Friday, January 21, 2011

The Case-maker Lepidostomatid (family: Lepidostomatidae)

This may be my favorite case-making caddis: probably for a number of reasons.  To begin with, they're normally found in the kinds of streams to which I like to go: small, upland, cold water streams -- the kinds of streams in which Trout can often be found!  But I also love their "teddy-bear" heads (see below), and the cases they make can be works of art.

The case made by the Lepidostomatid (there is no "common" name for this insect, by the way) is normally shaped like the one in this photo: it's four-sided and square, made of neatly squared pieces of leaves and bark, and at the top, there are often "projections" added on at least one side of the case (sometimes on two or three sides).  Presumably, these are there for protection; i.e. the larva can quickly hide its head when it has to.  But there are other cases we find on occasion -- spiral cases made out of sand.  This type of case is normally made by larvae in early instars; and when the larvae grow and mature, they often top off those cases with squared off pieces of bark (as though they finally realize what their cases are supposed to look like!).  Here are examples of the cases I mean.

And a few more to compare.

How do we know when the caddis we've found is a Lepidostomatid?  Well, if it's in its usual four-sided case, you can be pretty sure that that's what you've got.  If it's out of its case, or if the case is the little one made purely of sand, you'd better go back to your lab and get the microscope out.

There are two features that you'll be hoping to find.  1) This is the only case-making caddis larva that has only two humps, these on the sides of the first abdominal segment.  Recall that most case-makers have three (the third one on the back of the larva), while the "humpless" caddis (Brachycentridae) has none.  So, if the lateral humps are clear and no dorsal hump is present -- you've got a Lepidostomatid.  (Note the "nipple" like humps on the sides of the larva below.)

If you need further verification, get ready to squint.  The Lepidostomatid is the only caddis with its antennae located directly in front of its eyes.  But the antennae are extremely small, and they're hidden away inside a light colored dot:  it's the dot that you have to look for.  See if you can find it in the photo that follows.

When I worked with StreamWatch, this is a caddis we normally found in our very best streams, those that were deep in the woods: our reference sites (both in Albemarle and Fluvanna Counties), the upper reaches of Buck Mt. Creek, the upper reaches of the Doyles River, and on occasion in the Moormans.  It has, after all, a tolerance value of 1.  But we also found it in places that always surprised me: for some reason we consistently ran into some in the sites that we sampled on the Rivanna River itself.  This is one of those anomalies I cannot explain.

(Photo of a live caddis in a petri dish taken at the Rapidan River.)

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