I was killing these when i was lvl 61 (necro) and would almost get an entire yellow every kill. Would scent of terris (resist debuff) then snare, and dot, while running along the trench. Once i got to a certain point, i would turn around, and run back, sit down and let pet beat it. It would take a good 8-10 minutes to kill one, but was worth it. Took all my mana to kill em though.
Of course, this was before they started summoning. Went on a vacation, came back 3 weeks later and went back to my routine, and got summoned about 40 seconds into the fight. Got stunned, and quadded for 500's twice while stunned... Needless to say i got owned. Thats what i get for not having FD up.... wish i had read the game updates before going after 'em again.