This vant is running on a grid that wraps around from left to right and top to bottom. Also, the grid is initialized with a regular pattern of dots instead of all white or all black. I think this setup shows more fun behavior--in particular, sometimes it tears down and rebuilds things it's already built, because of a special kind of reversability the simplest vant rule has.
I made this applet run a lot faster by a hack: I avoided method calls! Apparently (at least in the browsers and applet viewers I'm using) there's a big speed penalty for calling a method within a thread. That's a ridiculous restriction and I hope it goes away in later implementations of Java. But the code of this applet isn't badly disfigured by my workaround.
The source code is in LangtonsAnt.java. It started out as a Life program that Peter N Lewis <email@example.com> wrote and MetroWorks distributed with their Code Warrior development environment.