Tuesday, January 18, 2011

The "Northern Case Maker" (family: Limnephilidae)



When Glenn Wiggins published his masterful Larvae of the North American Caddisfly Genera (Trichoptera) in 1977 (University of Toronto Press), the family Limnephilidae (Northern Case Makers) was the largest caddisfly family in North America with 52 genera.   It still is the largest caddisfly family, but now contains 39 genera; 13 previous Limnephilid genera are now lumped together in various ways to form three new caddisfly families -- Goeridae, Rossianidae, and Uenoidae (see the Second Edition of Wiggins, published in 1996).

With this many genera to look for, you might think we'd run into this caddis a lot in our samples: just the reverse is true.  In the two years that I worked with StreamWatch, I doubt that I saw more than 5-6 Northern Case Maker caddis.  (A caveat here -- the StreamWatch database records a good number of Limnephilid caddis found in samples over the years.  But in this case the database should not be relied upon.  That's because until two years ago Uenoid caddis larvae were mistakenly labelled "Limnephilid."
That is no longer done.  We actually have a lot of Uenoid case makers in our streams during the winters.)  StreamWatch probably sees so few Limnephilids because this is a caddis that hatches in late summer and fall.  So the larvae in their cases will be in our streams in late spring and summer -- at a time when StreamWatch does very few samples -- or samples streams where they are not typically found.

When it's not in its case, the Northern Case Maker larva has three defining characteristics, all of them pictured below.  They are: 1) it has three fleshy humps on abdominal segment 1, two on the sides (lateral) and one on the back (dorsal); 2) it has a "prosternal horn," something that looks like a needle sticking out from its chest up between the front legs (look closely); and 3) in contrast to the Uenoid caddis, the  front edge (anterior) of the mesonotum runs straight across -- there is no "W" shaped notch in the middle.   All of these traits can be seen in these photos.












Northern Case Maker cases tend to be genus specific, which helps, to a degree, with genus identification.  Still, a lot of cases are close enough in appearance that exact identification depends on microscope work with the larva.  Now, I have reached the limit of my amateur talents.  I find genus identification with Limnephilids to be a very difficult thing.  A lot depends on the size, shape, and location of sclerites on or around the lateral humps on the larva: bring on the pros!

This being said, I will still propose genus identification for three of the Limnephilids in my collection.
The following larva -- I am quite certain -- is genus Pycnopsyche.


This is the prettiest caddis case that I've ever seen, and it's characteristic of Pycnopsyche larvae in their early instars.  The case is slightly over 1" in length, and it's made out of neatly cut sections of leaves.  The leaves come together to form three corners, so the case resembles a pup tent with the sides sagging in.  This larva was found at the Albemarle County reference site used by StreamWatch.


This is the head and upper end of the pebble case of genus Pseudostenophylax.  The case is about 1" in length.  This beautiful larva and case were found in late May of last year at Byrom park in a high elevation, tiny, clear, cold water stream.   (The entire case appears in a photo below.)

 Genus Ironoquia.  This case is 1/4 - 1/2" in in length, so it's a much smaller larva than the two pictured above.   It's a Limnephilid that's often found in "temporary" streams, streams that run dry in the summer.
It has unique, very frilly clusters of gills that help to define it: but they're hard to see in this photo.


On this one I'm stuck, and if anyone out there can help please speak up.   The case make of twigs is ugly (it's about 1 1/2" long), and the larva itself it not much to look at: still, this is the most common Limnephilid I see.  There are a lot of these cases in two streams close to C'ville each summer: the Whippoorwill branch of the Mechums River, and the little stream that runs along Reservoir Road coming down from the reservoir at Ragged Mountain.  What's the genus?

One last photo.  I've assembled a number of cases from my collection to show some of the diversity in the Limnephilid cases we find.  With 39 genera, the reader can be sure that this is a very small sample.

2 comments:

  1. The stick case you were wondering about is also likely Pycnopsyche sp. They can use leaf disks, as pictured above, or sticks and bark (usually with the two longer framing sticks) prior to their final instar, during which they convert the case to stone. This allows for more efficient drift during most of larval development should environmental conditions change. I can't see the organism enough to give you a 100% definitive ID, but the case is very typical of the genus. I'll give you a 99% that it's a species of Pycnopsyche.

    Matt Lajoie
    SFS - Certified Taxonomist

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  2. Just another comment: if it helps, Neophylax sp. is the only eastern genus of Uenoidae. Also, Neophylax was historically part of Lymnephilidae.

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