Do you suspect it came from the feces or does it look more like an earthworm?

There are organisms called grindal worms that often live in humid vivariums, but these are not usually as long as you described. There are also small "worms" which inhibit the soil called nemerates.

Could you get pic? there are so many things which look like worms, and without a pic its hard to identify.
-----
A room of herps.
www.freewebs.com/kapoktree