Thanks Allen,


> >One must consider that the 'air' in the cluster must be recycled through a
> number of bees as it makes its way out of the tight cluster, at least when
> the cluster is down from the hive top.


Bees not generating heat, which would include those bees in the mantle, hold
their breaths as long as possible between breaths.


>  >Either that, or some mechanism must allow the air to escape through the
> tightly-packed bees as you suggest.
>

The most tightly packed bees are those beneath the mantle.  Even so, there
would be diffusion and convection of air and moisture.

>
> >If the bees were to re-breathe all the the air as it passes outwards, then
> each bee would in turn -- I imagine -- modify the humidity of that air and
> necessarily exhale it at less than 100% RH for that point in the cluster.


My guess would be that the exhaled air of a bee would always be close to
100% RH, since it was in contact with moist trachea.


>   >Since temperature drops progressively (but not linearly) outward from
> the centre, one would have to wonder at this point, since it would seem that
> each cooler bee would have to _remove_ moisture in such a scenario, whereas
> reason would suggest that the metabolism of each bee would be adding
> moisture, not removing it. ?????
>

Yes, for those few that are actually metabolizing.  That would be the bees
closer to center, which hold at about 80F.

>
> >As a point of interest, water vapour is quite a bit lighter than air


Good point, Allen!   That had never occurred to me, but you are absolutely
> right.  That would help to explain why the moist air rises from the
> cluster.  The bees are able to regulate the atmosphere within the
> cluster--they drop the oxygen content substantially, and raise the CO2 level
> to about 6%, which would kill a human.  This likely lowers the pH of their
> hemolymph, but I've never seen any data.  So they must slow the convection
> of air to some degree.
>


> >This discussion makes one realise why insulating lids of wintering hives
> in frigid environments, even if the hive is vented, is so important to
> successful wintering.
>

I agree!  Colonies in a typical tree cavity would have that insulating wood
above.  Even in my relatively mild Calif winters, I've been toying with
insulating my lids--have even purchased the foam to do so!

Randy Oliver

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