Twice in the last three weeks small swarms have taken over queenless NUCs in my apiary. They are not from my hives. AHB have been reported to take over hives like this, I've not seen it before (just another gap in my education ) and don't know how concerned I should be. No increased defensiveness in either NUC yet, I work them in shorts, bare arms and no gloves. At dusk last night a swarm was forming on a tree next to the beeyard behind my house. I noticed some bearding on a queenless NUC as it got dark and put a comb on a stick next to the baseball sized group of bees in the tree. The bees marched right onto the comb and I waited until morning to sort things out. Few bees on the comb in the tree this morning. The mating NUC with bearding on it last night was full of bees and I found a ball of bees with a queen inside. I marked the (virgin looking) queen and released her into the NUC after observing no aggression toward her. About three weeks ago, the same thing happened with another queenless mating NUC two feet from the NUC described above. That time, I let the bearding go on for three days before investigating becaue it was 105+ during the day that week. When I looked, I found three balls of bees containing piping queens. I rescued three virgin queens (all later died) and discovered a queen that began laying a few days later. I hypothecize there is a bee tree nearby throwing off small swarms in the dearth we have now. I live in AHB country, so will be particularly alert for that influence, but currently, my suspicion they are Africanized is low. Any thoughts?