I snuck off to a local stream for a while and managed to sample a few areas of the riverbed for insects near the shoreline today. There was lots of really good stuff, too, in the way of life forms. Scuds, nymphs, caddis larvae, little aquatic worms, few tiny snails, and a beautiful, big, ugly dragonfly nymph.
The scuds, nymphs, worms, and other stuff are great, the stream is rich with life, but the caddis larvae is what excites me this time of the year. Yes, when they show up in late January, early February, it means they are actively feeding - grazing - on the microplankton growing on and among the rocks and other organic stream bottom matter. What this means is that these caddis larva are moving about, drifting, and getting swept into the water column where the trout can easily feed on them. The trout this time of the year become quite accustomed to this "candy", and will take them readily from now through March.
The larvae are small, bright orangy-yellow or olive-green in color. The orangy ones are the larvae of the very common genus Chimarra - the Little-black Caddis. The olive-green ones are primarily of the genus Rhyacophila, which may be the most important caddis larva to the fish. Keep in mind, the olive-green coloration can vary widely from a dull gray green to a bright green, and even a pure olive. The naturals are mostly #16-18's with some being a #20, and therefore their imitations should be tied in these sizes.
The best way I have found to fish these imitations this time of the year is to fish them as a dropper off a larger nymph. Fishing them singularly does work, but this time of the year, its best to maximize your opportunities.
Here's one of my imiations of the Chimarra larva. Just substitute olive-green for the others and you're ready to go. You can use floss, dubbing, or any other material that will retain its color when wet and give you the straightforward silhouette of a simple caddis larva. Legs, gills, that kind of stuff is not necessary, but if it gets it done for you and your confidence when fishing the fly, by all means, add them. For this particular fly I used bright orange thread, yellow Uni-Flexx, and then tie off the fly with tobacco brown thread. The naturals have a very distinct head, but that's about it. The head on the olive-green larva should be black. (Yes, they have teeny, tiny legs, gills, and claspers, but the fish are looking for basic food forms, not anatomically correct bugs - they don't have time, every food opportunity is drifting by them on a watery conveyor belt.)
Have a ball! This is some fun fishing - matching the hatch below the surface!