This is author, fly tier and blogger Matt Grobert's very simple but effective Caribou Caddis. For a hook Matt uses a Dai-Riki #305 in a size 14 but 16's and 18's also work well. After flattening the barb and getting the hook firmly secured in his vise, Matt loads a bobbin with a spool of 6/0 olive Danville.
Start your thread on the hook shank leaving an eye length space behind the eye. Take wraps rearward to halfway between the point and the barb and then break or snip off the tag.
For the abdomen, select a color to match the naturals. Here Matt's using Hare-Tron in a light olive brown. It's a good looking mix of rabbit and Antron. Using only small amounts at a time, apply the dubbing to your tying thread to form a thin, lightly tapered dubbing noodle. Take adjacent wraps up the hook shank to form the abdomen of the fly. The dubbing should end at about the 2/3's point on the hook shank.
For the underwing of the fly, snip a strand of white Zelon free from the hank. Lay it on the near side of the hook using the thread torque from a couple of wraps to carry it to the top. Pulling rearward on the Zelon, shorten the butt ends so they don't need to be snipped off. Now take wraps of tying thread to cover the butts from behind the eye all the way back to the abdomen. Trim the underwing off using the outer bend of the hook as a guide.
Snip a small clump of natural colored caribou hair free from the hide. Strip out the shorter hairs from the butt ends and then drop the bundle tips first into a hair stacker and give it a good firm stacking. Keeping the tips aligned, remove the caribou from the stacker and measure to form a wing just slightly longer than the underwing. Take a loose collecting wrap of tying thread around the hair and then pull straight up to compress the wrap. Take a few more firm turns to secure the hair to the top of the hook shank. While still holding on to the wing, carefully snip the butt fibers off close. It looks a little messy but the technique works well. Take wraps to cover up the butt ends a little bit. Don't sweat this too much as they'll be covered up shortly.
Apply a light skim of ultra tacky wax to about an inch and a half of your tying thread. Lightly touch dub the thread with some natural hair's mask dubbing. Begin taking wraps in front of the wing. Occasionally pull the fibers rearward and continue wrapping. This raggedy looking mass will trap air bubbles adding to the fly's realism and helping it to float.
You can then complete the fly with a 5 or 6 turn whip finish and snip or cut your tying thread free. Caribou hair takes a bit of getting used to but is a terrific tying material and adds both form and function to this pattern.