These things seem to have a fairly large agro radius, still quad for a goodly amount of damage 700+ even when slowed. They are social with other witheran too.
Fairly large agro radius I say is a little to small more like huge. When I kill one it seems that all in the entire area will agro. Tried pulling them further away but that doesnt work they are like the Reavers in the City of Mist they just keep spawning after being killed or low on health. Pain in the butt.