They see invis, wander and cannot be snared or rooted. They don't hit that hard but they do hit FAST. They CAN be mezzed but are somewhat resistant. They can be SLOWED. They're PITA but they WILL extend their victims the courtesy of sweeping up their corpses after killing them. Their agro range is very small. If one is coming down a corridor you can usually avoid aggroing them at a "node" (the slightly bigger areas along the corridor) by hugging a wall.
The irony is in the heroic mission, if you get the step where you have to kill 5 of these, it can take some time to find 5 to kill since they don't respawn and there is no spot where these mobs are common. You just have to keep looking for them. Track helps but it's not perfect in a multi-level zone full of tunnels like this zone.