What are these things?

[ReeferMO85]

I have just noticed about 5 of these little worm like things. They are about 1cm long and crawling on the rockwork. They appear to be black and white banded. The diameter is very tiny, half the size of angle hair pasta. Sorry this is the best description I can give. Anyone have a clue what they are? Thanks.

 

[EdKruzel]

Sounds like a boring worm, completely harmless and quite beneficial.

Ed