>Sorry, but Carbon Dioxide (CO2) weights 44 units (C=12 plus O=16 - twice
>i.e. 12+16+16) and the air (a mixture of various gases) mean weight is 29
>(at 20 degrees C or 293 K). CO2 is really heavier at the same temperature.


Air is a mixture of gases, one of which is C02. When a bee breaths it takes
some O2 adds a little  CO2, water vapor and other trace elements to the
gases as well as heat. As long as there is enough heat in the process the
resulting gas mixture is going to expand. This expansion will result in the
gas now having more volume which will cause it to rise above the cooler air
(the difference in weight between the O2 and CO2 will be small compared to
the effect of the heat).

I doubt there is any danger in the CO2 levels, but I am sure the water vapor
will get you. I am not sure of the details but I would bet that a lot of
moisture in the hive would result in a lot more heat loss as the
condensation would be evaporated near the cluster and dump a lot of energy
when it recondenses away from the cluster.