Saturday, December 8, 2012

Misled by expectations -- and surprised by a Limnephilid at the Doyles River

I'm now on a quest to find some of the "other" large winter stonefly that populates a lot of our streams -- Strophopteryx fasciata -- and I thought I might find some at the Doyles River this morning.  I didn't .  Well, at least I don't think that I did -- but more on that later on.  What I found were the "usual suspects": large winter stoneflies, Taeniopteryx burksi/maura; small winter stoneflies, genus Allocapnia; common stoneflies, Acroneuria abnormis; Perlodid stoneflies, Clioperla clio; flatheaded mayflies, genus Maccaffertium; and, as I did last week at Lickinghole Creek, I found a lot of Uenoid caddisfly larvae and a lot of Glossosomatids (Saddle-case makers).

I took some photos of the Uenoids -- a lot of photos of the "Uenoid" in the picture at the top of the page: I really liked the case.  Also, I noticed its pale colored legs: the legs on every other Uenoid I've seen so far this year have been dark brown.   The pale colored legs ought to be useful in working out the species ID.

Then I noticed a problem.  Look closely at the leading edge of the mesonotum of that "Uenoid" at the top of the page:

It's straight: it lacks emargination (no medial dips or dents).  The Uenoid emargination is very clear on the Uneoid I featured last week (for a close-up see the entry from 11/27):

My pretty "Uenoid" was not a Uenoid at all: it was a Limnephilid, a "Northern case-maker" caddisfly. The shape of that leading edge of the mesonotum is one of the key things we use to tell the two apart.  Actually, I should have known this was not a Uenoid by the very thing that drew my attention to it: the case.  Most Uenoid cases are fairly rectangular in shape, with 3-4 larger stones attached to each side.  Like this:

The case of this caddis was shaped like a cone:

And the light colored top of the case (pointed down in this photo) was a "hood" under which the larva could hide.

So, lesson learned.  I have to look closely at those little stone cases clinging to rocks in the winter.  Most are surely Uenoids, but there may be a Limnephilid or two among them.  I "expect" to see Limnephilids in the spring -- not the winter -- and they're large: most are Pycnopsyche in terms of the genus.  This is a small one (this larva was only 3-4 mm in length), and the genus ID is something for me to explore -- maybe tomorrow.

A few other photos.

1. A beautiful Perlodid stonefly, Clioperla clio.

2. One of the many large winter stoneflies I found in the leaves -- Taeniopteryx burksi/maura.

3. And then there was this --

When I took this photo, I thought it was just a tiny, small winter stonefly -- but clearly it's not, not with that short abdomen and rather broad head.  A small Perlodid stonefly?  Probably, but with this transparent body, it was impossible to pick out key anatomical features using my scope.

Was it a small Strophopteryx larve winter stonefly?  I don't think so, as much as I'm hoping to see one.  But, we ought to be seeing them soon.  I found this one last year on my birthday -- 12/15.


And another look at our Limnephilid with its head tucked into its case.

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