I did a brood removal today as a varroa treatment, something I will not be doing again, as it took very long and was very invasive and stressful for the bees. Many, many bees were flying around by the time I was done, and a lot of bees were sitting on the neighboring hive's lid for an hour or two afterward, because I'd had the caged queen setting up there for part of the time I was working. Around 4:30, I went up to the apiary to check on things, and some bees were balling something on top of the hive. Curious as to what they were up to, I broke up the ball with a stick, and found only a single dead worker in the center of the ball. It seemed odd, but now that I'd broken them up, and since the bee who was the object of their aggression was dead, I figured they'd disperse. But about 15 minutes ago, 2 hours after I first noticed them, they had reformed around this worker and were still balling her. I broke up the cluster again to be sure. Why would they be balling a single dead worker like this, for this long?