I have a couple of worm flies that have not been used the one I like the looks of the best is made of two strands of olive catcus chennile tied at the tips with a red section of marabou, my version of a firetail on a plastic worm, then furl the strands to the length you like; secure to the hook and wrap forward; tied off and add a black hen hackle.

The only way I have found to keep medium or larger chenille from unraveling is to furl two pieces together.