Originally Posted by scuba_steve
how could they do this on a rock ??
They don't. If placed in a hole or crevace in the rock where the base of the tube can safely attach, the worm builds it's tube outwards from there.
I'm not saying you cannot place the duster in the sand. That will be fine as well. I have found that they seem to do better when placed on/in hard surfaces. The ones I have placed in sand typically do not fair as well or live as long. Couldn't really tell you why, it's just been my experience.