A request for the lowdown on Traps

Hello! Currently away from my PC and vicariously enjoying the new update here til I'm off for Christmas, but I haven't been able to pin down exactly how the new Kobold trap system works. I understand that it ramps up the attrition and fort defense of a province, but I'm seeing some berserk casualty numbers on here, is it just attrition or does it inflict direct casualties? Also how are they built, does it relate to the hoard? Any information greatly appreciated :]