These mobs are social, slowed one then another attacked, then another, then another...well you get the idea. The hardest hit I noticed was 137, that was on a 61 shaman with 1081 ac, only had self buffs on so when I got back will get some cleric buffs.
They where part of a quest called Wharf rats. The object is to explore the "L" shaped doc, then kill 25 wharf rats. There is another part of it but I haven't finished the killing part as of this post. I got the task from Zeke, the rats didn't spawn until about 5 minutes after I received quest. They were not there before when I didn't have the quest.
The one I killed before I got mobbed didn't drop anything. I will keep you posted on whatever else I find out.
Very social. As a 55 sk it was hard to get a single pull without resorting to FD and often losing the pet while doing so. They wander around a lot too, and often stop with 2 stacked on top of each other. I was getting hit for 60 - 180 and with only self-buffs some of the battles were difficult. They run at 20%, don't cast anything nor do they appear to drop anything. About 4% AA xp a kill at 55.