain, and it's certain that it was found in some local stream.  I've added it to our list of EPT species.

Additional notes:
Since writing this entry this morning, I've done some additional work, looking at Roger Rohrbeck's website, Pacific Northwest Caddisflies (  Two things.  1) On the case he comments: "case curved cones made of rock fragments and sand, or pieces of plant or twigs. (emphasis added by me.)  And at another location (,  he shows a case for Oecetis that is exactly like the one that I found in my vial.
Also,  let me quote from Wiggins (Larvae of the North American Caddisfly Genera, 1st edition (1977), p. 172): "Larval cases of Oecetis species are varied in both form and materials: small fragments of rock often combined with bark or leaves; and short lengths of stems and twigs placed transversely."  No longer see our case as a problem.

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