I have one hive in my bee yard that is infested with large black ants (carpenter ants?). I find them on the inner cover with a pile of eggs which I assume they are carrying out of the hive. I have moved the hive to a new stand a couple of feet behind their original stand, and covered the legs of the stand in petroleum jelly. I went back this morning to check, and the ants are there in full force. I haven't had this problem with any of the other hives. I have looked around the bottom of the stand, and occasionally see an ant or two (with my eyesight, there could be more but I can't see them), so I haven't been able to locate the colony. My next step will be coffee cans with mineral oil in them. Does anyone have any other suggestions?