He can be found around -207, 648 if you're using the /loc command and is accompanied by 5 other Treemites. Other sightings include:
-196, 641 Spawned twice while I was there. (11/10/2008 Moosaman)
After running around couple hours west/southwest of Retread Camp I found him direct north of Retread Camp, just 50 meters from the teleporter. Being annoyed of looking so long time for him following the location-hints for him, I waited for respawn and he DID respawn just a short bit away, just stay on the road and hug the mountainside and patrol a bit back and forth you WILL find him.
Killing him is straightforward, but as with most small enemies, targeting him can be unexpectedly hard. It's recommended to use [TAB] for target lock. (Reality ripper works excellent on tiny bug's..)