Finally got the first dynamism in the game. If there's an infestation of creatures they'll gradually build up and reproduce as they kill people in the town. That raises the danger level which in turn will eventually cause the ruler to step up patrols. Less diligent and compassionate rulers will take longer to act, causing the infestation to build up more before action is taken. The patrols suppress the creatures and kill some but not all of them, once the danger level is back down, the patrols will eventually go away, leaving the creatures able to build back up again. Quite happy with the more dynamic cycle this creates in the absence of external factors.