Dwarf fortress is one of my favorite examples of emergent behavior- the maneating carp, cat-explosions, cats getting drunk, etc. Actually, a lot of cat based bugs in general.
Fortress became unplayable due to catsplosion. I love this game.
Just put all cats in a cage and leave few males wandering around to deal with vermin. The last time I played (few years ago, don't remember the exact version) this worked flawlessly.