I clip them whenever they're long. Around once every two weeks. I used to bite them, got bored of it. Not I stick needles underneath and dig out the sticky dirt.
I hate those wierd habits..
I'm always doing something wierd with myself. 4th grade it was picking at my belly-button, 6-7 grade it was curling my lip, 8th grade it was bending the cartilage in my nose. Im kinda done with those habits..for now, atleast.