I have built quite a big mob grinder/xp farm. It has five floors but when I'm at the bottom of the grinder 1 mob comes down after a minute. I broke the top of the spawner and saw that there were mobs in there but none were going to the water. Does anybody know why they are doing this.enter image description here

This what the mob spawner looks like, i made it on xbox

enter image description here

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That's what it looks like inside enter image description here

That's what it looks like with no light. (gamma is on 100%)

  • Can we have more information and some pictures please?
    – imulsion
    Feb 18, 2015 at 13:34
  • I can't get a picture right now but I can give more information. It is comepletely dark inside, I have lit up most of caves and ravines around my spawner. This grinder spawns spiders as well. It is exactly like those simple spawners on YouTube except it has more floors than normal.
    – Yossof
    Feb 18, 2015 at 13:40
  • 2
    Do they spawn close enough to the water? If they have a huge area to walk on it seems likely they won't go in it.
    – Izzo
    Feb 18, 2015 at 13:57
  • Are you playing on an XBox?
    – MBraedley
    Feb 18, 2015 at 22:15

3 Answers 3


Typically mobs don't just run off ledges hanging in the air. They will however jump/be pushed into water at their level.

Judging by your pictures, there should also be more mobs - I would reckon that there are more caves and ravines to light up.

But, the important part is this: this design typically requires water streams at each level that funnels the mobs to the center. The mobs get pushed or jump into the water at their level and are funneled and dropped into the center. I have a similar setup, and this is what I have done, and it works adequately.

Please keep in mind the spawning rules as well: https://minecraft.wiki/w/Spawn. There are certain distances that must be observed or else mobs will despawn or not spawn at all.

  • 1
    To be precise, mobs will move into water if it is within three blocks below where they are standing - i.e. you can build up to a 3-block deep water trench and they'll walk into it. More than that and they won't go off the edge unless you trick them with trapdoors or something.
    – Johonn
    Feb 18, 2015 at 21:49

Mobs don't move at long ranges. At the distance of your first screen shot, it looks like the farm is > 32 meters, and at that distance mobs don't move. This kind of farm, you have to be very careful as to where you stand in order for it to work. The fact that you have mobs present indicates that you probably have the caves cleaned out "enough" but for massive spawn rates, I would recommend either cleaning out all the caves, or moving the spawner up quite a bit, (> 128) so that the only locations to spawn are in your facility.

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whilst the mob AI's aren't great, they won't just jump off a cliff, you need water to push them off

what you need

a series of 3 x 3 platforms, with a slab one block above the central one for them to spawn, then a water source immediately underneath it so that the mobs will be moved and die from fall damage


use signs to stop water without preventing the movement of mobs make sure to stay within range of the grinder so that mobs can spawn

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