Jim, try a similar pattern as to the green larva you have used without success, but change up the color scheme- an overall olive to olive brown color has been the most consistent for me, and best represents the most common coloration of the most abundant larva most places. Make a dark brown head, rib it with copper wire (or brown Maxima), and add a sparse beard of legs out of mottled hen saddle. Feel free to incorporate some Ice Dub in the pattern- blend a little into the mix, or use it straight for the head, or put one or two turns of pure Ice Dub between the abdomen & thorax. I usually skip the beard of leg fibers on #16 & smaller- just touch a dubbing teaser or velcro to the underside of the thorax and pick out a few fibers for legs. I most commonly tie them #14-16 on a scud hook such as TMC 2457 or Daiichi 1150 (my favorite, it has a slight up eye that allows me to put a beard of legs fibers right at the eye of the hook without it getting in the way), but 12's & 18's can be useful too- I suspect the #18's get taken for a midge larva too. Keep the flies slim and the brown thorax area short- most commercial ties are too bulky and the thorax is too long. Make sure to also tie the pattern well down into the bend to simulate the natural curl that the real larva have when drifting awash in the current. Flip some rocks and look at what the naturals look like, and see what size & color is most abundant where you fish. I've done well on the bright green at moments, but the olive and olive brown are way more consistent. Cased Caddis have been particularly productive for me in March & April. Free living/net spinning larva patterns work particularly well in the Winter & Spring where I fish in CT- the Housy & Farmington mainly, but also on other rivers in CT like the Salmon.

One problem with the bright green Caddis larva, aka "Rockworms", is that people fish it in the wrong water. It is strictly a fast water insect, and fishing it anywhere else makes the pattern way less effective. They can also get quite large, with patterns in the #8-10 range not too big at all in many places. Cased Caddis live in slower flows, but they can be effective in moderate to fast water too. You can also use a sinking line to crawl cased Caddis right on the bottom in back eddies and in slow pool water.

I suggest reading about the larva and some of the specific species and their pertinent info in "Caddisflies" by LaFontaine. Also look in his book "Trout Flies, Proven Patterns".

Try also using a black or copper metal bead for the head, or use a glass bead in root beer or black. You can use different wire colors for the rib- instead of copper use chartreuse, copper brown, green, red, etc. Or rib it with flashabou. The sky is the limit.

For Steelhead try tying it slightly bigger (#8-12) and use a bright orange bead for the head, make the abdomen in chartreuse or bright green or olive, or make the head out of Ice dub or dark olive Crystal Chenille.