Silithid Harvester is a level 34 rare beetle that can be found just north of Desolation Hold in the Southern Barrens. (I have indicated where he can be found with a red dot on the map below.) He drops the typical green item and decent experience for levelers. He shares the same model as many other beetles throughout the world, but he is the only one in this particular color scheme. He is tamable at level 34 and is a tenacity pet.
Silithid Harvester can be found with NPCScan. You will need to add it, his NPCScan ID is 3253.
You don't really need npcscan though or any macros to find this guy. He is pretty obvious when he is up. He always spawns in the same location (41.0,66.5) and never patrols far. As you can see in the video below he just kind of pats around between the rock formations just north of Desolation Hold and is the only bug there.
I can't really guess his spawn timer at this time, before he was moved and re-skinned for the cataclysm his timer seemed to be somewhere between 4-8 hours.