what are the spawning rules for the monsters? how far away & how close do you have to be? I saw where they should spawn at 24 blocks away from you & out to 144 blocks max from you. Will they spawn around villagers even if you are not there? I have a monster spawning farm for stuff & xp. They don't seem to spawn till I come around. And do they despawn after a time? In the trap where they fall, I know some monsters should be there, but when I go to kill them, they're gone.
Hostile mobs have a spawning cycle once every game tick(1/20th of a second)...
Mobs spawn naturally within a square group of chunks centered on the player. In single-player mode, this area will be 15×15 chunks (240×240 blocks), but in multi-player mode the size can vary with the server settings. When there are multiple players, mobs can spawn within the given distance of any of them. However, hostile mobs (and some others) that move farther than 128 blocks from any player will soon despawn (see Despawning), so even with a larger chunk loading radius, the mob spawning area is more-or-less limited to spheres with a radius of 128 blocks, centered at each player.
Mob caps are directly proportional to the total number of chunks eligible for spawning...
If a hostile mob tries to spawn in the overworld, then...
the light level of the spawning block must be 7 or darker, and more light increases the chance that the spawn will fail
sunlight falling on the spawning block further increases the chance that the spawn will fail, by up to 50%
...on the Xbox 360, the floor of the spawning area must be less than Y=128, or MOB spawning will fail.
...will not spawn on slabs or stairs or in water or in lava.
thanks for the answer. My mob trap works pretty good. I placed it in the center of my town.....at night while resting...I kill monsters in my trap for xp & stuff. during the day, when I'm out working...they will spawn If I'm close enough & when I go back there are quite a few waiting for death. I'm working on a slime trap now. Found a spawning spot. Dug out a room & went back several minecraft days later & had 2 full grown slimes bouncing around.....now to get them to the surface....Oh, anyone know the spawn rate for slimes?
Slimes are hostile MOBs... but they also only spawn in certain Chunks below Y=40 ... or in Swamp biomes.