What's this?

[MikeP]

What are these things? I've got quite a few. Are they bad? What looks like a tiny string or spider web comes out and then retracts every once in a while. The pictures aren't that great but what I'm tring to show is the little 'tube' on the side of the rock. I wanted to draw a circle around it but couldn't figure out how.

http://i134.photobucket.com/albums/q...2/IMG_2803.jpg

http://i134.photobucket.com/albums/q...2/IMG_2804.jpg

Thanks