Semperfli Dirty Bug Yarn
This yarn is an excellent substitute for dubbing on flies. It makes a great simple Walt's Worm, Sawyer's Killer Bug, or hare's ear type body as well as a body for Czech nymphs/caddis larva. It is small enough I've used it on a size 20 but can be wrapped loose and built up to use on larger flies. (Devin)
Here's what Semperfli says about it:
When we look closely at insects and invertebrates they are not just one color but a range of mixed colors across their body. So why do we often use single color dubbing to imitate nature? That was the big question the Semperfli Pro Team was asking. As a result we developed Dirty Bug Yarn. We call it Dirty Bug Yarn because it has the multiple colors found on insects and invertebrates, whether you are tying shrimp, baetis nymphs, caddis nymphs it does not matter. We decided to blend multiple color materials into Dirty Bug Yarn creating a 2 ply yarn so that you can tie larger nymphs or split the 2 ply yarn for smaller flies.