Cao,
My second Nuc that I bought had a defective queen, DWV, and after four or five weeks of it being in my Apiary it was full of laying workers. I was given a new queen by the seller. My inspector told me to do a shake out before she was released. I shook the bees at over 100 yards from my hives. I had two at that time. The day after the shake out I went back to the spot and there was a ball of bees the size of my fist on the ground. By this time there were no nurse bees in this hive, the original queen never made a maiden filthy, her wings were too curled up, every time I saw her, the bees were walking over her so none of the workers were new. By this time there were lots of drones coming out of the hive. I dispatched the queen my self so I know she was not in the middle of the ball. I looked through the ball, using a stick and all it was was bees. Is suspect the laying workers develop their ovaries enough to weigh them down. It is either that or the laying workers develop as such right after hatching and never leave the hive even to orient. There were a lot of them that never made it back to the hive.
Jim Altmiller