[He doesn't mind so much when Kid's questions aren't dumb. Karkat's hand has left his face by now, and his tone is easing back to its normal level.]

Lusus for short, plural lusii. The general term for their actual position as caretaker is "custodian" on our planet. And we don't learn solely from them, but also schoolfeeding - [Whatever that is, as unhelpful as canon is.] - and from basic trial and error in the course of growing up. Fuck up too much and you die one way or another, but that's basic for trolls.

... At least on Alternia. Beforan culture is different but you'd be better off asking someone actually from that version of the universe for the details.