I only used to feed mine about 1 cup or so, but once I had to leave them for the weekend, so I bought two grocery bags full of veggies, and left it all in their house. (Of course, I asked someone to come in and look after them, but I left them all that food incase she forgot to come in.) Anyway, I phoned the girl after about 12 hours of being away, and she said all the veggies were gone! So that made me think....if they can eat that much, it means they're hungry and they need it, right? Or maybe they just eat out of boredom...I dunno, I thought only humans did that.
