Tuesday, December 20, 2011
Continuing the March into Winter: The Uenoid Case-maker Caddis
I've been remiss in spending all of my time sorting through leaf packs: I've been ignoring the rocks. But it's the time of year when the Glossossomatids (Saddle-case-makers) and Uenoids (no common name) attach their cases to rocks, so I turned some rocks over this morning (Buck Mt. Creek). On one of the large rocks I looked at there were already three Uenoid cases (I also saw a Glossossomatid case, but it was empty).
Uenoid cases are made out of small pebbles and sand, and you'll find them in different shapes and sizes (though there are normally three larger pebbles on each side of the case). Of the three cases that I picked up, the one in the photo above had a long, tapered case; the second had a short, tubular case; and the third was shaped like a cone.
Tubular case (with a Large Winter stonefly swimming by).
Cone-shaped case: dorsal view.
Cone-shaped case: ventral view, in which you can see the larva.
Case composition -- in terms of the colors -- will vary, of course, from stream to stream, depending on the raw materials the larvae can use. Uenoid cases in Buck Mt. Creek tend to be blueish gray, not all that attractive, but remember this beauty that I found in Elk Run in the winter last season.
The Uenoid is in our streams in the winter: it's the most common case-maker we see this time of year.
Uenoids tend to pupate and hatch in early spring (though they may be around longer than that in more remote, cold water streams.) In the winter, if you see these cases attached to the tops, sides, and bottoms of rocks, you can be pretty sure that you've found some Uenoids. True, some Limnephilids (Northern case-makers) and some Leptocerid genera (e.g. Oecetis) make similar cases. But Limnephilids show up in late spring/early summer: The Leptocerid (Long-horned case-maker) is a mid-summer larva.
Identification? The shape of the case provides the first clue, especially when you can see the three large pebbles on the sides of the case, as in the photo directly above. But the key anatomical features are three. 1) There are dorsal and lateral "humps" (so a total of three). They're pretty clear in this photo.
2) The leading edge of the mesonotum is "notched" -- to my eye it looks like a "W". (Click on the photo to enlarge it.)
And 3) as Glenn Wiggins pointed out a long time ago (Larvae of the North American Caddisfly Genera (Trichoptera, 1977, p.262), when the Uenoid was still classified as a genus of Limnephilid (Neophylax), "The ventral apotome is distinctly T-shaped." For this we have to look at the underside of the head.
Not a lot else to report from this morning's trip to Buck Mt. Creek. Essentially, I saw what I expected to see: Large Winter stoneflies (both Taeniopteryx and Strophopteryx), Small winter stoneflies, and Perlodid stoneflies -- the genera Helopicus and Clioperla. I left the Clioperlas alone: as soon as you put them into your tray they start to chewing on everything else!
Large Winter: Taeniopteryx burksi
Large Winter: Strophopteryx fasciata
Perlodid stonefly: Helopicus subvarians