We have had one in the tank for 3 years, he's HUGE, he's nasty, and yet, he's a chicken, we rarely ever see him.
He never comes out from behind the rock when the lights are on, and forget it if you come near the tank, he runs like a startled pigeon.
One day he'll figure out he's bigger than the biggest fish in the tank, and its okay to come out and say hello. He must be 5" from front to back, but he's very shy!