Snail-case Caddisfly

Snorkeling in the clear water of our swimming hole on Bull Creek I saw hundreds of tiny snails clinging on the small gravel downstream. One larger rock I found had a depression on the underside where there were tiny gravel clusters attached. They were 1/10" round and appeared spiraled. They were very firmly attached with one I couldn't even pry off with my fingernail.

I assumed they were caddisfly larvae until under magnification I saw they were the shape of snails with fine sand granules attached. and I wasn't able to extract a caddisfly larva. Could they be freshwater snails that have sand attached to their shells? A dumb question but since Deb Finn* and I had been talking about a snail research project I reached out to her.

The white glistening patches I saw with a magnifier looked like it could be a snail foot but with the macro views I could see they were chert chunks in the glued on sand. After a few minutes one started to crawl slowly on the rock surface as seen in this video. I still couldn't extract a caddisfly larvae as I have in the past. Then I got Deb's response, letting me down gently.

 "Your first thought (caddisflies) was correct. I found a lot of them yesterday too in the creek upstream. They are in a genus called Helicopsyche, which was actually originally described (embarrassingly enough) as a snail. The family Helicopsychidae all make spiral cases in the shape of a snail. And it is extremely difficult to pull the larvae out of their cases."

Adult Helicopsychidae - boldsystems.org CC

It helped salve my ego that they are called "snail-case maker caddisflies" and were originally described as snails!  "The case is diagnostic for Helicopsychidae as all Helicopsychidae construct spiral cases and no other caddisflies do."  Caddisflies are famous for their larvae while the Rodney Dangerfield adults get no respect. The image to the right is the only Helicopsyche sp. adult I could find on the Internet.

Helicopsyche sp. are flying under the radar of the web and need a new press agent.  I went through 5 pages of Google before I found anything significant about their life history.  Finally I found a page on Lifeinfreshwater.net where they are described a "scrapers," grinding off algae that is clinging to rocks.  Their head and legs usually protrude from a single opening in the case. Photographs online show a curved larva, the price it pays for living full time in a circular case of glued sand.

The fly - Troutfisherman.co.uk

We examined caddisfly larvae as a group in this blog last year where the cases from further up stream were larger.  They were encrusted with larger gravel flakes which didn't show the spiral pattern.   Dr. David Bowles of MSU identified them for me as Helicopsyche borealis, which trout fishermen call a Speckled Peter.  The adult finally gets some respect from fly fishermen who tie a pattern called the Speckled Peter.
=====
* Dr. Debra Finn is a stream ecologist at Missouri State University and her team is studying Bull Creek.
MDC has a good brief overview of caddisflies in general.