There IS a way to find these other than running around aimlessly. Wherever there is one hiding underground, you can see its shadow. Look closely at the cracks in the ground and if you see a shadow, that's where the mob is hiding. If you are unsure, wait for a moment and watch to see if the shadow moves.
I personally haven't noticed the mob move to another area, but I HAVE seen it rotate. They spawn under cracks right around the area where you pop the NM, and once you kill one, it can respawn in another spot, so don't just go back to the same crack over and over. These were always DC to me at 75. If you're kiting one of these, be careful that you don't run over another one's shadow or you will be in big trouble.