How Do Hostile Mobs Spawn in Minecraft?

Question

So I found a village near where I originally spawned and I expanded on it. I thought I could keep it safe by building a 3-4 block high wall around the village, unfortunately this didn't help (now all my villagers are dead!). I still find mobs inside the city walls and inside of the university I built. The university has a basement, and although I usually keep the door to it closed I'll still find the occasional spider, zombie, skeleton warrior or even creepers.

So my question is how do mobs spawn? Does the presence or absence of light make any difference? Are other factors involved?

Answer 1

Yes, the light level makes a difference. In fact, it's probably the single most important factor for hostile mob spawning.

Hostile mobs won't spawn in any area that is above light level 7. Torches produce a light level of 14, and that light level decreases by one for every block (along an axis) out. Therefore, any place that is more than 7 blocks away from a torch could spawn a hostile mob. There are other methods of discouraging hostile mobs from spawning, but keeping a well lit area is key.

Answer 2

Also, try filling your university with the following blocks:

1. Half-blocks. These are not very convenient, but can work for flooring.
2. Glass. No mob can spawn on glass.
3. Liquids. If you have any empty space you cannot enter, wall it up and fill it up with water.

But lighting the areas is probably a better solution. If you add on to the few lights in the village, and light up every little dark space, you can drastically reduce the odds of a monster spawning. You can never be completely sure, however. Sometimes creepers spawn in semi-lit areas and catch you by surprise.

Answer 3

Minecraft has traditionally been about light management. Monsters spawn in the dark, and light keeps you safe, both in sunlit areas and via torches, glowstone, and other light sources such as lava.

However, an update (Feb 2012) added zombie sieges, which ignore light levels completely. They apparently have a 10% chance of occurring in a village each night. This will only happen when you are close enough for the game to be updating the village (so it doesn't happen when you're on a long trip), but it can happen while you're underground, or not near enough to be aware of it. On Hard difficulty, the zombies can even break down doors (putting the doors one block above ground level apparently avoids this). Zombies can spawn close to you (closer than normal) and even inside houses!

I've been playing other games and only recently returned to Minecraft, so the siege mechanic came as an unpleasant surprise. It seems counter to the entire idea of Minecraft's risk management, and it irritates me that my villagers can be killed if I work near or under the village but don't guard it each and every night :(

I hope they eventually put a No Sieges button in the options menu.

Answer 4

You will need to light up the village and maybe place an overhang around the top of your wall to stop spiders climbing in.

Answer 5

I'd say that creepers spawn under trees since there is shade under there. Also, if zombies spawn somewhere, and it's daytime just make them follow you into the sunlight. It'd also help if you didn't attack spiders in the day for then they're friendly. If there's no place with a light level below eight.

Answer 6

Light up the inside of the village and build a wall around it. Make sure the wall is three blocks/more tall, has an overhang or includes fences, and perhaps hide pufferfish under trapdoors such as this video by Grian:

Different light sources give off different light. Open f3 to make sure how much light it emits. And lastly, use Iron Golems and cats around your university. Rename them things to make them seem like Janitors or pets of students. Iron Golem kills mobs except for Creepers and cats scare away creepers. Bonus:adds to aesthetic.