Minecraft wiki entry for Spawn, associated text: Mobs are broadly divided into seven categories: hostile, friendly, water creature (squids and dolphins), underground water creature (glow squids), axolotls, water ambient (all 4 types of fish), and ambient (bat). Hostile and water mobs have a spawning cycle once every game tick (1⁄20 of a second). Friendly mobs have only one spawning cycle every 400 game ticks (20 seconds). Because of this, where conditions permit, hostile mobs spawn frequently, but passive mobs (animals) spawn rarely. Most animals spawn within chunks when they are generated.