Update to TurtleBoids Sandox: boids are mapped onto a torus, steering rules take this into account. See http://www.openprocessing.org/sketch/57265 for an explanation of the (fast) torus mapping algorithm. Based on Craig Reynolds' Steering behaviors with code adapted from Daniel Shiffman's Nature of Code http://www.shiffman.net and my own TurtleGraphics implementation from IgnoCodeLib, http://paulhertz.net/ignocodelib/ .
Press the mouse to attract the boids, the torus topology should be clear by their behavior. Press 't' to switch between plane and torus.