Found! Odontoceridae -- the Strong Case-maker Caddis

One of my friends who lives in Sugar Hollow told me last week that she had found Odontocerids in the North Fork of the Moormans.  She told me exactly where to go -- I went there this morning-- and sure enough, there they were!  They were easy to spot since they were crawling around on top of the rocks, and their light-colored cases stood out in contrast to the Greenstone composition of the rocks underneath.

The "Strong Case-maker" is not easy to find, and that for two reasons.  1) This is a critter that is extremely intolerant of stream impairment: Psilotreta libada -- probably the species we see -- has a TV of 0.5 (North Carolina Division of Water Quality).  So, if you want to look for this caddis in our part of Virginia, you'd better head to the clean, cold, rocky streams at the base of the Blue Ridge, streams like the North Fork of the Moormans and the Rapidan River.  2) The other thing that makes this one a problem to find is the fact that it apparently spends most of the year in the gravel of the substrate.  Two exceptions: for some reason, they tend to crawl around on the rocks in the fall (September and October), and their cases can be found on the rocks in the late spring right before they hatch out (in May and June).  (For a full discussion of Odontocerids and their importance for fly fishermen -- the "Dark Blue Sedge", be sure to read Thomas Ames Jr.'s Caddisflies: A Guide to Eastern Species for Anglers and Other Naturalists, pp. 209-214).)

I can't say for sure that the larvae I found were Psilotreta libada -- that's just a hunch: I do know for sure that the genus is Psilotreta.  This is easy for us to determine.  On the Psilotreta larva, the "anterolateral margins of [the] pronotum [are] produced into long, sharp, forward-projecting points" (Peckarsky, Freshwater Macroinvertebrates, p. 118).  And here is what those points look like in a microscope view.

The "Strong case-maker," by the way, clearly deserves its name.  I've tried to break these cases using my tweezers: can't be done.  Ames explains this in the following way: "The larvae spend at least a part of their lives out of harm's way, burrowed into moss or in the sand, silt, and gravel beneath the cobble of cool streams.  As protection against the grinding motions of the substrate they apply extra silk as mortar between the sand and tiny pebbles that make up their cases.  The result is the curved, crush-resistant, cylindrical case that gives the family its nickname." (Caddisflies, p. 209)

Cases are sometimes straight and tube-like, but they're often tapered.   In the photos I took this morning, I've got one of each.  Here are some of the photos for you to enjoy.  The orange and black striped head, by the way, can give this one away if you see it crawling around in your tray.