I was mining and notice i was lagging a lot in one particular area. I proceed mining bearing through the lag and come across what i believe to be the problem.
(http://i.imgur.com/IBbe4m1.png)
here's one where i got a bit closer and lit the area up
(http://i.imgur.com/hiDnhPi.png)
they dont attack, they dont despawn and they cant be killed
There are probably all going on a very long pilgrimage since all of them are walking in the same direction. That or they know where Froob's house is and walking towards it.
strange...