Minecraft wiki entry for Mob, associated text: Mobs spawn in various ways. Most mobs spawn naturally, depending on the light level, biome, and their surroundings. For example, most animals are found in bright areas on the surface, whilst hostile monsters are commonly found in the dark (whether if it’s a cave, dungeon, mansion or at night). Animals usually spawn upon chunk generation, while hostile monsters spawn and despawn in certain radii around the player. Some mobs including passive and neutral animals, and even hoglins have the ability to be bred by the player, creating offspring. Villagers also breed randomly depending on the time of day and the number of beds (though they can’t be directly bred by the player). Most mobs never spawn on transparent blocks, in water (except fish, dolphins, turtles, and other aquatic creatures), in lava (except for striders), on bedrock, or on blocks less than a full block tall (such as slabs placed on the bottom half). The exception is monster spawners, from which monsters can spawn naturally on any block including air.