There are 4 creatures you must lure out and pictures of what the bait looks like in and out of Wraith vision:
Go ahead and use
for Wraith vision and run around the map. As far as I know, the earliest point to get this achievement is in the second map, Cirith Ungol.
If you are having difficulty getting anything to spawn, find a Captain from the Feral Tribe (found under their strengths) and go to that area.
If you STILL can't find any, then make a Captain from the Feral Tribe one your followers and promote him overlord of your fortress. Might take some time, but it will spawn eventually