American Grannom Caddisflies - Brachycentrus americanus

American Grannom Larva in fast, shallow water

I wrote previously about watching Blackfly larvae in a feeder creek of the Dolores River. While I was on this trip, I also saw a strange Caddisfly larva cemented to the rocks in areas of fast current. The larvae had two pairs of their legs splayed out, filtering the water as it swept past them. The larvae were living inside long, four-sided cases made of twigs.

I didn’t expect to have much luck figuring out what type of Caddisflies these were, just based on my photographs. It turns out that I was not sufficiently considering the fly-fishing community.

American Grannom, with my finger for scale. The Grannom is just below the tip of my thumb. I scared the larva when I put my finger nearby, it’s pulled its legs back into the case. You can also see a group of Blackfly larvae in the lower right-hand quadrant of the photo.

The fly-fishing guys have all kinds of articles and websites set up for the identification of aquatic insects (see “Souces”, below, for two of them).

Larger American Grannom in deeper water

According to these sites, the larvae were probably the American Grannom, or “Log Cabin Casemaker”
American Grannom - the Log Cabin Casemaker (Brachycentrus americanus(?)).

Sources:

A fabulous website: The Aquatic Insects of Gunnison County, Colorado. Their page on Brachycentrus americanus was especially helpful.

The Orvis Website: Ted Fauceglia’s article “The American Grannom (Genus Brachycentrus) is a Springtime Gem”.